Solar Glossary — Solar Energy Terms & Definitions

Name: Six Rivers Solar
Address: 818 Broadway St., Eureka, CA, 95501, US
Telephone: +1-707-443-5652
Price range: $

Understand solar energy terminology with our comprehensive glossary of 134 terms. Browse terms by category or search for specific definitions.

A

AC Battery (Battery Storage): An AC battery integrates the battery cells and a battery inverter into a single unit that connects to the AC side of your electrical system. This makes it easy to retrofit to existing solar installations because it operates independently of the solar inverter. The Enphase IQ Battery and Tesla Powerwall are examples of AC batteries. The tradeoff is slightly lower efficiency when storing solar energy (due to DC→AC→DC conversion) compared to DC-coupled alternatives.
Related: DC Battery, AC-Coupled System, Solar Battery Storage
AC-Coupled System (System Components): In an AC-coupled system, solar panels connect to a standard solar inverter that converts DC to AC. The battery has its own separate battery inverter that converts AC back to DC for charging and DC back to AC for discharging. While slightly less efficient than DC-coupling for storing solar energy, AC-coupled systems are easier to retrofit to existing solar installations because the solar inverter doesn't need to be replaced. They also allow independent sizing of solar and storage components.
Related: DC-Coupled System, Solar Inverter, Solar Battery Storage
Agrivoltaics (Emerging & Specialty Terms): Agrivoltaics (or agri-PV) combines solar energy production with farming on the same parcel of land. Solar panels are elevated or spaced to allow crops, grazing animals, or pollinator habitats beneath and between them. Research shows benefits for both energy and agriculture: panels provide shade that reduces water evaporation and heat stress on crops, while vegetation under panels keeps them cooler and more efficient. Agrivoltaics addresses land-use competition between energy and food production, a growing concern as solar deployment scales up.
Related: Solar Canopy, Ground-Mount System
Automatic Transfer Switch (ATS) (System Design & Installation): An automatic transfer switch detects when grid power is lost and automatically transfers the electrical load to the backup power source (battery, generator, or both). When grid power returns, the ATS transfers back to grid power. In solar-plus-storage systems, the ATS ensures seamless transition to battery backup during outages. Some modern hybrid inverters have ATS functionality built in, eliminating the need for a separate device. Transfer time is typically 10–20 milliseconds — fast enough that most electronics don't notice the switch.
Related: Manual Transfer Switch, Island Mode, Whole-Home Backup
Avoided Cost Rate (Financial & Incentives): Under NEM 3.0, exported solar energy is compensated at the "avoided cost" — the amount the utility would have spent to generate or purchase that energy from other sources. This rate varies by time of day and month, reflecting the actual value of solar energy to the grid at that moment. Midday rates (when solar is abundant) are very low ($0.03–$0.05/kWh), while late afternoon rates are higher. The avoided cost rate is substantially lower than the retail electricity rate, which is why self-consumption and battery storage are emphasized under NEM 3.0.
Related: NEM 3.0, Time-of-Use (TOU) Rates, Net Energy Metering (NEM)

B

Battery Bank (Battery Storage): A battery bank is a group of batteries wired together to achieve the desired voltage and capacity for an energy storage system. Batteries can be connected in series (increasing voltage), parallel (increasing capacity), or series-parallel combinations. Battery banks are most common in off-grid solar systems where significant storage is needed to cover multiple days of low solar production. Proper sizing, matching, and management of a battery bank are critical for system performance and battery longevity.
Related: Solar Battery Storage, Usable Capacity, Off-Grid Solar System
Battery Energy Storage System (BESS) (Battery Storage): A Battery Energy Storage System encompasses all components needed for energy storage: the battery cells or modules, battery management system (BMS), inverter or power conversion system, thermal management, safety enclosure, and monitoring/control software. BESS can range from small residential units (5–20 kWh) to large commercial and utility-scale installations (100 kWh to multiple MWh). The term is commonly used in commercial and utility contexts.
Related: Solar Battery Storage, Battery Management System (BMS), Usable Capacity
Battery Management System (BMS) (Battery Storage): A Battery Management System is the intelligence behind modern battery storage. It continuously monitors individual cell voltages, temperatures, and current flow to prevent overcharging, deep discharge, overheating, and cell imbalance. The BMS also manages charge and discharge rates, calculates state of charge, communicates with the inverter, and triggers safety shutdowns when needed. A quality BMS is essential for battery safety, performance, and longevity — it's one of the key differentiators between battery products.
Related: State of Charge (SoC), Lithium-Ion Battery, Solar Battery Storage
Bidirectional Charging (Vehicle-to-Everything (V2X)): Bidirectional charging is the underlying technology that enables all V2X applications. Standard EV chargers only push energy into the battery (unidirectional). Bidirectional chargers can both charge and discharge the battery, allowing energy to flow to your home, the grid, or appliances. This requires compatible hardware on both the charger and vehicle sides, as well as communication protocols to manage the energy flow safely. Bidirectional charging is expected to become standard in most EVs and chargers within the next few years.
Related: Bidirectional EV Charger, V2X (Vehicle-to-Everything), CHAdeMO
Bidirectional EV Charger (System Components): A bidirectional EV charger enables two-way energy flow: it can charge an electric vehicle battery from the grid or solar panels, and it can also discharge the vehicle's battery to power your home (V2H), feed the grid (V2G), or run appliances directly (V2L). This effectively turns your EV into a mobile battery storage system. With EV batteries typically storing 60–100 kWh, bidirectional charging can provide significant backup power capacity during grid outages.
Related: EV Charger, V2H (Vehicle-to-Home), V2G (Vehicle-to-Grid), Bidirectional Charging
Building-Integrated Photovoltaics (BIPV) (Emerging & Specialty Terms): Building-Integrated Photovoltaics replace conventional building materials with solar-generating alternatives: solar roof tiles/shingles, solar facades, solar windows, and solar skylights. BIPV products serve dual functions — they protect the building envelope while generating electricity. Tesla's Solar Roof is the most well-known residential BIPV product. While typically more expensive per watt than traditional panels, BIPV can be cost-competitive when you factor in the cost of the building materials they replace and their aesthetic advantages.
Related: Solar Panel, Thin-Film Solar Panel

C

California Solar Mandate (Grid & Policy): California's solar mandate (Title 24, Part 6) requires solar photovoltaic systems on most new single-family homes, low-rise multifamily buildings (up to 3 stories), and some commercial buildings. Effective since January 2020 for residential, it was the first statewide solar requirement in the U.S. The 2022 code update expanded the mandate to include battery storage readiness. The required system size is based on the building's conditioned floor area and climate zone. Exemptions exist for heavily shaded properties or buildings with limited roof space.
Related: Solar System, Grid-Tied Solar System
Capacity Factor (Performance & Monitoring): Capacity factor expresses actual energy production as a percentage of the maximum possible production if the system ran at full rated power 24/7. Solar systems typically have capacity factors of 15–25% because the sun only shines during the day and output varies with weather and seasons. Northern California residential systems typically achieve 15–18% capacity factor. While seemingly low, this is normal for solar — the metric is more commonly used for comparing energy sources (wind, nuclear, gas) than for evaluating individual solar installations.
Related: System Performance Ratio, Energy Production, Peak Sun Hours
CCS (Combined Charging System) (Vehicle-to-Everything (V2X)): The Combined Charging System (CCS) is an international EV charging standard that supports both AC and DC charging through a single connector. CCS Type 1 (Combo 1) is the variant used in North America. While originally designed for unidirectional charging, CCS is being updated through the ISO 15118 standard to support bidirectional power flow for V2H and V2G applications. Most non-Tesla EVs sold in North America use CCS, though the industry is also adopting Tesla's NACS connector.
Related: CHAdeMO, Bidirectional Charging, EV Charger
CEC-Listed Equipment (Certifications & Standards): The California Energy Commission (CEC) maintains lists of approved solar panels and inverters that meet performance and safety criteria for California installations. CEC listing is required to qualify for California incentive programs and is standard practice for all installations in the state. The CEC list verifies manufacturer-submitted performance data (efficiency, power ratings) against independent testing, ensuring consumers receive accurately rated equipment. Installers should always use CEC-listed panels and inverters.
Related: UL Listing, NABCEP Certification
CHAdeMO (Vehicle-to-Everything (V2X)): CHAdeMO (CHArge de MOve) is a DC fast-charging protocol developed by Japanese automakers. It was the first widely deployed standard to support bidirectional power flow (V2G and V2H), making it significant for vehicle-to-grid applications. However, CHAdeMO is declining in market share outside Japan, with most Western automakers and the industry converging on the CCS standard. Some newer bidirectional implementations are being developed for CCS and NACS connectors.
Related: CCS (Combined Charging System), Bidirectional Charging, V2G (Vehicle-to-Grid)
Clipping Loss (Performance & Monitoring): Clipping occurs when a solar array generates more DC power than the inverter can convert to AC. The excess energy is "clipped" and lost. Some system designers intentionally oversize the array relative to the inverter (a higher DC-to-AC ratio) because clipping only occurs during a few peak midday hours and the overall energy harvest across the full day is greater with the larger array. Typical DC-to-AC ratios of 1.15–1.25 result in minimal clipping (1–3% of annual production) while significantly increasing morning and afternoon energy capture.
Related: Solar Inverter, System Performance Ratio
Combiner Box (System Components): A combiner box is a junction point where the wiring from multiple strings of solar panels comes together before being routed to the inverter. It typically contains fuses or circuit breakers for each string, providing overcurrent protection and a convenient point for disconnecting individual strings for maintenance. Combiner boxes are more common in larger residential and commercial systems; smaller systems may route strings directly to the inverter.
Related: String Inverter, Disconnect Switch, Solar Array
Community Solar (Emerging & Specialty Terms): Community solar (also called shared solar or solar gardens) allows multiple customers to benefit from a single, centrally located solar installation. Participants subscribe to a portion of the project's output and receive credits on their utility bills for their share of the energy produced. Community solar makes solar accessible to renters, homeowners with unsuitable roofs, and those who can't afford their own system. California's community solar programs are expanding, particularly targeting low-income households.
Related: Virtual Net Metering, Distributed Energy Resource (DER)
Critical Loads (System Design & Installation): Critical loads are the electrical circuits and appliances you designate as most important during a power outage — typically refrigeration, lighting, communication devices, medical equipment, and well pumps. In a partial-home backup configuration, only these critical loads are connected to the backup panel and powered by the battery during an outage. Identifying and properly wiring critical loads is a key design decision that affects battery sizing, backup duration, and installation cost.
Related: Whole-Home Backup, Partial-Home Backup, Automatic Transfer Switch (ATS)
Cycle Life (Battery Storage): Cycle life indicates how many times a battery can be fully charged and discharged before its capacity drops below a specified threshold (typically 70–80% of original). Modern lithium-ion solar batteries are rated for 4,000–10,000 cycles, translating to 10–25 years of daily cycling. LFP (lithium iron phosphate) batteries generally offer longer cycle life than NMC (nickel manganese cobalt) chemistry. Cycle life is one of the most important factors in determining the long-term value of a battery investment.
Related: Depth of Discharge (DoD), Degradation Rate, Lithium Iron Phosphate (LFP) Battery

