Alternating Current (AC): The electricity used in households is AC, or Alternating Current. AC electricity changes voltage periodically, typically 60 times a second.

Active Solar: technology that uses electrical or mechanical equipment to convert solar energy into usable light, heat, cause air-movement for ventilation or cooling, or store heat for future use.

Back up energy system: An uninterruptible power supply (UPS), also known as a battery backup, provides emergency power and, depending on the topology, line regulation as well to connected equipment by supplying power from a separate source when utility power is not available

BTU (British thermal unit): a unit of heat equal to the amount of heat required to raise one pound of water one degree Fahrenheit at one atmosphere pressure; equivalent to 251.997 calories.

Collector Efficiency: The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.

DC Current: an electric current that flows in one direction steadily. DC is produced by solar cells.

Drain Back Solar Thermal System: a closed loop solar thermal system in which the fluid in the solar loop drains into tanks when the system is not in use.

Electrical Grid: interconnected network for delivering electricity from suppliers to consumers.

Energy Audit: an inspection, survey and analysis of energy flows for energy conservation in a building, process or system to reduce the amount of energy input into the system without negatively affecting the output(s).

Fixed Tilt Array: a set (array) of solar power collectors that do not pivot to follow the track of the sun in the sky. In the Northern Hemisphere, they are usually mounted with a southern tilt that will maximize the amount of energy that they can receive.

Flat Plate Collector: a solar power collector that absorbs the sun's energy on a flat surface without concentrating or refocusing it.

Grid-Tied System: a solar electric system that sends the energy it produces back to a utility company’s electrical grid.

Heat Exchanger: A device designed to transfer heat between two physically separated fluids or mediums of different temperatures.

Interconnection: refers to the technical and practical aspects of connecting the solar generator to the grid. This includes the DC to AC power inverter, disconnect switches, distribution panel, and meter.

Inverter: a device that changes DC power at its input into AC power at its output. Also called a power converter.

Kilowatt (kW): a unit of power equal to 1000 watts

Kilowatt Hour (kWh): a unit of energy equal to the work done by a power of 1000 watts operating for one hour

Megawatt (mW): a unit of power equal to one million watts

Megawatt Hour (mWh): a unit of energy equal to the work done by a power of 1,000,000 watts operating for one hour

Monocrystalline: a crystalline solid in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.

North American Board of Certified Energy Practitioners (NABCEP): an organization that is committed to providing a certification program of quality and integrity for the professionals and consumer/ public it is designed to serve.

National Electrical Code (NEC): a United States standard for the safe installation of electrical wiring and equipment.

Net Metering: A practice used in conjunction with a solar electric system where your electric meter tracks your net power usage, spinning forward when you use electricity from the utility, and spinning backward when your system is generating more electricity than you need.

Passive Solar: technologies are means of using sunlight for useful energy without use of active mechanical systems.

Photovoltaic: refers to a technology which uses a device (usually a solar panel) to produce free electrons when exposed to light, resulting in the production of a DC electric current.

Photovoltaic Cell: An electric cell made from two layers of different materials that can produce an electric current when light shines on the cell.

Pressurized Solar Thermal System: a closed loop solar thermal system in which the fluid in the solar loop is always pressurized and present in all parts of the loop.

Renewable Energy: energy generated from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are naturally replenished.

Renewable Energy Credits (RECs): represent the environmental and economic value of electricity produced from clean, renewable, emission-free energy resources that are safe for our environment and will never be depleted. RECs hold real and quantifiable economic value and act like a form of currency that allows the environmental attributes of renewable energy generation to be separated from the electricity commodity and to be sold as a separate product.

Retrofit: The application of a solar energy technology to an existing building

Silicon (Si): a tetravalent non-metallic element; next to oxygen it is the most abundant element in the earth's crust; occurs in clay, feldspar, granite, quartz and sand; used as a semiconductor in transistors, such as photovoltaic cells.

Solar Array: a grouping of multiple solar panels

Solar Energy: energy from the sun that is converted into thermal or electrical energy

Solar Thermal: a technology for harnessing solar energy for thermal energy (heat).

Thin Film: employ materials such as amorphous silicon (a-Si, still silicon, but in a different form), cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS).   These materials have high light absorbency and a much thinner layer of material is required.

Watt: a unit of power equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a resistance of 1 ohm