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Glossary

A

AC

See Alternating Current

AGM Battery

also known as: Sealed, Glass mat

Abbreviation for "Absorbed (or Absorbent) Glass Mat". One of two types of Valve-Regulated Lead-Acid (VRLA, a.k.a. "sealed") batteries. In AGM batteries, the electrolyte is suspended in a fiberglass material rather than as a liquid. The advantages of this design are no outgassing of hydrogen and oxygen; the batteries can be placed in any orientation; and there are fewer shipping restrictions. Disadvantage: fewer charging cycles than with flooded batteries; that is, they don't last as long as flooded batteries.

Alternating Current

e.g. 120 VAC in your home
also known as: AC, VAC

The common form of electricity flow (CURRENT) available in the circuits of most households. Usually abbreviated "AC". AC has a regular, rapid change of the flow direction or POLARITY. In the U.S., AC is standardized at a FREQUENCY of 60 Hertz (cycles per second; abbr. Hz); that is, the direction of electricity flow changes 60 times per second. In Europe, the frequency is 50 Hz. Most household appliances use AC. See also DIRECT CURRENT.

Altitude

The angle formed between the horizon and a line drawn through the center of the sun; expressed in degrees (°) between 0 and 90. The angle changes constantly throughout the day as the sun arcs across the sky. The prefect tilt angle for a solar array at any given moment is the complement of the altitude angle. See TILT ANGLE.

Amorphous

Any Silicon PV module type that is non-crystalline and not based on individual cells; often used interchangeably with THIN-FILM. Though less efficient than crystalline cellular technologies, amorphous types use potentially less expensive manufacturing techniques and can be made into non-flat, or even flexible, modules. See also SOLAR CELL, THIN-FILM.

Amp

e.g. 50 Amp circuit breaker
also known as: Ampere, Current

Commonly used shortened form of "Ampere"; the unit of measure of electrical current. The Amp is a rate of current flow.

Amp-hour Capacity

e.g. 225 Ah

The measurement of stored energy in a battery. Specifically, the ability of a fully charged battery to deliver a specified quantity of electricity (Amp-hour, Ah) at a given rate (Amp, A) over a definite period of time (Hour). The actual capacity of a battery depends upon many factors, including type and construction of the battery(ies), discharge rate, temperature, internal and external resistance, age and prior use of the battery (or battery bank). Ah capacity figures are always based on a charge (C) rate; most common are C20 (20 hours) and C24 (24 hours).

Ampere

See Amp

Array

See PV Array

Array

also known as: PV Array

See PV ARRAY.

Array Mount

The structure used to support a PV ARRAY. Usually composed of a stiff gridwork of aluminum and/or steel rails and cross-members and associated hardware. Common types include rooftop FLUSH-MOUNT, ground or roof TILT-UP mount, TOP-OF-POLE or SIDE-OF-POLE mounts.

AWG

e.g. 10 AWG
also known as: wire gauge

Abbreviation for "American Wire Gauge", a standard for wire and cable diameter measurement where higher numbers signify smaller wires. There are 40 AWG size ratings, from "36" (0.005 inches) to "0000" (aka "4/0", 0.46 inches).

Azimuth

Refers to orientation of a PV ARRAY with respect to rotation around a vertical axis; expressed in degrees (°). Specifically, azimuth is the horizontal angle formed between true south and a point on the horizon directly beneath the sun's current position. Azimuth value changes throughout the day as the sun arcs across the sky from east to west; therefore a fixed orientation is usually selected as a compromise for best overall daily energy production. The normal orientation in the Northern hemisphere is to aim the PV array permanently toward TRUE SOUTH.

B

Ballast mount

A type of PV ARRAY MOUNT that does not use penetration anchors for attachment to the mounting surface, but instead relies on weights (ballast) to hold the structure in place against wind load forces. Ballast mounts are often used on flat-roof commercial installations; common ballast materials include cement blocks or pavers. See also GROUND/ROOF MOUNT.

Battery

e.g. 24V battery bank
also known as: storage, wet cell

A device used for chemical storage of electrical energy; consisting of cells (distinct from PV cells) commonly comprised of two compounds or elements of opposing electrical properties. Batteries release energy as DC electricity. CURRENT flows into or out of the battery when the battery is connected to a LOAD. Batteries used in renewable energy systems are DEEP CYCLE batteries.

Booster Pump

A surface pump used to increase pressure in a water line, or to pull water from a storage tank and pressurize a water system. See SURFACE PUMP.

Bulk Charge

The first stage of battery charging. In flooded lead-acid (FLA) battery charging, bulk charge precedes ABSORB CHARGE and FLOAT CHARGE. Bulk charging is the maximum charging rate of the controller, based on the selected battery type (flooded or sealed). The complete stages of FLA battery charging include: Bulk, Absorb, Float (or Trickle). EQUALIZATION CHARGE is a special, occasional stage for optimizing FLA batteries.

C

Cell Techology

e.g. Monocrystalline, Polycrystalline, Thin-film

Monocrystalline: These modules' cells are made from very thin wafers of purified silicon grown in single-crystal boules. They offer the highest efficiency of crystalline silicon module types.

Polycrystalline: These modules' cells are made from very thin wafers of purified silicon grown in multi-crystal ingots. They have similar characteristics to monocrystalline modules, at slightly lower efficiency and (usually) price.

