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Glossary
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alternating current (ac) - Electric current in which the
direction of flow is reversed at frequent intervals: usually
100 or 120 times per second, equivalent to 50 or 60 cycles
per second. Expressed as 50 Hz or 60 Hz, Hz being an abbreviation
for hertz. See hertz; direct current.
amorphous semiconductor - A non-crystalline semiconductor
material (such as copper indium diselenide, cadmium telluride,
gallium arsenide, or amorphous silicon) a few microns or
less in thickness, used in photovoltaic systems. Easier
and cheaper to produce than the more common crystalline
variety, but less efficient and degrades more rapidly over
time. Also called thin film.
ampere (amp) - A measurement of electrical current in
a circuit. Contrast with "volts”, which is a
measure of force, or pressure, behind the current. Multiplying
amps by volts derives "watts," the total measurement
of power.
array - An interconnected system of PV modules that function
as a single electricity-producing unit. The modules are
assembled as a discrete structure, with common support
or mounting. In smaller systems, an array can consist of
a single module.
Building Integrated Photovoltaics (BIPV) - Solar electrical
generation systems that are also part of the building envelope
(a building’s outer surfaces) and perform another
task such as roofing or glazing.
building permit - Authorization from
the local building inspection agency to construct or modify
a building from
an approved set of plans, usually required for solar energy
installations.
California Title 24 Energy Requirements - See Title 24
Energy Requirements, California
cell - The basic unit of a photovoltaic panel or battery.
See photovoltaic cell.
cell barrier - A very thin region of static electric
charge along the interface of the positive and negative
layers in a photovoltaic cell. The barrier inhibits the
movement of electrons from one layer to the other, so
that higher-energy electrons from one side diffuse preferentially
through it in one direction, creating a current and thus
a voltage across the cell. Also called depletion zone,
cell junction, or space charge.
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.
charge controller - Electronic device which regulates
the voltage applied to the battery system from the PV array.
It is essential for ensuring that the batteries obtain
maximum state of charge and longest life.
circuit breaker - Electrical switch that automatically
interrupts an electrical circuit when the current exceeds
safe limits. The circuit breaker must be manually reset
when the problem causing the interruption has been corrected.
circuit voltage - The amount of voltage in a specific
electrical circuit. 110 voltage is used for small electric
radiant projects while 220 voltage is used for larger area
applications
combined collector - A photovoltaic device or module that
provides useful heat energy in addition to electricity.
concentrator - A PV module that uses optical elements
to increase the amount of sunlight striking a PV cell.
Concentrating arrays must track the sun and use only direct
sunlight because the diffuse portion cannot be focused
onto the PV cells. Efficiency is increased, but lifespan
is usually decreased due to the high heat.
concentrator module, array, or collector - An arrangement
of photovoltaic cells that includes a lens to concentrate
sunlight onto small-area cells. Concentrators can increase
the “power flux” (or strength) of sunlight
hundreds of times.
conduit - Tubing made of metal, plastic, or other material
used to channel and protect electrical wiring from damage
or moisture.
conduit box - Also called a junction box. An electrical
box where electrical conduit is terminated. It serves as
both the termination point for the conduit and as a container
in which electrical wires can be terminated, redirected,
or joined. See junction box.
conversion efficiency (cell or module) - The ratio of
the electric energy produced by a photovoltaic device (under “one-sun” or
un-enhanced conditions) to the energy from sunlight incident
(or striking upon) the cell.
converter (dc to dc) - Electronic circuit to convert dc
voltages (i.e. PV module voltage) into other levels (i.e.
load voltage). Can be part of a maximum power point tracker
(MPPT).
cycle life - Number of discharge-charge cycles that a
battery can tolerate under specified conditions before
it fails to meet specified criteria as to performance (e.g.,
capacity decreases to 80-percent of the nominal capacity).
degradation - (1) The disintegration or deterioration
of parts or materials beyond a repairable condition, thus
requiring replacement. (2) Loss of efficiency of solar
cells over a long period of time.
deep discharge - Discharging a battery to 20-percent or
less of its full charge.
diffuse insolation - Sunlight received indirectly as a
result of scattering due to clouds, fog, haze, dust, or
other obstructions in the atmosphere. Opposite of direct
insolation.
direct current (dc) - Electric current in which electrons
flow in one direction only. See alternating current (ac).
direct insolation - Sunlight falling directly upon a collector.
Opposite of diffuse insolation. See diffuse insolation.
discharge rate - The rate, usually expressed in amperes
or time, at which electrical current is taken from the
battery.
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 an example of a distributed
system.
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 - flow of electrons creating electricity,
moving in a conductor; electricity as measured in amperes,
or amps. See ampere.
electrical grid - An integrated system of electricity
transmission and distribution, usually covering a large
area, to which most homes and businesses in the U.S. are
connected; the entire infrastructure that supplies power
to homes and businesses.
energy efficiency - The use of less fuel to achieve a
goal, such as heating a space, providing hot water, generating
electricity, powering lights, or operating appliances.
energy payback time - The time required for any energy
producing system or device to produce as much energy as
was required for manufacturing it. For solar electric modules,
this ranges from about 2 to 5 years, out of a 30 year lifespan.
fault - Failure in part of an electrical circuit.
flat-plate PV - Refers to a PV array or module that consists
of non-concentrating elements. Flat-plate arrays and modules
use direct and diffuse sunlight, but if the array is fixed
in position, some portion of the direct sunlight is lost
because of oblique sun-angles in relation to the array.
fuel efficiency - Percentage of energy released by fuel
combustion (i.e. “burning” of the fuel) that
is ultimately converted into useable energy. Fuel efficiencies
vary greatly among fuel sources.
gel-type battery - Lead-acid battery in which the electrolyte
is composed of a silica gel matrix.
grid, the (or utility grid) - See electric grid.
grid-intertied (PV system) - A solar electric (PV) system
that is connected to the utility grid. It is capable of
(1) recieving electricity from the utility grid when its
own output is inadequate to its needs, and (2) selling
excess power to the utility, provided that the usual utility
approval has been obtained and the necessary specialized
equipment has been installed. The grid is the entire infrastructure
that supplies power to homes and businesses.
hertz (Hz) - A unit of frequency of change in state or
cycle in an alternating current of one cycle per second.
