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Glossary

Photovoltaics

Alternating Current (AC): n. An electric current that reverses its direction many times a second at regular intervals, typically used in power supplies. Compare with direct current.

Array: n. Any number of photovoltaic modules connected together to provide a single electrical output at a specified voltage. Arrays are often designed to produce significant amounts of electricity.

Autonomous System: n. A stand-alone photovoltaic system that has no back-up generating source. May or may not include storage batteries.

Base Power: n. Power generated by a utility unit that operates at a very high capacity factor.

Battery: n. Two or more “cells” electrically connected for storing electrical energy. Common usage permits this designation to be applied also to a single cell used independently, as in a flashlight battery.

Battery Capacity: n. The total number of ampere-hours that can be withdrawn from a fully charged cell or battery.

Battery Cell: n. A galvanic cell for storage of electrical energy. This cell, after being discharged, may be restored to a fully charged condition by an electric current.

Battery Cycle Life: n. 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.

Building Integrated Photovoltaics: n. A term for the design and integration of photovoltaics (PV) into the building envelope, typically replacing conventional building materials.

Boron: n. Used as a doping chemical for making semiconductor layers in a solar cell, Boron is the chemical element of atomic number 5, a nonmetallic solid. (Symbol: B) Boron is usually prepared as an amorphous brown powder, but when very pure it forms hard, shiny, black crystals with semiconducting properties.

British Thermal Unit (BTU): n. The amount of heat energy required to raise the temperature of one pound of water 1 degree Fahrenheit at one atmosphere pressure. Roughly equivalent to the amount of energy released by burning one stick match, which is approximately 1055 Joules.

Combined Collector: n. A photovoltaic device or module that provides useful heat energy in addition to electricity.

Concentrator: n. A PV module that uses optical elements to increase the amount of incident sunlight on a PV cell. Concentrating arrays must track the sun and use only direct sunlight because the diffuse portion cannot be focused onto the PV cells.

Conversion Efficiency: n. The ratio of electric energy produced by a photovoltaic device (under full sun conditions) to the energy from sunlight incident upon the cell.

Current: n. The flow of electric charge in the conductor between two points having a difference in potential (voltage)

Diode n. Electronic component that allows current flow in one direction only.

Direct Current (DC): Electric current in which electrons flow in one direction only. Opposite of alternating current.

Efficiency: n. The ratio of output power to input power. Expressed as a percentage.

Energy Audit: n. A survey that shows how much energy you use in your house, apartment, or business. It can indicate your most intensive energy consuming appliances and even identify heating and cooling leaks that will help you find ways to use less energy.

Energy Density: n. The ratio of energy available from a a battery to its volume or mass.

Energy Pay Back Time: n. The time required for any energy producing system or device to produce as much energy as was required in its manufacture.

Fill Factor: n. The ratio of a photovoltaic cell’s actual power to its power if both current and voltage were at their maximum.  A key characteristic in evaluating cell performance.

Flat-plate PV: n. Refers to a photovoltaic array or module that consists of non-concentrating elements. Flat-plate arrays and modules use direct and diffuse sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun-angles in relation the the array.

Gel-type Battery: n. Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

Gigawatt: n. One billion watts. One million kilowatts. One thousand megawatts.

Grid-connected: n. A photovoltaic system in which the PV array acts like a central generating plant, supplying power to the grid. Also known as grid-interactive

Hybrid System: n. A photovoltaic system that includes other sources of electricity generation, such as wind or fossil fuel generators.

Incident Light: n. Light that shines onto the surface of a solar cell or module.

Insolation: n. Sunlight, direct or diffuse; from ‘incident solar radiation.’ Usually expressed in watts per square meter. Not to be confused with ‘insulation.’

Insulation: n. Materials that reduce the rate or slow down the movement of heat.

Interconnect: n. A conductor within a module or other means of connection which provides an electrical interconnection between the solar cells.

Inverter: n. Devices that convert DC electricity into AC electricity (single or multiphase), either for stand-alone systems (not connected to the grid) or for utility-interactive systems.

I-V Curve: n. A graphical presentation of the current versus the voltage from a photovoltaic device as the load is increased from the short circuit (no load) condition to the open circuit (maximum voltage) condition. Typically measured at 1000 watts per square meter of solar insolation at a specific cell temperature. The shape of the curve characterizes cell performance.

Junction Box: n. An electrical box designed to be a safe enclosure in which to make proper electrical connections. On PB modules this is where PV strings are electrically connected.

Kilowatt (kW): n. 1000 watts.

Kilowatt-hour (kWh): n. One thousand watt hours. The kWh is a unit of energy. 1 kWh=3600kJ.

Life Cycle Cost n. An estimate of the cost of owning and operating a system for the period of its useful life; usually expressed in terms of the present value of all lifetime costs.

Line-communicated Inverter: n. An inverter that is tied to a power grid or line. The communication of power (conversion from DC to AC) is controlled by the power line, so that, if there is a failure in the power grid, the PV system cannot feed power into the line.

Maximum Power Point (MPP) n. The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For typical silicon cell, this is about 0.45 V.

Maximum Power Point Tracker (MPPT): n. Mean of a power conditioning unit that automatically operates the PV generator at its MPP under all conditions.

Megawatt: n. 1 Million watts; 1000 kilowatts.

Nominal Operating Cell Temperature (NOTC): n. The reference cell (module) operating temperature presented on manufacturer’s literature. Generally the NOCT is referenced as 27 degrees Celsius, or 77 degrees Fahrenheit.

Nominal Voltage n. A referent voltage used to describe batteries, modules, or systems.

Non-renewable Fuels n. Fuels that cannot be easily made or “renewed.” We can use up nonrenewable fuels. Oil, natural gas, and coal are nonrenewable fuels.

