of Home Power
Magazine - "Solar,
Wind, and Microhydro Electricity, Home Energy Efficiency, Solar Hot
Water Systems, Space Heating and Cooling, Green Building Materials and
Home Design, Efficient Transportation"
The absorber is that part of a solar thermal collector that receives
the incident radiant energy and transforms it into heat energy.
SOLAR THERMAL SYSTEM
A system that traps the sun's energy with solar collectors and uses an
electromechanical subsystem to move that energy to its point of
intended use for water heating, space heating, pool heating, industrial
process heat, electrical generation and space cooling.
An electrical current in which the direction of electron flow reverses
periodically, usually many times per second. Most U.S. household
electrical systems use AC current rated at 120 volts and 60 cycles per
A mechanical device that generates alternating current electricity.
The angle of the sun above the horizon (at high-noon), measured in
degrees. In winter, the sun is at a low solar altitude, and in the
summer, the sun is at a high solar altitude.
A device used for measuring the current (amperage) at any point in an
A thin-film PV silicon cell having no crystalline structure.
Refers to the highest safe amount of electrical current through
conductors, overcurrent devices, or other electrical equipment.
Ampacity is determined by the cross-sectional area and the material of
the conductor, or the manufacturer’s equipment rating.
(AMP; A, I)
The rate of flow of electrical charge. Unit of electrical current. One
volt across one ohm of resistance causes a current of one ampere. One
ampere is equal to 6.235 x 10^18 electrons (one coulomb) per second
passing a given point in a circuit.
A measure of electron flow over time, used to measure battery capacity
and state of charge. For example, a current of 1 amp drawn from a
battery for 10 hours would result in 10 amp-hours of charge cycling
through the battery.
An instrument that monitors electron flow over time. Amp-hours are the
product of electron flow (in amperes) and time (in hours).
Generally refers to the maximum and minimum voltage attained by an
alternating or pulsed current in each complete cycle or pulse of that
The angle between the sun’s rays and a line perpendicular to the active
surface of a solar module or collector, in degrees.
The angle that a solar collector or PV module is positioned above
( Battery ) The electrode within a battery cell that undergoes the
chemical process of oxidation. Electrically, the anode is the cell's
heater) An aluminum or magnesium sacrificial rod installed within steel
tanks that is used to help prevent corrosion of the tank itself.
Any number of photovoltaic modules connected together electrically to
provide a single electrical output.
American Wire Gauge, a set of standards in the U.S. specifying the
diameter of wire. A higher number indicates smaller wire.
The angle between true south and a point on the horizon, measured in
degrees east or west of true south.
OF SYSTEMS (BOS)
Parts or components of a photovoltaic system other than the
photovoltaic array or other generating equipment.
A circuit used to condition and stabilize an electric current, for
example, in a fluorescent light.
SOLAR HOT WATER HEATER
The simplest of solar hot water systems. A tank of water within a
glass-covered insulated enclosure aimed at the sun. Water is heated in
the tank and then flows to the load or an auxiliary water heater.
Two or more electrochemical cells electrically interconnected in an
appropriate series/parallel arrangement to provide the required
operating voltage and capacity levels. Under common usage, the term
battery also applies to a single cell if it constitutes the entire
electrochemical storage system.
The total maximum charge, expressed in ampere-hours, that can be
withdrawn from a cell or battery under a specific set of operating
conditions including discharge rate, temperature, state of charge, age,
and cutoff voltage.
The simplest operating unit in a storage battery. It consists of one or
more positive electrodes or plates, electrolyte that permits ionic
conduction, one or more negative electrodes or plates, separators
between plates of opposite polarity, a container for all the above, and
posts or other terminals for electrical connection.
The number of cycles, to a specified depth of discharge, that a cell or
battery can undergo before failing to meet its specified capacity or
efficiency performance criteria.
The period during which a cell or battery is capable of operating above
a specified capacity or efficiency performance level. With lead-acid
batteries, end-of-life is generally considered when a fully charged
cell can deliver only 80 percent of its rated capacity. Beyond this
state of aging, deterioration and loss of capacity begins to accelerate
rapidly. Life may be measured in cycles or years, depending on the type
of service for which the cell or battery is intended.
The theoretical maximum energy that a wind generator can extract from
the wind—59.6 percent.
Any organic matter available on a renewable basis, including
agricultural crops, wastes, and residues; wood, wood wastes, and
residues; animal wastes and municipal wastes; and aquatic plants.
Biomass converted directly to energy or converted to liquid or gaseous
fuels, such as ethanol, methane and hydrogen.
The energy-capturing, aerodynamically designed part of a wind turbine,
which interacts directly with the wind.
A semiconductor connected in series with a solar-electric 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.
Device for stopping a wind turbine. This can be an electric brake that
shorts the output of the turbine (dynamic braking), or a mechanical
brake that physically stops the rotation, as with a brake drum and shoe.