In the United States, common house electrical supply is
at 60 hertz, meaning the current changes direction or polarity
120 times, or 60 cycles, a second. In Europe, line frequency
is 50 hertz, or 50 cycles per second.
hybrid solar energy system - A system that uses multiple
methods, either active or passive, of energy production
in its operation.
insolation - Derived from Incident Solar Radiation, the
amount or strength of sunlight or solar radiation - direct,
diffuse, and reflected – striking a surface. Equal
to about 1353 watts per square meter in space and about
1000 watts per square meter at sea level at the equator
at solar noon. It increases at higher altitudes. (Not to
be confused with 'insulation'.)
interconnect - A conductor within a module, some or other
means of connection, which provides an electrical interconnection,
or link, between the solar cells.
inverter - Device used to change the DC (direct current)
electricity produced by a PV (photovoltaic) module or array
of modules into the AC (alternating current) electricity
used by homes and businesses to power lights, appliances,
machinery etc.
junction box - In a PV system, an enclosure on the module
where PV strings are electrically connected and where electric
current protection devices can be located as necessary.
See conduit box.
kilowatt (kW) - 1000 watts.
kilowatt-hour (kWh) - One thousand watts acting over a
period of 1 hour. The kWh is a unit of energy. 1 kWh =
3,413 BTU (British thermal units).
line commutated inverter - An inverter that is tied to
a power grid or line. The commutation of power (conversion
from dc to ac) is controlled by the power line, so that,
if there is a failure in the power grid, the PV system
cannot feed power into the line.
line-tie - See grid-intertied PV system
load - Anything in an electrical circuit that, when the
circuit is turned on, draws power from that circuit, i.e.
lighting, electronic devices, appliances, machinery, etc.
maximum power point tracker (MPPT) - A power conditioning
unit that automatically operates the PV-generator at its
maximum power point under all conditions. An MPPT will
typically increase power delivered to the system by 10%
to 40%, depending on climate conditions and battery state
of charge. You usually get more gain in winter and in colder
weather due to the higher panel output.
module - An integrated assembly of interconnected PV cells
designed to deliver a selected level of working voltage
and current at its output terminals. Modules are produced
in standard sizes and power outputs, packaged for protection
against environmental degradation, and equipped for incorporation
into photovoltaic power systems. Sometimes referred to
as a panel.
multicrystalline - Material that is solidified at such
a rate that many small crystals (crystallites) form. The
atoms within a single crystallite are symmetrically arranged,
whereas crystallites are jumbled together. These numerous
grain boundaries reduce the device efficiency. A material
composed of variously oriented, small individual crystals.
(Also referred to as polycrystalline or semicrystalline).
net metering - Refers to a utility metering arrangement
where the power supplied by the utility and the power back-fed
by the local generator both run through the same meter,
and therefore the cost of energy from the utility and the
value of energy supplied by the local generator are the
same.
nonconductor - A material that is not a good conductor
of electricity, heat, sound or vibration. Nonconductors
are used for safety insulation, to minimize heat loss or
gain, and to provide noise control.
overload - An electrical current demand that exceeds the
amount of current for which a circuit is rated. Such an
overload causes automatic protective devices to actuate,
such as a fuse or circuit breaker. See circuit breaker.
parallel connection - A way of joining two or more electricity-producing
devices (i.e., PV cells or modules) by connecting positive
leads together and negative leads together; such a configuration
increases the current.
peak load; peak demand - The maximum load, or usage, of
electrical power occurring in a given period of time, typically
a day.
peak watts (Wp) - See photovoltaic peak watt.
photon - A particle of light that acts as an individual
unit of energy.
photovoltaic (PV) - Pertaining to the direct conversion
of light into electricity. Sometimes referred to as solar
electricity.
photovoltaic array - An interconnected system of PV modules
that function as a single electricity-producing unit. The
modules are assembled as a discrete structure, with common
support or mounting. In smaller systems, an array can consist
of a single module.
photovoltaic cell - The smallest semiconductor unit within
a PV module to perform the conversion of light into electrical
energy.
photovoltaic conversion efficiency - The ratio of the
electric power produced by a photovoltaic device to the
power of the sunlight incident on (or striking) the device.
photovoltaic efficiency - The ratio of electric power
produced by a cell at any instant to the power of the sunlight
striking the cell. This is typically about 9% to 14% for
commercially available cells.
photovoltaic generator - The total of all PV strings of
a PV power supply system, which are electrically interconnected.
photovoltaic module - An integrated assembly of interconnected
PV cells designed to deliver a selected level of working
voltage and current at its output terminals. Modules are
produced in standard sizes and power outputs, packaged
for protection against environmental degradation, and equipped
for incorporation into photovoltaic power systems. Sometimes
referred to as a panel.
photovoltaic panel - often used interchangeably with PV
module (especially in one-module systems), but more accurately
used to refer to a physically connected collection of modules
(i.e., a laminate string of modules used to achieve a required
voltage and current).
