Alternating current (AC) = the ‘traditional’ type of electric current that powers all electric appliances in your home – the most common type of household electricity. It is called ‘alternating’ because the direction of the electric current’s flow is reversed at frequent intervals, usually 100 or 120 times per second (50 or 60 cycles per second or 50//60 Hz).
Amorphous semiconductor = a non-crystalline semiconductor material used to make thin film solar panels. Although it’s easier and cheaper to make than crystalline semiconductors, it’s also less efficient. It slowly degrades over time. Also called thin film.
Amorphous solar cells = these blue, flexible, non crystalline structure solar cells are generally larger than the other panels. They offer better performance in shaded conditions.
Ampere or amp (A) = The unit of measurement for the electric current, the flow of electrons. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm. One amp is 1 coulomb passing in one second.
Ampere-Hour (Ah/AH) = A measure of the flow of current (in amperes) over one hour; used to measure battery capacity. Deep cycle batteries used in solar power for homes systems are rated in Ah (amp-hour).
Angle of incidence = Angle between the normal to a surface and the direction of incident radiation; applies to the aperture plane of a solar collector. Most modern solar panels have only minor reductions in power output within plus/minus 15 degrees.
Antireflection coating = A thin coating of a material applied to a photovoltaic cell surface that increases light transmission by reducing light reflection.
Array = a set or grouping of photovoltaic solar panels. For example, you may need several arrays on separate parts of your roof when installing your solar power for homes system.
Autonomous system = A stand-alone PV system that has no back-up generating source. May or may not include storage batteries. Most battery systems are designed for a certain minimum “days of autonomy” – which means that the batteries can supply sufficient power with no sunlight to charge the batteries. This varies from 3-5 days in the sunbelt to 5 to 10 days elsewhere.
Azimuth = Angle between the north direction and the projection of the surface normal into the horizontal plane; measured clockwise from north. As applied to the PV array. So, 180 degree azimuth means the array faces due south.

Battery = Two or more electrochemical cells connected to provide energy storage for the extra power your solar power for homes system generates. A home can use the stored power at night, on overcast dark days or in the event of a power outage when the solar system isn’t producing enough energy.
Blocking Diode = Effectively a one-way valve that allows electrons to flow forwards, but not backwards, this semiconductor or diode is connected in series with a solar cell or cells and a storage battery in order to block reverse current from flowing backward through a module in a circuit. It keeps the battery from discharging through the cell when there is no output, or low output, from the solar cell and is often used to prevent a battery from discharging through a Solar Array at night.
British thermal unit (BTU) = The total amount of heat energy needed to make the temperature of one pound of water rise from 60 degrees F to 61 degrees F in a room with an atmospheric pressure of one.
Building-integrated PV (BIPV) = Used to describe a structure where photovoltaic panels are integrated into the building replacing traditional materials.
Bypass Diode = A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell/s become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading, broken cells, or cell string failures of individual solar cells while other cells are exposed to full light. Alternatively, a diode that is connected in an anti-parallel across a part of the solar cells of a photovoltaic module.

