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| Glossary
of Solar Energy Terms
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| A |
Activated
shelf life: The time it takes for the capacity of a charged battery
to fall to an unusable level when stored at a specified temperature.
Activation voltage: The voltage at which
the controller will operate to protect the batteries.
AGM (Adsorbed Glass Mat): a newer type of
battery construction that uses saturated adsorbant glass mats rather than gelled
or liquid electrolyte. AGM batteries are typically more expensive than flooded
(liquid), but offer enhanced reliability.
Air mass: The air mass relates to the path length of solar radiation through the atmosphere. An air mass of 1.0 means the sun is directly overhead
and the radiation travels through one atmosphere thickness. Approximately equal to the secant
of the zenith angle, i.e. the angle from directly overhead to a line to the sun.
Alternating current (AC): Electrical current
that continually reverses direction of flow. The frequency at which it reverses
is measured in cycles-per-second, or Hertz (Hz). The magnitude of the current
itself is measured in amps (A).
Alternator: A device for producing Alternating
Current ("AC") electricity. Usually driven by a motor, but can also be driven
by other means, including water and wind power.
Ambient temperature: The temperature of the
surroundings.
Ammeter: A device used for measuring current
flow at any point in an electrical circuit.
Amorphous silicon: A thin-film solar PV
cell material which has a glassy rather than crystalline structure. Made by depositing layers
of doped silicon on a substrate normally using plasma-enhanced chemical vapor
deposition of silane.
Amp hour: The quantity of electrical energy
corresponding to the flow of current of one ampere for one hour. The term is used to quantify
the energy stored in a battery. Most batteries are rated in Ah.
Ampere (A) or amp: The unit for the electric
current; the flow of electrons. One amp is 1 coulomb passing in one second. One
amp is produced by an electric force of 1 volt acting across a resistance of 1
ohm.
Anemometer: A device used to measure wind
speed.
Angle of incidence: Angle between the normal
to a surface and the direction of incident radiation; applies to the aperture
plane of a solar panel. Only minor reductions in power output within plus/minus
15 degrees.
Anode: The positive electrode in a
battery. The positive terminal of a diode.
Anti-reflection coating: A thin coating of
a material with a specific refractive index applied to a cell to reduce the reflection
of light.
Array: A number of solar modules connected
together in a single structure.
Array current: The electrical current output
of a PV array when exposed to sunlight.
Array operating voltage: The voltage output
of a PV array when exposed to sunlight and feeding a load.
Autonomous system: A PV System that operates
without any other energy generating source.
Availability: The quality or condition of
a PV system that is available to provide power to a load. Usually measured in
hours per year.
AWG: American Wire Gauge: a standard system
for designating the size of electrical wire. The higher the number, the smaller
the wire. Most house wiring is #12 or 14.
Azimuth: The 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, 180 degree azimuth means the array faces
due south. |
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Balance
of system (BOS): All the parts of a PV System
excluding the solar module
Ballast: a circuit used to stabilize an electric
current, for example, in a fluorescent light.
Battery: A system in which stored chemical
energy is converted directly into electrical energy. Can be either rechargeable
or non-rechargeable. Different to a fuel cell in that it contains a fixed
quantity of stored chemical energy rather than a continuous supply of fuel.
Battery capacity: The total number of ampere-hours
(Ah) that a fully charged battery can output.
Battery cell: An individual unit of a battery that can store electrical energy and is capable of furnishing a current
to an external load. For lead-acid batteries the voltage of a cell (fully charged)
is about 2.2 volts dc. A battery may consist of a number of cells.
Battery charger: A device used to charge a
battery by converting (usually) mains voltage AC to a DC voltage suitable for
the battery. Chargers often incorporate some form of regulator to prevent overcharging
and damage to the battery.
Battery cycle Life: The number of times a
battery can undergo a cycle of discharge and recharge before failing. Cycle Life
is normally specified as a function of discharge rate and temperature.
Battery self-discharge: Energy loss by
a battery that is not under load.
Battery state of charge (SOC): Extent of
battery charge status as a percentage
of full charge. Also 100 per cent minus the Depth of Discharge.
BIPV: Building Integrated Photovoltaics. As the name suggests, this is where
PV modules are integrated in to the building construction materials as on integrated
unit.