photovoltaic peak watt - Maximum "rated" output
of a cell, module, or system. Typical rating conditions
are 0.645 watts per square inch (1000 watts per square
meter) of sunlight, 68 degrees F (20 degrees C) ambient
air temperature and 6.2 x 10-3 mi/s (1 m/s) wind speed.
photovoltaic system - A complete set of components for
converting sunlight into electricity by the photovoltaic
process, including the array and balance of system components.
photovoltaic-thermal (PV/T) system - A photovoltaic system
that, in addition to converting sunlight into electricity,
collects the residual heat energy and delivers both heat
and electricity in usable form. Also called a total energy
system.
plot plan - A plan view drawing (bird's eye view of an
the area being designed) of a site which includes: the
dimensions of the site and its key elements; the location
of any structures in relation to one another and to the
property boundaries; the elevations of key points; contour
lines; utility services; and compass directions.
polycrystalline - See multicrystalline.
power conditioning equipment - Electrical equipment, or
power electronics, used to convert power from a photovoltaic
array into a form suitable for subsequent use. A collective
term for inverter, converter, battery charge regulator,
and blocking diode.
PV - Abbreviation for photovoltaic(s).
qualification test, photovoltaic - A procedure applied
to a selected set of PV modules involving the application
of defined electrical, mechanical, or thermal stress in
a prescribed manner and amount. Test results are subject
to a list of defined requirements.
radiation - The flow of energy through open space via
electromagnetic waves, such as visible light.
rectifier - A device that converts ac to dc, as in a battery
charger or converter. See inverter.
reflected radiation - Sunlight that is reflected from
surrounding trees, terrain or buildings onto a surface
exposed to the sky.
remote system - A PV system that operates off the utility
grid, as in a rural area. See also stand-alone system.
resistance - Electrical resistance is a measure of the
degree to which a body opposes the passage of an electric
current. The unit of electrical resistance is the ohm.
(Its reciprocal quantity is electrical conductance measured
in siemens.) The rate at which electricity flows through
a circuit is affected by the resistance of the components
and/or wires in the circuit. Appliances, lights, power
tools can all be thought of as resisters.
resistive voltage drop - The voltage developed across
a cell by the current flow through the resistance of the
cell.
self
discharge - The rate at which a battery, without
a load, will lose its charge. This can vary considerably
depending on the type of battery and age. It can be as
low as 3% a month for a new AGM battery, and as high as
10% a week for an older Lead-Antimony (industrial) battery.
semiconductor - Any material that has a limited capacity
for conducting an electric current. Generally falls between
a metal and an insulator in conductivity. Certain semiconductors,
including silicon, gallium arsenide, copper indium diselenide,
and cadmium telluride, are uniquely suited to the photovoltaic
conversion process.
semicrystalline - See multicrystalline.
series connection - A way of joining photovoltaic cells
or batteries by connecting positive leads to negative leads;
such a configuration increases the voltage.
series regulator - Type of battery charge regulator where
the charging current is controlled by a switch, transistor,
or FET (field-effect transistor) connected in series with
the PV module or array. As opposed to a shunt regulator,
which gradually shorts out the panel output as the battery
gets charged up.
series resistance - Parasitic resistance to current flow
in a cell due to mechanisms such as resistance from the
bulk of the semiconductor material, metallic contacts,
and interconnections.
short-circuit current - The current flowing freely from
a photovoltaic cell through an external circuit that has
no load or resistance; the maximum current possible.
silicon (Si) - The most common semiconductor material
used in making photovoltaic devices. It is a chemical element,
atomic number 14, semi-metallic in nature, a common constituent
of sand and quartz.
sine wave inverter - An inverter that produces utility-quality,
sine wave power forms.
single-axis tracking - A photovoltaic array capable of
rotating on one axis in order to maintain optimum orientation
toward the sun for maximum efficiency. See tracking array.
single-crystal material - A material that is composed
of a single crystal or a few large crystals.
solar cell - See photovoltaic cell.
solar constant - The strength of sunlight; 1353 watts
per square meter in space and about 1000 watts per square
meter at sea level at the equator at solar noon. It increases
at higher altitudes.
solar energy – Electromagnetic energy (solar radiation)
from the sun that can be converted to other forms of energy
such as heat or electricity. The amount striking earth
is equivalent to about 420 trillion kilowatt-hours, a single
kilowatt hour being defined as one thousand watts acting
over a period of 1 hour.
solar-grade silicon - Intermediate-grade silicon used
in the manufacture of solar cells; less expensive than
electronic-grade silicon.
solar noon - That moment of the day that divides the daylight
hours for that day exactly in half. To determine solar
noon, calculate the length of the day from the time of
sunset and sunrise and divide by two. Solar noon may be
quite a bit different from 'clock' noon.
Solar Path Finder™ - A device used to determine
and map solar positions and to calculate shading when planning
a solar energy system. A panoramic view of the site reflected
on the surface of a transparent dome combines with the
transmitted image of the underlying sunpath diagram to
reveal the site’s solar potential for the year.
solar radiation - Solar energy; radiation emitted by the
sun.
solar spectrum - The total distribution of electromagnetic
radiation emanating from the sun.
solar thermal electric - Method of producing electricity
from solar energy by using focused sunlight to heat a working
fluid, which in turn drives a turbogenerator.
split-spectrum cell - A compound photovoltaic device in
which sunlight is first divided into spectral regions by
optical means. Each region is then directed to a different
photovoltaic cell optimized for converting that portion
of the spectrum into electricity. Such a device achieves
significantly greater overall conversion of incident sunlight
into electricity. See 'mulitjunction device.'