Ohm: n.The unit of resistance to the flow of an electric current.

One-axis Tracking n. A system capable of rotating about one axis, also referred to as single axis. These tracking systems usually follow the sun form east to west throughout the day.

Open Circuit Voltage (Voc): n. The maximum possible voltage across the cell in sunlight when no current is flowing.

Parallel Connection: n. A way of joining two or more electricity-producing devices such as PV cells or modules, or batteries by connecting positive leads together and negative leads together; such a configuration increases the current but the voltage is constant.

Passive Solar Building n. A building that utilizes non-mechanical. non-electrical methods for heating, cooling, and/or lighting.

Peak Load; Peak Demand: n. The maximum load, or usage, of electrical power occurring in a given period of time, typically a day.

Peak Power n. Power generated by a utility unit that operates at a very low capacity factor; generally used to meet short=lived and variable high demand periods.

Peak Sun Hours: n. The equivalent number of hours per day when solar irradiance averages 1000 w/m^2 (full sun).

Phosphorus: n. A chemical element, atomic number 15, used as a doping agent in making n0n-semiconductor layers.

Photon: n. A particle of light that acts as an individual unit of energy.

Photovoltaic n. PV, pertaining to the direct conversion of photons of sunlight into electricity.

Photovoltaic Array: n. An interconnected system of PV modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

Photovoltaic Cell: n. The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (DC voltage and current).

Photovoltaic Conversion Efficiency: n. The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

Photovoltaic Module n. The smallest environmentally protected, essentially planar assembly of solar cells and ancillary parts, such as interconnections, terminals, and protective devices such as diodes intended to generate DC power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstate) or the back layer (substrate).

Photovoltaic Panel: n. Often used interchangeably with PV module (esp in one-module systems), but more accurately used to refer to a collection of physically and electrically connected solar cells.

Photovoltaic Peak Watt: n. Maximum “rated” output of a cell, module, or system. Typical rating conditions are 0.645 watts per square inch of sunlight, 68 degrees F ambient air temperature and 6.2×10^-3 mi/s wind speed.

 

Wind

Airfoil:  The shape of the blade cross-section, which for most modern horizontal axis wind turbines, is designed to enhance the lift and improve turbine performance.

Ampere-hour: A unit for the quantity of electricity obtained by integrating current flow in amperes over the time in hours for its flow; used as a measure of battery capacity.

Anemometer: A device used to measure the wind speed.

Average wind speed: The mean wind speed over a specified period of time.

Blades: The aerodynamic surface that catches the wind.

Brake: Various systems used to stop the rotor from turning.

Converter: A device that converts a AC electrical power to DC.

Cut-in wind speed: The wind speed at which a wind turbine begins to generate electricity.

Cut-out wind speed: The wind speed at which a wind turbine ceases to generate electricity.

Density: Mass per unit of volume.

Downwind: On the opposite side from the direction from which the wind is blowing.

Furling: A passive protection for the turbine where typically the rotor folds either up or around the tail vane.

Grid: The utility distribution system. The network that connects electricity generators to electricity users.

HAWT: Horizontal axis wind turbine.

Inverter: A device that converts direct current (DC) to alternating current (AC).

KW: Kilowatt, a measure of power for electrical current (1000 watts).

KWh: Kilowatt-hour, a measure of energy equal to the use of one kilowatt in one hour.

MW: Megawatt, a measure of power (1,000,000 watts).

Nacelle: The body of a propeller-type wind turbine, containing the gearbox, generator, blade hub, and other parts.

O&M Costs: Operation and maintenance costs.

Power Coefficient: The ratio of the power extracted by a wind turbine to the power available in the wind stream.

Power Curve: A chart showing a wind turbine’s power output across a range of wind speeds.

PUC: Public Utility Commission, a state agency which regulates utilities. In some areas known as Public Service Commission (PSC).

PURPA: Public Utility Regulatory Policies Act (1978), 16 U.S.C. § 2601.18 CFR §292 that refers to small generator utility connection rules.

Rated Output Capacity: The output power of a wind machine operating at the rated wind speed.

Rated wind speed: The lowest wind speed at which the rated output power of a wind turbine is produced.

Rotor: The rotating part of a wind turbine, including either the blades and blade assembly or the rotating portion of a generator.

Rotor diameter: The diameter of the circle swept by the rotor.

Rotor speed: The revolutions per minute of the wind turbine rotor.

Start-up wind speed: The wind speed at which a wind turbine rotor will begin to spin. See also cut-in wind speed.

Swept area: The area swept by the turbine rotor, A = pi R 2 , where R is the radius of the rotor.

Tip speed ratio: The speed at the tip of the rotor blade as it moves through the air divided by the wind velocity. This is typically a design requirement for the turbine.

Turbulence: The changes in wind speed and direction, frequently caused by obstacles.

Upwind: On the same side as the direction from which the wind is blowing—windward.

VAWT: Vertical axis wind turbine.

Wind farm: A group of wind turbines, often owned and maintained by one company. Also known as a wind power plant.

Yaw: The movement of the tower top turbine that allows the turbine to stay into the wind.

Source: U.S. Department of Energy

 

Solar Thermal

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: Area on the solar panel that collects energy. When solar collectors are tested the energy collected is measured against the aperture area. When comparing collectors a reference area is important – that is, the surface area from which 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 does not 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 can produce more energy per meter squared of aperture area compared to flat plate collectors. This does vary on the brand used, some vacuum tubes do not produce as much energy as flat plates.

“Only after the last tree has been cut down, the last river poisoned, the last fish caught. You will find that money cannot be eaten.” Cree Prophecy

Source: http://greensystemsuk.com/glossaries/solar-thermal-glossary/

 

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