Friday, September 18, 2009

Solar Knowledge: Glossary of Solar Terms

If you have any additional terms, or would like to suggest a change, please contact me!


ABSORBER
The absorber is that part of a solar thermal collector that receives the incident radiant energy and transforms it into heat energy.

ACTIVE SOLAR THERMAL SYSTEM
A system that traps the sun's energy with solar collectors and uses an electromechanical subsystem to move that energy to its point of intended use for water heating, space heating, pool heating, industrial process heat, electrical generation and space cooling.

ALTERNATING CURRENT (AC)
An electrical current in which the direction of electron flow reverses periodically, usually many times per second. Most U.S. household electrical systems use AC current rated at 120 volts and 60 cycles per second.

ALTERNATOR
An mechanical device that generates alternating current electricity.

ALTITUDE ANGLE
The angle of the sun above the horizon, measured in degrees. In winter, the sun is at a low solar altitude, and in the summer, the sun is at a high solar altitude.

AMMETER
A device used for measuring the current (amperage) at any point in an electrical circuit.

AMORPHOUS SILICON
A thin-film PV silicon cell having no crystalline structure.

AMPACITY
Refers to the highest safe amount of electrical current through conductors, overcurrent devices, or other electrical equipment. Ampacity is determined by the cross-sectional area and the material of the conductor, or the manufacturer’s equipment rating.

AMPERE (AMP; A, I)
The rate of flow of electrical charge. Unit of electrical current. One volt across one ohm of resistance causes a current of one ampere. One ampere is equal to 6.235 x 10^18 electrons (one coulomb) per second passing a given point in a circuit.

AMPERE-HOUR (AMP-HOUR; AH)
A measure of electron flow over time, used to measure battery capacity and state of charge. For example, a current of 1 amp drawn from a battery for 10 hours would result in 10 amp-hours of charge cycling through the battery.

AMPERE-HOUR METER
An instrument that monitors electron flow over time. Amp-hours are the product of electron flow (in amperes) and time (in hours).

AMPLITUDE
Generally refers to the maximum and minimum voltage attained by an alternating or pulsed current in each complete cycle or pulse of that current.

ANGLE OF INCIDENCE
The angle between the sun’s rays and a line perpendicular to the active surface of a solar module or collector, in degrees.

ANGLE OF INCLINATION
The angle that a solar collector or PV module is positioned above horizontal.

ANODE
( Battery ) The electrode within a battery cell that undergoes the chemical process of oxidation. Electrically, the anode is the cell's positive terminal.

(Water heater) An aluminum or magnesium sacrificial rod installed within steel tanks that is used to help prevent corrosion of the tank itself.

ARRAY
Any number of photovoltaic modules connected together electrically to provide a single electrical output.

AWG
American Wire Gauge, a set of standards in the U.S. specifying the diameter of wire. A higher number indicates smaller wire.

AZIMUTH
The angle between true south and a point on the horizon, measured in degrees east or west of true south.

BALANCE OF SYSTEMS (BOS)
Parts or components of a photovoltaic system other than the photovoltaic array or other generating equipment.

BALLAST
A circuit used to condition and stabilize an electric current, for example, in a fluorescent light.

BATCH SOLAR HOT WATER HEATER
The simplest of solar hot water systems. A tank of water within a glass-covered insulated enclosure aimed at the sun. Water is heated in the tank and then flows to the load or an auxiliary water heater.

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

BATTERY 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, state of charge, age, and cutoff voltage.

BATTERY CELL
The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, a container for all the above, and posts or other terminals for electrical connection.

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. With lead-acid batteries, end-of-life is generally considered when a fully charged cell can deliver only 80 percent of its rated capacity. Beyond this state of aging, deterioration and loss of capacity begins to accelerate rapidly. Life may be measured in cycles or years, depending on the type of service for which the cell or battery is intended.