square wave inverter - The inverter consists of a dc source,
four switches, and the load. The switches are power semiconductors
that can carry a large current and withstand a high voltage
rating. The switches are turned on and off at a correct
sequence, and at a certain frequency. The square wave inverter
is the simplest and the least expensive to purchase, but
it produces the lowest quality of power.
stand-alone system - An autonomous or hybrid photovoltaic
system not connected to a grid. May or may not have electrical
storage, but most stand-alone systems require storage batteries
to provide energy when the system is not producing at required
levels due to darkness or inclement weather conditions.
standard test conditions (STC) - Conditions under which
a module is typically tested in a laboratory: (1) Irradiance
intensity of 1000 watts/square meter (0.645 watts per square
inch), AM (air mass) 1.5 solar reference spectrum, and
(2) a cell (module) temperature of 25 degrees C, plus or
minus 2 degrees C (77 degrees F, plus or minus 3.6 degrees
F).
state of charge (SOC) - The available capacity remaining
in the battery, expressed as a percentage of the rated
capacity.
substrate - The physical material upon which a photovoltaic
cell is made.
sulfation - A condition that afflicts unused and discharged
batteries; large crystals of lead sulfate grow on the plate,
instead of the usual tiny crystals, reducing battery storage
capacity and inhibiting recharging.
superstrate - The covering on the sun side of a PV module,
providing protection for the PV materials from impact and
environmental degradation while allowing maximum transmission
of the appropriate wavelengths of the solar spectrum.
thermal electric - Electric energy derived from heat energy,
usually by heating a working fluid, which drives a turbogenerator.
See solar thermal electric.
thermophotovoltaic (TPV) device - A device that converts
secondary thermal radiation, re-emitted by an absorber
or heat source, into electricity; The device is designed
for maximum efficiency at the wavelength of the secondary
radiation.
thick-crystalline materials - Semiconductor material,
typically measuring from 200-400 microns thick, that is
cut from ingots or ribbons.
thin film - A layer of semiconductor material (such as
copper indium diselenide, cadmium telluride, gallium arsenide,
or amorphous silicon) a few microns or less in thickness,
used to make photovoltaic cells. Easier and cheaper to
produce than the more common crystalline variety, but less
efficient and degrades more rapidly over time. Commonly
called amorphous.
tilt-up mounting - Technique for mounting a PV array on
a sloped roof, which involves mounting the modules a short
distance above the pitched roof and tilting them to the
optimum angle.
Title 24 Energy Requirements, California - The state of
California’s energy efficiency standards for residential
and nonresidential buildings that were established in 1978
in response to a legislative mandate to reduce California's
energy consumption.
total internal reflection - The trapping of light by refraction
and reflection at critical angles inside a semiconductor
device so that it cannot escape the device and must eventually
be absorbed by the semiconductor.
tracking array - PV array that follows the path of the
sun to maximize the solar radiation incident on the PV
surface. The two most common orientations are (1) one axis
where the array tracks the sun east to west and (2) two-axis
tracking where the array points directly at the sun at
all times. Tracking arrays use both the direct and diffuse
sunlight. Two-axis tracking arrays capture the maximum
possible daily energy. Typically, a single axis tracker
will give you 15% to 25% more power per day, and dual axis
tracking will add about 5% to that. Depends somewhat on
latitude and season.
transformer - Steps AC voltage up or down, depending on
the application.
two-axis tracking - A solar array capable of rotating
independently about two axes (e.g., vertical and horizontal)
and following the sun for maximum efficiency. See tracking
array.
utility-interactive inverter - An inverter that can function
only when tied to the utility grid, and uses the prevailing
line-voltage frequency on the utility line as a control
parameter to ensure that the PV system's output is fully
synchronized with the utility power.
volt (V) - A unit of measure of the force, or push, given
the electrons in an electric circuit. One volt is the amount
of force required to drive a steady current of one ampere
through a resistance of one ohm. Most electrical systems
in the U.S. have 120 volts.
wafer - A thin sheet of semiconductor material made by
mechanically sawing it from a single-crystal or multicrystal
ingot or casting.
watt (W) - The unit of electric power, or amount of work
(J), done in a unit of time. One ampere of current flowing
at a potential of one volt produces one watt of power.
An excellent online worksheet to convert anything (BTU,
HP etc) to watts is at the State of Texas website.
watt-hour (Wh) - See kilowatt-hour.
absorber - The darkened surface in a solar thermal collector
that absorbs solar radiation and converts it to heat energy.
See solar thermal collector.
absorptance - The ratio of solar energy absorbed by a
surface to the solar energy striking it.
active system - Solar heating system requiring external
mechanical power to move the collected heat.
altitude - The angular distance from the horizon to the
sun; the elevation of the sun. Both this elevation angle
and the azimuth angle at a solar energy site are important
parameters in determining the amount of solar energy received
on a solar module or collector. See azimuth.
ambient temperature - The temperature of the surrounding
air at a given location.
auxiliary heat - The extra heat provided by a conventional
heating system for periods of cloudiness or intense cold
when a solar heating system cannot provide enough heat.
azimuth - The angular distance between true south and
the point on the horizon directly below the sun. Both the
altitude (elevation angle) and the azimuth angle at the
solar energy site are important parameters in determining
the amount of solar energy received on a solar module or
collector. See altitude.
boiler - Appliance that heats water as a back-up for a
solar hot water system. Not a true “boiler” in
the sense that no steam is actually produced as was done
in old steam radiant systems.
BTU - British Thermal Unit(s). A measure of energy output
defined as the amount of heat needed to raise one pound
of water 1°F from a starting point of 39.2°F. Common
unit in measuring solar hot water performance and sizing
boilers or gas-fired water heaters.
building permit - Authorization from the local building
inspection agency to construct or modify a building from
an approved set of plans, usually required for solar energy
installations.