String Ribbon: This propriety cell technology, developed by Evergreen Solar of Massachusetts, is nearest in specification to polycrystalline technology, though slightly lower in efficiency. Production of these cells involves pulling two "strings" (wires) up from a vat of molten silicon, between which a film of the molten material rises, suspended, in a manner similar to drawing out a soap bubble from a bottle of soap solution with a bubble wand. String ribbon cells contain less silicon than crystalline cells, so tend to be slightly less expensive and to require less total energy for production, meaning more rapid payback of their embodied energy.

Amorphous-Si (also A-Si, where Si stands for Silicon): The term "thin-film" is often loosely applied to these modules but can also include elements other than. A-Si modules are not necessarily based on discrete cells wired in series, as in crystalline modules. The efficiencies of A-Si, and of thin-film in general, are significantly lower than for crystalline silicon modules; this means it will take more surface area of A-Si modules to produce the same amount of power as with crystalline modules.

C.I.G.S.: Copper Indium Gallium di-Selenide; an example of a thin-film PV technology that does not use silicon to produce the photovoltaic effect and electric current.

Centrifugal Pump

A pumping mechanism that moves water by spinning it with an impeller. Water is pushed out by centrifugal force. See also MULTI-STAGE.

Charge Controller

also known as: Charger

(A.k.a. CHARGER) The PV system component responsible for charging and monitoring the batteries. A charge controller directs a controlled electrical CURRENT, from an AC or DC source, into a BATTERY for the purpose of restoring the battery's nominal charge. Charge controllers have two main functions: to prevent battery over-charging and to prevent battery discharge, in reverse, toward the charging source (e.g., solar modules). They can employ various technologies, including Pulse Width Modulation (PWM) or Multiple Power Point Tracking (MPPT), and are typically rated against Amperage and Voltage capacities.

Charge Cycles

A measure of battery useful life. One cycle includes the complete discharge and recharge of a battery, bringing it back to its original state of charge (less any loss due to normal battery wear). The number of charge cycles possible from a given battery is directly related to their DEPTH OF DISCHARGE as well as ambient temperature.

Charger

See Charge Controller

Check Valve

A valve that allows water (or other fluid) to flow in only one direction. Check valves are often used in solar water heating systems.

Circuit

e.g. A closed circuit allows current flow.

An electrical circuit is a pathway of conductors (wires or system components) for electrical current. It is usually a formed as a "loop" of conductors, running from source, through load, back to source. A "closed" circuit has a complete path, allowing current to flow. The path of an "open" circuit has been interrupted (as by a switch or circuit breaker in the "off" position); no electricity can flow through an open circuit.

Cloud effect

See Edge-of-Cloud Effect

Combiner Box

An enclosure used to protect electrical connections between multiple SERIES STRINGs of PV MODULEs and the wiring leading to the rest of a system. Combiner boxes usually have FUSE holders or CIRCUIT BREAKERs, in a variety of quantities, and are typically rated for outdoor exposure.

Conductor

Any object through which electricity can flow, but usually referring to metal items such as wires and electrical devices intended to transmit electricity. Unintentional conductors include human beings-- please use caution when installing and servicing electrical systems!

Connector Type

e.g. MC1, MC2, Junction Box
also known as: Junction Box, MC Connector, Solarline, SAE Connector

PLEASE NOTE: Some manufacturers state that cutting any attached cables or connectors will void your product warranty! Read the warranty information carefully to find out if this rule applies before you cut anything!

Different manufacturers provide different electrical connection types for their modules. Most modules use one of four types:

A Junction Box (located on the back of a PV module.

1) Junction Box (also J-Box). No wires are provided, but simply a user-accessible junction box with (typically) screw terminals for wiring connections. You must supply cabling and seals (recommended) for the knock-out holes that such cabling passes through in the wall of the junction box (we offer "strain reliefs", also known as "dome nuts").

To the left is a photograph of a Junction Box (located on the back of a PV module):

Male and Female end of an MC1 connector.

2) MC1 connectors (most common type). Refers to Solarline 1 connectors from the trademarked brand Multi-Contact. MC1/Solarline 1 is an outdoor-rated, weather-tight electrical connector system designed to interconnect PV modules. The MC system can also link the modules to other MC-terminated cables that lead to other system components. PV modules designated "MC[1 or 2]" have fixed short wire lengths with MC ends emerging from sealed junction boxes on the backs of the modules. Connectors are embossed with + or - symbol to indicate polarity.

MC1 Connectors, a photo and an illustration to the right:

3) MC2 connectors (Multi-Contact's Solarline 2; increasingly common) are similar to MC1 but offer locking tabs to ensure a more secure connection. Again, modules with MC2 ends have permanently affixed short wire lengths emerging from sealed junction boxes. You can also buy lengths of MC-terminated cabling to connect your unwired PV (J-Box) modules to the rest of your system.

The ends of "MC2" male and female connectors offer a tabbed locking mechanism, as seen in this illustration:

MC2 Locking Connector.

SAE Plug used with Global Solar Panels

4) SAE (for Society of Automotive Engineers) is a snug-fitting, male/female, two-prong connection type based on an automotive industry standard. SAE connectors are used by Global Solar in their Sunlinq and P3 Portable Power Pack products and accessories. In the photograph to the right, the SAE connector is at the upper end.