BETZ LIMIT
The theoretical maximum energy that a wind generator can extract from the wind—59.6 percent.

BIOMASS
Any organic matter available on a renewable basis, including agricultural crops, wastes, and residues; wood, wood wastes, and residues; animal wastes and municipal wastes; and aquatic plants.

BIOFUELS (BIOMASS FUELS)
Biomass converted directly to energy or converted to liquid or gaseous fuels, such as ethanol methane, and hydrogen.

BLADE
The energy-capturing, aerodynamically designed part of a wind turbine, which interacts directly with the wind.

BLOCKING DIODE
A semiconductor connected in series with a solar-electric cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

BRAKE
Device for stopping a wind turbine. This can be an electric brake that shorts the output of the turbine (dynamic braking), or a mechanical brake that physically stops the rotation, as with a brake drum and shoe.

BREAKER
A manually operable switching device that also automatically opens a circuit in the event of overcurrent.

BRITISH THERMAL UNIT (BTU)
The amount of heat required to raise the temperature of one pound (one pint) of water, one degree Fahrenheit. 1 watt-hour = 3.413 BTU.

BULK CHARGE
The initial phase of battery charging, when the largest amount of energy is put into the battery.

BUSS
An electrical connection component that can accept multiple cables or wires. Also bus, bus bar, or busbar

BYPASS DIODE
A semiconductor device connected in parallel with a series block of parallel PV strings to prevent current from flowing back through any shaded or failed modules in the same block.

CAPACITANCE
An electrical effect in AC circuits that results in amperage peaking before voltage.

CATHODE
The electrode within a battery cell that undergoes the chemical process of reduction. Electrically, the cathode is the negative terminal of the cell.

CATHODIC PROTECTION
Systems that protect metal from corrosion by running small electrical currents along the metal. Most often used to protect well heads, and oil, gas, and water pipelines.

CELL (battery)
A single unit of an electro-chemical device capable of producing an electrical current by converting chemical energy into electrical energy. The cell is the basic unit used to store energy in the battery. The cell contains an anode, a cathode, and the electrolyte. 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 CONTROLLER
A component of photovoltaic systems that controls the charging of the battery to protect the batteries from overcharge and overdischarge. The charge controller may also indicate the system operational status. Standard charge controllers vary the current (A) based on preset voltage set points.

CHARGE RATE
The current applied to a cell or battery to restore its available capacity, specified in relation to total battery size. A C/20 rate is a charge rate that is 1/20th of the total battery capacity. Also called a “20-hour rate.”

CIRCUIT
A group of electrical components that make a complete electrical path, providing some function.

CIRCUIT BREAKER
See BREAKER.

CLOSED LOOP SYSTEM
A solar hot water system of which no part is vented to the atmosphere or fed with fresh liquid. The system liquid, usually some form of antifreeze solution, is recirculated. Closed loop solar systems are also known as glycol systems and indirect systems.

COB CONSTRUCTION
A traditional building technique using hand formed lumps of earth mixed with sand and straw.

COLLECTOR LOOP
The plumbing loop in a solar hot water system that includes the solar collectors. The collectors heat the fluid in the collector, and the heated fluid can be used directly (if water) or the heat can be exchanged to a potable water loop.

COMBINER BOX
A box where wires from individual PV modules or strings are combined into larger wires to run to the battery bank. Can also contain overcurrent protection devices.

COMPACT FLUORESCENT LIGHT (CFL)
A smaller version of standard fluorescent lamps that can directly replace incandescent lights. CFLs use 65 to 80 percent less energy, while producing the same lumens.

CONCENTRATOR
A photovoltaic module that includes optical components, such as lenses, to direct and concentrate sunlight onto a solar cell of smaller area. Most concentrator arrays must directly face or track the sun.

CONDUCTION
Heat transfer from a hot object to a colder object through direct contact.

CONDUCTOR
A material with relatively low resistance through which electricity will readily flow—wires, cables, busbars. The most common conductors are copper and aluminum.