A manually operable switching device that also automatically opens a
circuit in the event of overcurrent.
THERMAL UNIT (BTU)
The amount of heat required to raise the temperature of one pound (one
pint) of water, one degree Fahrenheit. 1 watt-hour = 3.413 BTU.
The initial phase of battery charging, when the
largest amount of
energy is put into the battery.
An electrical connection component that can accept multiple cables or
wires. Also bus, bus bar, or busbar
A semiconductor device connected in parallel with a series block of
parallel PV strings to prevent current from flowing back through any
shaded or failed modules in the same block.
An electrical effect in AC circuits that results in amperage peaking
The electrode within a battery cell that undergoes the chemical process
of reduction. Electrically, the cathode is the negative terminal of the
Systems that protect metal from corrosion by running small electrical
currents along the metal. Most often used to protect well heads, and
oil, gas, and water pipelines.
A single unit of an electro-chemical device capable of producing an
electrical current by converting chemical energy into electrical
energy. The cell is the basic unit used to store energy in the battery.
The cell contains an anode, a cathode, and the electrolyte. A battery
usually consists of several cells electrically connected together to
produce higher voltages. (Sometimes the terms cell and battery are used
The smallest, basic photovoltaic device that generates electricity when
exposed to light.
A component of photovoltaic systems that controls the charging of the
battery to protect the batteries from overcharge and overdischarge. The
charge controller may also indicate the system operational status.
Standard charge controllers vary the current (A) based on preset
voltage set points.
The current applied to a cell or battery to restore its available
capacity, specified in relation to total battery size. A C/20 rate is a
charge rate that is 1/20th of the total battery capacity. Also called a
A group of electrical components that make a complete electrical path,
providing some function.
A solar hot water system of which no part is vented to the atmosphere
or fed with fresh liquid. The system liquid, usually some form of
antifreeze solution, is recirculated. Closed loop solar systems are
also known as glycol systems and indirect systems.
A traditional building technique using hand formed lumps of earth mixed
with sand and straw.
The plumbing loop in a solar hot water system that includes the solar
collectors. The collectors heat the fluid in the collector, and the
heated fluid can be used directly (if water) or the heat can be
exchanged to a potable water loop.
A box where wires from individual PV modules or strings are combined
into larger wires to run to the battery bank. Can also contain
overcurrent protection devices.
FLUORESCENT LIGHT (CFL)
A smaller version of standard fluorescent lamps that can directly
replace incandescent lights. CFLs use 65 to 80 percent less energy,
while producing the same lumens.
A photovoltaic module that includes optical components, such as lenses,
to direct and concentrate sunlight onto a solar cell of smaller area.
Most concentrator arrays must directly face or track the sun.
Heat transfer from a hot object to a colder object through direct
A material with relatively low resistance through which electricity
will readily flow—wires, cables, busbars. The most common conductors
are copper and aluminum.
Metal or plastic tubing designed to protect electrical conductors.
The maximum amount of power an inverter may deliver to a load (or
loads) for a sustained period of time.
transfer by the movement of fluid (usually air or water).
transfer through either the natural or forced movement of air.
An electronic device for DC power that steps up voltage and steps down
current proportionally (or vice-versa).
A type of PV cell made from a single crystal or polycrystalline slice
Flow rate of electrons. See AMPERE.
Electrical equipment setting for the voltage level at which a battery
is considered to be empty, and the discharge process is terminated.
Most commonly found in inverters and charge controllers that include a
feature for low voltage disconnection.
complete charge/discharge cycle of a battery.
AC sine wave’s movement from zero to maximum positive, through zero, to
maximum negative, and back to zero.
Cycle life is the number of cycles a cell or battery will undergo
before being considered “worn out.” This point is usually defined as
when the battery’s capacity has decreased to 80 percent of its initial
The placement of windows and skylights to provide natural interior
lighting and to reduce daytime electrical demand.
The number of consecutive days that a stand-alone renewable energy
system will meet a defined load without additional energy input.
Direct current. A one-way flow of electrons. Typical sources of direct
current are solar-electric cells, rectifiers, and direct current
generators. To be used for typical 120 volt or 220 volt household
appliances, DC must be converted to AC (alternating current).
High-technology motor used in centrifugal-type DC submersible pumps and
other applications. The motor is filled with oil to keep water out. An
electronic system is used to precisely alternate the current, causing
the motor to spin.
The traditional DC motor, in which small carbon blocks called “brushes”
conduct current into the spinning portion of the motor. They are used
in many applications, including DC surface pumps and also in DC
submersible diaphragm pumps. Brushes naturally wear down after years of
use, and may be replaced.
MOTOR, PERMANENT MAGNET
variable speed motor that uses permanent magnets instead of wound
coils. Reduced voltage (in low sun) produces proportionally reduced
speed, and causes no harm to the motor.