Blocking diode: A diode used to prevent
current flow in an undesirable direction e.g. from the rest of the PV array to a failed module or from the
battery to the PV array when current generation is low.
British Thermal Unit (BTU): The amount of
heat energy required to raise one pound of water from a temperature of 60 degrees
F to 61 degrees F at one atmosphere pressure. One Watt hour equals 3,413 BTU.
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. [UL 1703] |
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Capacitor:
An electronic component used for the temporary storage of electricity,
as well for removing unwanted noise in circuits. A capacitor will
block Direct Current but will pass Alternating Current.
Capacity: See Battery Capacity.
Captive electrolyte battery: A battery with an immobilized electrolyte (gelled or absorbed in a material).
Cathode: The negative electrode in an electrochemical
cell. Also, the negative terminal of a diode.
Cathodic protection: A method of preventing
oxidation (rusting) of exposed metal structures, such as bridges and pipelines,
by imposing between the structure and the ground a small electrical voltage that
opposes the flow of electrons and that is greater than the voltage present during
oxidation.
Cell efficiency: The ratio of the electrical
energy produced by a photovoltaic cell (under full sun conditions or 1 kW/m2)
to the energy from sunlight falling upon the photovoltaic cell.
Cell junction: The area of immediate contact
between two layers (positive and negative) of a photovoltaic cell. The junction
lies at the center of the cell barrier or depletion zone.
Cell: The basic unit of a PV module or battery.
The most basic unit that contains the necessary materials, such as electrodes
and electrolyte in a battery, to produce electricity.
Charge: The process of inputting electrical energy
to a battery.
Charge controller: A component that controls
the flow of current to and from the battery subsystem to protect the batteries
from overcharge and over discharge. Essential for ensuring that batteries obtain
maximum state of charge and longest life. The charge controller may also monitor
system performance and provide system protection. Charge Controllers are also
sometimes called Regulators.
Charge factor: A number corresponding to the time
(in hours) for which a battery can be charged at a constant current without
damaging it. Usually expressed as a function of battery capacity, e.g. C/10 indicates a charge factor of
10 hours. Related to Charge Rate.
Charge rate: A measure of the current used to
charge
a battery as a proportion of its capacity.
Circuit: A continuous system
of conductors providing a path for electricity
Circuit breaker: A circuit breaker acts like an automatic switch that
can shut the power off when it senses too much current.
Cloud enhancement: The increase in solar intensity
due to reflected light from nearby clouds.
Cogeneration: The joint production
of electricity and useful heat at a single facility, resulting in more efficient
use of the thermal energy.
Concentrator: A photovoltaic device that uses optical elements (e.g. mirrors or lenses) to increase the amount of
light incident on a solar PV cell.
Concentrator arrays track the sun and use only direct sunlight since the diffuse
portion cannot be focused. Concentrators therefore work best in clear sky
locations. Efficiency is increased, but cell life may be reduced because
operating temperatures are higher.
Conductor: A material used to transfer, or
conduct, electricity, often in the form of wires.
Conduit: A pipe or elongated box used to house
and protect electrical cables.
Conversion efficiency: The ratio of the electrical
energy generated by a solar PV cell to the solar energy impacting the cell.
Cross-flow turbine: A turbine where the flow
of water is at right angles to the axis of rotation of the turbine. Crystalline
silicon: A type of PV cell material made from a single crystal or polycrystalline
ingot of silicon.
Current: Current is the flow of electric charge
in a conductor between two points having a difference in electrical potential
(voltage) and is measured in Amps.
Current at maximum power (Imp): The current
at which maximum power is available from a module. [UL 1703]
Cut-off voltage: The voltage levels
at which the charge controller (regulator) disconnects the PV array from the battery, or the load
from the battery.
Cycle: The discharge and re-charge
of a battery, one complete charge/discharge cycle of the battery.
Cycle life: Number of charge-discharge cycles
a battery can perform under specified conditions before it fails to meet its specified
performance (e.g. capacity decreases to 80% of nominal capacity). |
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Days
of storage: The number of days that a stand-alone system will power a
specified load without solar energy input. A measure of system autonomy.
DC to DC converter: Electronic circuit to
convert dc voltages (e.g., PV module voltage) into other levels (e.g., load voltage).
