Glossary of Alternative Energy Terms

Glossary of Alternative Energy Terms

Absorbed Glass Mat (AGM) Battery: A battery with a fiberglass mat which suspends the electrolyte between the

lead plates. The mat allows the battery to be used in many positions and assists the recombination of hydrogen and

oxygen into water after it is released from the electrolyte during charging.

Alternating Current (AC): Electric current from the power utility, a generator or inverter which changes direction of

flow at frequent intervals. In the Western Hemisphere this is 120 times per second (60 cycles or hz). Most of the rest

of the world operates on 50 cycles.

Amoprhous Silicon: A non-crystaline semiconductor material that is used in "thin-film" photovoltaic modules such

as those made by Uni-Solar and some of the earlier Solarex modules. The doped silicon is sprayed onto a sub-strate

such as glass or stainless steel. This type of module uses less photovoltaic grade silicon than a single or multi-crystal

module and also allows for a flexible panel with a metal or synthetic backin. They also will produce power in lower light

conditions than conventional modules.

Ampere (A) or Amp: The unit for electric current as in the flow of electrons. Describes the quantity of electrons passing

a point in one second. It will often be shown on a photovoltaic module label as "I" for intensity.

Ampere-Hour (AH): The quantity of electrical energy equal to the flow of one ampere of current for one hour. Deep

cycle storage battery capacity is often rated in amp hours.

Array: A number of photovoltaic modules wired together with a single output.

Autonomous System: A photovoltaic system that is stand-alone and has no backup power source. These usually

incorporate a battery bank for power storage.

Balance of System: The items in a photovolaic system, with the exception of the pv modules themselves, that make

up a complete system.

Battery: Two of more cells connected together to store electricity.

Battery Capacity: The number of amp-hours that a battery can store.

Battery Cycle Life: The number of charge and dis-charge cycles a battery can endure before it is no longer useful.

This is based on a specific depth of dis-charge (drawing the battery down to a given amp-hour capacity remaining.)

The more the battery is drawn down before recharging, the lower the number of charge/dis-charge cycles that will

be left.

Blocking Diode: In the "Olden Days" most photovoltaic charge controllers were either on/off or diversion types. At

night power could drain from the batteries back into the photovolaic modules. The modules would actually glow (when

viewed with light amplification equipment) like a huge led light. In those instances a blocking diode (or one-way electrical

gate), usually a Schottky diode, was used to prevent this. Todays charge controllers either have a built-in diode or

automatically disconnect the modules from the battery bank at night.

By-Pass Diode: PV modules can be connected in a series string (positive to negative) to increase voltage. If one of the

modules is shaded, the output from the other modules in that series string can feed into that shaded module causing damage

or a fire. When the modules have a by-pass diode in the junction box that dioded will pass the power through without allowing

it to go into the cells of the shaded module. Once the shading is removed, the diode has a higher resistance than the cells in

the module and the module starts producing power again. UL Listed modules will show a maximum series string voltage which

the by-pass diode in the module can handle.

Cell: The basic unit of a pv module or battery. In a pv module the cell produces around 0.45 to 0.5 volt, the more cells the higher

the voltage. A lead acid battery cell produces about 2.0 volts (a 12 volt battery will have 6 cells.)

Charge Controller: This is placed between the alternative energy power source and the battery bank to prevent over-charging.

Charge Rate: The rate in amp hours of charging current supplied to a battery.

Compact Fluorescent Lamp (CFL): Fluorescent lights which have an Edison (screw-in) base and use either short looped or

spiral fluorescent tubes.

Crystalline Silicon: A pv cell made of either a single crystalline or poly crystalline structure which have a controlled direction of

the crystals. An Amorophous structure has random patterns and directions.

Current: The flow of electricity (electrons) between two points having a difference in potential (voltage.)

Current at Maximum Power (Imp): The current rating of a pv module when the maximum power (watts) is being produced.

Days of Autonomy: The number of days a stand-alone system can power loads without incoming power from pv module input.

DC to DC Converter: A device which takes a direct current voltage and either steps it up or steps it down.

Deep Cycle Battery: A battery which is designed (usually with thick plates) to withstand being drawn down to a low state of charge

and still being able to be recharged.

Diode: A one-way electrical gate which allows current to travel in one direction only.

Direct Current: Electric current which travels in one direction only, such as that produced by a pv module or storage battery.

Discharge Rate: Usually shown in amp-hours (amps over time) which shows how much current is being taken from a battery.

Disconnect: Also a safety disconnect. A circuit opening device which can be placed between an alternative energy power source

and the charge controller, between the charge controller and batteries, as well as between the batteries and the loads.

Efficiency: This is the ratio of power put in verses power outputted. Usually shown as a percentage.

Electrical Circuit: The pathway from the power source to the load.

Electrical Grid: The system of power distribution from power generating plants to the customers. Usually operated by a public

utility company.

Electrolyte: The liquid in a storage battery. In a lead acid battery it is composed of water and sulfuric acid.