A battery designed to regularly discharge 50 to 80 percent of its
capacity before recharging.
A quantitative index reflecting demand for energy to heat or cool
buildings. Heating and cooling degree days show the difference between
the mean daily temperature and a 65°F base. The higher the heating
degree days at any location, the colder the winter. The higher the
cooling degree days at any location, the hotter the summer.
Difference in temperature.
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-hour rated cell
results in a 25 percent depth of discharge. Depth of discharge is the
opposite of state of charge (SOC).
Domestic hot water: refers to any system that provides hot water for
An electronic switch that turns off or on based on the difference
between two temperatures. In a solar hot water system, the controller
measures the temperature at the collector and compares it to the water
temperature in a storage tank to turn the pump on or off.
A device with multiple electrical measurement capabilities, such as
voltage, amperage, resistance, etc., commonly usable for both AC and DC
circuits. It has a digital display.
A semiconductor device that allows electrical current in only one
An electrical current that moves in one direction only.
In passive solar heating, a direct gain system relies on the sunshine
to directly hit the substance or mass being heated. Direct gain systems
used today usually rely on a layer(s) of glass to assist in holding the
heat within a space where the heat is desirable.
The rate at which energy is being drained from a battery.
Switch gear used to connect or disconnect components in a system.
In relation to a wind turbine, the direction away from the source of
wind. A downwind turbine has its blades on the downwind side of the
A tube added to the outfall of a hydro turbine to increase energy
production by taking advantage of the drop in the tailrace.
A solar hot water system that only fills the collector when the
temperature differential is appropriate. The water that is circulated
through the collectors is stored in a reservoir. Draining the
collectors provides freeze protection.
A solar hot water system that uses a special draindown valve that
redirects the collector fluid and drains it down when the collector
system pump is not operating. These systems have been prone to failure
and are not recommended.
The fraction of time a device or load actually uses energy in a unit of
time. For example, a load that uses energy for 5 seconds out of every
10 seconds has a 50 percent duty cycle.
Synonymous with “ground.”
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. A solar cell that converts 1/10 of the sun's
energy that strikes its surface to electricity has an efficiency of 10
The effectiveness of a device to convert energy from one form to
another, or to transfer energy from one body to another. An electric
pump that is 60 percent efficient converts 60 percent of the input
energy into work—pumping water. The remaining 40 percent becomes waste
Same as VOLTAGE.
The rate at which electrons flow through an electrical conductor,
usually measured in amperes (amps).
Energy flow resulting from the flow of charged particles, such as
electrons or ions.
The breaking down of a chemical compound into simpler compounds or
elements by the passage of electricity through the chemical compound.
Commonly used to describe the extraction of hydrogen (and oxygen) from
The fluid in a battery, which is the medium of ion transport within an
electrochemical cell. It provides a path for electron transfer between
the anode and cathode of a battery cell.
Magnetic radiation produced by a changing electrical current, such as
alternating current (AC).
A negatively charged particle. The movement of electrons in an
electrical conductor constitutes an electric current.
The energy consumed by all of the processes associated with the
production of a material. This includes the energy required in mining,
transport, manufacturing, administration, use, disposal, etc.
amount of work that a system or entity can do (potential energy) or
is doing (kinetic energy), measured in joules. The product of power and
time, measured in watt-hours. 1,000 watt-hours = 1 kilowatt-hour (KWH).
A ratio of a battery or cell's capacity to either its volume or weight.
Volumetric energy density is expressed in watt-hours per cubic inch.
Weight energy density is expressed in watt-hours per pound.
A machine that converts energy into mechanical force or motion. Sources
of energy include heat, chemical reaction, potential energy of elevated
The process of restoring all cells in a battery to an equal
state-of-charge. For lead-acid batteries, this is a charging process
designed to bring all cells to 100 percent state-of-charge.
A continuation of normal battery charging, at a voltage level slightly
higher than the normal end-of-charge voltage, in order to provide cell
equalization within a battery.
(SPRING & FALL)
The time when the sun crosses the plane of the earth's equator, making
night and day of equal length all over the earth, occurring about March
21st and September 21st.
The process of a liquid changing its state into a gas when heat is
added. In the most common occurrence on earth, water evaporation
requires 970 BTUs per pound (pint).
In wind generators, this refers to an adjustment of the blades so that
they catch less wind. This can prevent damage to the machine in high
The final stage of battery charging, when the battery is charged at a
slow rate over a long period of time.
Noticeable deformation of trees from prevailing winds. Flagging is an
indication of an effective wind site. Lack of flagging is not
necessarily an indication of a poor wind site.
A solar thermal collector that converts the sun’s radiation into heat
on a flat surface. Does not use reflecting surfaces or lens
arrangements to concentrate the sun’s energy.
