Solar Energy Terms & Energy Efficiency Glossary

AC Power — AC = Alternating Current. It's an electrical current with a magnitude and direction that constantly vary. Since homes and businesses receive their electricity in the form of AC, it is often called the "standard" type of electrical power.

Active Cooling — The use of mechanical heat pipes or pumps to transport heat by circulating heat transfer fluids.

Air Infiltration Measurement — A building energy auditing technique used to determine and/or locate air leaks in a building shell or envelope.

Air Leakage — Outside air that enters a house uncontrollably through cracks and openings.

Air Sealing — A seal to prevent passage of air or vapor.

Ampere (Amp) — This is simply a unit of measurement which tells you how much electrical current is flowing through your wires.

Appliance Energy Efficiency Ratings — The ratings under which specified appliances convert energy sources into useful energy, as determined by procedures established by the U.S. Department of Energy.

Average Demand — The energy demand for a given location over a period of time. For example, the number of kilowatt-hours used in a 24-hour period, divided by 24 hours, tells the average demand for that location in that time.

Blower Door — Machine used to measure the airtightness of buildings. It can also be used to measure airflow building zones, to test ductwork and help physically locate air leakage sites in the building envelope.

Building Envelope — The structural elements (walls, roof, floor, foundation) of a building that encloses conditioned space; the building shell.

Chimney Effect — The tendency of heated air or gas to rise in a duct or other vertical passage, such as in a chimney, or small enclosure, due to its lower density compared to the surrounding air or gas.

Crystalline Silicon — A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.

Demand — The level at which electricity is delivered to end-users at a given point in time. Electric demand is measured in kilowatts.

DC Power — DC = Direct Current. Unlike AC, it's an electrical current with a magnitude and direction that remain constant. Solar panels' photovoltaic cells capture solar energy in the form of DC, but it must be converted to AC power using an inverter before it can power your home or business.

Duct Leakage Tester — Diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow.

Electrical Current — Scientifically, this is simply the flow of charged electrons through a circuit. Current can either be alternating (AC) or direct (DC), depending on its behavior.

Electric Panel — AKA "breaker box" or "electrical cabinet", it's the place from which electricity is sent throughout the building. Circuit breakers are housed in this electrical distribution board.

Elements of a Solar System — Within the below definitions, the term ‘solar’ is interchangeable with ‘photovoltaics (PV)’.

  • Solar Cell: The smallest electrical element within a solar module that converts sunlight into electricity.

  • Solar Module: A physically connected collection of solar cells that converts sunlight into electricity, also referred to as a solar panel.

  • PV String: A number of modules or panels that are electrically interconnected in a parallel series to produce more current.

  • Solar Array: An interconnected system of solar modules that function as a single electricity-producing unit.

  • Solar System: The complete set of components for converting sunlight into electricity.

  • Solar Direct System: A simple system in which electricity can only be generated when exposed to sunlight.

Energy Audit — A survey that shows how much energy used in a home, which helps find ways to use less energy.

Fossil Fuels — These fuels - which include coal, oil, and gas - come from nonrenewable natural resources. There is only a finite supply of these resources and they're unequally distributed across the globe, which leaves them vulnerable to politics and causes unstable prices.

Greenhouse Gases (GHG) — Released by burning fossil fuels, these gases within Earth's atmosphere (such as the infamous carbon dioxide) contribute to climate change by slowly warming the planet. It's important to note that solar power is considered "clean energy" because the process of converting sunlight to electrical power doesn't produce any gases like these.

Grid Connected System — Solar system that is connected to the utility grid, allowing any additional electricity to be fed back to the grid.

Grid Parity — Occurs when the cost of generating alternative power costs less than or equal to the price of purchasing power from the grid.

Grounded Conductor — A circuit conductor that normally carries current, and is connected to ground. Also known as the neutral.

Ground Fault — Occurs when electricity travels outside an intended path and attempts to reach the ground by the shortest route.