Cell = the basic unit of a solar panel that converts light into solar power for homes (also known as ‘electricity’).
Cell barrier = A very thin region of static electric charge along the interface of the positive and negative layers in a photovoltaic cell that stops the movement of electrons from one layer to the other. Thereby, a voltage and current is created across the cell’s higher-energy electrons. Sometimes referred to as the depletion zone, space charge or cell junction.
Cell efficiency = The percentage level of electrical energy that a solar cell produces (under optimal conditions) as compared to the total amount of energy that hits the cell from the sun.
Cell junction = The area of immediate contact between the positive and negative layers of a photovoltaic cell. The cell junction is found at the center of the cell barrier or depletion zone.
Charge controller = The part of the PV system that regulates the state of the battery’s charge, controling the voltage applied to the battery system from the PV array. It controls the flow of current into and out of the battery and thereby protects the battery from overcharging and overdischarging. Sometimes the charge controller can also provide other system control functions. For example, it may also show the operational status of the photovoltaic system. The charge controller serves to ensure that the batteries maintain the maximum possible state of charge and the longest life.
Charge Rate = The amount of current needed for a battery to restore its energy capacity, ie to become fully charged or discharged. The rate refers to the battery’s charging to full capacity and within a designated time period. For example, the total current needed to charge a 100 ampere per hour battery from zero to full charge in five hours (20 amperes) is referred to as the battery’s C/5 rate.
Circuit = A set of conductors grouped into a system in order to convey electricity.
Circuit breaker = A safety device designed to switch off power when it senses a potential overload of electrical current.
Concentrator = A PV module that uses optical elements to increase the amount of sunlight landing on a PV cell. It tracks the path of the sun to capture direct sunlight (any diffuse portion cannot be optimally focused onto the PV cells). T the high heat this creates increases efficiency in the short term but normally will lead to a reduced lifespan fro the solar panels.
Concentrator array, module or collector = An set of PV cells (aka a PV array) arranged such that a lens or lenses, reflectors, mirrors or suchlike can concentrate the direct rays from the sun onto solar cells and thereby concentrate the solar energy striking any given area of solar panel. Good quality concentrators can multiply the power flux of sunlight by hundreds of times. They may reduce size of the solar panels needed bringing savings in materials and therefore overall costs.
Conductor = A material such as wiring that is designed to convey electricity.
Conversion efficiency = The percentage of electricity that is created by a solar cell as compared to the amount of energy needed to generate that electricity.
Current = Measured in amps, this is the flow of electricity between two points.
Current at Maximum Power (Imp) = The current at which maximum power is available from a module.
Cycle life = The number of charge to discharge cycles that a battery can tolerate under specified conditions before it fails to meet specified performance criteria.

DC to DC converter = Electronic circuit that converts DC voltages (PV module voltage) into other level voltages (load voltage). Can be part of a maximum power point tracker (MPPT).
Deep discharge = Discharging a battery to 20 percent or less of its full charge.
Depth of Discharge (DOD) = an alternate method to indicate the state of charge (SOC) in a battery or battery system. The DOD is the inverse of SOC. As one increases, the other decreases.
Diffuse insolation = The opposite of direct insolation, this is the level of sunlight received indirectly as a result of scattering due to clouds, fog, or other obstructions in the atmosphere.
Direct Current (DC) = a type of low voltage electrical current. DC electricity always flows in only one direction through electrical wires and can be produced by solar cells. Direct current must be converted into AC before it can be used in a house although it remains the most common form of electricity used in boats and RVs.
Direct insolation = The level of sunlight falling directly on solar panel.
Discharge rate = The rate in amperes or in time, at which electrical current can be taken from the battery.
Disconnect = Switch gear that connects or disconnects components in your solar power for homes system.
Duty Cycle = The ratio of active time to total time. This refers to the operating set up of appliances or loads in your solar power for homes system.

Efficiency = The ratio of output energy to input energy.
Electric circuit = The path followed by electrons/electricity that starts at the generating source of the power (from either a generator or a battery) and continues through the devices that use the electricity before returning back to the source through another line.
Electric Current = The flow of electrons/electrical energy/electricity in a conductor, measured in amps/amperes.
Electrical grid = A large integrated system or distribution network of electricity covering a wide area.
Electricity = The controlled flow of electrons through a conductor.
Electrode = A conductor that leads an electrical current into or out of a non-metallic part of a circuit.
Electrolyte = A liquid conductor of electricity, usually sulphuric acid in the case of batteries.
Energy = Usable stored energy or power that can become working energy. Measured in kWh.
Energy audit = A process to establish how much energy your house or apartment consumes.
Energy density = The ratio of energy available from a battery to its volume (Wh/1) or mass (Wh/kg). Also known as the “watts to weight” ratio.
Energy payback time = The time needed for any energy producing system or device to produce as much energy as was needed to make it.
EVA (Etheylene Vinyl Acetate) = Used between the glass cover and the solar cells in PV modules, EVAs need to be resilient, durable, transparent, resistant to corrosion and flame retardant.

Float charge = the voltage needed to counteract the self-discharge of the battery at a certain temperature.
Float life = The number of years that a battery can maintain its stated capacity when it is kept at the float charge (see above).
Flat-plate PV = A PV array or module that uses direct and diffuse sunlight. Not the most efficient because the array is generally fixed in position so a large amount of the direct sunlight is lost because of it hits the panel at an oblique angle to the array.
Fossil fuels = Fuels formed underground from the ancient remains of dead plants and animals. Over time they become oil, natural gas, and coal.
Fuel cell = An essential device that is highly praise because it is clean and quiet. The fuel cell converts the energy of a fuel directly to electricity. This conversion does not involve combustion. Therefore fuel cells give off few emissions. Because fuel cells have no moving parts, they are quiet.