A trickle charge to keep a battery fully charged at a safe voltage
level with minimal gassing.
A battery operation in which the battery is normally connected to an
external current source; for instance, a battery charger that supplies
the battery load under normal conditions, while also providing enough
energy input to the battery to make up for its internal losses, thus
keeping the battery always at full charge and ready for service.
In hydro-electric terms, flow refers to the quantity of water supplied
to a water source or exiting a nozzle per unit of time. Commonly
measured in gallons per minute.
An electric lamp coated on its inner surface with phosphor and
containing mercury vapor. When bombarded with electrons, the vapor
emits ultraviolet light that causes the phosphor to emit visible light.
A type of reaction hydro-turbine used in low to medium heads. It
consists of fixed vanes on a shaft. Water flows down through the vanes
and out sideways.
A wind generator tower with no guy wires. This can be either a lattice
tower or a monopole. Freestanding towers are the most expensive type of
tower, requiring large excavations and large amounts of concrete.
Lost energy due to friction.
In hydro systems, pipe sized too small can lead to serious friction
In any belt drive system, there will be some losses due to friction.
The full sun condition is the amount of power density received at the
surface of the earth at noon on a clear day—about 1 KW per m^2, or 1
Sun. Lower levels of sunlight are often expressed as 0.5 sun or 0.1 sun.
Reducing a wind generator’s swept area to protect it from high winds.
Common furling methods are to tilt the rotor (blades) up or sideways
out of the wind, or to feather (twist) the blades to degrade the
An electrical device that is designed to break a circuit by melting an
internal conductor when the current in the circuit exceeds the maximum
considered safe for the conductors or devices in the circuit.
The production of hydrogen and oxygen gas from one or more of the
electrodes in the cells of a battery. Gassing commonly results from the
electrolysis of water in the electrolyte during charging.
A device that converts mechanical energy into electrical energy.
A type of heat pump that uses the ground, ground water, or ponds as a
heat source and heat sink, rather than outside air. Compare to HEAT
Either of two different types of devices used with wind generator
towers. With a tilt-up tower, it describes the lever that helps tilt
the tower up. With a fixed tower, it describes a temporary crane used
to raise tower sections or the wind generator.
An antifreeze, heat transfer fluid that is circulated through closed
loop solar hot water collectors.
A device that limits the output of another device, such as a wind
Limiting the output of a device. In respect to small wind generators,
governing normally happens through furling.
Transmission line network used to distribute electrical energy,
generally by a commercial power utility.
Metallic contacts fused to the surface of a solar cell to provide a low
resistance path for electrons to flow out to the cell interconnect
A renewable energy system that is connected to the utility grid,
selling excess energy back to the utility. Also called a
The connection of electrical components to the earth and/or each other
for the purposes of dissipating static charge or protecting against a
short circuit or lightning.
Unwanted current path to ground.
A photovoltaic (PV) rack designed to be installed on the ground or
other flat surface.
A metal rod (typically 5/8 inch diameter) that is driven into the earth
(typically 8 feet deep) and is electrically connected to the negative
conductor and/or any metal parts, wiring enclosures, or conduit of an
Steel cables that support a tower.
The difference in elevation between two parts of a liquid-based system.
In hydro power, the difference between a source of water and the
location at which the water from that source may be used (synonym:
vertical drop). With pumps, the vertical distance the pump must move
A flume or channel that feeds water into a hydro turbine.
A device that is used to transfer heat between fluids or gases through
an intervening surface.
A device typically used for heating and cooling of buildings by drawing
from or dissipating into the ambient temperature of air or water. When
cooling, a heat pump works like a refrigerator. When heating, it also
works like a fridge, except the heat produced is used to heat a space.
A medium or container to which heat flows. Thermal mass walls and
floors in a passive solar home act as a heat sink during the day.
Heat is transferred from one substance or location to another by three
methods—radiation, convection and conduction. The sun's rays are a good
example of radiation; warm air rising is heat movement by convection;
and touching a hot iron or frying pan with your hand is heat transfer
Cycles per second. Generally refers to the number of complete cycles of
the AC sine wave per second, or the frequency at which a radio or
computer processor works.
Any electricity that is generated by the flow of water.
A device that converts hydrogen to DC electricity.
A hydrometer is an instrument for measuring the density of liquids in
relation to the density of water. The hydrometer is used to indicate
the state of charge
in lead-acid cells by measuring the specific
gravity of the electrolyte.
A type of heating system where water is heated in a solar collector or
boiler, and is pumped to heat exchangers or radiators in rooms. Radiant
floor systems have a grid of tubing laid out in the floor for
distributing the heat. Temperature of the space is controlled by
regulating the flow and/or temperature of the circulating water.
