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Alternating Current (AC) A type of electrical current, the direction of which is reversed at regular intervals or cycles. Electricity transmission networks use AC because voltage can be controlled with relative ease.

Azimuth: The angle between true south and the point on the horizon directly below the sun.


Balance of System (BOS) costs: All components of a photovoltaic system except the modules, e.g. the inverter, sub panels, wiring, switches, fuses, mounting system, flashing, batteries, labour, permitting, inspection and interconnection.

BTU: The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.


Charge Controller: An element in some photovoltaic systems that controls the flow of current to and from the battery to protect it from overcharging or over discharging.

Concentrating Solar Power (CSP): A system that concentrates solar rays onto a small area using lenses or mirrors and tracking devices. The concentrated light is then used as a heat source for a conventional power plant (called solar thermal electric). It can also be focused on a photovoltaic cell to increase its conversion efficiency.

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


Degradation Rate: Photovoltaic estimates of return on investment require accurate predictions of decreased power output over time. Degradation rates need to be known in order to predict power delivery. Years of research show an average degradation rate of 0.8%/year and a median value of 0.5%/year (Photovoltaic Degradation Rates – An Analytical Review, Jordan and Kurtz, 2012).

Degradation happens over time from the effects of temperature and UV exposure. Most modules come with 25 year efficiency warranties. This guarantees that after 25 years the module will still produce 80% of the power that it did when it was new. Note: PV manufactures often show a higher first year degradation rate, e.g. 2.5% and then subsequent years of 0.5%/year.

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. When used for most 120 volt or 220 volt household appliances, DC is converted to alternating current (AC).

Disconnect: A switching device used to connect or disconnect components in a photovoltaic system.


Easement: An oral or written legal agreement defining an interest in exclusive, common or bipartisan use of private property or air/space above that property. A common form of easement is the concept of “right of way,” as when an electric utility has the right of way to extend electrical transmission lines across private property.

Electric Current: The flow of electricity in a conductor, measured in amperes.

Electrical Grid: An integrated system of electricity distribution.

Electricity: Energy resulting from the flow of charge particles, such as electrons.

Energy: The amount of power consumed or produced over a given period of time, measured in watt-hours (Wh) or kilowatt-hours (kWh).

Energy Conservation: Reduces the need for energy by changing our behaviours, i.e. turning the lights off when not needed.

Energy Efficiency: Reduces the amount of electricity that is required to be produced in order to power an electrical device, i.e. a TV.

Equinox: March 21st (spring equinox) and September 23 (fall equinox). When the tilt of the Earth’s axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth’s equator.


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

Fossil Fuels: Fossil fuels are non-renewable sources of energy. Burning our remaining fossil fuels for energy will prevent us, and future generations, from the many beneficial uses (refined components of fossil fuels are used in thousands of household products, clothing, medicine, cosmetics, etc.)


Gigawatt (GW): A unit of power equal to 1 billion Watts, 1 million kilowatts, or 1,000 megawatts.

Grid Connected System: A solar electric or photovoltaic (PV) system that supplies power to the grid, similar to that of a power generating plant.


Heliostat: A mirror which tracks the sun’s movement across the sky and reflects the sun’s heat to a specific location or receiver located on top of a tower as is used in some solar thermal plants.

Hybrid System: A system that includes sources of electricity generation from more than one source, i.e., solar electric or photovoltaic, wind, or diesel generators.


Infrared Radiation: Electromagnetic radiation whose wavelengths lie in the range from 0.75 micrometer to 1000 micrometers; invisible long wavelength radiation (heat) capable of producing a thermal or photovoltaic effect, though less effective than visible light.

Inverter: A power converter that converts direct current (DC) electricity to alternating current (AC) electricity. Can be used in stand alone electrical power systems or when supplying power to the grid.

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.
(Western Canadian Insolation Map).


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 photovoltaic (PV) generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices can be located.


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

Kilowatt Hours: 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy.
1kWh = 3600 kJ.


Levelized Cost of Energy (LCOE): Measures the total cost of electrical generation over the lifetime of an asset. LCOE is arrived at by dividing total system cost by total lifetime energy produced.

Lifecycle Cost: The estimated cost of owning and operating a photovoltaic system for the period of its useful life.

Load Circuit: The wire, switches, fuses, etc. that connect the load to the power source.

Load Current (A): The current required by the electrical device.


Megawatt (MW): 1,000 kilowatts, or 1 million watts. A standard used to measure electric power plant generating capacity.

Megawatt-Hour: 1,000 kilowatt-hours or 1 million watt-hours.

Micro-inverter: Converts direct current (DC) electricity from a single solar module to alternating current (AC). The electric power from several micro-inverters is usually combined and fed into an existing electrical grid. Micro-inverters differ from conventional string or central inverter devices, which are connected to multiple solar modules.

  • Micro-inverters have advantages over conventional central inverters in that even small amounts of shading, debris or snow lines in any one solar panel, or a panel failure, does not disproportionately reduce the output of an entire array.
  • The main disadvantage is the higher equipment cost per peak watt than the equivalent power in a central inverter. Micro-inverters are also located near the panel thus making them harder to maintain. These issues are however balanced by micro-inverters having good durability and simplicity of initial installation.

