Renewable Energy Glossary

There are three different Glossaries here. The first is Photovoltaic, second is Solar Thermal and the third is Biomass. Each scrolls in alphabetical order.

PHOTOVOLTAIC GLOSSARY

AC
Alternating Current The direction of electrical current reverses, usually many (60) times per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.

Ampere or (amp)
A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere. One ampere is equal to 6.235 x 10 18
electrons per second passing a given point in a circuit.

Ampere Hour - Ah
A measure of current over time, used to measure battery capacity.

Amp Hour Meter
An instrument that monitors current with time. The indication is the product of current (in amperes) and time (in hours).

Array
Any number of Photovoltaic modules connected together electrically to provide a single electrical output. An array is a mechanically integrated assembly of modules or panels together with support structure (including foundation and other components, as required) to form a free-standing field installed unit that produces DC power.

Balance of Systems (BOS)
Parts or components of a photovoltaic system other than the photovoltaic array.

Battery
Two or more electrochemical cells enclosed in a container and electrically
interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term battery also applies to a single cell if it constitutes the entire electrochemical storage system.

Battery Capacity
The maximum total electrical charge, expressed in ampere-hours (AH), that a battery can deliver to a load under a specific set of conditions.

Battery Cell
The simplest operating unit in a storage battery. It consists of one or more
positive electrodes or plates, an electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, and a container for all the above.

Battery Available Capacity
The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, initial state of charge, age, and cutoff voltage.

Battery Energy Capacity
The total energy available, expressed in watt-hours (kilowatt-hours), that can be withdrawn from a fully-charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cutoff voltage. This term is more common to system designers than it is to the battery industry where capacity usually refers to ampere-hours.

Battery Cycle Life
The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

Battery Life
The period during which a cell or battery is capable of operating above a
specified capacity or efficiency performance level. For example, with lead-acid batteries, end-of-life is generally taken as the point in time when a fully charged cell can deliver only 80% of its rated capacity. Beyond this state of aging, deterioration and loss of capacity begins to accelerate rapidly. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.

Cell - Battery
A single unit of an electrochemical device capable of producing direct voltage by converting chemical energy into electrical energy. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably).

Cell - Solar
The smallest, basic Photovoltaic device that generates electricity when exposed to light.

Charge Rate
The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.

Charge Controller
A component of photovoltaic system that controls the flow of current to and from the battery to protect the batteries from over-charge and over-discharge. The charge controller may also indicate the system operational status.

DC Direct Current
A one way flow of electric current. Typical sources of direct currents are electric cells, rectified power units and direct current generators. This is the current flowproduced by a solar system. To be used for typical 120 volt or 220 volt household appliances, it must be converted to AC (alternating current).

Depth of Discharge - DOD
The ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-
hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%.

Diffuse Insolation
The radiant energy from the sky incident upon unit surface area during a specified time period (Same units as for direct insolation).

Direct Insolation
The radiant energy from the sun (and a small area of sky surrounding it, defined by the acceptance angle of the pyrheliometer) incident upon unit surface area during a specified time period. (MJ/m2 per hour, day, week, month or year, as the case may be).

Efficientcy
The ratio of power output of a Photovoltaic cell to the incident power from the sun or simulated sun sources under specified standard insolation conditions.

Electrolyte
The fluid used in batteries as the transport medium for positively and negatively charged ions.

Electric Current
The rate at which electricity flows through an electrical conductor, usually measured in amperes (amps).

Electricity
Energy resulting from the flow of charge particles, such as electrons or ions.

Electrons
A negatively charged particle. The movement of electrons in an electrical
conductor constitutes an electric current.

Equalization
The process of restoring all cells in a battery to an equal state-of-charge. For lead-acid batteries, this is a charging process designed to bring all cells to 100% state-of-charge. Some battery types may require a complete discharge as a part of the equalization process.

Equalizing Charge
A continuation of normal battery charging, at a voltage level slightly higher than the normal end-of-charge voltage, in order to provide cell equalization within a battery.

Float Service
A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger which supplies the battery load under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service.

Gassing
The evolution of gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from local action self-discharge) or from the electrolysis of water in the electrolyte during charging.

Grid
Transmission line network used to distribute electric power.

