P to Z
PITA Factor (Pain In The Ass
Factor): Cost you allocate to your psychological stress generated
from dealing with faulty or cheap equipment, adverse weather, and/ or
PTC: "PVUSA Test
Conditions." For rating solar modules. PTC watt rating is based on
1000 Watt/m2 solar irradiance, 20 degree Celsius ambient temperature,
and 1 meter/second wind speed. Since Cell temperatures of modules are
much higher than ambient temperature, the PTC watt rating is significantly
lower than the "Standard Test Conditions" (STC), a watt-rating
used by manufacturers.
PV Cell: The doped semiconductor
material that converts sunlight into electricity.
PV Module: Also known
as Solar Panel, Solar Module, and PV Panel. Made of a number of separate
PV cells soldered together, sealed, and framed into a single unit. Usually
wired for 12 or 24 VDC nominal output.
PV Array: A group of
photovoltaic (PV) modules connected together physically and/or electrically
as part of a PV system.
PV System: An electric
power generating system that gets some or all of its energy from a PV
Array, usually stores energy in Batteries, and often has an Inverter as
well as Balance of System equipment.
for Utility Scale Applications is a national public-private partnership
that began in 1986. PVUSA is supported by PG&E, the U.S. Department
of Energy, the California Energy Commission, among others. As of December
1993, PVUSAs 12 systems generated more than 2.5 million kWh. Our
founder Ray Walters worked on one of these projects for Entech, Inc. at
PG & E's Davis, CA site.
Panel: (See PV Module)
Parallel Connection: The interconnecting
of PV modules or batteries in which like terminals are connected together
(i.e. positive to positive, and negative to negative) Increases the current
while keeping voltage the same.
Peak Power: Current
produced by a module or array operating at the maximum power point of
the module. (See Maximum Power Point Tracking)
Peak Sun Hours: The
equivalent number of hours per day when solar irradiance averages 1,000
w/m². For example, six peak sun hours means that the energy received
during total daylight hours equals the energy that would have been received
had the irradiance for six hours been 1,000 w/m².
Peak Wattage: The amount
of power a photovoltaic module will produce at standard test conditions
(normally 1,000 w/m² and 25º cell temperature).
Phantom Load (ghost load):
Loads that take energy when they seem to be off (even after actually being
"switched" off). Any device that uses a remote control, or has
a clock, takes some power all day. The cure is to unplug those appliances
or switch them off with a switched outlet or power strip. Phantom loads,
while seemingly small can add up over a 24 hour period. Considering the
sun may only shine for 4 to 6 hours a day, you would need 50 watts of
PV to power a 10 watt phantom load.
Photovoltaic (PV): Specially
treated (doped) silicon that creates electricity from light.
Silicon: A material used to make PV cells which consists of many
crystals. Not as high a performance as single crystal cells.
Power: How fast energy
is produced or used, measured in watts. A higher power device will use
much more energy in a given time than a low power device. Even a low power
device can still use alot of energy if left on for a long time. Amps x
Power Factor (PF): This
is a measure of the relationship of the voltage wave to the current's
wave, in AC power. A power factor of 1 indicates current and voltage are
in phase and power is equal to the simple product of volts x amps (no
reactive power). When Power Factor is "bad," less than 1, current
and voltage peak at different times (are out of phase), and less power
is actually available to the load than the product of volts x amps. The
product of the volts x amps in a reactive circuit is called "apparent
power" and is measured in "volt-amps" or VA. The "true
power" that is useable by the load is measured in watts. The ratio
of apparent power to true power is called the power factor.
Puekert's Number: Formula
that expresses the relationship between battery capacity and rate of discharge.
As rate of discharge lowers (lengthens), useable battery capacity increases.
Less of a factor in residential power systems (with lower discharge rates--typically
functioning on a 20 to 100 hour rate) than in electric vehicles (with
higher discharge rates--typically functioning on a 1 to 6 hour rate).
Capacity: The term used by battery manufacturers to indicate the
maximum amount of energy that can be withdrawn from a battery under specified
discharge rate and temperature. (See Battery Capacity)
Rated Module Current:
The current output of a PV module in Amps, measured at standard test conditions
of 1,000 w/m² and 25ºC cell temperature.
Reactive Power: The
sine of the phase angle between the current and voltage waveforms in an
ac system. (See Power Factor)
Renewable Energy (RE): Energy
from sustainable sources (that are inexhaustible and/or self-renewing),
such as wind, hydro, solar, and biomass. As opposed to finite energy sources,
such as petroleum.
