AGM – Absorbed Glass Mat, a sealed battery that uses saturated absorbed glass mats rather than a gelled or liquid electrolyte between the plates. AGM batteries are more expensive than gell cell batteries or flooded types, but they have superior performance.
Alternating Current – Electric current in which the current changes direction (polarity) 120 times per second (in the U.S.) and is commonly referred to as 60 Hertz (cycles per second) AC. Many other countries use 50 Hertz as a standard.
Alternative Energy – A popular term for “non-conventional” energy systems usually on a smaller scale and includes solar electric systems, wind generator systems, and small hydroelectric systems.
Alternator – A generator producing AC (alternating current) rather than DC (direct current). Alternators are more efficient than DC generators and in automobiles the alternator output is converted to 12 volts DC using rectifier diodes built into the alternator.
Amorphous Semiconductor – A non-crystalline semiconductor material for solar cells also called thin film. Easier and cheaper to make than crystalline semiconductors for solar cells, but also less efficient.
Ampere – 1 Ampere (Amp) is the amount of current that flows in a circuit at an electromotive force (voltage) of one Volt and at a resistance of one Ohm.
Amp Hour – A measure current over a period of time. 1 amp being used or generated for one hour equals 1 AmpHour.
Angle of Incidence – For solar energy systems, the angle at which direct sunlight strikes the surface of the solar panel relative to perpendicular. Sunlight with an incident angle of 90 degrees is the most efficient. Angle of Inclination – For solar energy systems, the angle that a solar array is positioned above horizontal. (90 degrees would be vertical). A general rule of thumb is to set the angle of a solar array to the latitude +/- 15 degrees.
Anode – The positive electrode or connection of an electrolytic cell or semiconductor device.
Anti-reflection Coating – A thin coating of a material applied to a photovoltaic cell that reduces the reflection of light striking its surface.
AEER – (Appliance Energy Efficiency Ratings) Operating efficiency of appliances as set by the U.S. Department of Energy guidelines.
Array (Solar) – Any number of solar photovoltaic modules or panels connected together to provide a single electrical output.
Asynchronous Generator – An electric generator that produces alternating current that matches an existing power source.
Autonomous System – A stand-alone power system that has no Utility connection. Most systems are designed for 3 to 5 days of power from batteries without recharging from a solar source or standby generator.
AWG – The abbreviation for American Wire Gauge, a standard system for designating the size of electrical wires.
Backup Energy System – A back-up electric power system using batteries and an inverter, an AC generator, or both.
Battery – A device containing electrolytic cells to store electrical energy in chemical form. Blocking Diode – A semiconductor device used to stop the flow of current from one direction, but allow it in the opposite direction.
British Thermal Unit (BTU) – The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.
Bus (electrical) – An electrical conductor that serves as a common connection point for multiple connections.
Bypass Diode – A diode connected across a solar cell in a photovoltaic module such that the diode will conduct if the cell becomes reverse biased due to shading or the failure of other cells.
Cathode – The negative electrode or connection of an electrolytic cell or semiconductor device.
Cell (battery) – The basic unit of an electrochemical battery. A lead acid cell produces about 2.12 volts and a 12 volt battery uses 6 of these cells and fully charged measures about 12.72 volts. Cell (solar) – The basic unit of a photovoltaic solar panel. A 12 volt solar panel typically has 36 individual cells, a 24 volt solar panel uses 72 cells.
Charge Controller – An electronic device that regulates the voltage from the solar panel array to ensure maximum transfer of energy and prevent overcharging the battery bank.
Circuit – An arrangement of individual electronic components or devices that use the flow of electrical current thru them to perform useful work or functions.
Circuit Breaker – A safety device used to stop the flow of electricity in an electric device or circuit to prevent damage or fire when an overload condition occurs.
Combiner Box – A solar array junction box where multiple solar modules are electrically connected together and fusing devices may be located.
Conductor – Any material through which electricity can flow. Gold, silver, copper, and aluminum (in that order) make excellent conductors.
Conventional Power – Power generation from sources such as hydro, petroleum, natural gas, coal, or nuclear power plants.
Conversion Efficiency (solar panel) – The ratio of the energy produced by a photovoltaic device to the energy received or consumed expressed as a percentage. Solar panels are typically 9% to 14% efficient.