D

DC Battery (Battery Storage): A DC battery connects on the DC (direct current) side of the electrical system, typically paired with a hybrid inverter that manages both solar charging and battery operation. Solar energy flows directly to the battery without first being converted to AC, resulting in higher charging efficiency (3–5% more efficient than AC batteries). DC batteries are the preferred choice for new solar-plus-storage installations where the system is designed from the start to include storage.
Related: AC Battery, DC-Coupled System, Hybrid Inverter
DC-Coupled System (System Components): In a DC-coupled system, solar panels connect to a charge controller or hybrid inverter that charges the battery directly with DC power before converting to AC for home use. This avoids the efficiency losses of converting DC to AC and back to DC for battery charging. DC-coupled systems are typically 3–5% more efficient for storing solar energy and are the standard design for off-grid systems. They require a hybrid inverter or separate charge controller.
Related: AC-Coupled System, Hybrid Inverter, Solar Charge Controller
Degradation Rate (Performance & Monitoring): All solar panels slowly lose a fraction of their power output each year due to UV exposure, temperature cycling, moisture ingress, and other environmental factors. Modern panels typically degrade at 0.3–0.5% per year, meaning a panel rated at 400W will still produce about 360W after 25 years. Most manufacturers guarantee at least 84–87% of rated output after 25 years. First-year degradation (called LID — Light Induced Degradation) is typically higher at 1–3%, after which the rate stabilizes.
Related: Solar Efficiency, Temperature Coefficient
Demand Charge (Grid & Policy): Common in commercial utility rates, demand charges are based on your peak power draw (measured in kW) during any 15-minute interval in a billing cycle — regardless of when it occurs. A single brief spike in consumption can set your demand charge for the entire month. Solar panels and battery storage can help reduce demand charges through peak shaving — using stored energy to limit the maximum power drawn from the grid during peak periods. Demand charges can represent 30–50% of a commercial electricity bill.
Related: Peak Demand, Energy Arbitrage, Solar Battery Storage
Demand Response (Emerging & Specialty Terms): Demand response (DR) programs pay or incentivize electricity customers to reduce their consumption during peak demand periods when the grid is stressed. With solar and battery storage, homeowners can participate automatically — discharging batteries to reduce grid draw or shifting consumption to off-peak hours. Smart thermostats, water heaters, and EV chargers can also participate. DR events are typically triggered by extreme heat days or grid emergencies. Programs like OhmConnect and utility-specific DR programs offer bill credits or direct payments.
Related: Virtual Power Plant (VPP), Peak Demand, Smart Panel
Depth of Discharge (DoD) (Battery Storage): Depth of discharge measures how much energy has been drained from a battery relative to its total capacity. For example, a 10 kWh battery at 80% DoD has 2 kWh remaining. Most lithium-ion solar batteries are designed for 80–100% DoD, meaning you can use 80–100% of their rated capacity before recharging. Lead-acid batteries typically should not exceed 50% DoD to preserve their lifespan. A higher usable DoD means you get more practical energy from each charge cycle.
Related: State of Charge (SoC), Usable Capacity, Cycle Life
Disconnect Switch (System Components): Disconnect switches (also called safety disconnects or isolation switches) allow the solar system to be safely shut down for maintenance, emergency response, or utility work. Most installations require both a DC disconnect (between panels and inverter) and an AC disconnect (between inverter and electrical panel). Local fire codes may also require rapid shutdown capability, which allows first responders to quickly de-energize rooftop solar panels.
Related: Electrical Panel / Load Center, Solar Inverter
Distributed Energy Resource (DER) (Grid & Policy): Distributed Energy Resources include rooftop solar panels, battery storage systems, small wind turbines, EV batteries (V2G), and backup generators connected at the distribution level (homes and businesses) rather than at large centralized power plants. DERs are transforming the electrical grid from a one-way delivery system into a dynamic, two-way network. Utilities and grid operators are developing programs and technologies to coordinate millions of DERs to improve grid reliability, reduce infrastructure costs, and integrate more renewable energy.
Related: Virtual Power Plant (VPP), Demand Response, V2G (Vehicle-to-Grid)

E

Electrical Panel / Load Center (System Components): The electrical panel (also called the breaker panel, load center, or distribution board) is the central hub of a building's electrical system. Solar systems connect to the electrical panel via a dedicated breaker, allowing solar electricity to flow to the home's circuits. Panel capacity and available breaker space are important factors in solar system design — older homes with small panels (100A or 150A) may need a panel upgrade to accommodate a solar system and meet electrical code requirements.
Related: Disconnect Switch, Smart Panel
Energy Arbitrage (Grid & Policy): Energy arbitrage takes advantage of time-of-use rate differences by charging a battery during low-cost periods (midday when solar is abundant, or overnight off-peak) and discharging during high-cost peak periods (typically 4–9 PM in California). The difference between buy-low and sell-high rates generates savings. Battery storage systems with smart controls automate this process. Energy arbitrage is most valuable in areas with significant rate differentials, like California where peak rates can be 3–5x off-peak rates.
Related: Time-of-Use (TOU) Rates, Solar Battery Storage, Self-Consumption
Energy Consumption (Performance & Monitoring): Energy consumption is the total electricity a home or building draws over a period, measured in kWh. The average U.S. household consumes about 10,500 kWh per year (roughly 875 kWh/month). Understanding your consumption pattern — how much you use and when — is essential for sizing a solar system, evaluating battery storage needs, and estimating savings. Consumption monitoring is included with many modern solar monitoring systems, often using a current transformer (CT) sensor on the main electrical panel.
Related: Energy Production, Load Analysis, Solar Offset
Energy Density (Battery Storage): Energy density is measured in watt-hours per kilogram (Wh/kg) for gravimetric density or watt-hours per liter (Wh/L) for volumetric density. Higher energy density means a smaller, lighter battery for the same storage capacity. NMC lithium-ion batteries have higher energy density than LFP batteries, which is why LFP units are physically larger. Energy density is an important consideration when installation space is limited, such as in garages or indoor utility rooms.
Related: Lithium-Ion Battery, Lithium Iron Phosphate (LFP) Battery, Usable Capacity
Energy Management System (EMS) (Emerging & Specialty Terms): An Energy Management System coordinates all the energy assets in a home or building — solar panels, battery storage, EV charger, HVAC, water heater, and appliances — to optimize for cost savings, self-consumption, backup readiness, or carbon reduction. An EMS monitors real-time production, consumption, utility rates, and weather forecasts to make automated decisions about when to charge or discharge batteries, when to run appliances, and when to export to or import from the grid. Products like the Sigenergy system and Span Smart Panel integrate EMS functionality.
Related: Smart Panel, Self-Consumption, Solar Battery Storage, Sigenergy
Energy Production (Performance & Monitoring): Energy production is the total electrical output of a solar system over a given period — daily, monthly, or annually. It is measured in kilowatt-hours (kWh) and depends on system size, location, weather, shading, panel orientation/tilt, and equipment efficiency. A well-designed 7 kW system in Northern California typically produces 8,500–10,500 kWh per year. Monitoring energy production over time helps verify the system is performing as expected and identifies potential issues.
Related: Energy Consumption, Solar Offset, Kilowatt-Hour (kWh)
EV Charger (System Components): An EV charger (also called EVSE — Electric Vehicle Supply Equipment) provides safe, controlled charging for electric vehicles. Level 1 chargers use a standard 120V outlet (3–5 miles of range per hour). Level 2 chargers use a 240V circuit (25–30 miles per hour) and are the most common home installation. DC fast chargers are used commercially for rapid charging. Pairing an EV charger with a solar system allows you to fuel your vehicle with clean energy and maximize self-consumption.
Related: Bidirectional EV Charger, Self-Consumption, Smart Panel