Converter

An electronic device for DC power that steps up voltage and steps down current proportionally (or vice-versa). Electrical analogy applied to AC: See TRANSFORMER. Mechanical analogy: gears or belt drive.

Crystalline

e.g. Mono-crystalline silicon cell

A type of PV cell made from a highly purified silicon crystal. Commercially-produced mono-crystalline silicon cells have efficiency ratings between 15-17%; poly-crystalline cells' efficiencies range from 13-16%. See also AMORPHOUS, THIN-FILM.

Current

e.g. Current and voltage are related by Ohm's Law.

The flow of electricity through a circuit or conductor(s), to transfer energy or do work. Measured in Amperes, commonly called Amps. Analogous to the flow of water in a pipe.

Current

See Amp

D

Deep Cycle

A type of battery best suited for use in renewable energy systems. Deep cycle batteries are designed for relatively slow and steady charge cycles, as would normally occur in such systems; by contrast, automotive batteries are designed for rapid discharge (to start the engine) and rapid recharge by the engine's alternator.

Depth of Discharge

e.g. DoD, 50% DoD

(A.k.a. "DoD") The limit of energy withdrawal, per cycle, to which a battery (or battery bank) is subjected. DoD is expressed as a percent of total capacity. The further you discharge a battery in each cycle, the fewer cycles that battery will be capable of completing. 50% is a typical recommended limit, though lower limits for off-grid systems are common (e.g., 40%, 25%) as a compromise between available energy per charge cycle and battery expense over time.

Diaphragm Pump

A type of pump in which water is drawn in and forced out of one or more chambers by a flexible diaphragm. Check valves control water flow into and out of each chamber.

Direct Current

e.g. 12 VDC

The type of electricity produced by photovoltaic modules and by batteries. Direct current flows in one direction and polarity is fixed, defined as positive (+) and negative (-). See VOLTAGE, AMPERAGE.

Disconnect

An electrical device that permits the safe (usually manual) opening (breaking) of a circuit at specific locations in a system. Both AC and DC types are commonly used. Example: a fused, "knife-throw" disconnect placed between the array and the inverter in a PV system. Use of disconnects is mandated and regulated by the NEC in grid-connected systems.

E

Edge-of-Cloud Effect

also known as: Cloud effect

The natural tendency for temporary current spikes from a PV module or array to occur as the edge of a cloud shadow passes across the module. The effect is due to the refraction of sunlight caused by water vapor in the clouds themselves. Edge-of-cloud effect must be anticipated in system design and sizing in order to avoid current spikes that could damage system equipment or wiring.

Efficiency

The measure of the percentage of power that is converted to useful work in an energy system. Example: An electric pump that is 60% efficient converts 60% of the input energy (e.g., solar electricity) into the work of pumping water. The remaining 40% is lost as waste heat. Mono-CRYSTALLINE PV CELLs range from about 15-18% efficiency in converting the energy embodied in sunlight into electric current.

Electrolyte

The part of a battery, usually fluid or semi-fluid, that carries charge between the plates of a battery. In lead acid batteries, the electrolyte is a dilute solution of sulfuric acid (H2SO4) and water, while the plates are lead.

Energy

e.g. Watt-hours, Wh, Kwh, Amp-hours

Generally speaking, energy is the capacity to do work. In relation to renewable energy systems, energy usually refers to a quantitative measure of electrical power over time. Mathematically, it is the product of power and time, measured in Watt-hours. 1,000 Watt-Hours = 1 kilowatt-hour (abbreviation: kWh). Variation for batteries: the product of current and time is Ampere-hours, also called Amp-hours (abbreviation: Ah). A rate of 1,000 Amps for 1 hour = 1 Ah. See POWER.

Equalization charge

An occasional, controlled overcharge (higher voltage) of flooded lead-acid batteries (singly or in a bank) to bring all individual cells up to the same charge potential. Performed only on flooded batteries as sealed batteries run the risk of damage from outgassing under equalization charge voltages. Equalization can extend battery life by desulphating the lead plates, restore charge capacity and mix the electrolyte; the drawback is loss of fluid through outgassing. Some charge controllers can provide an equalization charge to connected batteries.

F

Fixed array

See Fixed tilt

Fixed tilt

e.g. Fixed tilt PV array
also known as: Fixed array

Refers to the tilt angle of a flat-plate solar ARRAY, in relation to the ground, being static and not adjustable. Some mounts, such as pole-top mounts and roof/ground mounts with adjustable legs, allow seasonal tilt adjustment. The rest are installed at a fixed tilt angle, usually equal to the location latitude, in degrees from horizontal.

FLA

See Flooded Lead-Acid Battery

Float Charge

The last stage of battery charging. In flooded lead-acid (FLA) battery charging, float charge happens after ABSORB CHARGE and the battery is "full". Float charge uses a lower voltage than Bulk or Absorb; it compensates for normal, standing discharge of the battery--"leakage", if you will. The complete stages of FLA battery charging include: Bulk, Absorb, Float (or Trickle). EQUALIZATION CHARGE is a special, occasional stage for optimizing FLA batteries.

