Key Solar Terms (Plain-English Glossary)

Going solar involves a lot of electrical and solar-industry vocabulary. This glossary gives short, practical definitions you can use while comparing quotes, reading specs, or planning a home PV system.

Jump to:

• Electrical basics
• Solar resource & geometry
• System design & programs
• Inverter [blocked] & performance terms
• Solar panel specification terms

Electrical basics

• Current — The flow of electric charge (measured in amps). If you want a refresher on how current relates to voltage and power, see the U.S. Energy Information Administration’s electricity basics.
• Alternating Current (AC) — The type of electricity used by most homes and the grid; it alternates direction. Solar equipment usually converts panel output into AC before powering your home or exporting to the grid (overview: EIA electricity basics).
• Direct Current (DC) — Electricity that flows in one direction; solar panels and batteries produce DC. Homes typically use AC, so an inverter is needed (overview: EIA electricity basics).
• Voltage — Electrical “pressure” that pushes current (measured in volts). Power is commonly calculated as P = V × I (background: EIA electricity basics).
• Volts — The unit used to measure voltage (see: EIA electricity basics).
• Electric Current — Another way to say “current”: charge moving through a conductor (see: EIA electricity basics).
• Watt (W) — A unit of power (rate of energy use or production). 1,000 W = 1 kW (definition reference: EIA glossary).
• Kilowatt (kW) — A unit of power equal to 1,000 watts (definition reference: EIA glossary).
• Watt-hour (Wh) — A unit of energy: using 1 watt for 1 hour.
• Kilowatt-hour (kWh) — A unit of energy equal to using 1,000 watts for 1 hour; it’s the billing unit on most electric bills (definition reference: EIA glossary).
• GW (Gigawatt) — A unit of power equal to 1 billion watts (definition reference: EIA glossary).
• MW (Megawatt) — A unit of power equal to 1 million watts (definition reference: EIA glossary).
• Transformer — Electrical equipment that steps voltage up or down between circuits (background: EIA electricity basics).
• Ground / Grounding — A safety method that connects metal parts and equipment to a reference potential to reduce shock and fault risk.
• Diode — A component that allows current to flow mainly in one direction; used in PV modules and electronics to reduce backflow and protect circuits.
• Series Circuit — A circuit with a single current path; if that path opens, current stops.
• Parallel Circuit — A circuit with multiple current paths; one path failing does not automatically stop current in other paths.
• VOC / OCV (Open Circuit Voltage) — The voltage a module/string produces when not connected to a load (no current flowing). This matters for inverter input limits in cold weather.
• VMP (Voltage at Maximum Power) — The operating voltage at which a module produces its maximum power under given conditions.

Solar resource & geometry

• Photons — Particles of light that carry energy from the sun.
• Solar Radiation — Energy emitted by the sun across wavelengths (including visible light and beyond).
• Solar Spectrum — The distribution of sunlight across wavelengths.
• Irradiance — Instantaneous solar power per area (commonly W/m²). For common irradiance components (e.g., DNI/DHI/GHI), see definitions such as SolarAnywhere’s field definitions or PV modeling references like the NREL PVWatts manual (PDF).
• Insolation — Solar energy received over time per area (often expressed as kWh/m²/day). A simple conceptual overview is here: Insolation on Earth (PBS LearningMedia).
• Direct Insolation — Solar energy arriving primarily in a direct beam from the sun (often associated with Direct Normal Irradiance / DNI; see: SolarAnywhere DNI definition).
• Diffuse Insolation — Solar energy scattered by clouds, haze, and aerosols before reaching the surface (often associated with Diffuse Horizontal Irradiance / DHI; see: SolarAnywhere DHI definition).
• Incident Light — Sunlight that strikes the surface of a PV module.
• Angle of Incidence — The angle between incoming sunlight and a line perpendicular to the panel surface; more “direct” sunlight generally improves output.
• Full Sun — Informal shorthand for strong midday irradiance; not a rating standard.
• Latitude — North-south position on Earth; affects sun path, seasonal daylight, and typical PV production.
• Longitude — East-west position; mainly affects clock time of “solar noon,” not annual solar resource by itself.
• Solar Noon — When the sun is highest in the sky for a given location (local solar time).
• True South — The geographic south direction (not magnetic south). PV orientation is typically referenced to true south in the Northern Hemisphere.