F

Federal Solar Tax Credit (ITC) (Financial & Incentives): The federal Investment Tax Credit (ITC) historically allowed homeowners and businesses to deduct 30% of the total cost of a solar energy system from their federal income taxes. Under the One Big Beautiful Bill Act of July 2025, the residential credit (Section 25D) ended for systems installed after December 31, 2025—homeowners whose systems were operational by that date can still claim it on their 2025 return. The commercial credit (Section 48E) also wound down: only projects that began construction by July 4, 2026 retain eligibility, subject to placed-in-service deadlines. Businesses with projects already underway should consult a tax professional about remaining eligibility.
Related: Solar Rebate, Solar Payback Period, Solar Return on Investment (ROI)
Feed-in Tariff (Grid & Policy): A feed-in tariff (FIT) is an energy policy that offers long-term contracts to renewable energy producers, paying a guaranteed above-market rate for electricity fed into the grid. FITs were instrumental in driving early solar adoption in countries like Germany. California had limited FIT programs, but they have largely been replaced by net metering and net billing policies. FITs differ from net metering in that they typically pay for all generation (not just exports) and are offered at a set rate for a fixed term.
Related: Net Energy Metering (NEM), Avoided Cost Rate

G

Grid Resilience (Grid & Policy): Grid resilience describes how well the electricity grid can prevent, absorb, and recover from events like wildfires, extreme weather, equipment failures, and cyberattacks. Distributed solar and battery storage improve grid resilience by decentralizing power generation and providing backup power at the building level. In fire-prone areas like Northern California, solar-plus-storage systems provide critical resilience against both Public Safety Power Shutoffs (PSPS) and wildfire-related outages.
Related: Public Safety Power Shutoff (PSPS), Island Mode, Solar Battery Storage
Grid-Tied Solar System (System Design & Installation): A grid-tied (or grid-connected) solar system is the most common type of residential installation. It connects to the local utility grid, allowing you to draw power when your panels aren't producing enough and export surplus energy back to the grid for credits. Grid-tied systems are the least expensive option because they don't require battery storage, but they will not function during a power outage unless paired with a battery and transfer switch.
Related: Off-Grid Solar System, Hybrid Solar System, Net Energy Metering (NEM)

H

Hybrid Inverter (System Components): A hybrid inverter (also called a multi-mode or battery-ready inverter) combines the functions of a solar inverter and a battery inverter into one device. It can convert DC from solar panels to AC for home use, charge and discharge batteries, and manage grid interaction — all from a single unit. Hybrid inverters simplify system design, reduce installation costs, and are the preferred choice for new solar-plus-storage installations. Many hybrid inverters also support backup power during grid outages.
Related: Solar Inverter, Solar Battery Storage, Hybrid Solar System
Hybrid Solar System (System Design & Installation): A hybrid solar system combines the benefits of grid-tied and off-grid configurations. It connects to the utility grid for net metering while also incorporating battery storage for backup power during outages and self-consumption optimization. Hybrid systems are increasingly popular due to falling battery costs, NEM 3.0 economics favoring self-consumption, and concerns about grid reliability. They offer the best of both worlds: utility access when needed and energy independence when the grid is down.
Related: Grid-Tied Solar System, Off-Grid Solar System, Solar Battery Storage

I

IEC 61215 (Solar Panel Standard) (Certifications & Standards): IEC 61215 is the primary international standard for crystalline silicon solar panel design qualification and type approval. It specifies a rigorous set of tests including thermal cycling, humidity-freeze, damp heat exposure, UV exposure, mechanical load testing, and hail impact testing. Panels that pass IEC 61215 have demonstrated their ability to withstand long-term environmental exposure. This certification is required by most markets worldwide and is a baseline requirement for any reputable solar panel product.
Related: UL Listing, CEC-Listed Equipment
IEEE 1547 (Certifications & Standards): IEEE 1547 (Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces) defines the technical requirements for connecting solar, battery storage, and other distributed generation to the utility grid. It covers voltage regulation, frequency response, anti-islanding, power quality, communication protocols, and testing requirements. The 2018 revision (IEEE 1547-2018) added requirements for smart inverter functions like volt-var support and ride-through capability, making solar inverters active grid participants rather than passive generators.
Related: Rule 21 (California), Interconnection Standards, Solar Inverter
Interconnection Agreement (System Design & Installation): An interconnection agreement is required before a grid-tied solar system can operate. It establishes the technical and safety requirements for connecting your system to the utility grid, outlines metering arrangements, and defines how you will be compensated for exported energy. The process involves an application, utility review, system inspection, and final approval before your system receives Permission to Operate (PTO). The interconnection process typically takes 2–8 weeks depending on the utility.
Related: Permission to Operate (PTO), Utility Interconnection, Grid-Tied Solar System
Interconnection Standards (Grid & Policy): Interconnection standards define the rules, equipment specifications, safety requirements, and approval processes for connecting distributed generation (like solar) to the utility grid. In the U.S., IEEE 1547 is the national technical standard, while states implement their own procedural rules (California uses Rule 21). These standards cover anti-islanding protection, power quality, voltage regulation, protective relaying, metering, and insurance requirements. Compliance is mandatory for all grid-tied solar installations.
Related: Rule 21 (California), IEEE 1547, Interconnection Agreement
Island Mode (System Design & Installation): Island mode (or islanding) occurs when a hybrid solar system detects a grid outage and automatically disconnects from the utility, forming a self-contained electrical "island." The system continues to power the home using solar panels and batteries without feeding energy back to the grid (which could endanger utility workers). The inverter or transfer switch manages the transition seamlessly, and the system reconnects to the grid automatically when utility power is restored.
Related: Hybrid Solar System, Automatic Transfer Switch (ATS), Grid-Tied Solar System

K

Kilowatt (kW) (Solar Fundamentals): A kilowatt is a standard unit for measuring the capacity of electrical systems. A typical residential solar panel produces 350–430 watts, so a 7 kW home system might use 18–20 panels. System size in kW refers to the maximum DC power output under Standard Test Conditions (STC), also called the nameplate capacity. The AC output (after inverter conversion) is typically 10–20% lower than the DC rating.
Related: Kilowatt-Hour (kWh), Watt (W), Watt-Peak (Wp), Solar Array
Kilowatt-Hour (kWh) (Solar Fundamentals): A kilowatt-hour is the standard unit for measuring and billing electricity consumption. The average U.S. household uses about 900 kWh per month. When evaluating a solar system, you compare its estimated annual kWh production against your annual kWh consumption to determine the solar offset. One kWh is enough energy to run a refrigerator for about 6 hours, a laptop for about 20 hours, or an LED light bulb for about 100 hours.
Related: Kilowatt (kW), Watt (W), Net Energy Metering (NEM), kWh