A measure of the capacity to generate energy or do work. 1 horsepower =
An energy system consisting of two or more generating subsystems, such
as the combination of a wind turbine or diesel generator and a
An electric lamp that is evacuated or filled with an inert gas and
contains a filament (commonly tungsten). The filament emits visible
light when heated to extreme temperatures by electric current through
it. Incandescent lightbulbs are one of the most inefficient ways to
light a home. They produce a great deal of heat along with the light,
and use three to four times as much energy for the same light output as
compact fluorescent lightbulbs.
A type of electric motor that requires a high surge to start, and a
stable voltage supply, making it a challenge to run using a
The amount of sunlight reaching an area. Usually expressed in watts per
In a hydro system, the structure that receives the water and feeds it
into the penstock (pipeline). Usually incorporates screening or
filtering to keep debris and aquatic life out of the system.
A device that converts DC electricity (anywhere from 12 to 600 VDC) to
AC electricity (typically 120/240 VAC).
An electrically charged particle or molecule.
See SHORT CIRCUIT CURRENT.
The graphical representation of the current versus the voltage of a
photovoltaic cell, module, or array as the load is increased from zero
voltage to maximum voltage, under standard test conditions.
A submerged pump mechanically activated by a rod extending above the
well head to a reciprocating engine, motor or any other rotating device.
The standard unit of energy (SI). One joule equals one watt-second, and
3600 joules = one watt-hour.
One thousand watts.
One thousand watt-hours. Unit of energy used to perform work (energy
and work are equivalent in units, energy being the potential value and
work the achieved value).
equivalents: One barrel of crude oil contains roughly 1,700 KWH
ton of coal contains roughly 7,500 KWH
gallon of gasoline contains roughly 37 KWH
cubic foot of natural gas contains 0.3 KWH
ton of uranium ore contains 164 million KWH
KWH = 3,400 BTU. Can be compared to 860 calories (food energy value).
A location's distance north or south of the equator measured in degrees.
EMITTING DIODE (LED)
A semiconductor device composed of a PN junction designed such that
electrons cause visible light during their migration across the
Devices that protect electronics from lightning-induced surges by
carrying the charge to ground.
The voltage drop or energy loss due to the resistance of wire in an
electrical circuit. See VOLTAGE DROP
CURRENT BOOSTER (LCB)
An electronic circuit that matches PV output directly to a motor by
converting unneeded voltage to higher usable current. Used in
array-direct water pumping.
Refers to equipment that is powered by electricity. Usually expressed
in terms of amperes or watts. Any device or appliance that uses energy
(such as a light or pump).
Glass coated with layers of metal or metal oxide. The coating emits
very little radiation in the long-wave (infrared) spectrum, which
diminishes heat loss from the building interior, and reduces heat gain
in hot weather.
A unit of measurement quantifying the amount of light emitted from a
The number of degrees east or west of true south from magnetic south.
The point on a PV module’s voltage/amperage curve where the product of
current and voltage is a maximum (measured in watts).
POWER POINT TRACKING (MPPT)
Electronically tracking the maximum power point of a PV module to
achieve the highest possible output, by (in simplest terms) using
surplus voltage to boost amperage.
Hydro-electric plants producing more than 100 watts and less than 2,000
The smallest nondivisible, self-contained, and environmentally
protected physical structure housing interconnected photovoltaic cells
and providing a single DC electrical output. Commonly called a “panel.”
A device that converts electrical energy into mechanical energy.
Any hydro plant that produces less than 100 watts.
ELECTRICAL CODE (NEC)
A document that describes the legal standards for residential and
commercial wiring practices with safety as the prime objective. Many
U.S. jurisdictions base their wiring inspections on the NEC.
State by state legislation that requires utilities to purchase
renewably produced electricity at the same price that they sell it,
until a building's monthly or annual energy use is offset.
A reference voltage used to describe batteries, modules, or systems
(for example, a 12 volt or 24 volt battery, module, or system).
The pointed piece farthest toward the wind on a wind generator,
designed primarily for cosmetic purposes, but also protects the blade
attachment points and generator from the weather.
The period of low energy demand, as opposed to maximum or peak demand.
Energy supplied during periods of relatively high system demands as
specified by the utility.
The unit that quantifies a material's resistance to electron flow.
Basic formula defining the relationship between voltage, amperage, and
resistance. Commonly stated as E = I x R, or Voltage = Amperage x
When an electrical circuit is interrupted by breaking the path at one
or more points, stopping the electrons from flowing. A light switch
opens an electrical circuit when it turns off the light.
CIRCUIT VOLTAGE (VOC)
The maximum possible voltage across a PV array, module, or cell. The
voltage across the terminals of a photovoltaic cell, module, or array
with no load applied when the cell is exposed to standard insolation
conditions, measured with a voltmeter.
A fresh water or "direct" solar hot water system, generally for use in
Placement according to the directions N, S, E, or W.
The emission of gasses by a material. See also GASSING.