System design & programs

• Photovoltaic (PV) — Technology that converts light into electricity. A concise official overview is available from the U.S. Department of Energy.
• Photovoltaic Effect — The physical process where light frees electrons in a material and creates electric current (overview: DOE PV basics).
• Solar Cell / PV Cell — The basic unit that converts light to electricity; modules contain many cells wired together.
• Solar Panels / Solar Modules — Packaged assemblies of PV cells, glass, encapsulant, frame, and backsheet designed for outdoor use.
• Utility — The local company responsible for delivering electricity and operating distribution infrastructure.
• Net Metering (NEM) — A billing arrangement where exported solar energy can be credited against imported energy on a customer’s bill (definition reference: EIA net metering overview and glossary resources such as the EIA glossary).
• Community Solar — A shared solar project that allows multiple customers to benefit without installing panels on their own roof (program concept background: DOE community solar overview).
• Jurisdiction — The authority (city/county/state) that enforces permitting and inspection rules for PV installation.
• Energy Audit — A review of building energy use to identify efficiency upgrades and load-reduction opportunities.
• Renewable Energy — Energy sources replenished naturally (e.g., solar, wind, hydro).
• Zero Net Energy — A building that produces roughly as much energy (over a period) as it consumes.
• Passive Solar Home — Building design strategies that use sunlight and building materials to reduce heating/cooling loads (not the same as PV).
• Fossil Fuels — Coal, oil, and natural gas; burned for energy and major contributors to CO₂ emissions.
• Carbon Dioxide (CO₂) — A greenhouse gas emitted by burning fossil fuels.

Inverter & performance terms

• Inverter — Converts PV/battery [blocked] DC power into AC power used by your home and the grid.
• Maximum Power — The highest power a PV module/system can produce under specific conditions (often referenced at standard test conditions).
• Maximum Power Point (MPP) — The operating point (voltage/current) at which a module produces maximum power under given conditions.
• Maximum Power Point Tracker (MPPT) — Hardware/software that adjusts operating voltage/current to stay near the MPP as conditions change.
• Clipping (Inverter Clipping) — When PV DC power exceeds the inverter’s maximum AC output and the excess is not converted (discussion in modeling context: NREL PVWatts manual (PDF)).
• Inverter Efficiency — The percentage of DC input converted to usable AC output; datasheets often list peak and weighted efficiencies.
• Microinverter — A small inverter used at the module level (one per panel, or similar “module-level” architecture).
• Optimizer — Module-level electronics that condition DC output before sending it to a central inverter (still requires the inverter for DC→AC conversion).

Solar panel specification terms

• Standard Testing Conditions (STC) — A lab reference condition used to rate PV modules so products can be compared. STC is commonly defined by irradiance, cell temperature, and spectrum assumptions (modeling/rating context: NREL PVWatts manual (PDF)).
• PTC (PVUSA Test Conditions) — A rating approach intended to better reflect “real-world” operating conditions than STC; commonly used in some U.S. reporting contexts (reference context: California Energy Commission (CEC) PV module rating resources).
• Nameplate Rating — The power rating printed on a panel (typically an STC DC rating).
• Nominal Power — Often used to mean the rated DC power under a specified test condition (check the datasheet for which condition is used).
• Peak Watts — Maximum rated output under the relevant rating condition (often STC).
• Panel / PV Efficiency — The percentage of incoming sunlight converted to electricity under specified conditions (usually STC). Higher efficiency means more power from the same area.
• Temperature Coefficient — A value on the datasheet showing how module output changes with temperature (often %/°C); it helps estimate losses on hot days.
• Degradation — Gradual decline in module output over time; typically specified as an annual rate in warranties.
• Anti-Reflection Coating — Coating on glass to reduce reflection and increase light transmission into the cells.
• Back Plate / Backsheet — The rear protective layer of a module that helps insulate and protect internal components.
• Frame — The structural edge that helps mount and protect the module.
• Monocrystalline — PV cells made from single-crystal silicon; often higher efficiency and commonly dark/black in appearance.
• Multicrystalline / Polycrystalline — Cells made from multiple silicon crystals; often slightly lower efficiency and visually more “blue” or mottled.
• Single-Crystal Structure — Crystal lattice with relatively continuous structure; used to describe mono-silicon cell material.
• Thin-Film Solar Panels — PV made by depositing thin semiconductor layers on a substrate; generally lower efficiency but can be lightweight and flexible depending on type.
• Building Integrated Photovoltaics (BIPV) — PV integrated into building materials (e.g., solar shingles, façade glass) so it serves as both building envelope and generator.
• Black-on-Black — An aesthetic configuration where frame, cells, and backsheet are all black (check datasheets, because “all-black” varies by brand).
• Premier Panels — Informal term often used by marketers/installers to indicate high-quality, well-supported modules; always verify with datasheets, warranties, and test certifications.
• American Manufacturer — Typically indicates modules or key components are manufactured domestically (definitions vary; verify the specific claim and documentation).
• Solar Shingles (Tiles) — Roof-integrated PV products designed to look like shingles while producing electricity.