L

Lead-Acid Battery (Battery Storage): Lead-acid batteries are the oldest rechargeable battery technology, using lead plates submerged in sulfuric acid. They come in flooded (wet cell) and sealed (AGM or gel) varieties. While less expensive upfront than lithium-ion, lead-acid batteries have significant disadvantages: lower round-trip efficiency (75–85%), shorter cycle life (500–1,500 cycles), limited depth of discharge (50%), higher maintenance requirements, and greater weight and size. They are still used in some budget off-grid installations but are being rapidly replaced by lithium-ion alternatives.
Related: Lithium-Ion Battery, Lithium Iron Phosphate (LFP) Battery, Off-Grid Solar System
Lithium Iron Phosphate (LFP) Battery (Battery Storage): Lithium iron phosphate (LiFePO₄ or LFP) batteries use iron phosphate as the cathode material. They offer superior thermal stability (lower fire risk), longer cycle life (6,000–10,000 cycles), and better performance in a wider temperature range compared to NMC lithium-ion batteries. The tradeoff is slightly lower energy density, meaning LFP batteries are physically larger for the same storage capacity. LFP is increasingly the preferred chemistry for residential solar storage, used in products like the Sigenergy system and many newer home batteries.
Related: Lithium-Ion Battery, Cycle Life, Energy Density
Lithium-Ion Battery (Battery Storage): Lithium-ion batteries use lithium compounds to shuttle ions between electrodes during charging and discharging. They offer high energy density, high round-trip efficiency (90–96%), long cycle life, and declining costs. The two main chemistries used in solar storage are NMC (nickel manganese cobalt) and LFP (lithium iron phosphate), each with different performance characteristics. Lithium-ion technology dominates the residential solar storage market with products from Tesla, Enphase, Sigenergy, and others.
Related: Lithium Iron Phosphate (LFP) Battery, Solar Battery Storage, Round-Trip Efficiency
Load Analysis (System Design & Installation): Load analysis examines how much electricity a building consumes, when it's consumed, and which appliances or systems draw the most power. Installers review 12 months of utility bills and may use monitoring equipment to create a detailed load profile. This data is essential for system sizing, battery sizing, and determining which loads to prioritize during backup power operation. A thorough load analysis considers planned future loads like EV chargers, heat pumps, or home additions.
Related: System Sizing, Critical Loads, Energy Consumption

M

Manual Transfer Switch (System Design & Installation): A manual transfer switch requires someone to physically flip the switch to transfer power from the grid to a backup source (generator or battery) and back again. They are less expensive than automatic transfer switches but provide no protection during unattended outages. Manual transfer switches are sometimes used with portable generators or in budget-conscious installations where the homeowner is comfortable managing the switchover. They are increasingly rare in solar-plus-storage systems, which almost always use automatic switching.
Related: Automatic Transfer Switch (ATS), Island Mode
Microinverter (System Components): Microinverters convert DC to AC at each panel rather than at a central location. This means each panel operates independently, so shading or a malfunction on one panel doesn't affect the others. Microinverters also enable panel-level production monitoring and typically carry longer warranties (25 years) than string inverters (10–12 years). Enphase is the leading microinverter manufacturer. Microinverters are ideal for complex roofs with multiple orientations or partial shading.
Related: Solar Inverter, String Inverter, Power Optimizer
Monocrystalline Solar Panel (Solar Fundamentals): Monocrystalline panels are manufactured from a single, continuous crystal structure of silicon, which allows electrons to flow more freely and results in higher efficiency (typically 20–23%). They are the most popular choice for residential installations because they produce more power per square foot, perform better in low-light conditions, and have a sleek black appearance. They cost slightly more than polycrystalline panels but offer better long-term value.
Related: Polycrystalline Solar Panel, Thin-Film Solar Panel, Solar Efficiency
MPPT (Maximum Power Point Tracking) (System Components): Maximum Power Point Tracking is an electronic technique used by inverters, charge controllers, and power optimizers to extract the maximum available power from solar panels under varying conditions. Solar panel output changes with temperature, irradiance, and shading — the "maximum power point" shifts constantly. MPPT algorithms adjust the electrical operating point hundreds of times per second to keep the system operating at peak efficiency, typically harvesting 15–30% more energy than non-MPPT systems.
Related: Power Optimizer, Solar Charge Controller, Solar Inverter

N

NABCEP Certification (Certifications & Standards): The North American Board of Certified Energy Practitioners (NABCEP) offers professional certifications for solar photovoltaic installers, designers, sales professionals, and inspectors. NABCEP certification requires documented experience, passing a rigorous exam, and ongoing continuing education. It is the most respected credential in the solar industry and demonstrates a professional's competency in system design, installation, safety, and code compliance. Choosing a NABCEP-certified installer provides confidence in the quality and safety of your solar installation.
Related: CEC-Listed Equipment, NEC (National Electrical Code)
NEC (National Electrical Code) (Certifications & Standards): The National Electrical Code (NFPA 70) is the benchmark for safe electrical design, installation, and inspection in the United States. Article 690 specifically covers solar photovoltaic systems, addressing wiring methods, grounding, overcurrent protection, disconnects, and labeling. Article 705 covers interconnection with other power sources (the grid). Article 706 covers energy storage systems. Local jurisdictions adopt the NEC (sometimes with amendments) and enforce it through building permits and inspections. Solar installers must comply with the current NEC edition adopted by their local jurisdiction.
Related: UL Listing, Rapid Shutdown
NEM 3.0 (Financial & Incentives): NEM 3.0 (officially the Net Billing Tariff) replaced NEM 2.0 in California in April 2023. Under NEM 3.0, the value of exported solar energy is based on the "avoided cost" to the utility rather than the retail electricity rate, resulting in export values of $0.04–$0.08/kWh versus retail rates of $0.35–$0.55/kWh. This dramatic reduction in export value makes battery storage significantly more attractive, as storing and self-consuming solar energy is now far more valuable than sending it to the grid.
Related: Net Energy Metering (NEM), Avoided Cost Rate, Self-Consumption, Solar Battery Storage
Net Energy Metering (NEM) (Financial & Incentives): Net Energy Metering allows solar system owners to receive credit on their electricity bill for surplus energy their panels send to the grid. When your panels produce more than you use during the day, the excess flows to the grid and your meter records the export. You draw from those credits at night or on cloudy days. NEM policies vary by state and utility. California has gone through three versions: NEM 1.0 (closed), NEM 2.0 (closed to new customers April 2023), and the current NEM 3.0 (Net Billing Tariff).
Related: NEM 3.0, Net Meter, Grid-Tied Solar System
Net Meter (System Components): A net meter (or bidirectional meter) measures electricity flowing in both directions: from the grid to your home, and from your solar system to the grid. When your solar panels produce more electricity than you're using, the excess flows to the grid and the meter records the export. Your utility uses this data to calculate net metering credits on your bill. Most utilities install a smart net meter at no charge when you go solar.
Related: Net Energy Metering (NEM), Production Meter, Grid-Tied Solar System
Net-Metered System (System Design & Installation): A net-metered system is a grid-connected solar installation that operates under a net energy metering agreement with the utility. The system exports surplus solar electricity to the grid and receives credits that offset electricity consumed from the grid at other times. Net-metered systems are the most common type of residential solar installation. In California, new systems are enrolled under NEM 3.0 (Net Billing), which values exports at lower avoided-cost rates rather than retail rates.
Related: Net Energy Metering (NEM), NEM 3.0, Grid-Tied Solar System

O

OCPP (Open Charge Point Protocol) (Vehicle-to-Everything (V2X)): The Open Charge Point Protocol is an international standard for communication between EV charging stations and central management systems. OCPP enables charger interoperability — a charger from one manufacturer can communicate with network software from another, avoiding vendor lock-in. OCPP 2.0.1 includes support for smart charging features like load balancing, demand response, and integration with home energy management systems, making it relevant for solar-plus-EV installations.
Related: EV Charger, Bidirectional EV Charger, Energy Management System (EMS)
Off-Grid Solar System (System Design & Installation): An off-grid solar system provides 100% of a building's electricity without any utility connection. These systems require substantial battery storage to cover nighttime and cloudy periods, and are typically paired with a backup generator for extended low-sun periods. Off-grid systems are common in remote areas of Northern California where grid connection is prohibitively expensive or unavailable. They require careful load management, larger arrays, and more batteries than grid-tied systems, making them more expensive per kilowatt-hour of delivered energy.
Related: Grid-Tied Solar System, Hybrid Solar System, Solar Battery Storage, Battery Bank