Grid Connected System
A PV system that is connected to the national grids by an inverter. The inverter will export unused electricity to the grid earning the user money. A Grid Connected PV system usually is made from Photovoltaic Modules and a Grid Connected Inverter.

Grid Lines
Metallic contacts fused to the surface of the solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.

Hemetic Seal
Being impervious to external influences. Typically associated with the sealing of a package so that oxygen, moisture, and other outside environments cannot enter the package.

Hybrid Systems
A power system consisting of two or more power generating systems combined.

Incident Light
The incident light is the amount of light reaching an object.

Insolation
The amount of sunlight reaching an area. Sometimes expressed in milliwatts per
square centimeter, or langleys.

Inverter
A device that converts electricity from DC to AC.

kWh
Unit of energy used to perform work (energy and work are equivalent in units, energy being the potential value and work the achieved value)

Fuel equivalents:
One barrel of crude contains roughly 1700 kWh
One ton of coal contains roughly 7500 kWh
One cubic foot of natural gas contains 0.3 kWh

Thermal unit:
One kWh = 3400 BTU. Can be compared to 860 calories (food value)

Load
Refers to equipment that is powered by electricity. Usually expressed in terms of amperes or watts. In an electrical circuit, any devise or appliance that uses power (such as a light bulb or water pump).

Maximum Power
The power at the point on the current-voltage characteristic where the
product of current and voltage is a maximum (measured in watts).

Module
The smallest non divisible, self-contained and environmentally protected physical structure housing interconnected Photovoltaic cells and providing a single DC electrical output.

Off-Grid System
A system which operates independently of the utility lines. An offgird system is made up from, PV Modules, Charge Controller, Battery Bank and an Inverter. It may draw additional power from a generator and is not capable of providing power to the utility.

Open Circuit Volatage - VOC
Voltage produced by a Photovoltaic cell with no load applied when the cell is exposed to standard insolation conditions, measured with a voltmeter.

Panel
A collection of one or more modules fastened together into a single unit, often factory
pre- assembled and wired, forming a field-installable unit.

Parallel Connection
A wiring configuration used to increase current (amperage). Parallel wiring is positive to positive (+ to +) and negative to negative (- to -). Opposite of a series connection.

Peak Power Point
Operating point of the I-V (current-voltage) curve for a Photovoltaic cell or module where the product of the current value times the voltage value is a maximum.

Peak Watts
The measurement of electricity produced by a solar generator at noon on a sunny day, under predetermined standard conditions.

Photon
The actual (physical) particle unit of light, as the electron is of electric charge and the atom and molecule are of matter. Light has both wave properties and particle properties. Violet light has relatively short wavelength and higher energy in its photons; red light has longer wavelength, lower-energy photons. The wavelength and/or energy spectrum of the sun extends in both directions beyond the visible range of light, of course, and the silicon module solar cell can capture some energy in both of these invisible zones. Photons not captured by the cell are either reflected or converted to heat in the solar array.

Photovoltaic Cell - PV Cell
A device composed of specially prepared semiconductor material or material combinations exhibiting the ability to convert incident solar energy directly into electrical energy.

Photovoltaic Effect
The phenomenon that occurs when photons, the 'particles' in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available.

Photovoltaic System
An installed arrangement of solar modules and other equipment generating power for a given application.

Power Factor
The ratio of real power (watts) to apparent power (volt-amps) in an AC circuit. Displacement power factor is the ratio of fundamental watts to fundamental RMS volts times

Semiconductor
A material such as silicon, which has a crystalline structure that will allow current to flow under certain conditions. Semiconductors are usually less conductive than metals but not an insulator like rubber.

Series Connection
A wiring configuration used to increase voltage. Series wiring is positive to negative (+ to -) or negative to positive (- to +). Opposite of parallel connection.

Silicon
A non-metallic element, that when specially treated, is sensitive to light and capable of transforming light into electricity. Silicon is the basic material of most beach sand, and is the raw material used to manufacture most photovoltaic cells.

Solar Cell
The basic photovoltaic device which generates electricity when exposed to sunlight.

Solar Panel
A collection of solar modules connected in series, in parallel, or in series-
parallel combination to provide greater voltage, current, or power than can be furnished by a single solar module. Solar panels can be provided to furnish any desired voltage, current, or power. They are made up as a complete assembly. Larger collections of solar panels are usually called solar arrays.

Stand Alone System
See Off-Grid System.