Gel-type battery = A type of lead-acid battery in which the electrolyte is made of a silica gel matrix.
Gigawatt = one billion watts
Greenhouse effect = When the sun’s heat gets trapped in the Earth’s atmosphere.
Greenhouse gases = The gases responsible for trapping sun’s heat within the Earth’s atmosphere – i.e. ozone, carbon dioxide, methane, chlorofluorocarbons, water vapor and/or nitrogen oxides.
Grid = a distribution network or system of high tension cables that distributes electricity to homes, businesses, and other buildings across a specified region. This may include the towers, poles, and wires that the energy company might use to deliver the electricity.
Grid tied/grid connected = A solar power for homes system in which the PV array acts like a central solar power generating plant. Both supplying and receiving power, it is connected to the national power grid and calls upon the grid from time to time as a backup source of power (at night time for example). It generates electricity for your home or business and re-routes any extra power back to the national power grid. Also known as on-grid or grid-connected.
Ground mount = a solar power for homes electrical system that stands on the ground rather than being mounted on a roof.
Ground loop = An unwanted feedback that happens when two or more circuits share the same electrical line, normally a grounded conductor.

Hertz (HZ) = The frequency of electrical current described in cycles per second. In the U.S. all appliances use 60 HZ.
Hot spot = An area where the solar cells within your solar power for homes system acts as a resistive load, causing overheating or melting of the cells.
Hybrid System = A solar power for homes system that also uses other methods to generate its electricity such as fossil fuel generators or wind power.

I-V curve = A graphical presentation plotting the current versus the voltage from the photovoltaic solar cell as the electrical load (or resistance) is increased from short circuit (no load) to the open circuit (maximum voltage). The shape of the curve characterizes the overall cell performance. Three important points to note on any IV curve are the short-circuit current, the open-circuit voltage and the peak or maximum power (operating) point.
Incident light = Light that shines onto the face of a solar cell or module.
Insolation = Shorthand term for ‘incident solar radiation’, insolation refers to either direct or diffuse sunlight. The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour. Not to be confused with ‘insulation.’
Interconnect = A conductor within a module or other means of connection that supplies an electrical connection between the solar cells.
Interconnection = the process of hooking up a solar electrical system to the power grid.
Inverter = A fundamental part of any photovoltaic system, this electrical device converts direct current (DC) electricity (from batteries or solar arrays for example) into alternating current (AC) electricity as required for domestic use. Inverters work either for stand-alone systems when not connected to the grid, or for utility-interactive systems.
Irradiance = Measured in kilowatts, the total quantity of solar energy that hits a surface during a specific time period.

Junction box = The point on a solar module where it connects to other solar modules. An enclosure where PV strings are electrically connected and where protection devices can be located, if necessary.
Junction diode = All solar cells act as junction diodes. Basically, a semiconductor device with a junction and a built-in potential that prefers to pass current in one direction rather than the other.

Kilowatt (kW) = A unit of electrical power equivalent to one thousand watts.
Kilowatt-hour (kWh) = A unit of energy equivalent to 1000 watts of power acting over a period of 1 hour. 1 kWh = 3600 kJ.

Life-cycle cost = The estimated total cost of owning, operating, and disposing of a photovoltaic system over its entire functional life.
Light-induced defects = Defects induced by exposure to light in an amorphous silicon semiconductor.
Light trapping = The effect of refracting and reflecting the light at critical angles is that the light is trapped inside a semiconductor material. Useful as trapped light will travel further in the material, thereby greatly increasing the likelihood of absorption and therefore of producing charge carriers.
Line-commutated inverter = An inverter tied to a power grid or line. The commutation of power (conversion from dc to ac) is managed by the power line, so that, if there were a failure in the power grid, the PV system could not feed power into the line.
Load = Anything that is connected to an electrical circuit and, when the circuit is turned on, draws power from that circuit. Usually expressed in terms of amperes or watts in reference to electricity.
Maximum Power Point Tracker (MPPT) = A power conditioning unit that automatically maintains the photovoltaic generator at its maximum power point (MPP) under all circumstances. Typically, an MPPT can increase the total power delivered to a solar power system by 10% to 40%, depending on climate conditions and the state of charge of the battery.