Resistive Load:any electrical
device that uses electricity like a simple resistor and has no inductive
behavior. As opposed to an Inductive Load.
Resistance (R): The
property of a conductor which opposes the flow of an electric current,
resulting in the generation of heat in the conducting material and the
lowering of voltage in the conductor. The measure of the resistance of
a given circuit is the voltage drop across that circuit divided by the
current passing through it. The unit of resistance is the ohm.
Reverse Current Protection:
Any method of preventing the reverse flow of electricity through PV modules
at night, when power is not being generated. (See Blocking Diode; Relay)
Sealed Battery: Battery
type that can't be opened to add water. Include "Maintenance free",
Absorbed Glass Mat, & Gel Cell batteries.
discharge of a battery in storage due to internal losses.
Sell back: The sale
of electric energy generated in a local RE grid-tied system to the grid.
(See Distributed Generation)
Semiconductor: A material
that has a limited capacity for conducting electricity. The silicon used
to make PV cells is a semiconductor.
Series Connection: The
interconnecting of PV modules or batteries in which opposite terminals
are connected together (i.e. positive to negative). Increases the voltage
while keeping the amount of current the same.
Shallow Cycle Battery:
type of battery that should not be discharged more than 25 percent. (I.e.
Auto starter battery)
Shock: Muscular spasm
caused by charge flow.
Short Circuit Current (ISC):
The current produced by an illuminated PV cell, module, or array when
its output terminals are shorted.
Single Axis Tracking:
(See Tracking Array)
Silicon: A semiconductor
material used to make photovoltaic cells.
Material with a single crystalline formation. Many PV cells are made from
single crystal silicon. (See Monocrystalline Cell)
Society of Automotive Engineers
(SAE): Provides standards for wiring of most low voltage DC systems
in the U.S. (i.e. autos & RVs). Automotive type fusing, battery cables,
& batteries are usually SAE approved, but may not be UL listed.
Solar Cell: (See Photovoltaic
Solar Insolation: (See
Solar Irradiance: (See
Solar Noon: The midpoint
of time between sunrise and sunset. The point when the sun reaches its
highest point in its daily traversal of the sky.
Solar panel: (See PV
Solar Resource: The amount of solar
insolation a site receives, usually measured in kWh/m²/day which
is equivalent to the number of peak sun hours. (See Insolation; Peak Sun
Solstice: Time of year
when the sun is at its highest (summer solstice) or lowest (winter solstice)
point in the sky. The summer solstice occurs around June 21 and is the
longest day and shortest night. The winter solstice is around Dec. 21
and is the shortest day and longest night.
South, True: Cardinal
direction opposite true north. Points directly towards the south pole
of the earth and the sun at solar noon. Direction you should face your
solar modules for optimum performance. (See North, True; North, Magnetic;
Specific Gravity: The
ratio of the weight of the solution to the weight of an equal volume of
water at a specified temperature. Battery acid can be measured with a
hydrometer for an indication of battery state of charge.
Stand-alone PV System:
A photovoltaic system that operates independent of the utility grid
Standard Test Conditions (STC):
All solar modules are rated under these conditions: 1 kW/m2 of light,
and cell temperature of 25ºC (77ºF). STC conditions are only
reached in the real world in ideal solar locations like Taos on cool clear
days. Some very high altitude sites at noon in mid winter can exceed STC
conditions by up to 25%. (See also PTC)
State of Charge (SOC):
(See Battery State of Charge)
Strand Count: number of seperate strands of copper
making a single wire or cable, A strand count of one is solid core wire,
while finely stranded welding cable can have a strand count of 418.
when the acid concentration varies from top to bottom inside the battery
electrolyte. Periodic equalization produces gassing that will mix the
electrolyte. (See Equalization)
String: A number of
solar modules or batteries connected in series to produce higher operating
voltages at the same current. (See Series Connection)
Subarray: An array,
usually 2 or more modules connected together electrically, which, along
with other subarrays, makes up a larger array.
Sulfating: The formation
of lead-sulfate crystals on the plates of a lead-acid battery, which reduces
its capacity. If the crystals get large enough, shorting of the cell may
occur. Light sulfate is dissolved when the battery is recharged
Surge Capacity: The
ability of an inverter or generator to deliver high AC current momentarily
when starting motors, etc.
Sustainable: Said of
a product or activity that can be replenished or continued indefinitely.