Flooded Lead-Acid Battery

also known as: FLA

Flooded lead-acid (FLA) batteries chemically store electrical energy. They are the most common, least expensive type of battery, capable of the greatest number of CHARGE CYCLES. FLAs contain a fluid electrolyte (usually sulphuric acid) which can become depleted through normal use; hence they require regular maintenance. Vent cap access ports allow replenishment fluid (distilled water) to be added to the cells. Ventilation is required for FLAs as they outgas hydrogren and oxygen gasses.

Flow Rate

e.g. 120 GPM

In hydropower systems, the rate at which water moves. Measured in liters per minute (l/m) or gallons per minute (gpm). In conjunction with head value, flow rate is used to determine the power and energy output potential of a given hydro turbine installation.

Flush Mount

A type of ARRAY MOUNT used on rooftops where the modules are parallel to the roof surface. A gap of 3-4" is normally left behind the modules to allow cooling air flow.

Foot Valve

e.g. Dankoff Foot Valve

A check valve placed in the piping before a surface pump to prevent water from flowing back down the pipe and causing the pump to lose prime. See check valve and priming.

G

Gel cell battery

One of two types of Valve-Regulated Lead-Acid (aka "sealed") batteries, in which the electrolyte is suspended in a gel, usually made from silica. These batteries are are virtually maintenance-free. Advantages of gel cells include no outgassing, battery placement in any orientation, fewer shipping restrictions, better cold-temperature performance. Disadvantage: fewer charging cycles and higher pricing than with flooded batteries.

GFCI

e.g. GFCI circuit breaker

Abbreviation for "Ground Fault Circuit Interrupter", an electrical safety device that rapidly de-energizes a circuit when measured current-to-ground exceeds a predetermined value (typically far less than 1 Ampere).

Glass mat

See AGM Battery

Grid-interactive

Referring specifically to electricity-producing renewable energy systems which have a two-way connection with the utility grid: capable of feeding the grid any excess power produced by the system as well as of taking in power from the grid. Can also be applied to inverters of this type. See also GRID-TIED.

Grid-tied

e.g. He bought a grid-tied system

Connected to the utility grid. Often specifically referring to an electricity-producing renewable energy system which can feed the grid any excess power produced by the system; though some systems are only one-way, permitting use of utility grid power for battery charging or loads while not allowing current to be sent out to the grid. See also ON-GRID.

Ground

The reference potential of a circuit. In automotive use, the result of attaching one battery cable to the body or frame which is used as a path for completing a circuit in lieu of a direct wire from a component. This method is not suitable for connecting the negative cable of an inverter to ground; instead, route the cable directly to the negative terminal of the battery.

Ground/roof mount

A type of solar PV ARRAY MOUNT designed for attachment to relatively level ground or nearly flat rooftops that typically includes fixed or adjustable legs to raise the "rear" side (northern side, in the Northern Hemisphere) of the array. Mounts with no tilt would normally be called FLUSH MOUNTs.

H

Head

e.g. 10' head

In hydropower systems, the vertical distance the water falls between capture (inlet) and the turbine itself. In conjunction with flow rate, head is used to determine the power and energy output potential of a given hydro turbine installation. Most turbines have specific operating ranges for head and flow values.

Hertz

e.g. 60 Hz

A unit of measure of the rate of directional change of electrical flow in alternating current (AC), expressed in cycles per second; abbreviated Hz. U.S. GRID power is standardized at 60 Hertz; European (and many other nations') grid power is 50Hz.

High profile

e.g. High profile ground mount

High profile PV mounting structures include multiple, stacked rows of PV modules. The design intent is to minimize installation footprint and can be used where wind loading or PV ARRAY visibility are not limiting factors. Most commonly installed as ground mounts. See also LOW PROFILE.

Hydrometer

A tool used with flooded lead-acid batteries to measure the specific gravity of the electrolyte solution. The measured value is related to the battery's state of charge.

I

Imp

See Maximum power current

Insolation

Sunlight energy. Specifically, total incoming solar radiation, direct or reflected, impacting a surface exposed to sunlight; expressed in units of ENERGY per unit of surface area per unit of time. Common unit is "peak sun hours" or "sun hours". Insolation data is available in tables based on location and array tilt and/or tracking capacity. See PEAK SUN HOURS.

Inverter

An electronic device that converts low-voltage DC to high voltage AC power. In solar-electric systems, an inverter may take the battery bank's 12, 24, or 48 Volts DC and convert it to 115 or 230 volts AC, conventional household power.

Inverter

An electrical device which converts DC electricity from batteries to AC electricity for use by common household LOADs, typically raising VOLTAGE in the process. Some models may include an integrated AC CHARGER to allow use of AC power from the GRID or a generator to charge the batteries during periods of low sun. Inverters can produce modified SINE WAVE or pure sine wave current.

J

Junction Box

See Connector Type

Junction Box

A Junction Box (located on the back of a PV module.

Junction Box (also J-Box). No wires are provided, but simply a user-accessible junction box with (typically) screw terminals for wiring connections. You must supply cabling and seals (recommended) for the knock-out holes that such cabling passes through in the wall of the junction box (we offer "strain reliefs", also known as "dome nuts").

K

Kilowatt

e.g. kW

A unit of measure that is a rate of electrical POWER; equal to 1,000 Watts. See also KILOWATT-HOUR.