Energy: The ability to do work - it is usually measured in watts.

Energy Density: The ratio of energy available in a battery (storage device) to the mass or weight of the battery.

Equalization Charge: Intentionally over-charging a battery for short periods of time at a higher than normal voltage to help mix up

the acid and water in the electrolyte and equalize, or balance, the cells in a battery.

Float Charge: This is a light maintenance charge to offset the battery losses caused by self-dischage in storage.

Float Life: This is the number of years a battery will retain its stated amp hour capacity when kept at a float charge.

Gassing Current: A portion of the charging current which is consumed by the electrolytic breakdown of the water into

oxygen and hydrogen during charging.

Gel Battery or Gel Cell: A sealed battery where the electrolyte is captured in a silica gel.

Grid-Tie: An alternative energy system that output alternating current into the building's wiring. Any power not used will feed into

the electrical grid.

Hybrid System: A power generating system that has more than one power source such as: photovoltaic, wind, hydro or

an auxillary generator.

Insolation: Sunlight, either direct or reflected which is usually measured in watts per square meter. Used to determine

the available sunshine in a given location for sizing a photovolatic system.

Interconnect: Wired connections between solar cells as well as between photovoltaic modules.

Inverter: A device which converts direct current from a battery (or photovoltaic modules in a grid-tie system) into

120 or 240 volt a.c.

Junction Box: An electrical enclosure where wiring circuits are connected. On the back of a pv module this is

commonly referred to as the "J" box.

Kilowatt: One thousand watts.

Kilowatt Hour: On thousand watt hours (i.e. 1000 watts either produced or consumed in an hour.)

Life Cycle Cost: The total system cost from the time of installation to the time it heads to the bone yard.

Load: Anything that draws power from a circut (i.e. lights, fan, radio, etc.)

Maximum Power Point Tracker (MPPT): A charge controller that operates a pv array at its maximum power

point voltage/amperage.

Megawatt: One million watts.

Module: A single photovoltaic module (solar panel).

Mulitcrystalline: Photovoltaic cells that have semi-random orientation of the structure. They look like broken sheets

of colored glass.

NEC: National Electrical Code. Sets standards for electrical installations - article 690 of the code refers to pv systems.

Nominal Operating Cell Temperature (NOCT): A reference temperature (usually 25 degrees C) for basing the

output voltage and amperage of a pv cell or module. Some modules show both a NOCT on the sticker for both

25 degrees C and 45 degrees C. The higher temperature will have lower outputs.

Nominal Voltage: The reference voltage for describing battery, pv modules and systems (i.e. 12, 24 or 48 volt.)

A 12 volt system usually operates from 12 to 14.5 volts.

Ohm: A unit of measurement dealing with the resistance to flow of electrons through a circuit.

One Axis Tracking: A pv system where the modules track the sun from East to West and return to East in the morning.

Open Circuit Voltage: The highest possible voltage a pv cell or module will produce when in full sun and without being

connected to a load.

Orientation: Aiming the pv module(s) to a compass heading, usually to true South in the Northern Hemisphere.

Parallel Connection: Connecting two or more electrical producing devices, such as pv modules, or storage devices,

such as batteries, so the the capacity (amperage or amp/hours) increases but the voltage remains the same. This is

done by connecting positive to positive and negative to negative.

Peak Load / Peak Demand: The most power consumed at a given moment in the day.

Peak Sun Hours: The number of hours in the day when solar irradiance (or insolation) averages 1000 watts per square

meter - also known as full sun.

Photovoltaic (PV): Refering to the direct conversion of light into electricity.

Photovoltaic Array: Connecting of one or more pv module(s) so they act as one electricity producing unit.

Photovoltaic Cell: The smallest sem-conductor part in a pv module, the building block of the module.

Photovoltaic Module: A series of photovoltaic cells mounted in a self-contained package, also known as

a solar panel.

Photovoltaic System: A complete assembly from the pv module(s) to the power consuming loads.

Polycrystalline: Photovoltaic cells that have semi-random orientation of the structure. They look like broken sheets

of colored glass.

Pulse-Width-Modulated Charge Controller: This is placed between the pv module(s) and the batteries. It operates

by allowing different width and different heights of voltage spikes to flow into the battery from the pv power source.

PV: PhotoVoltaic.

Remote Site: A location where the only power available is that which is produced on-site.

Resistance: The property of a conductor or electrical device to oppose the flow of electrons.

Series Connection: Connecting two or more electrical producing devices, such as pv modules, or storage devices,

such as batteries, so the the voltage increases but the capacity (amperage or amp/hours) remains the same. This is

done by connecting positive to negative and so on.

Short Circuit Current (Isc): The current (amps) flowing from a pv cell or module through a circuit that has no load or

resistance - the highest possible current.

Shunt Regulator: A photovoltaic charge controller that shorts out the pv module when the battery is charged.

Silicon: The primary material in most photovoltaic modules. Commonly found in sand and quartz.