Megawatt (mW) = One million watts or 1,000 kilowatts
Microgroove = A small groove filled with metal for contacts that is scribed into the surface of a cell.
Module = A solar panel, or a group of solar cells – a module that has a number of interconnected PV cells of standard size and output power that are sealed with an encapsulant. The smallest building block of the power generating part of a PV array.
Monocrystalline panel = a solar panel that’s made from a large, single silicon crystal and has a patchwork pattern. Monocrystalline panels are more expensive and more efficient than multi- or poly- crystalline panels.
Monocrystalline solar cells = A durable type of photovoltaic solar panel made from a thin slice of a single large silicon crystal that is black in color and has a rigid construction but does not fill the whole panel area. To pick up light effectively they must be aimed at the sun correctly. In excessive heat, monocrystalline solar cells generally do not perform as well as polycrystalline cells.
Monolithic = Made up and fabricated as one single structure.
Multicrystalline = Sometimes referred to as polycrystalline or semicrystalline, this is a material made from many small crystallite crystals and composed of variously oriented, small individual crystals. This material is solidified at such a rate that many small crystals (crystallites) form. The atoms within crystallites are jumbled together while a single crystallite is symmetrically arranged. Because there are numerous grain boundaries inherent in the design, the product is cheaper but the efficiency of the multicrystalline device is not as great as monocrystalline devices.
Multicrystalline panel = (also polycrystalline) a solar panel that’s made from small silicon crystals oriented in lots of different directions. Multicrystalline panels are less expensive and less efficient than monocrystalline panels.
Multijunction device = Used to achieve greater overall efficiency, this is a photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.

Net meter = an electricity meter that spins both forward and backwards. It can track how much electricity your solar system puts into the power grid and how much electricity your home pulls out of the grid.
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.
Nominal Operating Cell Temperature (NOCT) = The solar cell temperature at a reference environment defined as 800 W/m2 irradiance, 20°C ambient air temperature, and 1 m/s wind speed with the cell or module in an electrically open circuit state

Ohm = The unit of resistance to the flow of an electric current.
One-axis tracking = A system capable of rotating about one axis.
Open-Circuit Voltage (VOC) = The largest voltage possible across a photovoltaic solar panel; the voltage across the solar panel in sunlight when no current is flowing.
Orientation = The direction that a solar panel faces. Establish orientation by finding two components – the tilt angle (the angle the solar panel makes from the horizontal) and the aspect angle (the angle the solar panel makes from North).