P

PACE Financing (Property Assessed Clean Energy) (Financial & Incentives): PACE financing allows property owners to fund solar installations through a voluntary assessment added to their property tax bill. The repayment term is typically 10–25 years and the obligation transfers with the property if sold. PACE can make solar accessible with no upfront cost and no credit score requirement. However, PACE liens take priority over mortgage liens, which can complicate refinancing or selling. California has both residential (R-PACE, currently restricted) and commercial (C-PACE) programs.
Related: Solar Loan, Federal Solar Tax Credit (ITC)
Partial-Home Backup (System Design & Installation): Partial-home backup connects the battery to a dedicated backup subpanel (also called a critical loads panel) that feeds only essential circuits. This approach requires fewer batteries and lower installation costs than whole-home backup. The installer works with the homeowner to select which circuits to include based on priorities and battery capacity. Typical critical load panels include the refrigerator, some lighting, Wi-Fi router, phone charging, and any medical equipment.
Related: Whole-Home Backup, Critical Loads, Solar Battery Storage
Peak Demand (Grid & Policy): Peak demand refers to the highest instantaneous power consumption, measured in kilowatts (kW) for individual buildings or megawatts (MW) for the grid. For commercial customers, peak demand drives demand charges. For the grid, peak demand (typically hot summer afternoons in California when air conditioning loads are highest) determines the need for expensive peaker power plants and grid infrastructure. Solar and battery storage help reduce both building-level and grid-level peak demand.
Related: Demand Charge, Energy Arbitrage, Demand Response
Peak Sun Hours (Solar Fundamentals): Peak sun hours (PSH) represent the total solar energy received in a day expressed as the number of hours at full intensity (1,000 W/m²). This metric accounts for the varying intensity throughout the day and across seasons. For example, a location receiving 4,200 Wh/m² in a day has 4.2 peak sun hours. Northern California's North Coast averages 4.0–4.5 peak sun hours per day annually. Solar installers use PSH to estimate system production: a 7 kW system with 4.2 PSH produces roughly 29.4 kWh per day.
Related: Solar Irradiance, Solar Insolation, Kilowatt-Hour (kWh)
Permission to Operate (PTO) (System Design & Installation): Permission to Operate is the final step before a new solar installation can begin generating electricity and interacting with the grid. After installation is complete, the system passes a city/county building inspection and the utility verifies the interconnection meets all requirements. PTO approval ensures the system complies with safety and technical standards. The PTO process typically takes 1–4 weeks after the building inspection, during which the system should remain off.
Related: Interconnection Agreement, Utility Interconnection
Photovoltaic (PV) (Solar Fundamentals): Photovoltaic cells contain semiconductor materials (typically silicon) that release electrons when exposed to sunlight, generating direct current (DC) electricity. Multiple PV cells are wired together to form a solar panel (module), and multiple modules form a solar array. The term "PV" is often used interchangeably with "solar" in the context of electricity generation. PV technology has improved dramatically over the past decade, with modern panels achieving efficiencies above 22%.
Related: Solar Cell, Solar Panel, Solar Efficiency
Polycrystalline Solar Panel (Solar Fundamentals): Polycrystalline panels are made by melting raw silicon and pouring it into a mold, producing multiple crystal structures. This simpler manufacturing process makes them less expensive, but the crystal boundaries reduce electron flow, resulting in slightly lower efficiency (15–18%) compared to monocrystalline panels. They have a distinctive blue, speckled appearance and are a cost-effective option when roof space is not a constraint.
Related: Monocrystalline Solar Panel, Thin-Film Solar Panel, Solar Efficiency
Power Optimizer (System Components): Power optimizers are module-level power electronics (MLPEs) that condition the DC output of each solar panel before sending it to a central string inverter. They perform maximum power point tracking (MPPT) at the panel level, which mitigates the impact of shading, soiling, and panel mismatch. SolarEdge is the leading manufacturer. Power optimizers offer many benefits of microinverters (panel-level optimization and monitoring) while maintaining the cost advantage and reliability of a string inverter architecture.
Related: Solar Inverter, String Inverter, Microinverter, MPPT (Maximum Power Point Tracking)
Power Purchase Agreement (PPA) (Financial & Incentives): In a PPA arrangement, a third-party company installs and owns the solar system on your property. You agree to purchase the electricity it produces at a predetermined per-kWh rate, typically lower than the utility rate. PPAs require no upfront cost and the provider handles maintenance, but you don't own the system and you may be locked into a long-term contract (15–25 years). The rate may include an annual escalator. PPAs are more common for commercial installations and are not available in all states.
Related: Solar Lease, Solar Loan
Production Meter (System Components): A production meter (or generation meter) tracks the total kilowatt-hours produced by a solar system, independent of how much is consumed on-site versus exported to the grid. Some utilities and incentive programs require a production meter to verify solar generation for renewable energy credit programs. Most modern inverters include built-in production monitoring that serves the same purpose and provides more detailed data via web or mobile apps.
Related: Net Meter, Solar Monitoring System, Solar Renewable Energy Certificate (SREC)
Public Safety Power Shutoff (PSPS) (Grid & Policy): Public Safety Power Shutoffs are deliberate utility power outages implemented during high fire-risk conditions (high winds, low humidity, dry vegetation). PG&E and other California utilities use PSPS to reduce the risk of power lines igniting wildfires. PSPS events can last from several hours to multiple days and affect thousands of customers. Solar-plus-battery storage systems provide essential resilience during PSPS events, keeping homes powered when the grid is intentionally shut down.
Related: Grid Resilience, Solar Battery Storage, Island Mode

R

Roof Orientation (System Design & Installation): Roof orientation (or aspect) describes the compass direction a roof slope faces. In the Northern Hemisphere, south-facing roofs receive the most total sunlight and are ideal for solar. West-facing roofs are the second-best option, capturing valuable afternoon sun that aligns with peak electricity rates. East-facing roofs produce well in the morning. North-facing roofs receive the least direct sunlight and are generally avoided for solar installations. Many homes have multiple roof planes at different orientations, which can be leveraged with microinverters or power optimizers.
Related: Solar Azimuth, Tilt Angle, Solar Irradiance
Round-Trip Efficiency (Battery Storage): Round-trip efficiency (RTE) measures how much energy is lost during the charge and discharge cycle. If you store 10 kWh in a battery and can retrieve 9 kWh, the round-trip efficiency is 90%. Losses occur due to heat, chemical conversion, and power electronics. Modern lithium-ion solar batteries achieve 90–96% round-trip efficiency. Higher RTE means less energy waste and more savings, making it an important specification when comparing battery products.
Related: Usable Capacity, Lithium-Ion Battery, Lithium Iron Phosphate (LFP) Battery
Rule 21 (California) (Grid & Policy): Rule 21 is the California Public Utilities Commission (CPUC) tariff that describes the interconnection, operating, and metering requirements for distributed generation facilities (including solar) connecting to utility distribution systems. It establishes three application review tracks (Fast Track, Independent Study, Detailed Study) based on system size and grid impact. Rule 21 also defines smart inverter requirements, including grid-support functions like voltage regulation and frequency ride-through that modern solar inverters must provide.
Related: Interconnection Standards, IEEE 1547, Utility Interconnection