Converter (DC) – Typically, an electronic device for changing 120 volts AC to lower voltage DC. Crystalline Silicon
Photovoltaic Cell – A type of photovoltaic cell made from a single crystal or a polycrystalline slice of silicon. Individual cells are then joined together to form a solar module.
Current (Electrical) – The flow of electrons in an electrical circuit, measured in amperes (amps).
Cycle (AC) – In alternating current (AC), the current goes from zero to maximum in one direction then zero to maximum in the other direction then repeats. In the United States a complete positive/negative cycle occurs 60 times each second and is known as 60 cycle AC.
Deep Discharge – Discharging a battery down to 20 percent or less of its full charge condition.
Diffuse Solar Radiation – Unfocused sunlight scattered by atmospheric particles and arriving at the earth’s surface from all directions.
Dimmer (switch/control) – An electronic device that allows light levels to be adjusted from dim to full brightness.
Diode – A semiconductor device that allows current to flow in one direction only. Direct Current (DC) – Electric current in which the flow of electrons is in one direction only. Opposite of Alternating Current (AC).
Discharge Rate – The rate that energy is removed from a battery, usually expressed in AmpHours.
DOD (Depth of Discharge) – The percentage that a battery is discharged from a fully charged condition.
Earth Sheltered Home – A home with large earthen berms around exterior walls to provide wind protection and insulation.
Electrical Grid – An large integrated system of electricity distribution from centralized locations to individual homes and businesses.
Electric Circuit – See ‘circuit’. Electric Current – See ‘current’. Electrolyte – A liquid or gel type conductor of electricity that carries current by the movement of ions (instead of electrons) between the plates in batteries.
Electromagnetic Energy – Energy generated from an electromagnetic field produced by a magnet or an electric current flowing through a conductor.
Electromagnetic Field (EMF) – The electrical and magnetic fields produced by any device operating with electricity.
Electron – An elementary particle of an atom with a negative electrical charge and a mass of 1/1837 of a proton. Electrons surround the positively charged protons in the nucleus of an atom and the number of electrons determine the atomic element. Elements that loose electrons easily make good conductors and elements whose electrons are tightly bound together make good insulators. It is this movement of electrons which is the electric current in circuits.
Electronic Ballast – A high voltage transformer that excites the ions in fluorescent lamps.
Emissions – Substances or by products (usually polluting) resulting from energy production.
Energy Efficiency Ratio (EER) – A measure of the energy efficiency of room air conditioners based on the U.S. Department of Energy guidelines.
Equinox – The two times of the year when the sun crosses the equator and night and day are of equal length, occurring on March 21st (spring equinox) and September 23 (fall equinox) in the northern hemisphere.
Filament (tungsten) – A coil of tungsten wire suspended in a vacuum or inert gas-filled bulb. When electricity flows thru the tungsten “filament” it radiates energy in the form of heat and light. This is the basic operation of inefficient incandescent lamps.
Float Charge – The float charging voltage is the voltage required to maintain a battery in a fully charged condition after it has been charged.
Fluorescent Light – An electric lamp using a phosphor coated glass tube that glows when ions in the tube are excited with high voltage electricity. Much more efficient than incandescent type lamps.
Foot Candle – A unit of illuminance equal to one lumen per square foot.
Foot Pound – The amount of work done by lifting one pound one foot.
Fossil Fuels – Fuels such as oil, natural gas, and coal are fossil fuels believed to have been formed in the ground from the decayed remains of plants and animals over millions of years.
Frequency – The number of cycles through which an alternating current changes direction twice each second. In the U.S. the standard frequency for electricity is 60 cycles per second (60 Hertz). Fuel Cell – An electrochemical device that converts chemical energy directly into electricity.
Full Sun – The amount of energy in sunlight striking the earth’s surface at noon on a clear day (about 1,000 Watts per Square Meter).
Fuse – A safety device which stops the flow of electricity to prevent damage and fire under overload conditions. See ‘ciruit breaker’
Gel Battery – A lead-acid battery in which the electrolyte between the plates is composed of a gelled substance instead of water which is used in automotive batteries.