CONDUIT
Metal or plastic tubing designed to protect electrical conductors.

CONTINUOUS OUTPUT RATING
The maximum amount of power an inverter may deliver to a load (or loads) for a sustained period of time.

CONVECTION
  • Heat transfer by the movement of fluid (usually air or water).
  • Heat transfer through either the natural or forced movement of air.

  • CONVERTER
    An electronic device for DC power that steps up voltage and steps down current proportionally (or vice-versa).

    CRYSTALLINE SILICON
    A type of PV cell made from a single crystal or polycrystalline slice of silicon.

    CURRENT
    Flow rate of electrons. See AMPERE.

    CUTOFF VOLTAGE
    Electrical equipment setting for the voltage level at which a battery is considered to be empty, and the discharge process is terminated. Most commonly found in inverters and charge controllers that include a feature for low voltage disconnection.

    CYCLE
  • One complete charge/discharge cycle of a battery.
  • An AC sine wave’s movement from zero to maximum positive, through zero, to maximum negative, and back to zero.
  • CYCLE LIFE
    Cycle life is the number of cycles a cell or battery will undergo before being considered “worn out.” This point is usually defined as when the battery’s capacity has decreased to 80 percent of its initial rated capacity.

    DAYLIGHTING
    The placement of windows and skylights to provide natural interior lighting and to reduce daytime electrical demand.

    DAYS OF AUTONOMY
    The number of consecutive days that a stand-alone renewable energy system will meet a defined load without additional energy input.

    DC
    Direct current. A one-way flow of electrons. Typical sources of direct current are solar-electric cells, rectifiers, and direct current generators. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to AC (alternating current).

    DC MOTOR, BRUSHLESS
    High-technology motor used in centrifugal-type DC submersible pumps and other applications. The motor is filled with oil to keep water out. An electronic system is used to precisely alternate the current, causing the motor to spin.

    DC MOTOR, BRUSH-TYPE
    The traditional DC motor, in which small carbon blocks called “brushes” conduct current into the spinning portion of the motor. They are used in many applications, including DC surface pumps and also in DC submersible diaphragm pumps. Brushes naturally wear down after years of use, and may be replaced.

    DC MOTOR, PERMANENT MAGNET
    A variable speed motor that uses permanent magnets instead of wound coils. Reduced voltage (in low sun) produces proportionally reduced speed, and causes no harm to the motor.

    DEEP-CYCLE BATTERY
    A battery designed to regularly discharge 50 to 80 percent of its capacity before recharging.

    DEGREE DAY
    A quantitative index reflecting demand for energy to heat or cool buildings. Heating and cooling degree days show the difference between the mean daily temperature and a 65°F base. The higher the heating degree days at any location, the colder the winter. The higher the cooling degree days at any location, the hotter the summer.

    DELTA T
    Difference in temperature.

    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-hour rated cell results in a 25 percent depth of discharge. Depth of discharge is the opposite of state of charge (SOC).

    DHW
    Domestic hot water: refers to any system that provides hot water for household use.

    DIFFERENTIAL CONTROLLER
    An electronic switch that turns off or on based on the difference between two temperatures. In a solar hot water system, the controller measures the temperature at the collector and compares it to the water temperature in a storage tank to turn the pump on or off.

    DIGITAL MULTIMETER (DMM)
    A device with multiple electrical measurement capabilities, such as voltage, amperage, resistance, etc., commonly usable for both AC and DC circuits. It has a digital display.

    DIODE
    A semiconductor device that allows electrical current in only one direction.

    DIRECT CURRENT (DC)
    An electrical current that moves in one direction only.

    DIRECT GAIN
    In passive solar heating, a direct gain system relies on the sunshine to directly hit the substance or mass being heated. Direct gain systems used today usually rely on a layer(s) of glass to assist in holding the heat within a space where the heat is desirable.