Kilowatt-hour

e.g. kWh

A unit of ENERGY measurement equal to 1,000 Watt-hours. Commonly used as the unit for electrical energy commerce. Abbreviated kWh.

L

Load

Any device which consumes electricity. Examples include BATTERIES, lights, and electrical appliances such as computers, refrigerators, etc. Sometimes used collectively to refer to individual loads in aggregate.

Low profile

e.g. Low profile roof mount

Low profile PV mounting structures are designed for a single row of PV modules (or a single PV module). The design intent is to limit PV ARRAY height to reduce wind loading and/or eliminate or reduce array visibility. Commonly installed as rooftop or ground mounts. See also HIGH PROFILE.

Low Voltage Disconnect

Some inverters and some charge controllers have a Low Voltage Disconnect (LVD) that senses battery voltage and prevents the battery from deep discharge by turning off the loads connected to it. In the case of a charge controller, the LVD can control DC loads only. An LVD in an inverter can control AC loads.

M

Maximum power current

also known as: Imp

Refers to the peak current output of a solar module, at peak efficiency, when connected to a system. Abbreviated Imp. See also SHORT CIRCUIT CURRENT.

Maximum power point

e.g. An MPPT controller seeks the maximum power point.

The highest power output (in WATTs) from a given solar module under prevailing conditions. All PV modules' output can be graphed on an "I-V curve", showing the relationship of output current (I) to voltage (V). These curves are leg-shaped; the "knee" position on the curve is the maximum point point.

MC

See MC Connector

MC Connector

also known as: MC

Male and Female end of an MC Solarline 1 connector.

MC connectors refers to specialized electrical connectors of the trademarked brand Multi-Contact. Solarline 1 and Solarline 2 are outdoor-rated, weather-tight electrical connector systems designed to interconnect PV modules. MC connectors are also available as terminators on cable lengths used to link the modules to other system components. PV modules designated MC Solarline 1 and MC Solarline 2 have fixed short wire lengths with MC ends emerging from sealed junction boxes on the backs of the modules. Connectors are embossed with symbols, (+) or (-), to indicate polarity.

MC Connector

See Connector Type

Mod Sine

See Modified Sine Wave

Modified Sine Wave

also known as: Mod Sine

An AC electricity waveform that approximates (to varying degrees of smoothness) smooth sine wave current. Modified sine wave has voltage "steps" between equal positive and negative extremes of the AC waveform. Modified sine wave current is produced by some types of inverters in off-grid systems. See SINE WAVE.

N

NEC

e.g. NEC Section 690
also known as: the Code

Abbreviation for "National Electric Code", the set of U.S. standards for electrical component and installation safety, adopted by the states. NEC is published by the National Fire Protection Association (NFPA). Section 690 of the NEC pertains to photovoltaic systems and practices.

Negative

Designating or pertaining to electrical polarity or direction of current flow. The negative terminal is the point from which electrons flow during discharge.

Nominal Voltage

See Volts (Solar Panel)

Nominal voltage

e.g. 12V nominal module

Nominal voltage refers to a size class of DC system components, not an actual operating voltage. The term comes from the history of photovoltaic (PV) modules' use as an energy source to charge batteries. The values refer to standard battery bank voltages, since most PV modules were designed specifically to charge them: 12V and 24V being the most common sizes.

A 12V nominal PV module is designed to charge a 12V battery. To do so, it must produce a higher voltage than the battery. A fully charged 12V flooded lead-acid battery can register as high as 14.4V on a volt meter, so a 12V PV module typically produces about 17VDC at peak power-- high enough to force current into the battery for charging.

O

Off-grid

Referring to a location or site situation where utility grid power is not available or to a specific electrical system that is not connected to grid power. Typically, remote locations where utility power transmission lines are not present. See GRID-TIED.

Ohm

e.g. Ohm's Law

Unit if measure of electrical impedance or resistance. All electrical CONDUCTORs produce resistance to the flow of current in them. The amount of resistance is important to calculations of wire length, especially in DC circuits. Named for its discoverer, Georg Ohm. Symbol: Ω

Ohm's Law

Expresses the relationship between Voltage (V) and Current (I) in an electrical circuit with resistance (R): V = I x R. If any two of the three values are known, the third value can be calculated by using the formula. Also from Ohm's Law is taken the common expression of electrical power: W (Watts) = V x A (Amps).

On-grid

also known as: Utility Grid

Referring to a location or system connected to utility grid power. May generically refer to both GRID-INTERACTIVE and GRID-CONNECTED systems. See UTILITY GRID, GRID-TIED, OFF-GRID.

Open Circuit Voltage

e.g. 21 Voc

Abbreviated "Voc". In reference to a PV module, open circuit voltage is measured when the module is under full sunlight and not connected to a load. It is the highest voltage rating for a PV module and is used in system sizing calculations. A 12V "nominal" PV module will have a Voc rating of about 20V. In reference to a battery, it is measured when there is no load connected to the battery. This measurement is best taken when the battery has been at rest for at least 6 hours.

P

Parallel

A parallel connection is made by connecting the positive of one PV module (or battery) to the positive of the next PV module (or next battery). As similar solar modules are connected in parallel, the amperage (current) of the array becomes the sum of all the modules connected in parallel. The voltage remains the same as one of the modules. Example: four 12V, 125W PV modules, each with an operating current of 7.2A. Connected in parallel, the voltage of the array will be 12V, while the amperage of the array will be 28.8A (7.2A x 4). (Current is additive in parallel.) The wattage of the array is 4 x 125W = 500W regardless of the voltage configuration.