Generator (AC) – An electric generator driven by a internal cumbustion engine to produce electricity for stand-alone systems and for back-up electrical power. The fuel used may be gasoline, diesel, or propane (LPG).
Gigawatt (GW) – 1,000,000,000 watts, 1 million kilowatts, or 1,000 megawatts.
Green Power – A popular term for energy produced from clean, renewable energy resources such as wind, solar, or hydro electric systems.
Grid – A common term referring to an electricity transmission and distribution system run by large utility companies.
Grid Tie System – An independent electrical power system that is connected to the utility grid so that power can be supplied by the grid when needed and fed back into the grid during excess power production.
Ground – The electrical potential where voltage is zero or at a minimum. Connecting one side of the electric system and metallic surfaces of electric systems to ground potential prevents shocks by bleeding the voltage down to a safe level.
Hertz – Short hand for ‘cycles per second’. It is the frequency of an AC electric system and is 60 hertz in the U.S.A.
Hybrid System – A renewable or alternative energy system that uses two different sources for power, such as wind generators and solar photovoltaic arrays together to produce electricity.
Hydroelectric Power Plant – A power plant that produces electricity by using water pressure to turn large turbines.
Incandescent (lamp) – A fairly inefficient type of lamp that uses a wire filament suspended in a vacuum or inert gas-filled bulb that give off heat and light when electricity flows thru the filament.
Infrared Radiation – Electromagnetic radiation below the visible range. Also known as heat radiation.
Inverter (AC) – An electronic device that converts 12, 24, 48, or higher volts DC power from batteries or solar panels to 120/240 volts AC to operate normal appliances.
Kilowatt (KW) – A standard unit of electrical power equal to 1000 watts.
Kilowatt-Hour (KWH) – 1000 watts produced or consumed for a period of 1 hour.
Lead Acid Battery – An electrochemical battery that uses lead and lead oxide for electrodes and sulfuric acid for the electrolyte. When the sulfuric acid is mixed with water, it is known as a flooded battery. Batteries whose electrolyte is a gel or absorbed glass mat type are called sealed batteries. Not to be confused with sealed batteries, a maintenance-free battery simply has no way to add water and when low is just discarded.
Line Loss – Energy lost due to inherent inefficiencies in an electrical transmission and distribution system.
Load – The devices and appliances that draw power from an electrical supply system.
Long-Wave Radiation – Infrared or radiant heat energy.
Luminance – The measure of the apparent brightness of an object, measured in lumens.
Maximum Power Point (MPP) – The point on the current-voltage (I-V) curve of a solar panel, where the product of current times voltage equals maximum wattage.
Maximum Power Point Tracking (MPPT) – A charge controller technique that attempts to supply maximum power to the batteries by tracking the maximum power point (MPP) at all times achieving a 15% to 35% increase over other types of charging techniques.
Megawatt – 1 million watts or 1 thousand kilowatts (1,000,000 watts).
Megawatt-Hour – 1 million watts produced or used for a period of 1 hour.
Module (solar) – A number of individual solar cells connected together in an environmentally protected housing producing a standard output voltage and power. Multiple modules/panels can be assembled into an array for increased power and/or voltage.
Monolithic – Manufactured or assembled as a single structure. Monocrystalline – A material used in solar cells that uses a complicated crystal growth process. Long silicon rods are produced which are cut into slices of .2 to .4 mm thick discs or wafers which are then processed into individual cells.
Motor Speed Control – An electronic device that manually or automatically varies/controls motor speed as in a multi-speed fan.
Multicrystalline – A material composed of randomly oriented, small individual crystals. (Sometimes referred to as polycrystalline or semicrystalline).
Name Plate – An identifying tag usually located near the AC cord of an appliance that contains information such as model number, serial number, operating voltage, and power consumption.
National Electrical Code (NEC) – The NEC is a set of regulations and standards that most electrical equipment installations must follow making the electrical system in the United States one of the safest in the world.
Net Metering – Using a single meter to measure usage and generation of electricity by customers with a wind or solar power energy system. The net energy used or produced is either purchased from or sold to the power company.
Off-Peak (demand)– The times during a 24 hour period of low electricity demand. Opposite of peak-demand.
Ohm – The unit of resistance to the flow of electrons in an electric circuit.
