Solar decisions get unnecessarily confusing when power, energy, pricing and utility terminology are mixed together. This glossary keeps the definitions short and connects important terms to deeper calculators and guides.
AC (alternating current)
The form of electricity used by normal household circuits and the utility grid. Solar panels produce DC electricity, which an inverter converts to AC for most home uses.
Azimuth
The compass direction a solar array faces. In PVWatts-style modeling, 180° represents south, 90° east and 270° west.
Battery capacity (kWh)
The amount of electrical energy a battery can store. Capacity is different from power: a 13.5 kWh battery does not necessarily deliver 13.5 kW of power.
Battery power (kW)
How quickly a battery can deliver electricity at one moment. Continuous and short-duration peak power help determine which household loads can run at the same time.
Clipping
Energy that could have been produced by the solar array but is limited because inverter AC output has reached its maximum. Some clipping can be normal in a deliberately DC-oversized design.
Cost per watt ($/W)
Solar-only installed price divided by the system's DC watts. It is one of the cleanest ways to compare differently sized cash-price proposals when batteries and unrelated upgrades are separated.
Learn more →DC (direct current)
The form of electricity produced by photovoltaic modules and stored internally by many battery systems before conversion to household AC electricity.
DC system size
The nameplate capacity of all solar modules added together, normally expressed in kilowatts DC. A system with twenty 440 W panels is 8.8 kW DC.
Degradation
The gradual reduction in solar-panel output over time. Performance warranties normally define minimum retained output or a maximum annual degradation schedule.
Export rate
The value a utility assigns to electricity a home sends to the grid. The export rate can equal the retail rate under some programs or be materially lower under net-billing structures.
Learn more →Inverter
Equipment that converts DC solar electricity into grid-compatible AC electricity. Residential systems can use a central/string inverter, microinverters or other architectures.
kW (kilowatt)
A unit of power. Solar-array size and instantaneous battery output are commonly described in kW. It describes a rate of energy production or use, not an amount accumulated over time.
kWh (kilowatt-hour)
A unit of energy. Utility bills, annual home consumption, solar production and battery storage capacity are commonly expressed in kWh.
Net billing
A distributed-generation structure in which exported solar electricity is credited at a defined export value that can differ from the retail price paid for imported electricity.
Learn more →Net metering
A billing structure that credits customer-generated electricity exported to the grid according to program rules. Exact credit values, rollover rules and eligibility vary by utility and jurisdiction.
Learn more →PVWatts
A photovoltaic production model from the National Laboratory of the Rockies used by Home Solar Atlas for ZIP-specific planning estimates when location data are available.
Learn more →Solar offset
The share of a home's annual electricity consumption that a solar system is expected to produce over a year. A 100% annual offset does not mean the home is disconnected from the grid.
Solar yield (kWh/kW/year)
Annual solar production divided by installed DC system size. It makes it easier to compare production potential between locations and system sizes.
TOU (time-of-use) rate
An electricity tariff where the price of grid electricity changes by time of day or day type. TOU pricing can materially change the value of daytime solar and evening battery discharge.
Learn more →Usable roof area
The portion of a roof that can realistically host solar modules after orientation, shade, obstructions, access paths, setbacks and other design constraints are considered.
Learn more →Use the terms in a real calculation
Start with the Home Solar Calculator, compare solar-panel specifications, research utility tariffs and use the Quote Analyzer when an installer proposal arrives.