Storage Battery
A device capable of transforming energy from electric to chemical form and vice versa. The reactions are almost completely reversible. During discharge, chemical energy is converted to electric energy and is consumed in an external circuit or apparatus.

Sulfation
The formation of lead-sulfate crystals on the plates of a lead-acid battery.
Commonly used to indicate the large crystals which form in partially discharged cells as the result of temperature cycling. These large crystals are more difficult to reduce by the charging current than are the smaller crystals that result from normal and self-discharge reactions.
Sulfating can be caused by leaving the battery in a discharged state for long periods of time.

Tilt Angle
A fixed angle measured from the horizontal to which a solar array is tilted. The tilt angle is chosen to maximize the array output. Depending upon latitude, season and time of day this angle will vary.

Tracking Array
An array that is mounted on a movable structure that attempts to follow the path of the sun. Some tracking arrays are single axis while others are dual.

Voltage
A measure of the force or "push" given the electrons in an electrical circuit; a measure of electrical potential. One volt produces one amp of current when acting against a resistance of one ohm.

Watt
Unit of power. Power is the rate of using energy to do work.

SOLAR THERMAL GLOSSARY

AAV
Automatic Air Vent. This is an air valve that automatically releases air from the system without any manual intervention.

Absorber
The blackened surface in a collector that absorbs the solar radiation and converts it to heat energy.

Aperture
When comparing collectors a reference area is important - that is, the surface area from whish the collectors characteristic values are drawn. In the collector test methods according to EN 12975 the reference area is equal to either the aperture area or the absorber area.

Active System
A solar heating or cooling system that requires external mechanical power to move the collected heat.

Ambient Temperature
The temperature of the surrounding air.

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.

Azimuth
The angular distance between true south and the point on the horizon directly below the sun.

British Thermal Unit - BTU
The quantity of heat needed to raise the temperature of one pound of water one degree Fahrenheit.

Calorie
The quantity of heat needed to raise the temperature of one gram of water one degree Celsius.

Collector
The collector or panel usually is positioned on the roof of you house. When solar radiation falls on the collector it is absorbed by the selective coating on the absorber plate. This turns solar radiation or light into heat.

Collector Efficiency
The ratio of usable heat energy extracted from a collector to the solar energy striking the cover.

Concentrating Collector
A device which concentrates the sun's rays on an absorber surface which is significantly smaller than the overall collector area.

Controller
This is the brain of the system. The controller monitors the temperature in the collectors and in the bottom and top of the storage cylinder. When it is warmer in the collectors than the bottom of the storage cylinder the controller turns on the solar pump and pumps the heat round from the collectors to your storage cylinder, where it is stored ready for you to use.

Diffuse Radiation
Indirect sunlight that is scattered from air molecules, dust and water vapor.

Direct Radiation
Solar radiation that comes straight from the sun, casting shadows on a clear day.

Evacuated Tube
See Vacuum Tube.

Expansion Vessel
A large steel drum with a rubber balloon inside. This rubber balloon inflates and deflates with Tyfocor GLS as the solar system warms up and cools down. The expansion vessel is designed to take and thermal expansion and contraction that happens in the solar circuit.

Flat Plate Collector
A solar collection device in which sunlight is converted into heat on a plane surface without the aid of reflecting surfaces to concentrate the rays.

Heat Exchanger
A device, such as a coiled copper tube immersed in a tank of water, that is used to transfer heat from one fluid to another through a separating wall.

Indirect System
The solar circuit is called an indirect system and refers to the heat exchanger inside your storage cylinder. It is the most common form of solar water heating system. The storage cylinder is manufactured with two heat exchangers inside. The highest one is what the hot water from the boiler flows through (the boiler will heat 70% of the cylinder) and the lower heat exchanger is what the solar systems Tyfocor flows through (the solar system will heat 100% of the cylinder). The heat exchanger allows water from the boiler and Tyfocor from the solar circuit to pass through, but not mix with the water in the storage cylinder itself. Thus, in effect, it really consists of three systems that appear to join at the storage cylinder.

Insolation
The total amount of solar radiation direct, diffused and reflected-striking a surface exposed to the sky.

Night Time Cooling
The cooling of a building or heat storage device by the radiation of excess heat into the night sky.