PV = Abbreviation for photovoltaic. (See below)
Panel = A group of solar cells, also known as a module.
Parallel connection = A way of connecting two or more devices that produce electricity (for example, modules or PV cells) by connecting negative leads together and also positive leads together. This style of configuration increases the flow of electrical current.
Passive solar home = A house that utilizes part of the building, such as a room or another part of the building, as a solar collector. The alternative is active home solar (see above).
Peak load = The largest amount, or maximum load, of electricity being used at any one point during a given period of time, normally over the course of one full day.
Peak watt = A unit used to rate the performance of solar cells, modules, or solar arrays; representing the maximum rated output of a photovoltaic device, stated in watts and established under standardized test conditions. Typical rating conditions are 0.645 watts per square inch, or 1,000 watts per square meter, of sunlight, 68 degrees F (20 degrees C), ambient air temperature and a wind speed of 6.2 x 10-3 mi/s (1 m/s).
Photon = A “packet” or particle of light energy acting as an individual unit of energy.
Photovoltaic = the process of directly converting light into electricity. Photo is Greek for “light”. Voltaic means “electric”.
Photovoltaic (PV) array = An interconnected system of photovoltaic modules that are all linked together, functioning as a single electricity-producing unit. In smaller systems, a PV array may consist of just one single module.
Photovoltaic (PV) cell = The smallest semiconductor element within a PV module, the basic unit of a solar panel that collects energy from the sun. Mostly made from silicon, they convert light into electrical energy (dc voltage and current).
Photovoltaic (PV) effect = The basic physical process when a solar cell converts sunlight into electricity. Sunlight is made up of packets of solar energy known as photons. The PV Effect has taken place when photons (the “particles” in a beam of sunlight) knock electrons loose from the atoms they strike. When photons strike a Photovoltaic cell some are absorbed producing electricity. The energy from the photons is transformed into an electron in an atom within the solar cell. As an electron, the energy can now escape the atom and flow as current in an electrical circuit. When this effect is passed into a semiconductor, electrons flow in one direction across a junction which sets up a voltage. Add circuitry to all this and current will naturally flow. Thereby electrical power is made available. (Here endeth the physics lesson!)
Photovoltaic (PV) efficiency = The ratio of electrical energy generated by a cell at any instant, to the power of the sunlight that is striking the cell. Commercially available cells average out about 9 percent to 14 percent.
Photovoltaic (PV) generator = The total of all electrically interconnected PV strings of a PV power supply system.
Photovoltaic (PV) module = The basic solar panel, the assembly of solar cells and ancillary parts, interconnections, terminals, (and protective devices such as diodes) that are protected from the environment by their layers of glass, plastic and metal frame. They re designed to generate dc electrical power from sunlight. They collect energy from the sun.
Photovoltaic (PV) panel = Also known as a PV module, this is a physically connected collection of modules or a laminate string of modules used to achieve a pre-stated level of voltage or current. Photovoltaic system = All the various parts needed to convert the light from the sun into electricity we can use. This will include the array and balance of system components. In addition to converting sunlight into electricity, the PV system collects the residual heat energy, gathers everything up and delivers both heat and electricity to us in usable form. A PV system might also be known as a ‘total energy system’.
Polycrystalline = see Multicrystalline.
Polycrystalline Solar Cells = Polycrystalline solar cells are very durable solar panels that are generally blue in color. These panels ensure that the individual crystals they consist of are made visible from many angles. Generally, the cells are square, thereby offering the most efficient power production from any solar panel size. The angle the panel is set at is not as important with polycrystalline solar cells as these cells can make use of light from many different angles. They are more efficient in low light and perform well in high temperatures.
Power conditioning equipment = A collective term for battery charge regulator, inverter, converter and blocking diode, this is the electrical equipment that is used to convert power from a photovoltaic array into a form suitable for subsequent use.
Power factor = The ratio of the average power and the apparent volt-amperes.

Qualification test = The official test, subject to a list of pre-defined requirements, that is applied to a selected set of PV modules. This test involves the application of defined mechanical, electrical or thermal stress in a prescribed manner and amount. If the module passes the test, it becomes qualified

Rated power = Nominal power output of an inverter; not all units can produce rated power continuously.
Rectifier = Converts AC to DC electric current, as in a battery charger or converter.
Remote systems = Off-grid energy systems.
Resistive voltage drop = The voltage developed across a cell by the current flow through the resistance of the cell.
Reverse bias = Condition where the current producing capability of a PV cell is significantly less than that of other cells in its series string. This can occur when a cell is degraded (shaded, cracked etc) or when it is poorly matched electrically with other cells in its string

Schottky barrier = A cell barrier that creates an interface between a semiconductor, such as silicon, and a sheet of metal.
Self discharge = The rate at which a battery will lose its charge.
Semiconductor = Uniquely suited to the photovoltaic conversion process, the semiconductor is a material that has a limited ability to conduct electric current between a metal and an insulator. Semiconductors used in different types of solar panels might include copper indium diselenide, cadmium telluride gallium arsenide, and silicon.
Semicrystalline = See ‘Multicrystalline.’
Series connection = A way of joining photovoltaic cells or batteries by connecting positive leads to negative leads; such a configuration increases the voltage.
Series regulator = Type of battery charge regulator where the charging current is controlled by a switch, transistor, or FET connected in series with the PV module or array.
Series resistance = Parasitic resistance to current flow in a cell due to mechanisms such as resistance from the bulk of the semiconductor material, metallic contacts, and interconnections.
Shelf life of batteries = The length of time, under pre-specified conditions, that a battery can be stored and still retain its stated capacity.
Short-circuit current (Isc) = Also known as the maximum current possible, this is the current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance.
Silicon (Si) = This semi-metallic chemical element with atomic number 14, is an excellent semiconductor material. In nature it is dark gray and is a common constituent of sand and quartz. Silicon is by far the most common semiconductor material used in making photovoltaic devices and computer chips.
Single-crystal silicon = Silicon material with a single crystal structure, commonly used in the production of solar photovoltaic cells.
Solar constant = The strength of sunlight. The average amount of solar radiation that reaches the earth’s upper atmosphere, equal to 1353 watts per square meter in space and about 1000 watts per square meter at sea level at the equator at solar noon.
Solar energy/solar power = radiant energy that is generated by the sun – aka power obtained by harnessing the energy from the sun’s rays
Solar noon = the time of day when the sun reaches its highest point in the sky. This time divides the daylight hours for that day exactly in half. To determine solar noon, calculate the length of the day from the time of sunset and sunrise and divide by two. Solar noon may be quite a bit different from ‘clock’ noon.
Solar Panel = a panel designed to absorb the sun’s rays as a source of energy for generating electricity or heating.
Solar spectrum = The total distribution of electromagnetic radiation emanating from the sun.
Solar thermal electric = Method of producing electricity from solar energy by using focused sunlight to heat a working fluid, which in turn drives a turbo generator.
Stand alone = An autonomous or hybrid energy (also known as off-grid) a solar electric system that is not connected to a power grid. A battery bank is most likely used to store any unused daylight production for night time power. Often found in remote regions such as mountains, ocean platforms or communication towers.
State of charge (SOC) = The available capacity remaining in the battery, expressed as a percentage of the rated capacity.
Substrate = The physical material upon which a photovoltaic cell is made.
Sulfation = A condition that afflicts unused and discharged batteries; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge.
Sun Tracker = Tracking system where the Solar Panels automatically adjust their position to best capture the solar energy at any time of day. Two axis tracking follows the suns elevation and azimuth in the sky so is superior.
Superstrate = The covering on the sun side of a PV module, providing protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.