S

Self-Consumption (Performance & Monitoring): Self-consumption rate measures how much of your solar production you use in real-time or store in batteries versus exporting to the grid. Under California's NEM 3.0, maximizing self-consumption is financially advantageous because exported energy earns much less than the retail rate. Strategies to increase self-consumption include battery storage, shifting energy-intensive tasks (laundry, dishwasher, EV charging) to daytime hours, and using smart home automation to align appliance usage with solar production.
Related: Solar Offset, NEM 3.0, Solar Battery Storage, Energy Management System (EMS)
Shading Analysis (System Design & Installation): Shading analysis identifies and quantifies the impact of shadows from trees, buildings, chimneys, vents, and other obstructions on potential solar panel locations throughout the year. Tools like the Solmetric SunEye, Solar Pathfinder, drone-based LiDAR, and satellite imagery software (Aurora, Helioscope) create shade maps that show hourly and seasonal shadow patterns. Even small amounts of shading can significantly reduce energy production, especially with string inverter systems. Accurate shading analysis is essential for realistic production estimates and optimal panel placement.
Related: Solar Pathfinder, Solar Site Assessment, Microinverter
Sigenergy (Emerging & Specialty Terms): Sigenergy is a smart energy company that provides an integrated platform combining solar inverters, battery storage, and EV charging in a single, cohesive ecosystem. Their system uses a modular design with a high-voltage DC-coupled architecture for maximum efficiency, LFP battery chemistry for safety and longevity, and built-in energy management intelligence. Sigenergy's unified approach simplifies installation, reduces components, and provides seamless coordination between solar production, battery storage, home consumption, and EV charging through a single app and control system. Six Rivers Solar is a Sigenergy installer.
Related: Hybrid Inverter, Solar Battery Storage, Energy Management System (EMS), DC-Coupled System
Smart Energy Ecosystem (Emerging & Specialty Terms): A smart energy ecosystem represents the convergence of solar generation, battery storage, EV charging, smart appliances, and intelligent software control into a unified system. Rather than operating as separate components, everything works together: solar charges the battery and EV during optimal times, the battery provides backup and peak-shaving, smart loads adjust based on solar availability and electricity prices, and the EV can even feed energy back to the home. Companies like Sigenergy and Tesla are building integrated ecosystems that manage all energy flows through a single platform.
Related: Energy Management System (EMS), Sigenergy, V2H (Vehicle-to-Home), Smart Panel
Smart Panel (System Components): A smart electrical panel (such as the Span Smart Panel or Lumin) replaces or supplements your traditional breaker panel with digitally controlled circuits. It provides real-time monitoring of individual circuits, remote on/off control, automated load prioritization during battery backup, and energy usage insights via a mobile app. Smart panels are particularly valuable in solar-plus-storage systems because they can automatically manage which circuits receive power during an outage based on priority settings.
Related: Electrical Panel / Load Center, Whole-Home Backup, Energy Management System (EMS)
Soiling Loss (Performance & Monitoring): Soiling loss refers to the reduction in solar panel output caused by accumulated surface contamination. In most areas, rain provides adequate natural cleaning, and annual soiling losses are 2–5%. However, in dry seasons, near agricultural operations, or in areas with heavy pollen or bird activity, soiling can increase significantly. Panel tilt angle matters: steeper panels shed debris more easily. Professional panel cleaning is recommended when soiling losses exceed 5% or when monitoring shows sustained underperformance.
Related: Degradation Rate, System Performance Ratio
Solar Array (Solar Fundamentals): A solar array is the complete collection of solar panels in an installation. A residential array typically consists of 15–30 panels arranged on a rooftop or ground-mount structure. The array size is measured in kilowatts (kW) of DC capacity. Panels within an array can be wired in series (strings) to increase voltage or in parallel to increase current, depending on the inverter configuration and system design.
Related: Solar Panel, Kilowatt (kW), String Inverter
Solar Azimuth (System Design & Installation): Solar azimuth describes the horizontal orientation of your solar panels. In the Northern Hemisphere, south-facing panels (azimuth of 180°) typically produce the most total energy over a year. However, west-facing panels (azimuth ~270°) can be advantageous for capturing afternoon sun during peak electricity pricing periods under time-of-use rates. System designers optimize azimuth based on roof geometry, shading patterns, electricity rate structure, and self-consumption goals.
Related: Roof Orientation, Tilt Angle, Time-of-Use (TOU) Rates
Solar Battery Storage (Battery Storage): Solar battery storage allows homeowners and businesses to store surplus electricity generated by their solar panels during the day and use it at night, during peak rate periods, or when the grid is down. Lithium-ion batteries are the dominant residential technology, with products like the Tesla Powerwall, Enphase IQ Battery, and Sigenergy offering 10–20 kWh of usable storage per unit. Battery storage is essential for off-grid systems and increasingly valuable under California's NEM 3.0 for maximizing self-consumption.
Related: Battery Energy Storage System (BESS), Lithium-Ion Battery, Usable Capacity
Solar Canopy (Emerging & Specialty Terms): Solar canopies are raised structures that support solar panels while creating covered space underneath. They are commonly installed over parking lots, outdoor seating areas, walkways, and agricultural operations. Solar canopies serve a dual purpose: generating clean energy while providing shade, rain protection, and even EV charging infrastructure. They are particularly popular for commercial properties where roof space is limited, unsuitable, or already occupied by HVAC equipment.
Related: Solar Carport, Ground-Mount System
Solar Carport (Emerging & Specialty Terms): A solar carport is a specific type of solar canopy designed for parking areas. It provides covered parking while generating electricity from panels mounted on the canopy roof. Solar carports are ideal for commercial, institutional, and multi-family properties with large parking areas. They can integrate EV charging stations, lighting, and rainwater management. While more expensive than rooftop solar due to structural requirements, carports utilize otherwise unproductive space and provide visible demonstration of a property's sustainability commitment.
Related: Solar Canopy, EV Charger
Solar Cell (Solar Fundamentals): A solar cell (or photovoltaic cell) is the fundamental component that performs the light-to-electricity conversion. Most cells are made from crystalline silicon wafers that have been doped with other elements to create a positive-negative (p-n) junction. When photons from sunlight strike the cell, they knock electrons free, creating an electrical current. A typical residential solar panel contains 60–72 cells wired in series.
Related: Photovoltaic (PV), Solar Panel, Solar Efficiency
Solar Charge Controller (System Components): A solar charge controller sits between the solar panels and battery bank, regulating voltage and current to protect batteries from overcharging, deep discharge, and reverse current flow at night. There are two main types: PWM (Pulse Width Modulation) controllers are simpler and less expensive, while MPPT (Maximum Power Point Tracking) controllers are more efficient and can harvest 15–30% more energy from the panels. Charge controllers are essential in off-grid and some hybrid systems.
Related: MPPT (Maximum Power Point Tracking), Solar Battery Storage, Off-Grid Solar System
Solar Efficiency (Solar Fundamentals): Solar efficiency measures how much of the sunlight hitting a panel is converted to electrical energy. Modern residential panels range from 19% to 23% efficiency, with premium models exceeding 22%. Higher efficiency panels produce more power per square foot, which is important when roof space is limited. Efficiency is affected by cell technology, temperature (panels lose efficiency in extreme heat), shading, soiling, and panel age. Laboratory cells have achieved efficiencies above 47%, but commercial panels are limited by manufacturing costs and real-world conditions.
Related: Photovoltaic (PV), Degradation Rate, Temperature Coefficient
Solar Energy (Solar Fundamentals): Solar energy is radiant light and heat from the sun that is harnessed using a range of technologies. Photovoltaic (PV) panels convert sunlight directly into electricity, while solar thermal systems capture heat for water or space heating. Solar energy is the most abundant renewable energy source on Earth, and modern PV technology makes it practical for residential, commercial, and utility-scale electricity generation.
Related: Photovoltaic (PV), Solar Panel, Solar Irradiance
Solar Incentive Programs (Financial & Incentives): Solar incentive programs encompass the full range of financial mechanisms designed to reduce the cost or improve the economics of going solar. These include utility rebates, performance-based incentives, property tax exemptions for solar, sales tax exemptions on equipment, accelerated depreciation (for commercial), net metering/billing policies, and low-interest loan programs. The Database of State Incentives for Renewables & Efficiency (DSIRE) is the most comprehensive source for incentive information by state and utility.
Related: Federal Solar Tax Credit (ITC), Solar Rebate, Net Energy Metering (NEM)
Solar Insolation (Solar Fundamentals): Solar insolation measures cumulative solar energy — typically expressed in kWh per square meter per day (kWh/m²/day). While irradiance is an instantaneous measurement (like speedometer reading), insolation is cumulative (like odometer reading). Insolation data is essential for system design because it determines how much energy a solar array will produce at a given location throughout the year. The NREL National Solar Radiation Database provides detailed insolation data for locations across the United States.
Related: Solar Irradiance, Peak Sun Hours
Solar Inverter (System Components): The inverter is a critical component of any solar energy system. It converts the direct current (DC) produced by solar panels into alternating current (AC) used by your home and the electrical grid. Inverters also perform system monitoring, grid synchronization, and safety functions. There are several types: string inverters, microinverters, power optimizers paired with string inverters, and hybrid inverters that integrate battery management. The inverter's quality and sizing significantly affect overall system performance.
Related: String Inverter, Microinverter, Power Optimizer, Hybrid Inverter
Solar Irradiance (Solar Fundamentals): Solar irradiance measures the intensity of sunlight reaching the Earth's surface at a specific moment. It varies by location, time of day, season, altitude, and weather conditions. Standard Test Conditions (STC) for rating solar panels use an irradiance of 1,000 W/m². Northern California's North Coast receives moderate irradiance levels that are well-suited for solar production, particularly during the long summer days when irradiance can exceed 1,000 W/m² at midday.