Current that exceeds the rated current of the equipment or the ampacity
of a conductor, resulting from overload, short circuit, or ground fault.
A safety fuse or breaker designed to open a circuit when an overcurrent
An electrical circuit with more than one possible path for electron
flow. When wiring PV modules, this wiring configuration increases
amperage (current), while voltage remains the same. Parallel wiring is
positive to positive (+ to +) and negative to negative (- to -).
Opposite of a series connection.
Any use of the sun's energy in a manner that is found in nature without
the use of mechanical aid like pumps or fans. For example, heating a
thermal mass (a concrete wall or slab, for instance) during the day
with direct sunlight, and using the stored heat in that mass to warm a
greenhouse or home at night.
The period of time it takes for an energy generating device or system
to pay for itself in fuel savings.
The maximum load or electrical power draw occurring in a given period
Operating point of the IV (current-voltage) curve for a photovoltaic
cell or module where the product of the current value times the voltage
value is a maximum. Also called the “maximum power point.”
The equivalent number of hours per day when solar irradiance averages
1,000 watts per meter squared.
A common impulse turbine runner—the wheel that receives the water,
changing the pressure and flow of the water to circular motion to drive
an alternator, generator, or machine. Pelton wheels (named after
inventor Lester Pelton) are made with a series of cups or “buckets”
cast onto a hub.
The pipe in a hydro system that carries the water from the intake to
A device that consumes energy even when its switch is off, such as the
digital clock on a VCR.
The actual (physical) particle unit of light, as the electron is a
particle of electric charge. Solar-electric modules use photons to
generate electricity. Photons not captured by the cell are either
reflected, pass through the panel, or are converted to heat in the
A collection of solar modules connected in series, parallel, or
series-parallel combination to provide greater voltage, current, or
power than can be furnished by a single solar module. Solar-electric
arrays can be designed to furnish any desired voltage, current, or
A device composed of specially prepared semiconductor material or
material combinations exhibiting the ability to convert incident solar
energy directly into electrical energy.
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, electrons will flow and
electrical energy will be available.
A PV module consists of series and/or parallel wired cells typically
made from layered silicon crystals that convert light energy to DC
electricity. The number of modules in a given system varies depending
on the combined load being powered.
LOSS (Frictional head loss)
The amount of energy or pressure lost due to friction between a flowing
liquid and the inside surface of a pipe.
The semiconductor junction in a photovoltaic cell that shunts electrons
into a circuit. Electrons are bumped across this junction by photons
A PV mount that is installed on the top or side of a pole usually set
in concrete. Can be fixed or seasonally tilted.
A wafer of silicon with a multi-grained structure. All grains have the
same atomic crystal lattice, however, each grain has a unique
orientation in space, producing a unique reflection of light, resulting
in a "patchy" mottled appearance. AKA multicrystalline cell.
AND BEAM CONSTRUCTION
A traditional building technique in which post and beam framing units
are the basic load-bearing members. Post and beams may be of wood,
structural steel, or concrete. In this system, there are fewer framing
members, leaving more open space for in-fill. Often used in straw bale
The rate of energy use or generation per unit time, measured in watts.
1 watt = 1 joule per second.
The ratio of real power (watts) to apparent power (volt-amps) in an AC
circuit. Power factor describes the offset between voltage and amperage
peaks in AC. 1 is called “unity” power factor, and is when voltage and
amperage peak at the same time—they are then said to be “in phase.”
Power factor is calculated by dividing W by VA.
The “push” behind liquid or gas in a tank, reservoir, or pipe. Water
pressure is directly related to “head”—the height of the top of the
water over the bottom. Every 2.31 feet of vertical head gives 1 psi
(pound per square inch) of water pressure.
A primary cell is an electrochemical cell (battery) that cannot be
recharged. The chemical process within the primary cell is only one
way—discharge. When a primary cell is discharged it is discarded.
Common flashlight batteries are primary cells; they are disposable
batteries that should be avoided.
WIDTH MODULATION (PWM)
Varying the amount of DC energy sent to a load or other device by
changing the length of time a pulse is left on compared to when it is
off. The wider the pulse, the greater the energy transfer.
The Public Utility Regulatory Policies Act, passed in 1978. Requires
utilities to purchase excess generation from small-scale generators.
However, without net metering, this can amount to a fraction of retail
Two or more photovoltaic modules wired in series or parallel.
The use of electricity directly from a photovoltaic array, without
batteries or other electrical storage. Many solar water pumps work this
way, using a tank to store water.
The sun's energy that comes to earth in the form of direct, diffuse,
and reflected rays.
The transfer of heat through electromagnetic waves, without heating the
air between objects.
A two-way radio system that enables use of a regular telephone but with
radio instead of wires.