Pressure Gauge
Informs the user about the current pressure in ‘bar’ in the solar circuit. The black hand will point to the systems pressure. This gauge will normally read 1-1.5 bar. It can read as high as 6 bar. It should never read 0. If it does turn off the solar system and call Green Systems UK.

PRV
Pressure Relief Valve. This is a safety valve that will only open up and release liquid if the pressure in the system becomes to great and reaches 6 bar.

Pump
The solar pump is usually located in your airing cupboard or in the loft space. It is a different pump to your central heating pump. The solar pump will only work when there is heat to be transferred from the collectors to the cylinder.

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.

Retrofitting
The application of a solar heating or cooling system to an existing building.

Scale Inhibitor
Fitted inline to the storage cylinder. This inhibits scale formation in the cylinder increasing life expectancy and efficiency of the product.

Selective Coating or Surface
This is where the science is in new solar collectors and makes them much more efficient than solar collectors of years gone by. The selective coating is a special paint that absorbs solar radiation and doesn’t let much reflect out again. It absorbs radiation of one wavelength (for example, sunlight) but emits little radiation of another wavelength (for example, infrared). This way most of the radiation that falls onto the collector is turned into heat.

Solar Radiation (Solar Energy)
Electromagnetic radiation emitted by the sun.

Standby Heat Loss
Heat lost though storage tank and piping walls.

Storage Cylinder
This is where all the heat collected during the day is kept. The storage cylinder is usually sited where your old cylinder was. Warm water is stored here for you to use when washing or bathing.

Tilt Angle
The angle that a flat plate collector surface forms with the horizontal plane.

TMV
Thermostatic Mixing Valve. This valve located in you airing cupboard near the storage cylinder will mix cold water with the hot water coming out of the cylinder. This will reduce the risk of scalding and allow the solar to store temperatures of 85 degrees C in the cylinder. You can change the temperature of the hot water coming out of you cylinder by rotating the knob on top of the TMV.

Tyfocor GLS
Tyfocor GLS is a solar anti-freeze that flows through the pipes on the solar circuit. It is designed to protect down to –28 degrees C. It can also withstand very high temperatures that occur in solar thermal systems without degrading. Tyfocor GLS is not a harmful product.

Vacuum Tube
Vaccum tubes are solar collectors with the absorber surface coating sealed inside a vacuum. Collectors that are produced like this have better insulation and produce more energy per m2 of aperture area compared to flat plate collectors.

BIOMASS GLOSSARY

Bioenergy
Useful, renewable energy produced from organic matter. The conversion of the complex carbohydrates in organic matter to energy. Organic matter may either be used directly as a fuel or processed into liquids and gases.

Biofuel
See biomass fuel.

Biogas
A combustible gas derived from decomposing biological waste under anaerobic conditions. Biogas normally consists of 50 to 60 percent methane.

Biomass
Organic matter available on a renewable basis. Biomass includes forest and mill residues, agricultural crops and wastes, wood and wood wastes, animal wastes, livestock operation residues, aquatic plants, fast-growing trees and plants, and municipal and industrial wastes. We only deal with appliances that burn wood pellets, wood chips, logs and grain

Biomass fuel
Liquid, solid, or gaseous fuel produced by conversion of biomass. Examples include bioethanol from corn, charcoal or woodchips and biogas from decomposition of wastes.

Biomass energy
See Bioenergy.

British thermal unit - Btu
A non-metric unit of heat, still widely used by engineers. One Btu is the heat energy needed to raise the temperature of one pound of water from 60°F to 61°F at one atmosphere pressure. 1 Btu = 1055 joules (1.055 kJ).

Capacity
The maximum power that a machine or system can produce or carry safely. The maximum instantaneous output of a resource under specified conditions. The capacity of generating equipment is generally expressed in kilowatts or megawatts.

Char
The remains of solid biomass that has been incompletely combusted, such as charcoal if wood is incompletely burned.

Chips
Woody material cut into short, thin wafers. Chips are used as a raw material for gardens, fibreboard or as biomass fuel.

Conifer
Tree, usually evergreen, with cones and needle-shaped or scale like leaves, producing wood known commercially as softwood.

Combustion
Burning. The transformation of biomass fuel into heat, chemicals, and gases through chemical combination of hydrogen and carbon in the fuel with oxygen in the air.

Combustion air
The air fed to a fire to provide oxygen for combustion of fuel.