    DISCHARGE RATE
    The rate at which energy is being drained from a battery.

    DISCONNECT
    Switch gear used to connect or disconnect components in a system.

    DOWNWIND
    In relation to a wind turbine, the direction away from the source of wind. A downwind turbine has its blades on the downwind side of the tower.

    DRAFT TUBE
    A tube added to the outfall of a hydro turbine to increase energy production by taking advantage of the drop in the tailrace.

    DRAINBACK SYSTEM
    A solar hot water system that only fills the collector when the temperature differential is appropriate. The water that is circulated through the collectors is stored in a reservoir. Draining the collectors provides freeze protection.

    DRAINDOWN SYSTEM
    A solar hot water system that uses a special draindown valve that redirects the collector fluid and drains it down when the collector system pump is not operating. These systems have been prone to failure and are not recommended.

    DUTY CYCLE
    The fraction of time a device or load actually uses energy in a unit of time. For example, a load that uses energy for 5 seconds out of every 10 seconds has a 50 percent duty cycle.

    EARTH
    Synonymous with “ground.”

    EFFICIENCY (PV modules)
    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. A solar cell that converts 1/10 of the sun's energy that strikes its surface to electricity has an efficiency of 10 percent.

    EFFICIENCY
    The effectiveness of a device to convert energy from one form to another, or to transfer energy from one body to another. An electric pump that is 60 percent efficient converts 60 percent of the input energy into work—pumping water. The remaining 40 percent becomes waste heat.

    ELECTRICAL POTENTIAL
    Same as VOLTAGE.

    ELECTRIC CURRENT
    The rate at which electrons flow through an electrical conductor, usually measured in amperes (amps).

    ELECTRICITY
    Energy flow resulting from the flow of charged particles, such as electrons or ions.

    ELECTROLYSIS
    The breaking down of a chemical compound into simpler compounds or elements by the passage of electricity through the chemical compound. Commonly used to describe the extraction of hydrogen (and oxygen) from water.

    ELECTROLYTE
    The fluid in a battery, which is the medium of ion transport within an electrochemical cell. It provides a path for electron transfer between the anode and cathode of a battery cell.

    ELECTROMAGNETIC RADIATION (EMR)
    Magnetic radiation produced by a changing electrical current, such as alternating current (AC).

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

    EMBODIED ENERGY
    The energy consumed by all of the processes associated with the production of a material. This includes the energy required in mining, transport, manufacturing, administration, use, disposal, etc.

    ENERGY
    The amount of work that a system or entity can do (potential energy) or is doing (kinetic energy), measured in joules. The product of power and time, measured in watt-hours. 1,000 watt-hours = 1 kilowatt-hour (KWH).

    ENERGY DENSITY
    A ratio of a battery or cell's capacity to either its volume or weight. Volumetric energy density is expressed in watt-hours per cubic inch. Weight energy density is expressed in watt-hours per pound.

    ENGINE
    A machine that converts energy into mechanical force or motion. Sources of energy include heat, chemical reaction, potential energy of elevated water, etc.

    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 percent state-of-charge.

    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.

    EQUINOX (SPRING & FALL)
    The time when the sun crosses the plane of the earth's equator, making night and day of equal length all over the earth, occurring about March 21st and September 21st.

    EVAPORATION
    The process of a liquid changing its state into a gas when heat is added. In the most common occurrence on earth, water evaporation requires 970 BTUs per pound (pint).

    FEATHERING
    In wind generators, this refers to an adjustment of the blades so that they catch less wind. This can prevent damage to the machine in high winds.

    FINISH CHARGE
    The final stage of battery charging, when the battery is charged at a slow rate over a long period of time.

    FLAGGING
    Noticeable deformation of trees from prevailing winds. Flagging is an indication of an effective wind site. Lack of flagging is not necessarily an indication of a poor wind site.