Ohm’s Law – The various formulas that define the relationship between resistance(R), voltage(E), and current(I) as in E=I*R, I=E/R, R=E/I, etc.
One-Axis Tracking – A solar tracking system that moves in only 1 direction or axis generally following the sun in its arc across the sky from east to west.
Open-Circuit Voltage (Voc)- The maximum possible voltage across a photovoltaic cell or module in sunlight when no current is flowing.
Ovonic – A device (solar cell) that converts sunlight directly into electricity, invented by Standford Ovshinsky.
Panel (Solar) – A solar photovoltaic device composed of groups of individual solar cells connected in series, in parallel, or in series-parallel combinations to produce a standard output. See ‘module’.
Parallel – A wiring technique where multiple devices are wired together to increase current but voltage remains the same.
Payback Period – The amount of time required before the savings resulting from an energy producing system equals the cost of the system, typically 5 to 10 years. This number has been steadily decreasing as alternative energy systems become more popular and more practical.
Peak Sun Hours – The equivalent number of hours per day when solar radiation averages 1 KiloWatt per square meter. For example, 5 peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the solar radiation for 5 hours been 1 KiloWatt per square meter.
Peak Watt – The maximum nominal output of a PV (solar) device, in Watts (Wp) under standardized test conditions. (usually the most favorable!).
Phantom Load – The small power used by an appliance even when it is turned off. Examples of phantom loads include appliances with electronic clocks or timers and devices with remote controls whose circuits remain active in order to detect the remote control signal to power up.
Photon – A particle of light that acts as an individual unit of energy.
Photovoltaic Array – A group of solar photovoltaic modules connected together to increase voltage and/or power to the level required for a given system.
Photovoltaic Cell – Specially processed semiconductor materials such as silicon, cadmium sulfide, cadmium telluride, and gallium arsenide that convert sunlight directly into electricity. Three common types are mono-crystalline, multi-crystalline, and amorphous/thin film.
Photovoltaic Conversion Efficiency – The ratio of the energy produced by a photovoltaic device to the energy received or consumed expressed as a percentage. Solar panels are typically 9% to 14% efficient. Photovoltaic Module or Panel – See ‘module’ or ‘solar module’.
Poly-crystalline – A semiconductor (photovoltaic) material composed of randomly oriented, small, individual crystals.
Power – Useful energy that performs work measured in horsepower, Watts, or Btu’s. Electrical power is rated in Watts and is equal to the Voltage(E) times the Current(I). As in P=E*I.
Radiation – The transfer of heat energy through matter or space by means of electromagnetic waves.
Reflective Glass – A window glass that has been coated with a reflective film to reduce unwanted solar heat gain during the summer.
Renewable Energy – Energy from sources that are not easily depleted such as moving water (hydro, tidal and wave power), biomass, geothermal energy, solar energy, wind energy, and energy from solid waste treatment plants.
Resistance (electrical)– The inherent characteristic of a material to inhibit the flow of electrons producing heat in conductors, devices, or components and is measured in Ohms.
Resistor – An electrical device that resists the flow of electrons in electric circuits.
Ribbon Cells (Photovoltaic) – A type of solar photovoltaic device made by pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin continuous sheet of material.
Safety Disconnect – A switch that disconnects one circuit from another circuit to isolate power generation or storage equipment from each other.
Self Discharge (rate) – The rate at which a battery, without being used will lose its charge over time.
Semiconductor – Any material that has a limited capacity for conducting an electric current. It is neither a good conductor nor a good insulator. This characteristic allows it to perform controlled operations as transistors, diodes, and integrated circuit packages. Semiconductor material can be densely packed and layered thru photographic processes and has given rise to the modern world of electronics. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.
Series – A wiring technique where multiple devices are wired together to increase voltage but current remains the same. Shallow
Cycling – Allowing a battery bank to only loose 20% of its full charge when being used, then recharging back to full charge. With a large bank of batteries, this technique can supply sufficient power between charge cycles and will greatly increase the life and performance of the batteries.
Short Circuit – A generally unwanted condition where maximum current flows freely through an external circuit that has no load or resistance, usually due to the catastrophic failure of a device or component.