CADD - Computer aided design and drafting, a system for
creating and viewing layouts and plot plans; often utilizes
AutoCad, a popular CADD computer program.
California Title 24 Energy Requirements – See Title
24 Energy Requirements, California
Closed-loop solar system - Solar hot water system in which
the fluid circulated throughout the solar thermal collectors
is separate from the potable water. In a closed loop solar
system, the solar heat is transferred to the potable water
by way of a heat exchanger.
coefficient of heat transmission - Rate of heat loss in
BTU per hour through a building surface when the difference
between indoor and outdoor air temperatures is one degree
Fahrenheit.
collector - See solar thermal collector
collector efficiency - The ratio of useable heat energy
extracted from a collector to the solar energy striking
the collector.
concentrating collector - A device which concentrates
the sun's rays on an absorber surface which is significantly
smaller than the overall collector area.
conductance - The rate of heat flow (in BTUs per hour)
through an object when a 1° F. temperature difference
is maintained between the sides of the object.
conduction - Either (1) the transfer of heat from an object
of a higher temperature to one of a lower temperature,
or (2) the flow of electricity or fluid.
conductive heat - Direct transmission of heat through
a medium or object, exemplified by a skillet on a hot burner
or water passing through a solar heated absorber in order
to heat the water.
conductivity - A measure of the ability of a material
to permit conduction of heat flow through it.
conductor - A material that conducts or allows the flow
of heat, sound, electricity or other forms of energy.
convection - The transfer of heat by circulation through
a gas or liquid.
convection heat - Heat which is conducted by air or transferred
by air currents, exemplified by the transfer (or loss of)
heat from your body to cool surrounding air, or the transfer
of heat resulting from the opening of a door separating
a warm room from the cold outdoors.
cover plate - A sheet of glass or transparent plastic
placed above the absorber in a flat plate collector.
degradation - (1) The disintegration or deterioration
of the parts or materials beyond a repairable condition,
thus requiring replacement. (2) The loss of efficiency
of solar cells over a long period of time.
design heat load - The total heat loss from a house under
the most severe winter conditions likely to occur.
design temperature - The lowest estimated temperature
expected for a location, used to determine the design heat
load. See design heat load.
direct open loop system – A solar hot water system
where the solar energy is transferred directly to the potable
water running through the solar collector.
drain back (closed loop hot water) system – A closed-loop
solar hot water system that uses an atmospheric pressure
drainback tank.. In order to avoid freezing or overheating
the water flowing through the collectors drains back into
a storage tank when not being pumped. A coil-type heatexchanger
in the tank then transfers the solar heat to the targeted
fluid.
drain back pool system - Hot water system for
pools wherein pool water is circulated directly through the collectors.
Water drains back into the pool when not pumping in order
to avoid freezing.
drain down system - Uses a draindown valve (no longer
manufactured) to drain collectors when not in use.
electronic ignition - Device that automatically lights
the pilot flame and main burner of a gas fueled hot water
tank or boiler when water heating is required by the system.
evacuated tube - A solar thermal collector with the absorber
contained in an evacuated glass cylinder. See absorber.
expansion tank - A tank used in a hot water system or
radiant heating system that provides space for the expansion
of the heat transfer fluid.
flash water heater - See tankless water heater.
flat plate collector - A solar energy collection device
in which sunlight is converted into heat using a metal
plate, typically copper, over which the water flows. It
typically consists of a metal frame, glazing (protective
sheet of glass or plastic), energy absorbers (usually metal),
and insulation and uses a pumped liquid as the heat-transfer
med
GPM - Gallons per minute.
galvanic corrosion - Accelerated corrosion resulting in
harmful degradation of metal parts occurring when a conducting
liquid links a metal with a less active metal or nonmetallic
conductor which are not sufficiently isolated physically
or electrically.
header - Pipe running across the bottom and top of a collector
plate. The header distributes the heat transfer fluid from,
or to, the risers (channels) in the individual collectors,
thus insuring that equal flow rates and pressure are maintained.
heat capacity - A property of a material denoting its
ability to absorb heat.
heat exchanger - (1) Device that transfers heat. Typically
in solar hot water systems the heat exchanger will transfer
heat from the fluid in the solar collector loop to the
potable water.
heating season - The period from early fall to late spring
(in the northern hemisphere) during which additional heat
is needed to keep a house comfortable for its occupants.
heat pump - An electricity powered device that extracts
available heat from one area (the heat source) and transfers
it to another (the heat sink) to either heat or cool an
interior space.
heat sink - A medium or container to which heat flows.
heat source - A medium or container from which heat flows.
heat storage - A device or medium that absorbs collected
solar heat and stores it for use during periods of inclement
or cold weather.
heat storage capacity - The amount of heat which can be
stored by a material.
heat transfer - Movement of heat energy from one medium
to another through the action of radiation, conduction,
convection, or evaporation from one source to another.
hybrid solar energy system - A system that uses multiple
methods, either active or passive, of energy production
in its operation.
indirect water heating - An efficient hot water system
in which water that has been heated in a boiler is circulated
through a heat exchanger located inside a separate water
storage tank to transfer its heat to the supply of water
in the storage tank.
insolation - The total amount of solar radiation direct,
diffused and reflected-striking a surface exposed to the
sky.
insulating properties - The ability of a material to resist
or impede the transfer or loss of heat.
insulation - A material with high resistance (R-value)
to heat flow.
insulation rating - A standard number assigned to a form
of insulation to indicate its effectiveness at impeding
the transfer or loss of heat. For example, a material that
has an R-Value (resistance value) of 30 has a greater insulating
ability than a material with an R-value of 11. See R-value.
insulation, reflective - Type of insulating material utilizing
a surface that reflects heat, such as: aluminum foil; sheet
metal; or paper based products that are coated with a reflective
oxide compound.
insulation, thermal - Materials employed to minimize
the transfer of heat in or out of pipes, tubing, rooms,
buildings, etc. , such as fiberglass, cellulose, straw,
various types of foam, and others.