The manufacturer's specification for the amount of charge that may be
stored in a battery, commonly expressed in amp-hours at a specific rate
The manufacturer’s specification for power output of a generating
device. In most cases, this is not the most accurate measure to look
at, since it predicts output only for ideal circumstances.
The amount of energy per unit time that is being added to the battery.
Rate of charge is commonly expressed as a ratio of the battery or
cell’s rated capacity to charge duration in hours. Example: A C/20 rate
on a 100 AH battery would be 5 amps, the capacity of the battery
divided by 20.
A device that prevents overcharging of batteries by controlling the
charge cycle, and usually adjustable to conform to specific battery
needs. Regulators do not step the voltage down, but control the rate of
charge so the battery stays at a specified voltage. Also called CHARGE
Flows of energy that are regenerative or virtually inexhaustible from
natural ecological cycles. Most commonly includes solar (electric and
thermal), biomass, geothermal, wind, tidal, wave, and hydro power
Refers to how well a material conducts a flow of electrons, measured in
ohms (Ω). Resistance is the property of materials to impede a flow of
electrons through the material. All materials have some resistance.
Those of low resistance are known as conductors, while those of high
resistance are known as insulators. The unit used to measure resistance
is the Ohm.
A device with a known amount of resistance used in electrical circuits.
The voltage of a fully charged cell or battery that is neither being
charged or discharged.
Any radiation of a frequency that may be received or radiated by
radios. Common usage: RF interference (RFI); refers to the interference
of radio frequency radiation with the operation of devices or
appliances such as radios, televisions, computers, etc.
Root mean square; defines a time averaged value of a varying sinusoidal
parameter, such as AC voltage, amperage, or wattage. The square root of
the average of the squares of a set of numbers.
A PV or solar collector rack intended to be installed on a roof. For
PVs, its elevation angle can be fixed or seasonally adjustable.
The blades of a wind generator, shaped to spin when exposed to wind,
harnessing the wind's energy.
The part of a hydro turbine that accepts the water and turns its energy
into rotating motion.
The measure of a material's resistance to heat flow. The higher the
R-value, the greater its insulating capabilities.
An incandescent lamp filled with halogen gas. Somewhat more efficient
than standard incandescents.
Secondary cells are batteries (electrochemical cells) that are
rechargeable. The chemical reaction within the secondary cell is
reversible, allowing the cell to be recharged many times.
The tendency of all batteries to lose energy. Self-discharge represents
energy lost to internal chemical reactions within the cell. This energy
is not and cannot be used from the battery or cell’s output terminals.
Sensing device that changes its electrical resistance according to
temperature. Used in the control system of a solar thermal system to
measure collector and storage tank temperatures.
A wiring configuration used to increase voltage from more than one
supply. Series wiring is positive to negative (+ to -) or negative to
positive (- to +). Opposite of parallel connection. Series circuits
have only one possible path for electron flow.
A device that prevents overcharging of a battery by disconnecting the
charging source as the battery voltage approaches some upper limit.
A group of PV modules or batteries wired in series.
A circuit in which two source leads of opposite polarity or dissimilar
potential are connected directly to each other with no regulation or
load in between, allowing the full energy potential of the source to
flow through the circuit. A short circuit will trip the breaker or
fuse, and may damage components, or even cause a fire.
CIRCUIT CURRENT (ISC)
The current between two points in a circuit when the points are
electrically connected with a conductor with essentially zero
resistance. Normally applied to PV modules, which can be short
circuited safely because they are limited current devices.
1. A resistive load through which electron flow is diverted, typically
used to heat air or water.
A component with a precise, known resistance used to determine amperage
by measuring the voltage across it and using Ohm's law (I = V/R).
To divert electrical current to a separate circuit or load.
A device that prevents overcharging of a battery by diverting some (or
all) of the charging current to a resistive load when the battery
voltage reaches a preset upper limit.
A PV mount installed on the side of a pole. May be fixed or seasonally
A nonmetallic element, which 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.
A wafer of silicon that has a perfect, continuous, crystal lattice (on
the atomic level).
An estimation of a location for its potential for solar, hydro, or wind
A solar collector is a device designed to absorb incident solar
radiation and to transfer the energy to the fluid or air passing
A device that converts the sun's energy into heat energy, which is then
used to cook food.
Energy coming directly from the Sun.
(SUMMER & WINTER
The longest and shortest days of the year. The longest day (Summer
Solstice) is about June 21st in the Northern Hemisphere. The shortest
day (Winter Solstice) is about December 21st in the Northern Hemisphere.
A system that operates independently of the utility lines. It may draw
supplementary electricity from the utility, but is not capable of
providing electricity to the utility.
TEST CONDITIONS (STC)
The standardized conditions of 1,000 watts per meter squared of solar
insolation at 25°C (77°F) for testing PV module ratings.
OF CHARGE (SOC)
A ratio, expressed in percent, of the energy remaining in a battery in
relation to its capacity when fully charged.