    FLAT PLATE COLLECTOR
    A solar thermal collector that converts the sun’s radiation into heat on a flat surface. Does not use reflecting surfaces or lens arrangements to concentrate the sun’s energy.

    FLOAT CHARGE
    A trickle charge to keep a battery fully charged at a safe voltage level with minimal gassing.

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

    FLOW
    In hydro-electric terms, flow refers to the quantity of water supplied to a water source or exiting a nozzle per unit of time. Commonly measured in gallons per minute.

    FLUORESCENT LIGHT
    An electric lamp coated on its inner surface with phosphor and containing mercury vapor. When bombarded with electrons, the vapor emits ultraviolet light that causes the phosphor to emit visible light.

    FRANCIS TURBINE
    A type of reaction hydro-turbine used in low to medium heads. It consists of fixed vanes on a shaft. Water flows down through the vanes and out sideways.

    FREESTANDING TOWER
    A wind generator tower with no guy wires. This can be either a lattice tower or a monopole. Freestanding towers are the most expensive type of tower, requiring large excavations and large amounts of concrete.

    FRICTION LOSS
    Lost energy due to friction.

  • In hydro systems, pipe sized too small can lead to serious friction losses.
  • In any belt drive system, there will be some losses due to friction.
  • FULL SUN
    The full sun condition is the amount of power density received at the surface of the earth at noon on a clear day—about 1 KW per m^2, or 1 Sun. Lower levels of sunlight are often expressed as 0.5 sun or 0.1 sun.

    FURLING
    Reducing a wind generator’s swept area to protect it from high winds. Common furling methods are to tilt the rotor (blades) up or sideways out of the wind, or to feather (twist) the blades to degrade the airfoil.

    FUSE
    An electrical device that is designed to break a circuit by melting an internal conductor when the current in the circuit exceeds the maximum considered safe for the conductors or devices in the circuit.

    GASSING
    The production of hydrogen and oxygen gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from the electrolysis of water in the electrolyte during charging.

    GENERATOR
    A device that converts mechanical energy into electrical energy.

    GEOTHERMAL HEAT PUMP
    A type of heat pump that uses the ground, ground water, or ponds as a heat source and heat sink, rather than outside air. Compare to HEAT PUMP.

    GIN POLE
    Either of two different types of devices used with wind generator towers. With a tilt-up tower, it describes the lever that helps tilt the tower up. With a fixed tower, it describes a temporary crane used to raise tower sections or the wind generator.

    GLYCOL (Propylene Glycol)
    An antifreeze, heat transfer fluid that is circulated through closed loop solar hot water collectors.

    GOVERNOR
    A device that limits the output of another device, such as a wind generator.

    GOVERNING
    Limiting the output of a device. In respect to small wind generators, governing normally happens through furling.

    GRID
    Transmission line network used to distribute electrical energy, generally by a commercial power utility.

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

    GRID-TIE SYSTEM
    A renewable energy system that is connected to the utility grid, selling excess energy back to the utility. Also called a utility-interactive system.

    GROUND
    The connection of electrical components to the earth and/or each other for the purposes of dissipating static charge or protecting against a short circuit or lightning.

    GROUND FAULT
    Unwanted current path to ground.

    GROUND MOUNT
    A photovoltaic (PV) rack designed to be installed on the ground or other flat surface.

    GROUND ROD (ELECTRODE)
    A metal rod (typically 5/8 inch diameter) that is driven into the earth (typically 8 feet deep) and is electrically connected to the negative conductor and/or any metal parts, wiring enclosures, or conduit of an electrical circuit.

    GUY WIRES
    Steel cables that support a tower.

    HEAD
    The difference in elevation between two parts of a liquid-based system. In hydro power, the difference between a source of water and the location at which the water from that source may be used (synonym: vertical drop). With pumps, the vertical distance the pump must move the water.

    HEADRACE
    A flume or channel that feeds water into a hydro turbine.