Sine Wave Inverter: A dc to ac inverter which produces alternating current (usually 120 volt a.c. in the Western Hemisphere)

that is of the same wave form as that delivered by the utility company.

Also known as a pure or true sine-wave inverter.

Single Crystal Material (pv cell): A pv cell where the crystal orientation is in the same direction. With current technology these

are the most efficient, as well as the most expensive to manufacture.

Solar Cell: An eary term for a photovoltaic cell which is the building block of a pv module.

Solar Constant: The strength of sunlight which is about 1000 watts per square meter at sea level at the equator.

Solar Energy: Energy from the sun.

Solar Grade Silicon: A grade of silicon which is used to manufacture photovoltaic cells.

Square Wave Inverter: These are the earliest d.c. to a.c. inverters. Instead of producing a curved waveform like a sine wave

inverter, these produce a very low grade and inefficient form which is flatten (square) at the top and bottom.

Staebler-Wronski Effect: The nature of amorphous (thin-film) photovoltaic devices is that they can lose up to 10% of their

output in the first year of being exposed to light. This is why manufacturers under-rate the output on the pv module label (it shows

the output after the first year) and why the controll and protection devices in a pv system have to be up-sized to handle the

output of the pv modules for the first year.

Stand-Alone System: A system that relies on power produced by itself with no incoming power from the utility grid.

Stand-Off Mounting: This is when pv modules are roof mounted a few inches from the roof surface and tilted at the optimum

angle for the site latitude. This also allows the back of the modules to cool which helps maintain output voltage.

Standard Test Conditions: When pv module output is measured for the labelling they are tested in a controlled laboratory.

The irradiance (light source) supplies the standard 1000 watts per square meter and the temperature is 25 degrees C.

State of Charge: The available "useable" capacity remaining in a battery. This is usually measured in percent. In theory,

a 100 amp hour battery that has had 50 amp hours removed from it would have a 50% state of charge.

Sulfation: A lead-acid battery has lead plates and an electrolyte composed of water and sulfuric acid. As the battery

discharges the sulfuric acid migrates into the lead plates. If it is allowed to remain in the plates sulfate crystals form on

the surface and insulate the lead from the electrolyte. This can permanently reduce the storage capacity of the battery.

Superstrate: This is the top covering of the pv cells in a pv module. It is usually low-iron tempered glass but can also

be a flexible synthetic material.

Surge or Surge Rating: When an electric motor is first started it requires a greater amount of amperage than the name

plate rating. This is because the motor has to overcome the inertia of the moving parts at rest and get them moving.

Surge Capacity: This is the ability of an inverter or generator to output a higher power than the name plate rating for a

few seconds to start an electric motor.

Temperature Compensation: This is the ability of a charge controller to adjust the voltage going into a battery to allow

for higher or lower than normal battery temperature.

Thin-Film: A non-crystaline semiconductor material that is used in "thin-film" photovoltaic modules such

as those made by Uni-Solar and some of the earlier Solarex modules. The doped silicon is sprayed onto a sub-strate

such as glass or stainless steel. This type of module uses less photovoltaic grade silicon than a single or multi-crystal

module and also allows for a flexible panel with a metal or synthetic backin. They also will produce power in lower light

conditions than conventional modules.

Tilt-Angle: This is the angle of a pv module in relation to level which will orient it as close as possible to being perpendicular

to the sun for maximum power production.

Tracking PV Array: A photovoltaic array that follows the path of the sun to maximize the solar radiation incident to the

pv surface. The two most common orientations are a one axis where the array tracks the sun east to west and a two

axis where the array points directly at the sun at all times. Tracking arrays use both the direct and diffused sunlight.

The most common drive mechanisms are electric, using pv modules at each end of the array to keep it centered on

the sun and a freon driven which uses the heat differential between each end of the array.

Transformer: An electromagnetic device which steps up or steps down an alternating current.

Trickle Charge: A low charge rate which compensates for for the self-discharge, or parisitic losses, of a

battery.

Utility Active Inverter: A d.c. to a.c. inverter which accepts direct current from a pv array or wind generator and

feeds it directly into a buildings' electrical service entrance (breaker panel) and the utility grid.

VAC: Volts alternating current.

VDC: Volts direct current.

VOC: Volts open circuit - the most a pv module can produce under full sun and with no load attached to the output.

Volt (V): A unit of electrica force or push. One volt produces one amp of current when acting against one ohm of resistance.

Voltage at Maximum Power (Vmp): The voltage at which maximum power (wattage) is available from a photovoltaic

module. This is the "sweet spot" where the curve of amperage and voltage meet to produce the most power.

Watt (W)(James Watt): The unit of electrical power or amount of work done. One ampere of current flowing at a potential of one

volta produces one watt of power.

Watt - Hour (Wh): A quantity of electrical energy when one watt is used for one hour.

Waveform: The shape of and alternating current curve graphically representing the change in a AC signal

voltage and current amplitude with respect to time.

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