Peak Power Voltage

e.g. Vmp

The voltage at which a photovoltaic module or array transfers the greatest amount of POWER (WATTs). A "12 Volt Nominal" PV module will typically have a peak power voltage of around 17 Volts. Higher-voltage modules/arrays will produce higher voltages. Abbreviation: Vmp.

Peak Sun Hours

e.g. 4.5 peak sun hours

Also: "sun hours". An approximate unit of measure of solar radiant energy, expressed in hours or fractions thereof. It is based on the approximation that 1 KILOWATT of POWER per square meter impacts earth's surface under full sunlight conditions at solar noon. Peak Sun Hours are used to approximate and compare available solar energy at different locations, in order to aid in system design and sizing calculations. See INSOLATION.

Photovoltaic

e.g. Solar Panels

Photovoltaic - The phenomenon of converting light to electric power. Photo = light, Volt = electricity. Abbreviation: PV. PV - The common abbreviation for photovoltaic.

Photovoltaic Cell

also known as: PV Cell

The minimum electricity-producing unit within a cell-based solar PV module. CRYSTALLINE silicon cells are thin slices cut from ingots of highly purified silicon and doped with specific VOLTAGE-inducing impurities that allow the cell to produce electric current when exposed to sunlight. Cells are wired together in SERIES and/or PARALLEL within MODULEs to produce CURRENT within specific parameters. See also MODULE, PANEL, ARRAY.

Photovoltaic Effect

The natural process through which an electrical current is produced by (sun)light's interaction with certain elements and chemicals. In a typical SILICON PHOTOVOLTAIC CELL, thin wafers of purified silicon are doped (chemically treated), front and back, with specific impurities that together introduce an electrical potential (VOLTAGE) across the normally neutral silicon. In a PV cell connected to a CIRCUIT, this potential is realized as CURRENT, and channeled, through CONDUCTORs (e.g., wires), to LOADS.

Positive

Designating or pertaining to electrical polarity or current flow direction; opposite of negative. The positive battery terminal is the point where electrons return to the battery during discharge.

Power

e.g. Watts (W), kilowatts (kW)

The rate at which work is done. It is the product of Voltage and Current, measured in Watts. 1,000 Watts = 1 kilowatt. An electric motor requires approximately 1 kilowatt per horsepower (after typical efficiency losses). 1 kilowatt for 1 hour = 1 kilowatt-hour (kWh). Contrast with ENERGY.

Primary Battery

A type of electrical battery that can deliver energy but cannot be recharged. Renewable energy systems do not use primary batteries for energy storage.

PV Array

See Array

PV Array

e.g. A 2 kW Array
also known as: Array

A solar PV array is a collection of one or more solar modules forming a single electrical input to a given PV system. Array modules are usually wired in SERIES and/or PARALLEL to produce a specified total VOLTAGE and AMPERAGE. Multiple, independent arrays can be connected to some specialized inverters, though one array per system is most common. See also MODULE, PANEL.

PV Array-Direct

e.g. PV-direct water pumping

PV Array-Direct - The use of electric power directly from a photovoltaic array, without storage batteries to store or stabilize it. Most solar water pumps work this way, utilizing a tank to store water.

PV Cell

See Photovoltaic Cell

PV Module

The technically correct term for a discrete, self-contained, electrical circuit of individual solar CELLs, designed to produce a specific VOLTAGE and AMPERAGE of electricity when exposed to full sunlight. Modules are usually framed in a weatherproof unit. See also PANEL, ARRAY.

PV Module

See PV Panel

PV Panel

also known as: PV Module, Solar Panel

See PV Module.

S

SAE Connector

See Connector Type

Sealed

See AGM Battery

Secondary Battery

A type of electrical battery than can be recharged after discharge. Renewable energy systems use secondary (rechargeable) batteries as their main energy storage, if any energy storage is required.

Separator

A divider made of porous material that is placed in between the positive and negative plates in a battery cell, allowing current to flow through it while preventing direct contact between the plates (which would cause a short circuit).

Series

A series connection is made by connecting the positive of one PV module (or battery terminal) to the negative of the next PV module (or next battery terminal). As similar solar modules are connected in series, the voltage of the array becomes the sum of all the modules connected in series. The amperage (current) remains the same as one of the modules. Example: four 125W, 12V PV modules, each with an operating current of 7.2A. Once connected in series, the voltage of the array will be 48V, while the amperage of the array will be 7.2A. The wattage of the array will be 4 x 125W = 500W regardless of the voltage configuration.

Series String

One or more PV modules connected by SERIES wiring. Technically, one module can comprise a string.

Series-parallel Connection

A method of wiring PV modules or batteries together, in a combination of SERIES and PARALLEL connections, in order to achieve a particular array or bank voltage and amperage.

Short Circuit Current

e.g. Isc

The current measured when a PV module is not connected to a load or any other resistance and is exposed to full-intensity sunlight. This value is the basis for calculating the appropriate size for a charge controller. This is often abbreviated as Isc and the value can be found on the label on the back of each solar module.