Module: The smallest environmentally protected assembly of solar cells and ancillary parts, such as interconnections, terminals, 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 Zero Building: A building that generates as much energy as it uses.

Nominal Voltage: A reference voltage used to describe batteries, modules, or systems, i.e., a 12-volt or 24-volt battery, module, or system.


Ohm: A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

One-Axis Tracking: A sun tracking system capable of rotating about one axis.


Panel: Often used interchangeably with PV module (especially in one-module systems), but more accurately used to refer to a physically connected collection of modules.

Peak Watt: A unit used to rate the performance of solar cells, modules, or arrays. The maximum output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.

Photovoltaic Array: An system of interconnected PV modules that function as a single unit to produce electricity. The modules are assembled together with a common support and mounting. In a small systems, an array could be a single module.

Photoelectric Cell: Is an electrical device that works by converting light energy falling on it, into electricity.

Photovoltaic Efficiency: The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

In 1883 Charles Fritts invented a solar cell that produced 1% or so conversion efficiency form light to electricity. Some of today’s solar companies are claiming rates up to 40%

Photovoltaic System (PV System): The complete set of components for converting sunlight into electricity by the photovoltaic process. A system is made up of one or more solar photovoltaic (PV) panels, an AC/DC power inverter, a racking system that holds the solar panels, and the interconnections and mounting for the other components.

Polycrystalline Silicon: Is a material used to make photovoltaic cells, which consists of many silicon crystals. It differs from single-crystal silicon and from amorphous silicon, used for thin film devices and solar cells. Polycrystalline cells are recognized by a visible grain in the silicon, a “metal flake effect”.

Power: Power equals volts times current.

Volts × Current = PowerV × I = P Power ÷ Current = VoltsP ÷ I = V Current = Power ÷ VoltsI = P ÷ V

Power Purchase Agreement (PPA): A long-term contract between an energy provider and a client to purchase electrical power.


Quad: A quad is a unit of energy equal to 1015 (a short-scale quadrillion) BTU, or 1.055 × 1018 joules (1.055 exajoules or EJ) in SI units.

The unit is used by the U.S. Department of Energy in discussing world and national energy budgets. The global primary energy production in 2004 was 446 quad, equivalent to 471 EJ.

Some common types of an energy carrier approximately equal 1 quad are:

  • 8,007,000,000 Gallons (US) of gasoline
  • 293,083,000,000 Kilowatt-hours (kWh)
  • 36,000,000 Tonnes of coal
  • 970,434,000,000 Cubic feet of natural gas
  • 5,996,000,000 UK gallons of diesel oil
  • 25,200,000 Tonnes of oil


Regulator: Prevents batteries from being overcharged by controlling the charge cycle, usually adjustable to conform to specific battery needs.

Reserve Capacity: The amount of generating capacity a central power system must maintain to meet peak loads.

Restrictive covenant: A specialized type of easement that can be used to protect access to sunlight or wind flow for solar or wind energy applications.


Semiconductor: Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Semiconductors are the foundation of modern electronics, including radio, computers, and telephones. Semiconductor-based electronic components include transistors, solar cells, many kinds of diodes including the light-emitting diode (LED), the silicon controlled rectifier, photo-diodes, and digital and analog integrated circuits.

Smart Grid: A smart grid is an electrical grid that uses information and communications technology to gather and act on information, such as information about the behaviors of suppliers and consumers, in an automated fashion to improve the efficiency, reliability, economics, and sustainability of the production and distribution of electricity.

Solar Energy: Electromagnetic energy transmitted from the sun (solar radiation). The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year.  In one hour this is more energy than the world used in an entire year. Solar energy technologies include solar heating, solar thermal electricity and solar architecture.


Thin-Film: A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make photovoltaic cells.

Tilt Angle: The angle at which a photovoltaic array is positioned to face the sun relative to its horizontal position. This angle can be adjusted to maximize energy collection.

Tracking Array: A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. A single axis tracking system tracks the sun from east to west. A dual axis tracking system points directly at the sun at all times. Dual axis tracking arrays capture the maximum possible daily energy, but can add substantial costs to a system.

Transformer: An electromagnetic device that changes the voltage of alternating current electricity. Transformers range in size from a pebble sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used in power stations, or to interconnect portions of power grids.


Utility-Interactive Inverter: An inverter that can function only when tied to the utility grid. It uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the photovoltaic system’s output is fully synchronized with the utility power.


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. The volt is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery.

Voltage: The amount of electric potential difference, measured in volts, that exists between two points.

Voltage is equal to Current multiplied by Resistance.

Current × Resistance = Volts I × R =  V Volts ÷ Resistance = Current V ÷ R = I Volts ÷ Current = Resistance V ÷  I = R



Wafer:  The thin slice of semiconductor material, silicon crystal, made by cutting it from a single crystal or ingot,  used in the fabrication of photovoltaic material.

Watt: The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt.  It is the product of voltage and current (amperage). W = V x A




Zenith Angle: the angle between the direction of interest (of the sun, for example) and the zenith, an imaginary point directly “above” a particular location.

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