Petroleum products are not sustainable since petroleum is being used up
and cannot be replaced. Wind and sunshine are examples of sustainable
power sources. They will continue regardless of what we do. Timber CAN
be sustainable, if replanting, and thinning techniques are used instead
of clear cutting.
System Operating Voltage:
The nominal DC voltage at which the batteries, inverter, charge controller,
etc. are designed to operate.
TC: Wire type that is
outdoor rated, sunlight resistant, and flexible. Consists of 2 or more
insulated stranded wires within an outer jacket. Excellent for interconnect
wiring of solar arrays
THHN: Common wire type
that needs to be protected either by placement in conduit or junction
An allowance made in charge voltages of charge controllers and battery
chargers for battery temperature. Feature recommended when battery temperatures
are expected to exceed ±5ºC from ambient.
Temperature Factors: It is common
for three elements in PV system sizing to have distinct temperature corrections.
A factor used to decrease battery capacity at cold temperatures. A factor
used to decrease PV module voltage at high temperatures. A factor used
to decrease the current carrying capacity of wire at high temperatures.
Terrorist: Any person,
group, or government that uses violence or threats of violence to get
Thin Film PV Module:
A PV module constructed with sequential layers of thin film semiconductor
materials. (See Amorphous Silicon)
Three Stage Charging:
Battery charging sequence that consists of bulk charge, absorption charge,
and then is held indefinitely at float charge. This type of charging allows
batteries to be more fully charged without being overcharged.
Tilt Angle: The angle
of inclination of a solar collector measured from the horizontal.
Torque: a rotational force measured in Foot - Lbs,
Inch - Lbs, & Newton - Meters (metric). 1 foot-lb. is 1 lb exerted
against a 1 ft lever (like a wrench) around a pivot point (the screw).
1 in-lb. of torque is 1 lb. of force applied to 1" of leverage. Finally,
12 inch-lbs = 1 ft-lb. see Torque Table in Wire
Tracking Array: A PV
array that follows the path of the sun. This can mean single-axis, east
to west (azimuth) daily tracking, or dual-axis tracking where the array
follows the sun's azimuth and seasonal elevation.
Transformer: A device
that transforms AC electricity from one voltage to another (up or down).
(See EMF; Inductance)
Trickle Charge: A small
charge current intended to maintain a battery in a fully charged condition.
wire type that is outdoor rated, water proof, sunlight resistant, and
suitable for direct burial.
USE: Single conductor
wire type that is outdoor rated, water proof, sunlight resistant, and
suitable for direct burial.
UL Listed: Means that
a specific electrical device or complete assembly has been tested and
approved by UL.
UL Recognized: Means
that a device is a component that has been tested and approved by UL for
a specific purpose and that it can be used with other UL recognized components
to make a UL listed assembly. The specific assembly of UL recognized components
would still need to be tested to gain a full UL listing. Often it is cost
prohibitive to test every possible arrangement of components for full
listing. Generally, for home systems to pass local inspection a full system
listing is unnecessary, and an unlisted assembly of UL recognized components
assembled to be NEC code compliant will almost always be satisfactory.
(UL): Nonprofit organization that tests electrical equipment and
labels equipment with its seal of approval to indicate it's safe design.
Uninterruptible Power Supply
(UPS): A device that provides temporary, emergency power when normal
power (from electrical grid) fails. Often used with computers to prevent
the loss of data. Usually consists of a mod-sine inverter, batteries,
and automatic transfer switch.
Ultra Violet (UV)radiation:
Higher frequency light radiation on the upper end of the visible light
Volt (V): The unit of
electromotive force that will force a current of one ampere through a
resistance of one ohm.
Voltage (E): Can be
thought of as electrical "pressure," the force that moves electricity.
It is not an indication of electrical capacity, because the same pressure
can exist in a tiny capillary and a huge viaduct which have very different
capacities. Also known as electromotive force and electrical potential.
Volt-Amps (VA): (See
Written guarantee from the manufacturer of a product that they will repair
or replace defective parts for a specified time after the purchase
Watt (W): The unit of
electrical power. The power developed when a current of one ampere flows
through a potential difference of one volt. One watt = one volt x one
amp. One watt = 1/746 of a horsepower.
Wattage (P): This is
the rate of energy flow, the amount of power in a circuit.
Watt Hour (Wh): A unit
of energy equal to one watt of power connected for one hour.
Waveform: The characteristic
shape of an AC current or voltage output.