Side-of-Pole Mount

A type of ARRAY MOUNT for attaching a small number of modules (usually no more than two) to a vertical pole using clamps or other hardware, and allowing for a range of (or a single specific) TILT ANGLE of the module(s). See TOP-OF-POLE MOUNT.

Sine

See Sine Wave

Sine Wave

also known as: Sine

Sine wave current is the type available in most utility grid systems. Specifically, it is an AC electricity waveform characterized by smooth (sinusoidal) oscillation between equal positive and negative values. It is normally produced electromechanically by rotating turbines or alternators (e.g., coal-fired steam generators or hydroturbines). Sine wave is preferred by some loads, such as inductive loads (e.g., motors) and sensitive electronics. See MODIFIED SINE WAVE.

Solar Panel

See PV Panel

Solar Tracker

e.g. Solar trackers are often used in water pumping applications.

A mounting rack, and associated motion hardware, for a PV array that automatically tilts and/or pans to follow the daily path of the sun through the sky. Tracking technology may be "active" (using electric motors) or "passive" (using gas phase-change weight transfer). A tracking array will produce more energy over the course of the day than a fixed array, particularly during the long days of summer. Solar trackers are always complete racking systems, not available as add-ons to existing ARRAY MOUNTS.

Solarline

See Connector Type

Specific Gravity

The density of a solution relative to the density of water. In reference to batteries, the density of the fluid electrolyte (acid); measured with a hydrometer. Specific gravity of battery acid is related to the state of charge of the battery and measured values can be used to determine battery state of charge with reasonable accuracy.

STC

See Watts of solar

storage

See Battery

Stratification

In reference to battery chemistry, a condition where the concentration of acid is greater at the bottom of the battery than at the top. This condition is caused by undercharging; if not corrected, it can cause premature battery failure. Stratification can be prevented by periodic equalization charging.

Sulphation

e.g. desulphator

A condition common to batteries in use over time and characterized by reduced charge capacity. In a lead-acid battery, during the discharge part of its operation cycle, lead sulfate crystals form on both the positive and negative electrodes (plates). This is a normal and manageable consequence of battery operation. If the battery is allowed to remain in a discharged state for a prolonged period of time, the sulfate crystals continue to grow. These larger crystals reduce the effective plate area and are difficult to dissolve back into the electrolyte solution with normal charging. Thus, they reduce the overall capacity of the battery. This condition can be prevented (or at least slowed) by recharging the battery immediately following a discharge. This condition can also be remediated by occasional use of an EQUALIZATION CHARGE on the battery.

System voltage

e.g. His array is 48V but his system voltage is 24V.

System voltage refers to the NOMINAL VOLTAGE of a battery-based renewable energy system as a whole. The DC source voltage may be higher (where MPPT charge controllers are used). System voltage is the same as the voltage of the battery bank. It will usually be the same voltage as the inverter, if present in the system.

T

the Code

See NEC

Thin-film

A generic name for photovoltaic modules that is based on non-crystalline technology that may or may not use Silicon as the basis for the PV Effect. Thin-film modules are typically made using spray, printing, or deposition processes, as opposed to sliced crystals wafers. Can be made into irregular surfaces, and some types can be flexible. See AMORPHOUS.

Tilt Angle

e.g. 42° array tilt

The angle, from horizontal, at which a solar panel or ARRAY is set for maximum solar exposure; expressed in degrees (°) between 0 and 90. The goal is to face the array so that sunlight strikes it perpendicularly. At any given moment, the ideal tilt angle is the complement of solar ALTITUDE (90° - Altitude°); but the sun's position constantly changes in the sky daily as well as seasonally. For a fixed array (not using a SOLAR TRACKER), a compromise angle is selected, usually equal to the LATITUDE of the location (best annual production). The tilt angle can be adjusted (seasonally or permanently) to boost production during the year: +15° during winter, -15° during summer, in Northern latitudes. See ALTITUDE.

Tilt-up Mount

A type of ARRAY MOUNT used to attach modules to flat, or nearly flat, surfaces. In most tilt-up mounts, tilt legs lift up one end of the modules to produce the desired array TILT ANGLE.

Top-of-Pole Mount

A type of ARRAY MOUNT for attaching a PV array (usually 1-24 modules) to a vertical pole using clamps, gimbals, or other hardware, and allowing for a range of (or a single specific) TILT ANGLEs of the array. Some top-of-pole mounts include SOLAR TRACKERS. See also SIDE-OF-POLE MOUNT.

Transformer

e.g. X240, T240

Transformer - An electrical device that steps up voltage and steps down current proportionally (or vice-versa). Transformers work with AC only. For DC, see converter. Mechanical analogy: gears or belt drive.

True South

Also known as solar south; in the northern hemisphere, true south is the direction at which the sun reaches its peak apparent height (ALTITUDE) in the sky. A magnetic compass may not point to true north, since the earth's magnetic and rotational axes differ as measured in some locations.

TSC

Abbreviation for "Temperature Sensitive Charging." The ability of a battery charger to adjust its charging voltage based on the temperature sensed at the battery bank where a temperature probe is used.