Related: Peak Sun Hours, Solar Insolation, Solar Efficiency
Solar Lease (Financial & Incentives): A solar lease lets you use a solar system on your property for a fixed monthly payment without owning it. The leasing company installs, owns, and maintains the system, and you benefit from reduced electricity costs. While leases require no upfront cost, you typically save less over the system's lifetime compared to purchasing because you're paying for the system plus the leasing company's profit. Lease terms typically run 20–25 years with an annual escalator of 1–3%.
Related: Solar Loan, Power Purchase Agreement (PPA)
Solar Loan (Financial & Incentives): A solar loan lets you finance the purchase of a solar system, spreading the cost over 10–25 years with fixed monthly payments. Unlike leases or PPAs, you own the system outright and benefit from any incentives that apply. Many solar loans are unsecured (no collateral required) and offer competitive interest rates. Ownership means you capture 100% of the energy savings and any system value added to your home.
Related: Solar Lease, Power Purchase Agreement (PPA), Federal Solar Tax Credit (ITC)
Solar Module (Solar Fundamentals): Solar module is the industry-standard term for what is commonly called a solar panel. A module is a factory-assembled unit of interconnected solar cells laminated between protective glass and backing material, framed in aluminum, and fitted with a junction box and wiring connectors. Modules are tested and rated under Standard Test Conditions (STC) to provide comparable performance specifications.
Related: Solar Panel, Solar Cell
Solar Monitoring System (Performance & Monitoring): A solar monitoring system provides visibility into how your solar system is performing. Most modern inverters include built-in monitoring accessible via web portals and mobile apps. Monitoring systems display real-time power production, daily/monthly/annual energy generation, consumption data, battery status, and system alerts. Panel-level monitoring (available with microinverters and power optimizers) shows the output of each individual panel, making it easy to identify issues. Popular monitoring platforms include Enphase Enlighten, SolarEdge, Tesla, and Sigenergy.
Related: Production Meter, Energy Production, Microinverter
Solar Mounting System (System Components): A solar mounting system encompasses all hardware used to secure panels in place: rails or rail-less clamps, roof attachments or ground foundations, and panel fasteners. Mounting systems are designed for specific applications — flush roof mounts, tilted roof mounts, ground mounts, pole mounts, or carport structures. The mounting system must be engineered for local building codes, weather conditions, and the specific roof type or ground conditions at the installation site.
Related: Solar Racking, Tilt Angle, Solar Azimuth
Solar Offset (Performance & Monitoring): Solar offset compares annual solar energy production to annual electricity consumption. A 100% offset means the system produces as much energy as the building consumes over a year (though not necessarily at the same times). Most residential systems target 80–110% offset. Under NEM 2.0, a 100% offset was ideal. Under NEM 3.0, the optimal offset depends on battery storage, self-consumption patterns, and time-of-use rate alignment. Going slightly over 100% accounts for system degradation over time.
Related: Energy Production, Energy Consumption, System Sizing
Solar Panel (Solar Fundamentals): A solar panel (also called a solar module) is the primary building block of a solar energy system. It consists of multiple photovoltaic cells wired together and enclosed in a protective glass-and-aluminum frame. Modern residential panels typically produce 350–430 watts each and are rated for 25–30 year lifespans. Panels are available in monocrystalline, polycrystalline, and thin-film varieties, each with different efficiency and cost characteristics.
Related: Solar Module, Solar Cell, Monocrystalline Solar Panel, Polycrystalline Solar Panel
Solar Pathfinder (System Design & Installation): The Solar Pathfinder is a field measurement tool used during site assessments to evaluate shading. It uses a transparent, reflective dome placed at the proposed panel location to display a panoramic reflection of the surrounding horizon. The installer can see exactly where and when obstructions (trees, buildings, etc.) will cast shadows on the panels throughout the year. The data is used to calculate an annual solar access percentage and optimize panel placement. Digital tools are increasingly supplementing or replacing physical Pathfinder measurements.
Related: Shading Analysis, Solar Site Assessment
Solar Payback Period (Financial & Incentives): The solar payback period is the time it takes for cumulative electricity savings and incentives to recover the initial investment in a solar system. In California, typical payback periods range from 6–9 years for residential systems, depending on system cost, electricity rates, financing method, self-consumption rate, and available incentives. After the payback period, electricity from the system is essentially free for the remaining 17–20+ years of the system's useful life.
Related: Solar Return on Investment (ROI), Federal Solar Tax Credit (ITC)
Solar Racking (System Components): Solar racking (or mounting) systems provide the structural foundation for solar panels. Roof-mounted racking attaches to rafters or structural members using specialized flashings, rails, and clamps. Ground-mount racking uses driven piles, helical screws, or concrete footings. Quality racking is engineered to withstand local wind loads, snow loads, and seismic activity while maintaining proper panel orientation and tilt for maximum energy production. Major manufacturers include IronRidge, Unirac, and Quick Mount PV.
Related: Solar Mounting System, Tilt Angle, Roof Orientation
Solar Rebate (Financial & Incentives): Solar rebates are financial incentives that reduce the out-of-pocket cost of going solar. Unlike tax credits (which reduce your tax bill), rebates typically provide a direct payment or bill credit based on the system size or energy production. Rebate programs vary by location and may come from utilities, state agencies, or local governments. In California, rebate availability has decreased as solar adoption has grown, but programs like the Self-Generation Incentive Program (SGIP) still offer incentives for battery storage.
Related: Federal Solar Tax Credit (ITC), Solar Incentive Programs
Solar Renewable Energy Certificate (SREC) (Financial & Incentives): A Solar Renewable Energy Certificate (SREC) represents the renewable energy attributes of 1 megawatt-hour (1,000 kWh) of solar electricity generation. SRECs are separated from the physical electricity and can be sold in SREC markets, providing an additional revenue stream for solar system owners. SREC values vary widely by state based on supply and demand. California does not have an active SREC market, but some other states (New Jersey, Massachusetts, Illinois) offer significant SREC income.
Related: Net Energy Metering (NEM), Solar Incentive Programs
Solar Return on Investment (ROI) (Financial & Incentives): Solar ROI measures the total financial benefit of going solar relative to the cost. It accounts for electricity savings, incentive payments, financing costs, maintenance, and system degradation over the system's 25–30 year lifetime. Residential solar systems in California typically achieve 150–300% ROI (meaning you earn $1.50–$3.00 for every dollar invested). ROI varies significantly based on electricity rates, system cost, financing terms, and how much energy you self-consume versus export.
Related: Solar Payback Period, Federal Solar Tax Credit (ITC)
Solar Site Assessment (System Design & Installation): A solar site assessment (or site survey) is the first step in designing a solar system. An assessor evaluates roof condition, structural integrity, orientation, tilt, shading from trees or structures, available space, electrical panel capacity, utility meter configuration, and local code requirements. The assessment may include drone imagery, satellite analysis, shade measurements using tools like a Solar Pathfinder, and electrical system evaluation. This data informs system sizing, panel layout, and equipment selection.
Related: Shading Analysis, Roof Orientation, System Sizing
Solar System (Solar Fundamentals): A solar system (or solar energy system) includes all the components needed to generate, convert, and deliver electricity from sunlight: solar panels, inverters, racking/mounting hardware, wiring, disconnects, monitoring equipment, and optionally battery storage. Systems are categorized as grid-tied, hybrid, or off-grid depending on their connection to the utility grid.
Related: Solar Array, Solar Inverter, Grid-Tied Solar System, Off-Grid Solar System
State of Charge (SoC) (Battery Storage): State of Charge is the battery equivalent of a fuel gauge — it tells you how much energy remains as a percentage of total capacity. A battery at 100% SoC is fully charged; at 0% SoC, it's fully depleted. Battery management systems continuously monitor SoC to prevent overcharging and deep discharge, both of which can damage battery cells and reduce lifespan. Most home battery apps display SoC as the primary battery status indicator.
Related: Depth of Discharge (DoD), Battery Management System (BMS)
String Inverter (System Components): A string inverter serves as a single conversion point for a group (string) of solar panels wired in series. They are reliable, cost-effective, and easy to service. However, because panels in a string are interdependent, shading or a problem on one panel can reduce the output of the entire string. String inverters work best on roofs with consistent sun exposure and minimal shading. Adding power optimizers can mitigate shading issues while maintaining the cost advantage of a string inverter.
Related: Solar Inverter, Microinverter, Power Optimizer
System Performance Ratio (Performance & Monitoring): The performance ratio (PR) compares actual energy output to the theoretical maximum output if the system operated at its rated efficiency under actual irradiance conditions. A typical well-designed residential system achieves a PR of 75–85%. Losses from temperature, shading, soiling, wiring, inverter conversion, and clipping reduce the PR below 100%. Performance ratio is a useful metric for comparing system quality and identifying underperformance because it normalizes for differences in location and system size.
Related: Solar Offset, Degradation Rate, Clipping Loss
System Sizing (System Design & Installation): System sizing is the process of calculating the right combination of solar panels, inverter capacity, and battery storage to meet a customer's energy goals and budget. Designers consider historical electricity consumption, utility rate structure, available roof or ground space, shading, local climate, future energy needs (EV charging, heat pumps), and financial parameters. Oversizing wastes money; undersizing leaves energy goals unmet. Proper sizing balances production, consumption, storage, and export to maximize financial return.
Related: Load Analysis, Solar Array, Solar Offset

