Every field has its jargon, and solar planning, sizing, and financing is worse than most. This glossary covers the 41 terms that come up again and again in our guides and in the questions readers send us. Definitions are short on purpose: enough to unblock you, with links to deeper guides throughout the site when you want the full story.

Amperage

The measure of electric current flow in a circuit, expressed in amps (A). Higher amperage means more electricity is flowing through a wire or device at any given moment.

Azimuth

The compass direction a solar panel faces, measured in degrees from north (0°). South-facing panels at 180° typically receive the most sun in the Northern Hemisphere.

Battery Storage

Batteries that store excess solar energy for use when the sun isn’t shining, such as at night or on cloudy days. This allows homeowners to use their own generated power on demand.

Capacity Factor

The ratio of actual energy output to the theoretical maximum a solar system could produce under perfect conditions. Most residential solar systems have capacity factors between 15% and 25%.

Combined Heat and Power

A system that captures both electricity and usable heat from a single energy source. This improves overall efficiency compared to systems that generate only electricity.

Degradation

The gradual loss of a solar panel’s efficiency over time, typically around 0.5% per year. This is a normal part of a panel’s aging process.

Demand Charge

A fee utilities charge based on the highest amount of power you use during a specific time period, rather than total energy consumed. Businesses often face higher demand charges than residential customers.

Disconnect Switch

A safety device that allows you to safely shut off power between your solar system and the rest of your electrical system. This is required for installation and maintenance.

Efficiency Rating

The percentage of sunlight that a solar panel converts into usable electricity. Modern residential panels typically have efficiencies between 15% and 22%.

Federal Investment Tax Credit

A government incentive that allows you to deduct a percentage of your solar installation costs from your federal income taxes. The percentage varies by year and is set by federal law.

Fixed Tilt System

A solar panel installation where panels are set at a permanent angle and do not move. This is simpler and less expensive than tracking systems but captures less energy than adjustable options.

Frequency

The number of times alternating current (AC) completes a full cycle per second, measured in Hertz (Hz). In North America, standard household frequency is 60 Hz.

Grid-Tied System

A solar installation connected to the public electrical grid, allowing you to draw power when needed and send excess generation back to the grid. Most residential solar systems are grid-tied.

Gross System Nameplate Capacity

The total maximum power output of all the solar panels in your system under ideal conditions, measured in kilowatts. Actual output will typically be lower due to weather, shading, and other factors.

Insolation

The amount of solar energy that hits a specific area of the Earth’s surface, usually measured in kilowatt-hours per square meter per day. Higher insolation areas get more consistent solar production.

Interconnection Agreement

A contract between you and your utility company that outlines the rules for connecting your solar system to the grid. This agreement specifies safety requirements and how net metering will work.

Inverter

An electronic device that converts direct current (DC) electricity from solar panels into alternating current (AC) electricity used in homes. Inverters are a critical component of any solar system.

Kilowatt

A unit of power equal to 1,000 watts. One kilowatt is used to describe the capacity of solar panels or the amount of power an appliance uses.

Kilowatt-Hour

A unit of energy equal to using 1,000 watts of power for one hour. Electricity bills are typically measured in kilowatt-hours of consumption.

Levelized Cost of Electricity

The average cost per kilowatt-hour to generate electricity from a particular source over its entire lifetime, including upfront costs and maintenance. This helps compare the true cost of different energy sources.

Load Profile

A record of how much electricity your home or business uses at different times of day and throughout the year. Understanding your load profile helps determine the right solar system size.

Microgrid

A small-scale energy system that can operate independently or connected to the main grid, often including solar generation, storage, and controls. Microgrids can provide backup power during outages.

Microinverter

A small inverter installed on individual solar panels rather than one central inverter for the whole system. Microinverters can improve performance if some panels are shaded.

Net Metering

A billing arrangement where you receive credit for excess solar electricity sent to the grid at the same rate you pay for electricity consumed. This helps offset your electricity costs.

Off-Grid System

A solar installation not connected to the public electrical grid, typically with battery storage for power when the sun isn’t shining. Off-grid systems must be sized to meet all energy needs independently.

Operations and Maintenance

The ongoing costs and work needed to keep a solar system running efficiently, including cleaning, monitoring, and repairs. These costs are typically minimal for residential systems.

Peak Sun Hours

The number of hours per day when solar irradiance is at an equivalent intensity of 1,000 watts per square meter, the standard test condition. Peak sun hours vary by location and season.

Permitting

The process of getting official approval from local authorities before installing a solar system. Permits ensure the installation meets building codes and safety standards.

Power Purchase Agreement

A long-term contract where a solar company installs and owns the system on your property, and you buy the electricity generated at a fixed price. This allows you to go solar with little or no upfront cost.

Racking System

The mounting hardware that secures solar panels to your roof or ground. The racking system must be strong enough to withstand wind and snow loads.

Residential Energy Code

Local building standards that specify energy efficiency requirements for homes, including rules about solar installations. These codes vary by location and change periodically.

Rooftop Solar

A solar installation mounted on the roof of a building rather than on the ground. Rooftop systems save space and are the most common residential installation type.

Self-Consumption Rate

The percentage of solar electricity your household uses immediately rather than sending it to the grid. Higher self-consumption rates reduce your reliance on grid power.

Shading Analysis

An evaluation of how trees, buildings, and other obstacles block sunlight from reaching your solar panels throughout the year. Significant shading can reduce solar production by 20% or more.

Solar Irradiance

The power of solar radiation hitting a surface, measured in watts per square meter. Irradiance changes throughout the day and varies by location and weather.

System Size

The total capacity of your solar installation measured in kilowatts, based on the combined power rating of all panels. System size should match your energy needs and available roof space.

Tilt Angle

The angle at which solar panels are sloped relative to the ground or roof. The optimal tilt angle depends on your latitude and changes seasonally for maximum energy capture.

Time of Use Rate

An electricity pricing structure where rates vary depending on the time of day or season. Solar systems can be valuable when paired with time of use rates by shifting energy use to low-cost hours.

Voltage

The electrical potential difference that pushes electricity through a circuit, measured in volts (V). Household electricity in North America is typically 120 or 240 volts.

Watt

The basic unit of electrical power, representing the rate at which electricity is used or generated. One kilowatt equals 1,000 watts.

Watt-Peak

The maximum power output of a solar panel under standard test conditions of 1,000 watts per square meter of sunlight. Solar panel capacity is labeled in watts or kilowatts peak.