Can be part of a maximum power point tracker (MPPT).
Dealer: A Retailer of PV products and/or PV Systems
Deep cycle battery: A battery designed to
regularly discharge 80% of its capacity before recharging.
Deep discharge: Discharging a battery by more than 80% of its full charge.
Depth of discharge (DOD): the amount of energy
withdrawn from a battery or cell expressed as a percentage of its rated capacity.
Design month: The month in which the combination
of insolation and load requires the maximum energy from the array.
Diffuse insolation: Incident sunlight received indirectly because of
scattering due to clouds, fog, particulates, or other obstructions in the atmosphere.
The other component of sunlight is Direct.
Diffuse radiation: Radiation received from
the sun after reflection and scattering by the clouds, fog, haze, dust or other
substances in the atmosphere, and the ground.
Diode: Electronic device that allows current
flow only in one direction.
Direct beam radiation: Radiation received
by direct sunlight. Measured by a pyrheliometer with a solar aperture of 5.7°
to transcribe the solar disc.
Direct current (DC): Electrical current that
flows only in one direction, although it may vary in magnitude. Contrasts with
alternating current.
Direct insolation: Sunlight falling directly
upon a collector. Opposite of diffuse insolation.
Direct radiation: Light that has traveled
in a straight path from the sun (also referred to as beam radiation). An object
in the path of direct radiation casts a shadow on a clear day.
Discharge: Withdrawal of electrical energy
from a battery.
Discharge factor: A number equivalent to the
time in hours during which a battery is discharged at constant current usually
expressed as a percentage of the total battery capacity, i.e., C/5 indicates a
discharge factor of 5 hours.
Discharge rate: A measure of the current withdrawn
from a battery over time, expressed as a percentage of battery capacity. A C/5 discharge rate indicates a current
of one-fifth of the rated capacity
of the battery.
Disconnect: Switch used to connect or
disconnect components in a PV system.
Dispatchability: The ability of a generating unit
or other source of electric power to vary output.
Dispatchable power: Energy output that can be planned
on and typically provides a continuous power output. Solar power and Wind power
in not dispatchable without configuration with out some other power or storage
mechanism. Hydrocarbon based power plants or nuclear plants are dispatchable.
Distributed systems: Systems that are installed at or near the location
where the electricity is used, as opposed to central systems that supply electricity
to grids. A residential photovoltaic system is a distributed system.
Distributor: Using means a wholesaler of PV products
Downtime: Time when the PV system cannot provide
power to the load, expressed either in hours per year or as a percentage.
Dry cell battery: A battery that uses a solid
paste for an electrolyte.
Duty cycle: The ratio of active to total
time, used to describe the operating regime of loads in PV systems.
Duty rating: The amount of time an inverter can
operate at full rated power. Some inverters can
operate at their rated power for only a short time without overheating.
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Earth:
Refers to physically connecting a part of an electrical system to the ground,
done as a safety measure, by means of a conductor embedded in suitable soil.
Earth-leakage circuit breaker (ELCB): A device
used to prevent electrical shock hazards in mains voltage power systems, including
independent power systems. Also known as residual current devices (RCD's).
Efficiency: The ratio of output power or
energy to input power or energy, expressed as a percentage.
Electric circuit: Path followed by electrons
from a power source (generator or battery) through an external line (including
devices that use the electricity) and returning through another line to the source.
Electric current: The flow of electrons measured
in Amps.
Electrical grid: A network for electricity
distribution across a large area.
Electricity: The movement of electrons (a
sub-atomic particle), produced by a voltage, through a conductor.
Electrode: An electrically conductive material,
forming part of an electrical device, often used to lead current into or out of
a liquid or gas. In a battery, the electrodes are also known as plates.
Electrolysis: A chemical reaction caused by
the passage of electricity from on electrode to another.
Electrolyte: The medium that provides ionic transport
between the electrodes of a battery.
All common batteries contain an electrolyte, such as the sulfuric acid used in
lead-acid batteries.
Energy density: The ratio of the energy available
from an energy storage device such as a battery to its volume (Wh/m3) or weight (Wh/kg).