    HEAT EXCHANGER
    A device that is used to transfer heat between fluids or gases through an intervening surface.

    HEAT PUMP
    A device typically used for heating and cooling of buildings by drawing from or dissipating into the ambient temperature of air or water. When cooling, a heat pump works like a refrigerator. When heating, it also works like a fridge, except the heat produced is used to heat a space.

    HEAT SINK
    A medium or container to which heat flows. Thermal mass walls and floors in a passive solar home act as a heat sink during the day.

    HEAT TRANSFER
    Heat is transferred from one substance or location to another by three methods—radiation, convection and conduction. The sun's rays are a good example of radiation; warm air rising is heat movement by convection; and touching a hot iron or frying pan with your hand is heat transfer by conduction.

    HERTZ (Hz)
    Cycles per second. Generally refers to the number of complete cycles of the AC sine wave per second, or the frequency at which a radio or computer processor works.

    HYDRO-ELECTRICITY
    Any electricity that is generated by the flow of water.

    HYDROGEN FUEL CELL
    A device that converts hydrogen to DC electricity.

    HYDROMETER
    A hydrometer is an instrument for measuring the density of liquids in relation to the density of water. The hydrometer is used to indicate the state of charge in lead-acid cells by measuring the specific gravity of the electrolyte.

    HYDRONIC HEATING SYSTEM
    A type of heating system where water is heated in a solar collector or boiler, and is pumped to heat exchangers or radiators in rooms. Radiant floor systems have a grid of tubing laid out in the floor for distributing the heat. Temperature of the space is controlled by regulating the flow and/or temperature of the circulating water.

    HORSEPOWER
    A measure of the capacity to generate energy or do work. 1 horsepower = 746 watts.

    HYBRID SYSTEM
    An energy system consisting of two or more generating subsystems, such as the combination of a wind turbine or diesel generator and a photovoltaic system.

    INCANDESCENT LIGHT
    An electric lamp that is evacuated or filled with an inert gas and contains a filament (commonly tungsten). The filament emits visible light when heated to extreme temperatures by electric current through it. Incandescent lightbulbs are one of the most inefficient ways to light a home. They produce a great deal of heat along with the light, and use three to four times as much energy for the same light output as compact fluorescent lightbulbs.

    INDUCTION MOTOR (AC)
    A type of electric motor that requires a high surge to start, and a stable voltage supply, making it a challenge to run using a solar-electric system.

    INSOLATION
    The amount of sunlight reaching an area. Usually expressed in watts per square meter.

    INTAKE
    In a hydro system, the structure that receives the water and feeds it into the penstock (pipeline). Usually incorporates screening or filtering to keep debris and aquatic life out of the system.

    INVERTER
    A device that converts DC electricity (anywhere from 12 to 600 VDC) to AC electricity (typically 120/240 VAC).

    ION
    An electrically charged particle or molecule.

    ISC
    See SHORT CIRCUIT CURRENT.

    IV CURVE
    The graphical representation of the current versus the voltage of a photovoltaic cell, module, or array as the load is increased from zero voltage to maximum voltage, under standard test conditions.

    JACK PUMP
    A submerged pump mechanically activated by a rod extending above the well head to a reciprocating engine, motor or any other rotating device.

    JOULE
    The standard unit of energy (SI). One joule equals one watt-second, and 3600 joules = one watt-hour.

    KILOWATT (KW)
    One thousand watts.

    KILOWATT-HOUR
    One thousand watt-hours. 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 oil contains roughly 1,700 KWH

    One ton of coal contains roughly 7,500 KWH

    One gallon of gasoline contains roughly 37 KWH

    One cubic foot of natural gas contains 0.3 KWH

    One ton of uranium ore contains 164 million KWH

    1.34 horsepower-hours.

    1 KWH = 3,400 BTU. Can be compared to 860 calories (food energy value).

    LATITUDE
    A location's distance north or south of the equator measured in degrees.