Ground Mount — A solar energy system mounted on racking on the ground.

HVAC — Heating, ventilation, and air conditioning. It is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality.

Interconnection — This essential link is what allows electrical power to move effortlessly in either direction between your building and your utility company.

Inverter —  Converts DC power produced by solar modules to AC power.

  • Micro-inverters: An inverter that converts DC generated by a single solar module to AC. Micro-inverters contrast with conventional string and central solar inverters, which are connected to multiple solar modules or panels of the PV system.

  • String Inverter: A device for converting DC to AC power from a string of solar panels.

Insolation — The solar power density incident on a surface of stated area and orientation. It is commonly expressed as average irradiance in watts per square meter (W/m2) or kilowatt-hours per square meter per day (kW·h/(m2·day)) (or hours/day). In the case of photovoltaics it is commonly measured as kWh/(kWp·y) (kilowatt hours per year per kilowatt peak rating)

Junction Box — A container for electrically connected PV strings, intended to conceal them from site and deter tampering.

Kilowatt (kW) — While Amps measure current, Kilowatts measure power. (So do Watts; 1 kW is 1,000 Watts.) We use kW to measure the size of a solar energy system: 5 kW is a typical home solar installation, while 100 kW is a system for a medium-sized business.

Kilowatt Hour (KWh) — This measurement can be your friend or your enemy, since it's what your utility company uses to see how much you owe on your electric bill! Thus, KWh measures energy consumption. 1 KWh is the amount of energy consumed in 1 hour by a 1,000-Watt appliance running constantly.

Net Metering — A billing mechanism that credits solar system owners for the electricity they add to the grid. Allows residential and commercial customers who generate their own electricity from solar power to feed electricity they do not use back into the grid. Some states have passed net metering laws to encourage the use of renewable energy, while other states oppose the mechanism.

Net Zero — A building that generates as much energy as it uses.

On/Off Grid System — If your solar energy system is connected to the utility grid, it's an "on-grid" or "grid-tied" system. If it is not connected and instead has battery storage, it's an "off-grid" system.

Photovoltaic (PV) Panels — A device that produces an electric reaction to light, thereby producing electricity.

Photovoltaic (PV) Array — An interconnected system of PV modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

Photovoltaic (PV) Conversion Efficiency — The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

Polycrystalline Silicon — A material used to make photovoltaic cells, which consist of many crystals unlike single-crystal silicon.

Roof Mounted System — The majority of solar systems are roof mounted, which simply means that the solar panels are mounted directly on a roof.

Smart Home — A home equipped with lighting, heating, and electronic devices that can be controlled remotely by smart phone or computer.

Solar Array — Another term for a group of solar panels.

Solar Energy — Transmitted by the sun, this electromagnetic energy needs to be captured by solar panels and converted to AC electrical power in order to be used in homes and businesses.

Solar Panel — Also known as solar modules, these panels are made of a group of solar cells. They capture energy from the sun and convert it to DC power.

Stand-Alone System — Also known as off-grid system, these are not connected to the utility grid. This means that they need to be connected to storage units, so that continuous power can be provided even during the night.

Tilt Angle — Depending on location, solar arrays can either be installed flat or at a tilt for maximum exposure to sunlight. The tilt angle is simply the angle at which an array is toward the sun.

Time-of-Use Rates (TOU Rates) — A way of utility billing, the price of electricity in this system depends on the time of day it is used. These rates are highest in the afternoon, when many people are using electricity, and lowest at night, when there is less demand.

Utility Grid — "The Grid" is comprised of the power lines, transformers, and substations that delivers energy to homes and businesses. Utility companies own and manage this vast infrastructure.

Volt (V) — This measures the amount of force required to maintain a steady electrical current. In most homes in the United States, it's 120 V.

Watt (W) — A thousand times less than a Kilowatt, this is the standard unit of measurement for both power capacity and demand. As you may have noticed, light bulbs are classified by their wattage.