MBH - Thousands of BTU per hour, used to express natural
gas inputs.
natural convection - See gravity convection.
natural gas - Methane, a gas formed in the earth in oil-bearing
areas, that is used to fuel, among other things, furnaces
and water heaters.
nocturnal cooling - The cooling of a building or heat
storage device by the radiation of excess heat into the
night sky.
passive system - A solar heating or cooling system that
uses no external mechanical power to move the collected
solar heat.
plot plan - A plan view drawing (bird's eye view of an
the area being designed) of a site which includes: the
dimensions of the site and its key elements; the location
of any structures in relation to one another and to the
property boundaries; the elevations of key points; contour
lines; utility services; and compass directions.
pump - Device that raises, moves or compresses fluids
by pressure or suction, used to circulate water or other
fluid throughout some solar water systems or move water
through a hydronic radiant heating system.
radiation - The flow of energy through open space via
electromagnetic waves such as visible light.
reflected radiation - Sunlight that is reflected from
surrounding trees, terrain or buildings onto a surface
exposed to the sky.
retro-fit - To provide a system in an existing building
where no prior system existed (in contrast to the installation
being part of a new construction), or to replace an undesirable
or defective hot water system with a newer and better system.
risers - The flow channels or pipes that distribute the
heat transfer liquid across the face of an absorber in
a solar thermal collector.
solar energy - Electromagnetic energy (solar radiation)
from the sun that can be converted to other forms of energy
such as heat or electricity. The amount striking earth
is equivalent to about 420 trillion kilowatt-hours, a single
kilowatt hour being defined as one thousand watts acting
over a period of 1 hour.
Solar Path Finder™ - A device used to determine
and map solar positions and to calculate shading when planning
a solar energy system. A panoramic view of the site reflected
on the surface of a transparent dome combines with the
transmitted image of the underlying sunpath diagram to
reveal the site’s solar potential for the year.
solar radiation - Solar energy; electromagnetic radiation
emitted by the sun.
solar thermal collector - A device designed to receive
solar radiation and convert it into thermal (heat) energy
in order to heat water. Generally, a collector is composed
of a sturdy frame, an absorber (heat absorbing panel with
water channels), glazing (protective sheet of glass or
plastic) on the sun-facing side, and insulation on the
back and sides.
standby heat loss - Heat that is lost though the walls
of the storage tank, pipes, and tubes.
stratification - Condition resulting from the tendency
for heated fluids to rise and colder fluids to sink, resulting
in the temperature layering of water within a tank. Utilized
in the operation of some hot water systems. See gravity
convection; thermosiphoning.
tankless water heater - Relatively small, very efficient,
water heating unit, fueled by natural gas or electricity,
that admits cold water and “flash” heats it
on demand; it requires no continuously heated storage tank
and can provide an endless supply of hot water.
thermosiphon system - A solar hot water system in which
the circulation of the collection fluid through the storage
loop is derived from the natural movement of fluids caused
by the temperature and density difference between hot and
cold fluids, in this case between the water in a warm collector
and that in a cool storage tank above it. See thermosiphoning;
gravity convection; stratification.
thermosiphoning - The process that makes water circulate
automatically between a warm collector and a cooler storage
tank above it. See gravity convection.
tilt angle - Angle that a flat plate collector surface
forms with the horizontal plane.
Title 24 Energy Requirements, California - The state of
California’s energy efficiency standards for residential
and nonresidential buildings that were established in 1978
in response to a legislative mandate to reduce California's
energy consumption.
aerated concrete - Concrete with air bubbles incorporated
into the mix, making it relatively lightweight.
aggregate base - Inert filler material made up of sand,
stone or gravel which is used to strengthen cement and
form concrete. New pour applications for radiant heat often
use an aggregate base.
air duct - Large thin-walled conduit (pipe or tunnel-like
object), usually of sheet metal or fiberglass, used for
directing air through buildings in a traditional heating,
ventilating, and air conditioning (HVAC) system. Radiant
heating systems can often eliminate the need for air ducts
used for the purpose of heating.
air elimination vent - Device which automatically eliminates
trapped air in a water line of a hydronic system
air expansion tank - See expansion tank.
air vent - A valve to vent air out of a water system such
as a hydronic radiant heating system.
allergens - Particles in the air, such as pollen and dust
mites, which cause allergic reactions and are known to
be circulated by forced air heating systems.
ambient temperature - The temperature of the air at a
location. Radiant heating systems can be designed to
activate in response to either ambient or floor temperature.
aquastat - Temperature control device.
automatic air vent - See air elimination vent
baseboard radiant - Hydronic radiant heating system in
which hot water tubing is run through low-profile metal
enclosures attached at wall baseboards running along the
perimeter of a space. Heating is accomplished by convection
without the use of any fans. Less efficient than floor
heating, it is used for heating in an area where the floor
coverings have already been installed or where retrofitting
the floor would be difficult.
boiler - Appliance that heats water for radiant heating
systems or as part of a solar hot water system. Not a true “boiler” in
the sense that no steam is actually produced as was done
in old steam radiant systems.
