Glossary
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Alternating current (AC) Electric
current in which the direction of flow is reversed at frequent intervals.
The most common type of household electricity.
Ampere or amp (A) The unit of measurement for the electric
current. One amp is produced by an electric force of 1 volt acting across
a resistance of 1 ohm.
Annual solar savings The amount of energy saved by using
a solar system as compared to a nonsolar system.
Array see photovoltaic array
Building-integrated PV (BIPV) Used
to describe a structure where PV replaces conventional materials and is
integrated into the building.
Capacitor A passive electrical
component that can store energy between two conductors (plates). They
are often used to improve power factor in industrial settings in order
to lower electrical demand and reduce costs.
Cell see photovoltaic cell
Cell efficiency The percentage of electrical energy that
a solar cell produces (under optimal conditions) as compared to the total
amount of energy from the sun falling on the cell.
Circuit A system of conductors that convey electricity.
Circuit breaker A safety device that shuts off power
when it senses too much current.
Conductor A material that is used to convey electricity,
i.e. wires.
Conversion efficiency The percentage of electricity that
is created by a solar cell as compared to the amount of energy needed
to generate that electricity.
Current The flow of electricity between two points. Measured
in amps.
Direct current (DC) Electrical
current that flows only in one direction. The most common form of electricity
used in boats and RVs.
Distributed systems Installed 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 solar system is
a distributed system.
Efficiency The ratio of output
energy to input energy.
Electric circuit The path followed by electricity, beginning
from the generating source, continuing through the devices that use the
electricity, and then traveling back to the source.
Electric current The flow of electrons measured in amps.
Electrical grid A large distribution network that delivers
electricity over a wide area.
Electricity The controlled flow of electrons through
a conductor.
Energy Usable power. Measured in kWh.
Energy audit A process that determines how much energy
you use in your house or apartment.
Fossil fuels Fuels that are formed
underground from the remains of dead plants and animals. i.e. oil, natural
gas, and coal are fossil fuels.
Greenhouse effect When heat from
the sun becomes trapped in the Earth's atmosphere due to certain gases.
Greenhouse gases The gases responsible for trapping heat
from the sun within the Earth's atmosphere. i.e. water vapor, carbon dioxide,
methane, ozone, chlorofluorocarbons, and nitrogen oxides.
Grid A distribution network, including towers, poles,
and wires that a utility uses to deliver electricity.
Grid-tied PV system A solar system that is tied in to
the utility's network. When generating more power than necessary, the
system supplies the surplus to the grid. At night, the system draws power
from the grid.
Hertz (HZ) The frequency of electrical
current described in cycles per second, i.e. Appliances in the United
States use 60 HZ.
Inverter An inverter converts
the electricity generated from a solar system from direct current (DC)
to alternating current (AC) for use in the home and/or electrical grid.
Irradiance the amount of solar energy that strikes a
surface during a specific time period. Measured in kilowatts.
I-V curve A graph that plots the current versus the voltage
from the solar cell as the electrical load (or resistance) is increased
from short circuit (no load) to open circuit (maximum voltage). The shape
of the curve characterizing cell performance. Three important points on
the IV curve are the open-circuit voltage, short-circuit current, and
peak or maximum power (operating) point.
Junction box The point on a solar
module where it connects, or is strung, to other solar modules.
Kilowatt (kW) A unit of electrical
power, one thousand watts.
Kilowatt-hour (kWh) One thousand watts acting over a
period of one hour. The kWh is a unit of energy.
Life-cycle cost The estimated
cost of owning, operating, and disposing of a system over its useful life.
Load Anything that is connected to an electrical circuit
and draws power from that circuit.
Megawatt (MW) One million watts;
1,000 kilowatts.
Module see photovoltaic module
Monocrystalline solar cell A type of solar cell made
from a thin slice of a single large crystal silicon.
Multicrystalline Material composed of many small crystals
(crystallites). Because of the numerous grain boundaries, devices that
employ this design will operate with reduced efficiency.
National Electrical Code (NEC)
The U.S. minimum inspection requirements for all types of electrical installations,
including solar systems.
National Electrical Manufacturers Association (NEMA)
The U.S. trade association that develops standards for the electrical
manufacturing industry.
NREL The National Renewable Energy Laboratory. A national
lab that concentrates on studying and developing renewable energy sources.
Net metering A practice used in conjunction with a solar
electric system where your electric meter tracks your net power usage,
spinning forward when you use electricity from the utility, and spinning
backward when your system is generating more electricity than you need.
Off-grid PV See Stand alone
PV
Orientation A term used to describe the direction that
a solar module faces. The two components of orientation are the tilt angle
(the angle the panel makes from the horizontal) and the aspect angle (the
angle the panel makes from North).
Panel A term used to describe
a solar module.
Passive solar home A house that utilizes part of the
building as a solar collector, as opposed to active solar, such as PV.
Peak load The largest amount of electricity being used
at any one point during the day.
Photovoltaic (PV) the conversion of light into electricity.
Photo means "light", voltaic means "electric."
Photovoltaic array An interconnected system of solar
modules that function as a single electricity-producing unit.
Photovoltaic cell Made from silicon, this is the basic
unit of a solar module that collects the sun's energy.
Photovoltaic module The layers of glass, plastic, and
silicon cells framed in metal, which collect the sun's energy.
Photovoltaic system A complete set of components that
convert sunlight into usable electricity.
Polycrystalline solar cell See multicrystalline
Power Factor The ratio of working power to apparent power
(KW/KVA). In other words, the portion of power your electrical equipment
draws from the utility (or other power source) that is used towards work
divided by the total power apparently used in the process.
PV An abbreviation for photovoltaic.
Rated power Nominal power output
of an inverter; some units cannot produce rated power continuously.
Renewable Energy Credit (REC) Credit that is earned by
a renewable energy producer for producing renewable energy. In the case
of solar energy, one credit is earned for every 1,000 kw generated on
an annual basis. Many states have adopted their own requirements (Renewable
Portfolio Standards) for utilities to generate a certain percentage of
their power via renewables or face fines. These RECs are sold on the open
market; therefore prices will fluctuate depending on market conditions.
Silicon (Si) A chemical element
that is the most common semiconductor material used in making PV cells.
Single-crystal silicon Silicon material with a single
crystal structure. A common material for the construction of solar PV
cells.
Solar cell see photovoltaic cell
Solar energy Energy from the sun.
Solar module see photovoltaic module
Solar power Electricity generated from sunlight.
Stand alone PV A solar system that operates without connection
to a grid or another supply of electricity. A battery bank stores unused
daylight production for nighttime power. Commonly used in remote regions
such as mountains, ocean platforms or communication towers. Also called
“off-grid” solar.
Thin film A solar PV module constructed
with sequential layers of thin film semiconductor materials usually only
micrometers thick. Currently, thin-film technologies account for around
12 percent of all solar modules sold worldwide.
This share is expected to increase, since thin-film technologies represent
a potential route to lower costs.
Tilt angle The angle of inclination of a module measured
from the horizontal.
Volt (V) The measurement of the
force given the electrons in an electric circuit.
Watt (W) The unit of electric
power done in a unit of time. One ampere of current flowing at a potential
of one volt produces one watt of power.
Watt-hour (Wh) A unit of energy equal to one watt of
power being used for one hour.
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