Thermal electric = Electric energy derived from heat energy, usually by heating a working fluid, which drives a turbo generator.
Thermophotovoltaic (TPV) device = A device that converts secondary thermal radiation, re-emitted by an absorber or heat source, into electricity.
Thick-crystalline materials = Cut from ribbons or ingots, this type of semiconductor material is usually about 200-400 microns thick.
Thin film = Commonly called amorphous film, this is a layer of semiconductor material, such as copper indium diselenide, cadmium telluride, gallium arsenide, or amorphous silicon, a few microns or less in thickness, used to make photovoltaic cells.
Thin film panel = It is a solar photovoltaic module that has been 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 offer less costs through less materials used. A solar panel that is thin and flexible. The term can refer to either amorphous photovoltaic solar panels, which use silicon as their semiconductor, or panels that use other semiconductors like cadmium telluride and copper indium gallium diselenide.
Tilt = the angle a solar panel makes against the horizon. The ideal tilt for a location will mean that the panels absorb as much sunlight as possible.
Tilt angle = The angle of inclination of a module measured from the horizontal.
Total internal reflection = The trapping of light by refraction and reflection at critical angles inside a semiconductor device so that it cannot escape the device and must eventually be absorbed by the semiconductor.
Tracking array = A PV array that follows the path of the sun to maximize the solar radiation landing 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. Typically, a single axis tracker will give you 15% to 25% more power per day, and dual axis tracking will add about 5% to that. These results depend on the time of the year and the array location’s latitude.
Tracking panels = solar panels that can change the direction they face to follow the sun’s movements.
Transformer = Steps AC voltage up or down, depending on the application.
Trickle charge = A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.
Two-axis tracking = A system capable of rotating independently about two axes (e.g., vertical and horizontal) and following the sun for maximum efficiency of the solar array.

Utility-interactive inverter = An inverter that only functions when connected to the grid. It uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the PV system’s output is fully synchronized with the utility power.

VAC = AC electrical volts
VDC = DC electrical volts
Voc = Term for open-circuit voltage
Volt (V) = A unit of measure of the force, or ‘push,’ given to the electrons in an electric circuit. One volt produces one ampere of current when acting on a resistance of one ohm.
Vmp – aka voltage at maximum power = The voltage at which maximum power is available from a module.

Wafer = A thin sheet of semiconductor material made by mechanically sawing it from a single-crystal or multi-crystal ingot or casting.
Watt (W) = The unit of electric power equal to amps times volts, or amount of work (J) done in a unit of time. One ampere of current flowing at a potential of one volt produces one watt of power.
Watt-hour (Wh) = A unit of energy equal to one watt of power being used for one hour. See ‘Kilowatt-hour.
Waveform = The shape of the curve graphically representing the change in the ac signal voltage and current amplitude, with respect to time.