T

Temperature Coefficient (Performance & Monitoring): Solar panels are rated at 25°C (77°F), but rooftop panels routinely reach 50–70°C on hot days. The temperature coefficient (typically -0.3% to -0.4% per °C for crystalline panels) tells you how much output drops for each degree above the test temperature. A panel with a -0.35%/°C coefficient loses about 8.75% of its output at 50°C. Lower temperature coefficients are better. This is one reason solar panels in Northern California's mild coastal climate can outperform panels in hotter inland areas relative to their rating.
Related: Solar Efficiency, Degradation Rate
Thin-Film Solar Panel (Solar Fundamentals): Thin-film solar panels are made by depositing one or more layers of photovoltaic material (such as cadmium telluride, amorphous silicon, or CIGS) onto glass, metal, or plastic substrates. They are lighter and more flexible than crystalline panels, making them suitable for surfaces that can't support heavy panels, such as curved roofs or building facades. However, they are generally less efficient (10–13%) and require more space to produce the same power output.
Related: Monocrystalline Solar Panel, Polycrystalline Solar Panel, Building-Integrated Photovoltaics (BIPV)
Tilt Angle (System Design & Installation): Tilt angle (also called pitch or inclination) affects how directly sunlight strikes the panel surface. The optimal tilt angle varies by latitude and season. For year-round production in Northern California (around 40° latitude), a tilt of 30–35° is generally ideal. Steeper tilts favor winter production; shallower tilts favor summer. Roof-mounted panels typically follow the existing roof pitch, while ground-mount systems can be set to the optimal angle. Flat-roof commercial installations often use ballasted tilt mounts.
Related: Solar Azimuth, Roof Orientation, Solar Racking
Time-of-Use (TOU) Rates (Financial & Incentives): Time-of-use rates charge different prices for electricity depending on when you use it. Peak rates (highest prices, $0.45–$0.55/kWh in California) typically apply during late afternoon and evening hours (4–9 PM) when grid demand is greatest. Off-peak rates apply overnight and midday. TOU rates make battery storage particularly valuable because you can charge your battery with cheap midday solar energy and discharge it during expensive peak hours, maximizing savings and avoiding high-cost grid electricity.
Related: NEM 3.0, Self-Consumption, Solar Battery Storage, Energy Arbitrage

U

UL Listing (Certifications & Standards): UL (Underwriters Laboratories) listing is a widely recognized product safety certification. For solar equipment, key UL standards include UL 1703/UL 61730 for solar panels, UL 1741 for inverters, UL 9540 for energy storage systems, and UL 9540A for battery fire safety testing. UL listing is typically required by building codes, electrical inspectors, and utilities before solar equipment can be installed and interconnected. It verifies that products have been tested for electrical safety, fire safety, and environmental exposure.
Related: CEC-Listed Equipment, NEC (National Electrical Code)
Usable Capacity (Battery Storage): Usable capacity is the practical energy storage of a battery, which is always less than the total (or nameplate) capacity. Manufacturers set minimum state-of-charge limits to protect battery longevity, and conversion losses reduce the energy available. For example, a battery with a 13.5 kWh total capacity might have 13.5 kWh usable if designed for 100% DoD. Always compare usable capacity (not total capacity) when evaluating battery products, as it reflects the energy you can actually use.
Related: Depth of Discharge (DoD), Round-Trip Efficiency, Solar Battery Storage
Utility Interconnection (System Design & Installation): Utility interconnection encompasses everything involved in connecting a solar energy system to the electrical grid: the physical wiring, metering equipment, safety disconnects, and the regulatory approval process. Proper interconnection ensures that solar energy can safely flow to the grid, that exported energy is accurately measured, and that the system automatically disconnects during grid outages to protect utility workers (anti-islanding). Requirements vary by utility and are governed by state rules such as California's Rule 21.
Related: Interconnection Agreement, Permission to Operate (PTO), Rule 21 (California)
Utility Rate Escalator (Grid & Policy): Utility rate escalation refers to the historical and projected increase in electricity prices over time. California electricity rates have risen 5–8% annually over the past decade and are projected to continue increasing. This escalation is a key factor in solar economics: the higher future electricity rates go, the more valuable your solar investment becomes. A solar system with a 25-year lifespan locks in your energy cost, providing increasing savings each year as utility rates rise. Financial projections for solar ROI typically assume 3–5% annual rate escalation.
Related: Solar Payback Period, Solar Return on Investment (ROI), Time-of-Use (TOU) Rates

V

V2G (Vehicle-to-Grid) (Vehicle-to-Everything (V2X)): Vehicle-to-Grid enables EVs to export energy to the utility grid during periods of high demand, effectively turning parked EVs into distributed energy resources. EV owners can potentially earn revenue by providing grid services like peak demand reduction and frequency regulation. V2G is still in early stages of commercial deployment, with regulatory frameworks and utility programs developing. It requires bidirectional charging hardware, utility interconnection agreements, and compatible EV models.
Related: V2X (Vehicle-to-Everything), Bidirectional Charging, Demand Response
V2H (Vehicle-to-Home) (Vehicle-to-Everything (V2X)): Vehicle-to-Home allows an EV's battery to discharge energy to your home's electrical system through a bidirectional charger. During a power outage, your EV can serve as a massive backup battery — a typical EV with 75 kWh of storage could power an average home for 2–3 days. During normal operation, V2H can shift energy usage to avoid expensive peak electricity rates. V2H requires a compatible bidirectional charger and a home energy management system to coordinate power flow.
Related: V2X (Vehicle-to-Everything), Bidirectional EV Charger, Bidirectional Charging
V2L (Vehicle-to-Load) (Vehicle-to-Everything (V2X)): Vehicle-to-Load is the simplest form of V2X — it provides AC power from an outlet built into the EV or through an adapter cable. V2L can power tools, camping equipment, tailgate setups, or essential appliances during outages. Unlike V2H, it doesn't integrate with your home's electrical system; you simply plug devices directly into the vehicle. Many modern EVs include V2L capability as a standard or optional feature, typically providing 1.9–3.6 kW of power.
Related: V2X (Vehicle-to-Everything), V2H (Vehicle-to-Home), Bidirectional EV Charger
V2X (Vehicle-to-Everything) (Vehicle-to-Everything (V2X)): Vehicle-to-Everything (V2X) encompasses all forms of bidirectional energy flow from an electric vehicle's battery to external loads. This includes V2H (vehicle-to-home), V2G (vehicle-to-grid), and V2L (vehicle-to-load). V2X technology transforms EVs from simple transportation into mobile energy assets that can provide backup power, participate in grid services, and optimize household energy costs. As EV batteries typically store 60–100 kWh, V2X can significantly expand a home's energy storage capacity when paired with solar.
Related: V2H (Vehicle-to-Home), V2G (Vehicle-to-Grid), V2L (Vehicle-to-Load), Bidirectional Charging
Virtual Net Metering (Financial & Incentives): Virtual net metering (VNM) allows the output from one solar installation to be credited across multiple utility accounts, even if they're not at the same address. This enables community solar projects, multi-unit residential buildings (apartments, condos), and campus settings to share solar benefits. California's VNM programs allow landlords to install solar on a building and distribute credits to tenant utility accounts, making solar accessible to renters and those who can't install panels on their own property.
Related: Net Energy Metering (NEM), Community Solar
Virtual Power Plant (VPP) (Emerging & Specialty Terms): A virtual power plant aggregates hundreds or thousands of distributed energy resources — rooftop solar systems, home batteries, EV chargers, smart thermostats — and coordinates them through software to function like a traditional power plant. During grid stress events, a VPP operator can dispatch stored energy from participating homes and businesses to stabilize the grid. Participants typically receive compensation for their contribution. Tesla's VPP programs, OhmConnect, and utility-specific programs are active examples in California.
Related: Distributed Energy Resource (DER), Demand Response, Solar Battery Storage

W

Watt (W) (Solar Fundamentals): A watt is the fundamental unit of power in the International System of Units. In solar energy, watts measure the instantaneous power output of panels and systems. A single solar cell might produce 5–8 watts, while a complete panel produces 350–430 watts. Watts measure the rate of energy production or consumption at any given moment, while watt-hours (Wh) or kilowatt-hours (kWh) measure total energy over time.
Related: Kilowatt (kW), Watt-Peak (Wp), Kilowatt-Hour (kWh)
Watt-Peak (Wp) (Solar Fundamentals): Watt-peak (Wp) is the rated power output of a solar panel measured under Standard Test Conditions: 1,000 W/m² irradiance, 25°C cell temperature, and AM1.5 solar spectrum. This standardized rating allows fair comparison between panels from different manufacturers. In real-world conditions, actual output varies based on temperature, irradiance, shading, and other factors — panels typically produce 75–90% of their Wp rating on average.
Related: Watt (W), Kilowatt (kW), Solar Efficiency
Whole-Home Backup (System Design & Installation): Whole-home backup means the battery system is sized and connected to support the entire electrical panel during a power outage, not just selected critical loads. This provides a seamless experience — everything in the home continues to work — but requires a larger battery bank and often a smart panel or automatic transfer switch to manage power flow. Whole-home backup is more expensive than partial backup but is increasingly popular, especially with higher-capacity battery systems and smart load management.
Related: Partial-Home Backup, Critical Loads, Smart Panel, Automatic Transfer Switch (ATS)