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GMI Solar Glossary of Terms

AC or Alternating Current The direction of electrical current reverses, usually many (60) times per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.

Ampere (amp) A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere. One ampere is equal to 6.235 x 10 18 electrons per second passing a given point in a circuit.

Ampere hour meter An instrument that monitors current with time. The indication is the product of current (in amperes) and time (in hours).

Angle of incidence The angle between the direct solar beam and the normal (90 degrees) to the active surface. (degrees)

Array Any number of Photovoltaic modules connected together electrically to provide a single electrical output. An array is a mechanically integrated assembly of modules or panels together with support structure (including foundation and other components, as required) to form a free-standing field installed unit that produces DC power.

Balance of systems (BOS) Parts or components of a photovoltaic system other than the photovoltaic array.

Battery Two or more electrochemical cells enclosed in a container and electrically
interconnected in an appropriate series/parallel arrangement to provide the required operating
voltage and current levels. Under common usage, the term battery also applies to a single cell if
it constitutes the entire electrochemical storage system.

Blocking diode A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

Cell The smallest unit of a solar module.

Crystalline Having a repeating atomic structure in all three dimensions.

DC or Direct Current A one way flow of electric current. Typical sources of direct currents are electric cells, rectified power units and direct current generators. This is the current flow
produced by a solar system. To be used for typical 120 volt or 220 volt household appliances, it must be converted to AC (alternating current).

Depth of discharge (DOD) The ampere-hours removed from a fully charged cell or
battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-
hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge.
Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of
discharge can exceed 100%.

Diffuse insolation The radiant energy from the sky incident upon unit surface area during a specified time period (Same units as for direct insolation).

Direct insolation The radiant energy from the sun (and a small area of sky surrounding it, defined by the acceptance angle of the pyrheliometer) incident upon unit surface area during a specified time period. (MJ/m2 per hour, day, week, month or year, as the case may be).

Efficiency The ratio of power output of a Photovoltaic cell to the incident power from the sun or simulated sun sources under specified standard insolation conditions.

ELC or Energy Conservation Loan Program Provides low interest financing to single or multi-family property owners for the purchase and installation of cost saving energy conservation improvements. The program is administered to by the Connecticut Housing Investment Fund (CHIF). For more information please contact them toll-free directly at 1-800-992-3665 EXT 2019 or 2023.

Electric current The rate at which electricity flows through an electrical conductor, usually measured in amperes (amps).

Full sun The full sun condition is the amount of power density received at the surface of the earth at noon on a clear day - about 100 mW/cm2. Lower levels of sunlight are often expressed as 0.5 sun or 0.1 sun. A figure of 0.5 sun means that the power density of the sunlight is one-half of that of a full sun.

Grid More or less the line or highway of power coming into your home from the electrical company.

Grid-Connected (photovoltaic) A photovoltaic (PV) system in which the PV array supplies power to the grid. Systems can be operated by the utility or by individual buildings.

Grid lines Metallic contacts fused to the surface of the solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.

Incident light The incident light is the amount of light reaching an object.

Insolation The amount of sunlight reaching an area. Usually expressed in milliwatts per
square centimeter, or langleys.

Inverter A device that converts electricity from DC to AC.

Kilowatt-hour Unit of energy used to perform work (energy and work are equivalent in units, energy being the potential value and work the achieved value) Example: The "average" American home uses about 24 kWh of electricity per day. Heating 3 gallons of water from 75 degrees to the boiling point requires 1kWh. A 200 watt Photovoltaic array of six, 50 watt solar modules will generate 1kWh in an “average” day (annualized average equivalent of 5 hours peak sunlight per day).

Load Refers to equipment that is powered by electricity. Usually expressed in terms of amperes or watts. In an electrical circuit, any devise or appliance that uses power (such as a light bulb or water pump).

Maximum power The power at the point on the current-voltage characteristic where the
product of current and voltage is a maximum (measured in watts).

Module (photovoltaic) Cells wired together in series to form a module.

Open circuit voltage (VOC) Voltage produced by a Photovoltaic cell with no load applied when the cell is exposed to standard insolation conditions, measured with a voltmeter.

Net Metering Measuring the energy produced from a solar installation monthly. When a system produces excess energy you do not use, it is fed back to the grid (utility company) as future money credit to you.

Peak Power The maximum rate of energy output available for a sustained period of time, typically 10 to 30 seconds.

Peak watts The measurement of electricity produced by a solar generator at noon on a sunny day, under predetermined standard conditions.

Photovoltaic (PV) Direct conversion of light into electrical energy.

Photovoltaic effect The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is
combined with the properties of semiconductors, electrons flow in one direction across a
junction, setting up a voltage. With the addition of circuitry, current will flow and electric power
will be available.

Power conditioner The electrical equipment used to convert power from a photovoltaic array into a form suitable for subsequent use. Loosely, a collective term for inverter, transformer, voltage regulator and other power controls.

Propylene Glycol Heat transfer agent safely contained in the solar panels to prevent freeze so algae will not grow inside panels. Safe and nontoxic.

Renewable energy Flows of energy that are regenerative or virtually inexhaustible. Most commonly includes solar (electric and thermal), biomass, geothermal, wind, tidal, wave, and hydro power sources.

Semiconductor A material such as silicon, which has a crystalline structure that will allow current to flow under certain conditions. Semiconductors are usually less conductive than metals but not an insulator like rubber.

Silicon A non-metallic element, that when specially treated, is sensitive to light and capable of transforming light into electricity. Silicon is the basic material of most beach sand, and is the raw material used to manufacture most photovoltaic cells.

Solar panel A collection of solar modules connected in series, in parallel, or in series-
parallel combination to provide greater voltage, current, or power than can be furnished by a
single solar module. Solar panels can be provided to furnish any desired voltage, current, or
power. They are made up as a complete assembly. Larger collections of solar panels are usually called solar arrays.

Stand-alone system (SA) A system which operates independently of the utility lines. It may draw supplementary power from the utility but is not capable of providing power to the utility.

Solar Thermal Produces energy for both your electrical needs as well as hot water needs.

Tilt angle A fixed angle measured from the horizontal to which a solar array is tilted. The tilt angle is chosen to maximize the array output. Depending upon latitude, season and time of day this angle will vary.

Tracking array An array that is mounted on a movable structure that attempts to follow the path of the sun. Some tracking arrays are single axis while others are dual.

Voltage A measure of the force or "push" given the electrons in an electrical circuit; a
measure of electrical potential. One volt produces one amp of current when acting against a
resistance of one ohm.

Watt Unit of power. Power is the rate of using energy to do work.

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