Solar Definitions

Array - An interconnected system of photovoltaic modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting.

Alternating Current (AC) - A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.

Btu (British Thermal Unit) - The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.

Balance of System - Used to describe the AC and DC breakers, fuses and other electrical safety components of a utility or grid tied solar electric system. Components other than the solar modules, mounting structure, and inverter.

BIPV (Building-Integrated Photovoltaics) - A term for the design and integration of photovoltaic (PV) technology into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading "eyebrows" over windows; or other building envelope systems.

Cell - The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy.

Direct Current (DC) - A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120-volt or 220-volt household appliances, DC must be converted to alternating current, its opposite.

Electrical Grid - An integrated system of electricity distribution, usually covering a large area.

Grid-Tie System (GTS) - A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, supplying power to the grid. Also called a Grid-Connected System.

Hybrid System - A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.

Irradiance - The direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation .

Inverter - A device that converts direct current electricity to alternating current, either for stand-alone systems or to supply power to an electricity grid.

Joule - A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.

Junction Box - A PV generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices can be located, if necessary.

Watt Hours - 1,000 (thousand) watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.

Kilowatt -- A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

Module - The smallest environmentally protected, essentially planar assembly of solar cells and ancillary parts, such as interconnections, terminals, [and protective devices such as diodes] intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Net Metering - The practice of exporting surplus solar power during the day (to actual power needs) to the electricity grid, which either causes the home owner electric meter to (physically) go backwards and/or simply creates a financial credit on the home owner's electricity bill. (At night, the homeowner draws from the electricity grid in the normal way).

Off-Grid System - An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most off-grid systems require batteries or some other form of storage. Also called a stand-alone system.

Parallel Connection - A way of joining solar cells, photovoltaic modules, or photovoltaic panels by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.

Panel - often used interchangeably with PV module, but more accurately used to refer to a physically connected collection of modules.

Peak Sun Hours - The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 w/m2.

Photovoltaic (PV) - Pertaining to the direct conversion of light into electricity.

Rack Mounts - In a rack mount, the photovoltaic modules (solar panels) are supported by a metal framework and are set at a predetermined angle. The rack-mounted solar array is placed above the roof with the rack's members bolted to the roof's structural members.  Please don't hesitate to contact us for consultation if you have related questions.

Renewable Energy Resource - An energy resource that is regenerative or virtually inexhaustible. Typical examples are wind, solar, geothermal, and water.

Series Connection -Electrical connection where the positive terminal of one device is attached to the negative terminal of the next in a series string. In this type of connection.

Tilt Angle - The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

Tracking Array - A PV array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.

Volt - A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.

Voltage - The amount of electromotive force, measured in volts, that exists between two points.

Watt - The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).