Energy payback time: The time required for
any energy producing system or device to produce as much energy as was required
in its manufacture. For solar electric panels, this is normally in the range 6-36
months.
Energy: Power consumed multiplied by the duration
of use. For example, 1000 Watts used for four hours is 4000 Watt hours.
Equalization charge: Periodical overcharging the batteries for a short
time to mix the electrolyte solution in batteries.
EVA (Ethylene Vinyl Acetate): An encapsulant used between the glass
cover and the solar cells in PV modules. It is durable, transparent, resistant
to corrosion, and flame retardant. |
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Fill
factor: On an I-V (current-voltage) curve characterizing the output
of a solar cell or module, the ratio of the maximum power to the product of the
open-circuit voltage and the short-circuit current. The higher the fill factor
(FF) the "squarer" the shape of the I-V curve.
Fixed tilt array: A solar PV array set at a fixed
angle to the horizontal.
Flat-plate PV: A solar PV array or module that does
not contain concentrating devices and so responds to both direct and diffuse sunlight.
Float charge: A battery charge current that is equal to, or slightly greater than, the self-discharge rate.
Float life: The time (usually in years) a
battery can maintain its stated capacity when kept at float charge.
Flooded cell battery: A form of rechargeable
battery where the plates are completely immersed in a liquid electrolyte. Most
cars use flooded-cell batteries. Flooded cell batteries are the most commonly
used type for independent and remote area power supplies.
Fluorescent light: A form of lighting that
uses long thin tubes of glass which contain mercury vapor and various phosphor
powders (chemicals based on phosphorus) to produce white light. Generally considered
to be the most efficient form of home lighting.
Frequency: The number of cycles or repetitions per unit
time of a complete waveform, in electrical applications usually expressed in
cycles per second or Hertz (Hz). Electrical equipment in the United
States requires 60 Hz, in Europe 50Hz.
Fresnel lens: A concentrating lens, positioned
above and concave to a PV material to concentrate light on the material.
Fuel cell: An electrochemical device that
converts the energy of a fuel directly into electricity and heat and is therefore
very energy efficient.
Fuse: A fuse is a device used to protect electrical
equipment from short circuits. Fuses are made with metals that are designed to
melt, when the current passing through them is high enough. When the fuse melts,
the electrical connection is broken, interrupting power to the circuit or device.
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Gassing:
Gaseous by-products when charging a battery, e.g. hydrogen from a lead acid
battery.
Gel-type battery: Lead-acid battery in which
the electrolyte is immobilized in a gel. Usually used for mobile installations
and when batteries will be subject to high levels of shock or vibration.
Generator: A mechanical device used to produce
DC electricity. Power is produced by coils of wire passing through magnetic fields
inside the generator. Most alternating current generating sets are also referred
to as generators.
Gigawatt (GW): A measurement of power equal
to a thousand million Watts.
Gigawatt-hour (GWh): A measurement of energy.
One Gigawatt-hour is equal to one Gigawatt being used for a period of one hour,
or one Megawatt being used for 1000 hours.
Grid: An electrical
utility distribution network.
Grid-connected: An energy producing system
connected to the utility transmission grid. Also called Grid tied.
Ground loop: An undesirable feedback condition
caused by two or more circuits sharing a common electrical line, usually a grounded
conductor. |
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Halogen
lamp: A special type of incandescent globe made of quartz glass and
a tungsten filament, enabling it to run at a much higher temperature than a conventional
incandescent globe. Efficiency is better than a normal incandescent, but not as
good as a fluorescent light.
Harmonic content: Frequencies
in the output waveform in addition to the primary frequency (usually 50 or 60 Hz.) Energy
in these harmonics is lost and can cause undue heating of the load.
Head: The vertical distance that water will
fall from the inlet of the collection pipe to the water turbine in a hydro power
system.
Hertz (Hz): Unit of measurement for frequency.
Home mains power is normally 50Hz in Europe and 60Hz in the USA. The magnitude
of the current is measured in Amps.
High voltage disconnect: Voltage at which
the charge controller will disconnect the array to prevent overcharging the batteries.
Hot spot: A phenomenon where one or more cells
within a PV module or array act as a resistive load, resulting in local overheating
or melting of the cells.
Hybrid system: A PV system that includes solar PV
and some other electricity generating power source. |
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