BTU (or Btu) - British Thermal Unit(s). A measure of energy
output defined as the amount of heat needed to raise one
pound of water 1°F from a starting point of 39.2°F.
In a radiant heating system, the amount of energy required
to heat a space to a specified temperature is expressed
in BTUs or Btu. It is also used as a standard efficiency
comparison between different heating fuels. BTUH stands
for British Thermal Unit Per Hour to measure BTU input
or output over time. MBH stands for 1,000 BTUH.
building permit - Authorization from the local building
inspection agency to construct or modify a building from
an approved set of plans.
CADD - Computer aided design and drafting, a system for
creating and viewing layouts and plot plans; often utilizes
AutoCad, a popular CADD computer program.
coefficient of heat transmission - Rate of heat loss in
BTU per hour through a building surface when the difference
between indoor and outdoor air temperatures is one degree
Fahrenheit.
conduction - Either the transfer of heat from an object
of a higher temperature to one of a lower temperature or
the flow of electricity or fluid.
conductive heat - Direct transmission of heat through
a medium or object, exemplified by a skillet on a hot burner,
or water passing through a solar heated absorber in order
to heat the water.
conductivity - A measure of the ability of a material
to permit conduction of heat flow through it.
conductor - A material that conducts or allows the flow
of heat, sound, electricity or other forms of energy.
convection - The transfer of heat by circulation through
a gas or liquid.
convection heat - Heat which is conducted by air or transferred
by air currents, exemplified by the transfer (or loss of)
heat from your body to cool surrounding air, or the transfer
of heat resulting from the opening of a door separating
a warm room from the cold outdoors.
degradation - The disintegration or deterioration of parts
or materials beyond a repairable condition and thus requiring
replacement.
distribution manifold - Device used to connect the radiant
system piping to a centralized point where, with the use
of valves, the water flow rate can be regulated.
duct - See air duct.
electric floor heat - System using electrical elements
embedded in the floor to provide heat. Typically used in
small homes or in a few rooms of a larger home, it is not
as cost effective as hydronic floor heating which uses
tubing carrying hot water to provide the heating.
electronic ignition - Device that automatically lights
the pilot flame and main burner of a gas fueled hot water
tank or boiler when water heating is required by the system.
expansion tank - A tank used in a hot water system or
radiant heating system that provides space for the expansion
of the heat transfer fluid.
flash water heater - See tankless water heater
flooring - Any of several materials serving as the visible
floor of a structure or individual room. Most common types
are: carpet, ceramic tile, concrete, hardwood, linoleum,
marble, or stone.
forced air heating - Heating system employing a furnace
to heat air to about 110 to 115 degrees Fahrenheit, and
utilizing fans and ducts to force the warmed air into a
living space.
fuel efficiency - Percentage of energy released by fuel
combustion (i.e. “burning” of the fuel) that
is ultimately converted into useable energy. Fuel efficiencies
vary greatly among various fuel sources.
fuel source - Medium utilized by a boiler or furnace to
generate heat or other energy. Common sources are natural
gas, electricity, propane, oil, wood, coal or a combination.
furnace (heating) - Air heating device in which heat is
generated by burning a fuel, such as natural gas, electricity,
propane, oil, wood, coal or a combination.
galvanic corrosion - Accelerated corrosion resulting in
harmful degradation of metal parts occurring when a conducting
liquid links a metal with a less active metal or nonmetallic
conductor which are not sufficiently isolated physically
or electrically.
gravity convection - The natural movement of heat that
occurs when a warm fluid rises and a cool fluid sinks under
the influence of gravity. See stratification; thermosiphoning.
GPM - Gallons per minute, commonly used as a measure of
the water passing through, processed, or utilized by a
system or device.
heat exchanger - (1) Device that transfers heat. Typically
in radiant heating system the heat exchanger will transfer
heat from the fluid in the heating loop to the potable
water. See indirect water heater.
heat, hydronic - See radiant heat; hydronic.
heat, panel - See radiant heat; radiant panel.
heat, radiant - See radiant heat
heating panel - A medium, such as a concrete slab, which
provides heat to a living space by absorbing heat from
one source and radiating it to another source.
heating, ventilating, and air conditioning (HVAC) - The
system and process of regulating temperatures and atmosphere
inside residential or commercial buildings.
heat transfer - Movement of heat energy from one medium
to another through the action of radiation, conduction,
convection, or evaporation from one source to another.
high mass - Refers to systems that utilize various heavy
(high mass) materials such as concrete as a radiant “panel” to
absorb and store heat during the day, giving off the heat
at night.
hydronic - Refers to water based heating systems.
hydronic floor heat - System providing radiant heat to
a building by the circulation of hot water through tubing
placed underneath or embedded in the floor.
indirect water heating - An efficient hot water system
in which water that has been heated in a boiler is circulated
through a heat exchanger located inside a separate water
storage tank to transfer its heat to the supply of water
in the tank for use as home or commercial hot water.
insulating properties - The ability of a material to resist
or impede the transfer or loss of heat.
insulation rating - A standard number assigned to a form
of insulation to indicate its effectiveness at impeding
the transfer or loss of heat. For example, a material that
has an R-Value (resistance value) of 30 has a greater insulating
ability than a material with an R-value of 11. See R-value.
insulation, reflective - Type of insulating material utilizing
a surface that reflects heat, such as: aluminum foil; sheet
metal; or paper based products that are coated with a reflective
oxide compound.
insulation, thermal - Materials employed to minimize
the transfer of heat in or out of pipes, tubing, rooms,
buildings, etc. , such as fiberglass, cellulose, straw,
various types of foam, and others.
lag period - Time between when the radiant panel, flooring,
or baseboard unit is heated by the boiler water and when
heat is radiated into the living space.
loop - In a hydronic radiant heating system, a single
circuit of tubing that circulates hot water, of an efficient
length and thickness, usually of similar size to all loops
in system. Loops are usually placed in evenly spaced layouts
under or inside the finished floor of a home.
low mass - Radiant heating panel wherein the weight and
density of the panel material is specifically reduced in
order to reduce the lag period (i.e. speed up the reaction
time between when heat is called for and when it is delivered).