Combustion efficiency
(actual heat produced by combustion) divided by (total heat potential of the fuel consumed)

Emissions
Waste substances released into the air or water.

Energy crops
Crops grown specifically for their fuel value. These include food crops such as corn, and non-food crops such as poplar trees and switchgrass. Currently, two energy crops are under development: short-rotation woody crops, which are fast-growing hardwood trees harvested in 5 to 8 years, and herbaceous energy crops, such as perennial grasses, which are harvested annually after taking 2 to 3 years to reach full productivity.

Fossil fuel
Solid, liquid, or gaseous fuels formed in the ground after millions of years by chemical and physical changes in plant and animal residues under high temperature and pressure. Oil, natural gas, and coal are fossil fuels.

Gigawatt - GW
A measure of electrical power equal to one billion watts (1,000,000 kW). A large coal or nuclear power station typically has a capacity of about 1 GW.

Greenhouse Effect
The effect of certain gases in the Earth's atmosphere in trapping heat from the sun.

Greenhouse Gases
Gases that trap the heat of the sun in the Earth's atmosphere, producing the greenhouse effect. The two major greenhouse gases are water vapour and carbon dioxide. Other greenhouse gases include methane, ozone, chlorofluorocarbons, and nitrous oxide.

Hardwoods
Usually broad-leaved and deciduous trees.

Herbaceous
Non-woody type of vegetation, usually lacking permanent strong stems, such as grasses, cereals and rape.

HETAS
HETAS is the official body recognised by government to approve solid fuel domestic heating appliances, fuels and services. Its work in approving products covers boilers, cookers, open fires and stoves and roomheaters.

HETAS collaborates with the National Association of Chimney Sweeps (NACS) in supervising a solid fuel orientated course for chimney sweeps which results in successful candidates being 'HETAS Approved'.

In association with the Solid Fuel Association (SFA), HETAS operates a registration scheme for heating engineers with special skills in the installation and maintenance of solid fuel and biomass heating systems.

HETAS represents the industry with government in matters such as Building Regulations and in the setting of standards both in the UK and Europe where its staff manage and chair committees drafting new British and European Standards. Its 'three tick' logo is the approval mark to be looked for in solid fuel domestic heating products and services.

Hopper
Storage container for wood pellets or chips usually sited next to the boiler. This container is usually filled by hand and would typically need weekly filling for pellets. Or every other day with wood chips.

Hydrocarbon
Any chemical compound containing hydrogen, oxygen, and carbon.

Joule
Metric unit of energy, equivalent to the work done by a force of one Newton applied over a distance of one meter (= 1 kg m2/s2). One joule (J) = 0.239 calories (1 calorie = 4.187 J).

Kilowatt - kW
A measure of electrical power equal to 1,000 watts. 1 kW = 3,413 Btu/hr = 1.341 horsepower. See also watt..

Kilowatt hour - kWh
A measure of energy equivalent to the expenditure of one kilowatt for one hour. For example, 1 kWh will light a 100-watt light bulb for 10 hours. 1 kWh = 3,413 Btu.

Megawatt - MW
A measure of electrical power equal to one million watts (1,000 kW). See also watt.

Moisture content - MC
The weight of the water contained in wood, usually expressed as a percentage of weight, either oven-dry or as received.

Moisture content, dry basis
Moisture content expressed as a percentage of the weight of oven-dry wood, i.e.:

[(weight of wet sample - weight of dry sample) / weight of dry sample ] x 100

Moisture content, wet basis
Moisture content expressed as a percentage of the weight of wood as-received, i.e.:

[(weight of wet sample - weight of dry sample) / weight of wet sample ] x 100

Monoculture
The cultivation of a single species crop.

Organic Compounds
Chemical compounds based on carbon chains or rings and also containing hydrogen, with or without oxygen, nitrogen, and other elements.

Silo
A large store for wood fuel deliveries. Usually stores wood pellets in 3 to 5 tonnes deliveries for domestic installations. Sizes would be larger for wood chips.

Sustainable
An ecosystem condition in which biodiversity, renewability, and resource productivity are maintained over time.

Tonne
One metric tonne (tonne) = 1,000 kilograms (2,205 pounds)

Watt
One Watt = 3.413 Btu/hr. See also kilowatt.

"You might not see things yet on the surface, but underground, it's already on fire." Indonesian writer Y.B. Mangunwijaya