See BATTERY and SECONDARY CELL.
The movement of heat by convection in gasses and liquids causes heat to
stratify in layers, the warmest being on top. Stratification is caused
by gravity, since the warmer gases and liquids are less dense than the
A building technique using straw bales for the walls. See POST AND BEAM
INSULATED PANELS (SIPs)
A no-cavity solid building system of wall and roof panels "sandwiching"
polystyrene insulation between an outer and inner sheathing panel
(typically oriented strand board (OSB) or metal).
A material or energy source, which if managed carefully, will provide
at current levels indefinitely.
The formation of lead-sulfate crystals on the plates of a lead-acid
battery, which decreases battery capacity by impeding the opportunity
for chemical reaction within a cell. Sulfation can be caused by leaving
the battery in a discharged state for long periods of time.
The maximum amount of AC power an inverter may deliver to a load (or
loads) for a short period of time, such as when starting a motor.
The area (in square feet or meters^2) that a wind generator’s rotor
(blades) sweep. This is the collector area for a wind generator. The
larger the collector, the more energy it will capture.
A device that breaks an electrical circuit, halting the flow of
electrons through the circuit.
The part of a wind generator that makes the rotor face into the wind.
Often the tail is also involved in governing the machine, by folding
down or sideways to swing the rotor out of the wind.
The pipe, flume, or channel in a hydroelectric system that carries the
water from the turbine runner back to the stream or river.
A material of low thermal conductivity placed in such a way as to
reduce the flow of heat between two materials of high thermal
A material that has the ability to absorb, store, and release heat
energy. The more heat energy that is required to change the temperature
of high-density materials (concrete, bricks, tiles), the more thermal
mass the materials have.
Passive solar hot water systems that rely on the natural convection of
liquids to collect energy. Designed with the tank above the collection
A PV manufacturing technique where silicon is vapor deposited, a few
molecules thick, onto another material.
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, the optimum angle
A nonclimbable wind generator tower that tilts up and down to allow
installation and servicing of the turbine on the ground. Normally these
employ a gin pole—a horizontal lever arm that helps raise and lower the
MOUNT (POLE MOUNT)
A mounting rack for a PV array that automatically tilts to follow the
daily path of the sun through the sky. A “tracking array” will produce
more energy through the course of the day than a “fixed array”
(nontracking), particularly during the long days of summer. Some
trackers are single-axis while others are dual-axis.
An electrical device that steps up voltage and steps down current
proportionally (or vice-versa). Transformers work with AC only.
A large strainer at the input to a hydro system. Used to remove debris
from the water before it enters the pipe.
An engine that produces rotary motion through reaction or impulse, or
both, with moving fluid or gas. The resultant rotary motion is usually
used to drive an alternator generator.
In hydroelectric systems, a type of impact hydro runner optimized for
lower heads and higher volumes than a Pelton runner.
POWER SUPPLY (UPS)
A power supply providing continuous, uninterruptible service—commonly
used in telecommunications and computer networks.
In relation to a wind turbine, toward the wind. An upwind turbine has
its blades on the upwind side of the tower.
Commercial electrical energy distribution system. Synonyms: Mains, Grid.
See GRID-TIE SYSTEM.
The volt is the unit used in the measurement of electromotive force
(electrical “pressure”). A standard electrical definition of the volt
is: an electromotive force of 1 volt is necessary to move a current of
1 ampere through a 1 Ω resistor. It is often also referred to as
electrical potential difference or potential difference.
A measure of the force or "push" given the electrons in an electrical
circuit; a measure of electrical potential. Analogy: pressure in a
water pipe. AKA Potential.
Loss of voltage (electrical pressure) caused by the resistance in wire
and electrical devices. Proper wire sizing will minimize voltage drop,
particularly over long distances. Voltage drop is determined by four
factors: wire size, current (amps), voltage, and length of wire. Water
analogy: friction loss in pipe.
A way of naming a range of voltage to a standard. Example: A “12 volt
nominal” system may operate in the range of 10 to 20 Volts. We call it
“12 volts” for simplicity.
See OPEN CIRCUIT VOLTAGE
PEAK POWER POINT (Vpp)
The voltage at which a photovoltaic module or array generates at the
highest power (watts). A “12 volt nominal” PV module will typically
have a peak power voltage of around 17 volts. A PV array-direct solar
pump should reach this voltage in full sun conditions. In a higher
voltage array, it will be a multiple of this voltage.
A device for measuring the voltage difference between any two points in
an electrical circuit.
Unit of power. Power is the rate of generating or using energy. One
watt is the power developed or dissipated in a one volt circuit in
which there is a current of one ampere (6.28 million million electrons
per second). Watts = amps X volts.
A unit of measurement quantifying an amount of
energy used or
generated. A load that consumes 1 watt for 10 hours uses 10 watt-hours.