When shopping for solar energy or maintaining your existing residential solar system, you'll likely come across many different terms that might be confusing. Our solar energy glossary can help you navigate residential solar and make sure your system works for you.


Azimuth: A term to describe the direction your roof faces in the context of solar, measured in degrees of the angle between your rooftop and true north.


Community solar: Also known as a solar garden or shared renewable energy plant, a community solar system is shared by more than one household and can be an alternative to rooftop solar.


Electric vehicle (EV): A vehicle that runs on electric power or a combination of gas and electricity rather than solely gas. Solar panels can produce the energy needed to power an electric vehicle.


Federal income tax credit (ITC): A tax credit (not deduction) provided by the federal government based on solar installations. This credit decreases every year and will be gone by 2024, but is currently at 26% of installation costs. Learn more about solar tax credits.


Grid parity: When the power generated by solar panels costs the same or less than power from conventional resources like natural gas. Maryland and Massachusetts are at grid parity today.


Grid-tied system: Solar system that remains connected to the power grid. This type of system generates power for the home and delivers any excess back into the grid.


Installation partners (IPs): Companies we partner with that are experts in delivering and installing solar equipment onto homes. 


Interconnection agreement: Contract between a homeowner and local utility allowing the homeowner to connect their solar panels to the grid. In some areas, this also enables net metering.


Inverter: Electricity from the sun is gathered in direct current (DC) electricity. Homes and businesses use alternating current (AC) electricity. Inverters convert DC electricity to AC electricity. They come either in one central unit that is connected to all the panels or in a smaller unit (micro-inverters) where each panel has its own inverter. The benefit of micro-inverters is that one panel going down won’t drag the whole system down.


Kilowatt hour (kWh): Common unit of power consumption. 1 kWh is 1,000 Watt-hours, meaning a 60-watt lightbulb burning for 60 minutes has consumed 1 watt-hour of energy. Most households use between 8 and 14 kWh of energy each year.


Megawatt hour (mWh): Unit of power consumption. 1 mWh is 1,000 kWh.


Meter: Meters monitor electricity usage (and energy production of home solar). Solar systems require a bi-directional or digital meter. Please see “net metering” for information on how you can put excess energy back into the grid to lower your monthly energy bill.


Net metering: When a grid-tied system produces more energy than is needed, it can feed the excess back into the power grid. A net meter will record how much energy a solar system feeds into the grid vs. how much the home consumes from the grid. The monthly utility bill will account for net metering by crediting or charging the utility customer accordingly. Some version of this program is available in 44 states. Find your state's rules


Off-grid system: Solar system that is not connected to the grid and needs a storage solution to use any excess energy it generates. 


Offset: This term is used to describe how solar power and other renewable energy sources can produce cleaner energy that replaces fossil fuel usage, providing the owner more control over their energy.


Photovoltaic (PV) cell, panel, and array: A photovoltaic cell is the smallest semiconductor part within a PV system that converts light into energy. A PV cell is a type of solar cell. Many cells make a solar panel, and a set of panels form an array.


Renewable energy: Sources of energy that come from natural forces like wind, sunlight, or water. These sources won't run out, as opposed to fossil fuels such as coal and natural gas, which deplete over time and will run out one day. Using renewable sources of energy is more sustainable and emits less CO2 than fossil fuels.


Solar cell: A single, light-capturing unit in a solar panel made of silicone. Cells are very thin and light.


Solar design: Layout and orientation of a solar system, optimized to produce maximum energy.


Solar-plus-storage: A type of solar solution that uses batteries to store excess energy during the day to be reused during periods of lower energy production like nighttime or rainy days.


Temperature coefficient: How well a solar system does in high heat, expressed in percentage decrease in output for every 1 degree Celsius over 25 C (77 F). Most panels have a temperature coefficient of -0.3%, but it also depends on type of panel and placement on the roof. Extreme temperatures can negatively affect the performance of your solar system.


Zero net energy (ZNE): When a home or building produces as much energy as it consumes.

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