Glossary of Terms

Alternating current (AC): Electric current in which the direction of flow is reversed at frequent intervals. This is the most common type of household electricity. In the USA and Canada, the direction of flow is
reversed 120 times a second, resulting in 60 complete cycles per second.

Ampere or amp (A): The unit of measurement for electric current. One amp is one coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm. A normal household lightbulb uses a current of about 0.5 amps, whereas an electric oven may have 20 amps or more passing through it.

Angle of incidence: Describes the angle between the surface of an object and the direction of incident solar radiation. Solar cells produce most power when the cell surface is exactly perpendicular to the direction of sunlight. In solar parks, motorized trackers keep each cell pointed in the optimum direction as the sun moves across the sky.

Balance of system (BOS): Represents all components and costs other than the PV modules. It includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, batteries, indirect storage, and related costs.

Building-integrated PV (BIPV): Used to describe a structure where photovoltaic (PV) material replaces conventional materials and is integrated into the building.

Cell efficiency:  The percentage of electrical energy that a solar cell produces (under optimal conditions) as compared with the total amount of energy from the sun falling on the cell. Typical cell efficiency is currently between 12% and 19%, although this value is improving all the time.  When cells are connected into a module, the efficiency of the module will be lower than the efficiency of individual cells due to other factors.

Clean energy: Clean energy can be generally defined as energy from renewable sources such as biomass, wind, or solar power. The goal of clean energy is to have a low environmental impact, with low or zero emissions, and a minimal impact on the physical surroundings.  Hydropower can be defined as clean energy due to zero emissions, but today's hydropower still often has substantial impacts on aquatic
ecosystems. Waste-burning and wood-burning systems that capture emissions can be clean energy generators. Fossil fuels do not provide clean energy because of their emissions and environmental impacts.

Conversion efficiency: The percentage of electricity that is created by a solar cell as compared with the amount of energy needed to generate that electricity.

Current: The flow of electricity between two points. Measured in amps.

Direct current (DC):  Electrical current that flows only in one direction.  The most common form of electricity used in cars, boats and RVs. Small devices such as torches or radios use DC current, usually powered by batteries.


Distributed systems: Installed systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential solar system is a distributed system. Generating power close to where it is needed means less electricity is lost due to inefficiencies of transmission lines or other equipment.

Efficiency:  The ratio of output energy to input energy.

Electrical grid:  A large distribution network that delivers electricity over a wide area.

Feed-In-Tariff (FIT): An agreement that allows owners of PV systems to sell energy to the electric grid.  The grid is required to buy the power at rates that are higher than the usual retail price.  The price declines with age of the installation, thereby encouraging new investment in PV panels in order to capture a higher tariff.

Grid: A distribution network, including towers, poles, and wires that a utility uses to deliver electricity.

Grid-connected PV system: A solar system that is tied in to the utility's network. When generating more power than necessary, the system supplies the surplus to the grid. At night, the system draws power from
the grid.

Insolation:  Short form of "incident solar radiation", or the amount of sunlight falling on an object. Not to be confused with "insulation". Equal to about 1000 watts per square metre at high noon.

Inverter: An inverter converts the electricity generated from a solar array from direct current (DC) to alternating current (AC) for use in the home or for export to the grid.

Irradiance:  The amount of solar energy that strikes a surface during a specific time period. Measured in kilowatts.

I-V curve: The power output from a solar module is equal to the voltage (V) multiplied by the current (I) at which it is operating. A given solar module in a given set of lighting conditions will have an I-V curve representing a range of possible operating points at those specific conditions. Three important points on the IV curve are the open-circuit voltage, short-circuit current, and peak or maximum power point.

Kilowatt (kW): A unit of electrical power, one thousand watts.

Kilowatt-hour (kWh):  One thousand watts acting over a period of one hour. The kWh is a unit of energy. A typical Canadian household uses about 10,000 kWh per year.

Life-cycle cost: The estimated cost of owning, operating, and disposing of a system over its useful life.

Load: Anything that is connected to an electrical circuit and draws power from that circuit.

Megawatt (MW): One million watts; 1,000 kilowatts.

Monocrystalline solar cell: A type of solar cell made from a thin slice of a single large crystal silicon.

Multicrystalline:  Material that is solidified at such as rate that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged, whereas crystallites are jumbled together. These numerous grain boundaries reduce the device efficiency. A material composed of variously oriented, small individual crystals. (Sometimes referred to as polycrystalline or semicrystalline).

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 home: A house that utilizes part of the building as a solar collector, as opposed to active solar, such as photovoltaic (PV).

Peak load: The largest amount of electricity being used at any one point during the day.

Photovoltaic (PV): The direct conversion of light into electricity. Photo means "light", voltaic means "electric".

Photovoltaic array: An interconnected system of solar modules that function as a single electricity-producing unit.

Photovoltaic cell: A photovoltaic (PV) cell is the most basic element of a solar photovoltaic system. Each cell is made from semiconductor materials, and creates an electrical charge in reaction to sunlight that can be transformed into a current of electricity

Photovoltaic module: A photovoltaic (PV) module is one or more photovoltaic cells covered with a layer of glass, an anti-reflective sheet or coating, and a backing and frame to provide support for installation. It
can be used as a source of clean power for homes and businesses, and multiple panels can be configured into an array.

Renewable Energy: Renewable energy comes from sources that can be replenished on a human time scale, such as biomass (wood), or that are essentially inexhaustible, such as waste and geothermal, wind, and solar energy. Fossil fuels are non-renewable energy sources; there is a finite supply of them. Renewable energy is also often clean energy; it can be generated with few or zero emissions and little to no environmental damage.

Silicon (Si): A chemical element, atomic number 14, semi-metallic in nature, dark gray, an excellent semiconductor material. A common constituent of sand and quartz (as the oxide).  Crystallizes in face centered cubic lattice like a diamond. The most common semiconductor material used in making photovoltaic devices, and one of the most abundant elements on the planet.

Solar constant: The strength of sunlight; 1353 watts per square metre in space and about 1000 watts per square metre at sea level at the equator at solar noon.

Solar-grade silicon:  Intermediate grade silicon used for making photovoltaic cells. Less expensive than electronic-grade silicone.

Thin film: A solar PV module constructed with sequential layers of thin film semiconductor materials usually only micrometers thick. Currently, thin-film technologies account for around 12 percent of all solar modules sold worldwide. This share is expected to increase, since thin-film technologies represent a potential route to lower costs. Commonly called amorphous.

Volt (V): The measurement of the force or 'push' given to the electrons in an electric circuit. One volt produces one ampere of current when acting against a resistance of one ohm.

Watt (W): A unit of power, or the amount of work done in a period of time. One ampere of current flowing at a potential of one volt produces one watt of power. A typical household lightbulb uses 60 watts of power.  A person climbing a flight of stairs uses 200 watts of power.

Watt-hour (Wh): A unit of energy equal to one watt of power being used for one hour.

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