Turbulence

Referring to wind turbine systems, turbulence is disturbances to air flow. Undisturbed airflow is called "laminar" flow. Moving air masses that encounter obstacles, such as trees or buildings, become turbulent. Wind turbine efficiency is inversely proportional to turbulence in the air flow; power production can be dramatically decreased in turbulent air streams. As a general guideline, avoid turbulence by situating the turbine at least 30 feet above any obstruction within 300 feet. The higher the turbine, the less turbulence will be present in the air stream and the greater the energy production will be.

U

Utility Grid

See On-grid

Utility Grid

e.g. Grid-connected PV system

(Also known as MAINS.) The regulated, standardized system of distribution of electricity (AC), including power generation, distribution, and end-user delivery systems. The U.S. grid power frequency is standardized at 60 Hertz (60Hz). Transmission voltages vary with distances to be covered. End-user (consumer) electricity may be delivered at 240VAC. See also POWER, FREQUENCY.

V

VAC

See Alternating Current

Volt

e.g. 24V
also known as: Voltage

The unit of measure of electric potential or electromotive force. In the water analogy, voltage is equivalent to water pressure, either in a pipe or a standing column of water.

Voltage

See Volt

Voltage Drop

Loss of voltage (electrical "pressure") caused by the resistance in wires and electrical devices. Proper wire sizing will minimize voltage drop, particularly over long distances. Voltage drop is determined by four factors: wire size (gauge), current (Amps), voltage, and length of wire. It is determined by consulting a wire sizing chart or formula available in various reference texts and is expressed as a percentage. Water analogy: Friction Loss in pipe. See VOLTAGE.

Voltage window

e.g. This inverter's voltage window is 150-450VDC.

Grid-tied inverters are rated to accept DC voltages from the DC source (e.g., a PV ARRAY) within specified ranges. Values vary among models. There is a minimum value to turn on the inverter and a maximum safe value; the range is called the voltage window. The MPPT function of the inverter may only operate within a subset range of the main operating voltage window range.

Volts (Solar Panel)

e.g. 12V, 18V, 24V
also known as: Nominal Voltage

"Volts" in reference to solar modules means "nominal voltage". Nominal voltage comes from the history of photovoltaic (PV) modules' use as an energy source to charge batteries. It refers to standard battery voltages, since most PV modules were designed specifically to charge them: 12V and 24V being the most common sizes. There are other important voltage figures associated with PV modules, such as Peak Voltage (often abbreviated Vpmax or Vmp), and Open Circuit Voltage (Voc), but in our brief PV module descriptions or names we mean nominal voltage.

A 12V nominal PV module is designed to charge a 12V battery. To do so, it must produce a higher voltage than the battery. A fully charged 12V flooded lead-acid battery can register as high as 14.4V on a volt meter, so a 12V PV module typically produces about 17VDC at peak power--- high enough to force current into the battery for charging.

"So where does 18V come from? There are no 18V batteries!" The answer lies in the recent industry transition from dominantly off-grid (battery-based systems) sales to on-grid sales. Since batteries are not usually used in on-grid PV installations, matching standard battery voltages is no longer necessary. Instead, PV module manufacturers can build modules to meet other requirements of voltage and amperage. In grid-tied systems, modules must be series-wired (additive voltages) to meet the high input voltage "windows" of the inverters they feed, typically 100-500VDC.

W

Water Analogy

A traditional, convenient conceptual tool for understanding electrical circuits and systems. In this analogy, water is equated with electricity; water flow volume (e.g., gallons per minute) is CURRENT; water pressure (e.g., psi) is VOLTAGE.

Watt

e.g. W = A x V

The unit of measure of electrical power; i.e., the rate of doing work, in moving electrons by or against an electric potential. Contrast with WATT-HOUR. (Per Ohm's Law: Watts (power) = Amperes x Volts)

Watt-hour

e.g. 1,000 Wh = 1 kWh

The unit of measure of electrical ENERGY. Abbreviated Wh. Contrasted with the Watt, which is a measure of Power, i.e., a rate. Watt-hours are calculated as Watts x Hours. Electricity consumers typically pay for electricity based on kilowatt-hours consumed (kWh = 1,000 Wh). Example: a 15W compact fluorescent lamp consumes 60 Wh of electrical energy in 4 hours of operation.

Wattage

See Watts of solar

Watts of solar

e.g. 125 W PV module
also known as: STC, Wattage

"Watts" here refers to the rated power-generating capacity of the module, based, in most cases, on Standard Test Conditions (STC), an industry standard for module ratings. The number does not mean that the PV module will always produce that Wattage, even under optimal, full-sunlight conditions. There are too many variables involved in real-world conditions to guarantee such output under all possible circumstances; hence, manufacturers rely on standardized industry testing to rate modules so that there can be some scale, however rough, to compare them. Other standards have been adopted in certain areas, including California's CEC (California Energy Commission) ratings, and PTC (PV USA Test Conditions). These newer standards were created in part to bring module ratings closer to actual conditions of use. They tend to offer a more accurate measure of PV modules' real-world output, but STC ratings are still the primary industry standard.

wet cell

See Battery

Wet Cell Battery

A type of battery that uses a liquid electrolyte. Most common type is Flooded Lead-Acid. The wet cell battery requires periodic maintenance: cleaning the connections, checking the electrolyte level and performing equalization charges. The advantages are lower cost and more charge cycles than with sealed batteries, if properly maintained.

wire gauge

See AWG