A low mass radiant floor heating system has a fast response
time, easily controls room temperatures, and requires lower
operating water temperatures. See lag period.
manifold - See distribution manifold; zone manifold
MBH - Thousands of BTU per hour, used to express natural
gas inputs.
natural gas - Methane, a gas formed in the earth in oil-bearing
areas, that is used to fuel furnaces and water heaters.
nonconductor - An insulator; a material that does not
conduct much electricity or heat, or that does not conduct
much sound or other vibration. Such materials are used
for safety, to minimize heat loss or gain, and to provide
noise control.
perimeter heat loss - Heat loss through the perimeter,
or outside surfaces, of a building which is exposed to
the exterior elements. Effective wall insulation, double-pane
windows, and insulated doors can be used to help control
this heat loss.
PEX tubing - An acronym for cross linked polyethylene,
a type of tubing that can withstand high fluidic pressures
and temperatures, commonly used in hydronic radiant heat
systems.
plot plan - A plan view drawing (bird's eye view of an
the area being designed) of a site which includes: the
dimensions of the site and its key elements; the location
of any structures in relation to one another and to the
property boundaries; the elevations of key points; contour
lines; utility services; and compass directions.
pounds per square inch - See PSI.
pressure reducing valve - A safety device which supplies
the boiler with reduced water pressure from the city supply
(common pressure setting is 12 PSI.); also maintains the
water level in the boiler if a loss of water occurs in
the panel.
pressure relief valve - A safety device which releases
boiler and system pressure should it exceed a preset level.
The normal pressure setting of these devices for the low
pressure boiler is 30-45 PSI. The preset level should never
exceed the operating pressure of the boiler.
pressure switch - An adjustable safety device which prevents
boiler operation when the system pressure falls below the
preset level, usually 5 PSI. It helps prevent boiler coil
and heat exchanger damage by preventing the boiler from
firing during unsafe low water pressure conditions.
pressure / temperature gauge - A device which monitors
water pressure and temperature of the heating system.
pressure test - A hydrostatic (water) test of the concealed
radiant panel used to determine the "tightness" and "leak-free" condition
of the tubing. The test should always result in "no
loss" of the pressure and be performed in accordance
with code approved procedures. The introduction of helium,
nitrogen, oxygen, or other type of air to pressurize the
system for testing is not an acceptable test and will likely
result in inaccurate conclusions.
PSI - Pounds per square inch, a measure of pressure, a
load applied by one object on another, including fluids
(liquid and gas), a consideration for radiant heating in
new pour construction.
pump - Device that raises, moves or compresses fluids
by pressure or suction, used to circulate water or other
fluid throughout some solar water systems or move water
through a hydronic radiant heating system.
radiant baseboard - A heat distribution device containing
hot water inside a cast-iron or copper-finned radiator
that runs along a wall's baseboard.
radiant flooring - Special polymer tubing that is run
underneath the sub-floor or fastened down on top of the
sub-floor or onto a wire grid imbedded in lightweight concrete.
Its low-temperature water is circulated through the tubing
to produce radiant heat.
radiant heat - Type of heating where warmth is delivered
into a space via a heated surface. In home heating systems,
the surface is usually heated via hot water, electrical
heating elements, or steam pipes embedded in ceilings,
walls, and most commonly, floors. Heat is absorbed into
the room surface material and is then radiated into the
space. Radiant heating systems eliminate problems such
as cold spots, drafts, and allergens typically associated
with forced air systems.
radiant operating temperature - The floor temperature
should never exceed 85°F.
radiant panel - (1) The mass of concrete, flooring or
other materials which, when heated, stores and releases
radiant heat energy into the living space. All objects,
people, furniture, walls, etc., are warmed by absorbing
and transferring the radiated energy. All areas within
the living space are evenly heated. (2)A solar collector
panel with integral passages for the flow of warm fluids,
either air or liquids. Heat from the fluid is conducted
through the metal and transferred to the rooms by thermal
radiation.
radiation - The transfer of heat by direct rays from your
body to cooler objects around you.
recovery rate - The rate in gallons per hour at which
a water heater or boiler can heat water to a desired temperature.
A radiant boiler should be able to re-heat 1 1/2 times
its storage amount to about 125 degrees Fahrenheit within
one hour.
remodel - To alter or restore an existing structure.
resistance - (As regards radiant heating) the pressure
within multiple circuits of tubing in a system. In order
to equalize resistance and pressure and insure even distribution
of the water and heat, all circuits should be approximately
the same length and utilize the same size tubing.
retro-fit - To replace an undesirable or defective radiant
heat or hot water system with a newer and better system,
or to provide a system in a building where no prior system
existed (in contrast to the installation being part of
a new construction).
return line - A pipe, usually insulated, conducting water
back to the heat source.
R-Value - Resistance Value. A unit of measure of thermal
resistance (resistance to heat flow). The higher the value,
the better the heat-insulating capabilities of the material.
Used to determine the heat-loss calculation for a home
in designing a heating system and to determine which materials
are best to use in construction or remodeling.
sleepers - A system of boards, or other “risers” or
strapping, placed on an existing floor to form "sleeper
bays", or hollow spaces, in whic | 