Silicon – A chemical element, of atomic number 14, that is semi-metallic, and an excellent semiconductor material because the atoms in the outer shell are neither tightly bound nor loosely bound to the nucleus.
Sine Wave – The wave generated by alternating current generators and sine wave solid-state inverters.
Single-Crystal Material – See ‘monocrystalline’. Sizing – The process of designing a solar electric system to meet the required operating loads based on the total wattage of all appliances in the system.
Solar Array – See ‘Photovoltaic Array’.
Solar Cell – The basic unit of a photovoltaic solar panel. A 12 volt solar panel typically has 36 individual cells, a 24 volt solar panel uses 72 cells.
Solar Constant – The average amount of solar radiation that reaches the earth’s upper atmosphere on a surface perpendicular to the sun’s rays; equal to 1353 Watts per square meter or 492 Btu per square foot.
Solar Energy – Electromagnetic energy transmitted from the sun (solar radiation). The amount that reaches the earth is equal to one billionth of total solar energy generated, or the equivalent of about 420 trillion kilowatt-hours. Solar
Module (Panel) – A number of individual solar cells connected together in an environmentally protected housing producing a standard output voltage and power. Multiple modules/panels can be assembled into an array for increased power and/or voltage.
Solar Noon – The time of the day, at a given location when the sun reaches its highest point in the sky.
Solar Radiation – The various wavelengths of electromagnetic radiation that is emitted by the sun including the visible light we can see.
Solstice – The two times of the year when the sun is apparently farthest north and south of the earth’s equator occurring on or around June 21 (summer solstice) and December 21 (winter solstice) in the northern hemisphere.
Square Wave Inverter – A type of inverter that produces square wave output. The square wave inverter is the simplest and the least expensive to purchase, but it produces the lowest quality of power.
Stand-Alone Inverter – An inverter that operates independent of any utility company grid or electric transmission and distribution network.
Stand-Alone System – An system that operates independent of any utility company grid or electric transmission and distribution network. Stand-By Power – See ‘Phantom Power’.
State of Charge (SOC) – The remaining charge available in a battery, expressed as a percentage of the battery when fully charged.
Synchronous Inverter – An inverter that produces alternating current electricity from direct current electricity and uses another alternating current source, such as the electric power grid or a generator to synchronize its output voltage and frequency to the external power source.
Thin-Film – A layer of semiconductor material a few microns or less in thickness, used to make solar photovoltaic cells.
Tilt Angle (of a Solar Array) – The angle at which a solar array is set to face the sun relative to a horizontal position and is usually adjusted seasonally due to the changing declination of the sun.
Tracking Solar Array – A solar array that follows the path of the sun during the day to maximize the solar radiation it receives. A single axis tracker tracks the sun east to west and a two-axis tracker tracks the daily east to west movement of the sun and the seasonal declination movement of the sun.
Transformer – An electromagnetic device that changes the voltage of AC up or down. It consists of an induction coil with an iron core and a primary and secondary winding, the ratio of which determines output voltage versus input voltage.
Trickle Charge – The small charging voltage required to maintain a battery in a fully charged condition after it has been charged.
Ultraviolet Radiation– Electromagnetic radiation ranging from 4 to 400 nanometers in wavelength. Utility Company – Do we have to spell it out for you?
Visible Radiation – The visible portion of the electromagnetic spectrum ranging from 0.4 to 0.76 microns in wavelength.
Volt – A unit of electrical measurement. One volt will cause a current of one ampere to flow through a resistance of one ohm.
Voltage – The difference in electrical potential that exists between two points in a circuit measured in volts.
Wafer – A thin section of semiconductor material made by slicing it from a single crystal or rod.
Watt – The unit of electric power in a circuit. One watt equals one ampere under an electrical pressure of one volt.
Watt-Hour – 1 watt produced or consumed for a period of 1 hour. Wattmeter – A device for measuring power production or usage displayed in watts
A Practical Guide to Solar Power System Design For Homeowners
Version 08.08.12 Compiled, edited, & updated by Vince Lombardi, B.S. / M.S. Engineering Mechanics, Virginia Tech 1988/1990.
A compilation and update of free solar design/build resources from www.freesunpower.com and other on-line/ free information sources.