    LIGHT EMITTING DIODE (LED)
    A semiconductor device composed of a PN junction designed such that electrons cause visible light during their migration across the junction.

    LIGHTNING ARRESTOR
    Devices that protect electronics from lightning-induced surges by carrying the charge to ground.

    LINE/WIRE LOSS
    The voltage drop or energy loss due to the resistance of wire in an electrical circuit. See VOLTAGE DROP

    LINEAR CURRENT BOOSTER (LCB)
    An electronic circuit that matches PV output directly to a motor by converting unneeded voltage to higher usable current. Used in array-direct water pumping.

    LOAD
    Refers to equipment that is powered by electricity. Usually expressed in terms of amperes or watts. Any device or appliance that uses energy (such as a light or pump).

    LOW-E GLASS
    Glass coated with layers of metal or metal oxide. The coating emits very little radiation in the long-wave (infrared) spectrum, which diminishes heat loss from the building interior, and reduces heat gain in hot weather.

    LUMEN
    A unit of measurement quantifying the amount of light emitted from a light source.

    MAGNETIC DECLINATION
    The number of degrees east or west of true south from magnetic south.

    MAXIMUM POWER POINT
    The point on a PV module’s voltage/amperage curve where the product of current and voltage is a maximum (measured in watts).

    MAXIMUM POWER POINT TRACKING (MPPT)
    Electronically tracking the maximum power point of a PV module to achieve the highest possible output, by (in simplest terms) using surplus voltage to boost amperage.

    MICROHYDRO
    Hydro-electric plants producing more than 100 watts and less than 2,000 watts.

    MODULE
    The smallest nondivisible, self-contained, and environmentally protected physical structure housing interconnected photovoltaic cells and providing a single DC electrical output. Commonly called a “panel.”

    MOTOR
    A device that converts electrical energy into mechanical energy.

    MULTICRYSTALLINE CELL
    See POLYCRYSTALLINE CELL

    NANOHYDRO
    Any hydro plant that produces less than 100 watts.

    NATIONAL ELECTRICAL CODE (NEC)
    A document that describes the legal standards for residential and commercial wiring practices with safety as the prime objective. Many U.S. jurisdictions base their wiring inspections on the NEC.

    NET METERING
    State by state legislation that requires utilities to purchase renewably produced electricity at the same price that they sell it, until a building's monthly or annual energy use is offset.

    NOMINAL VOLTAGE
    A reference voltage used to describe batteries, modules, or systems (for example, a 12 volt or 24 volt battery, module, or system).

    NOSECONE
    The pointed piece farthest toward the wind on a wind generator, designed primarily for cosmetic purposes, but also protects the blade attachment points and generator from the weather.

    OFF-PEAK
    The period of low energy demand, as opposed to maximum or peak demand.

    ON-PEAK
    Energy supplied during periods of relatively high system demands as specified by the utility.

    OHM (Ω)
    The unit that quantifies a material's resistance to electron flow.

    OHM’S LAW
    Basic formula defining the relationship between voltage, amperage, and resistance. Commonly stated as E = I x R, or Voltage = Amperage x Resistance.

    OPEN CIRCUIT
    When an electrical circuit is interrupted by breaking the path at one or more points, stopping the electrons from flowing. A light switch opens an electrical circuit when it turns off the light.

    OPEN CIRCUIT VOLTAGE (VOC)
    The maximum possible voltage across a PV array, module, or cell. The voltage across the terminals of a photovoltaic cell, module, or array with no load applied when the cell is exposed to standard insolation conditions, measured with a voltmeter.

    OPEN LOOP SYSTEM
    A fresh water or "direct" solar hot water system, generally for use in freeze-free climates.

    ORIENTATION
    Placement according to the directions N, S, E, or W.

    OUTGASSING
    The emission of gasses by a material. See also GASSING.

    OVERCURRENT
    Current that exceeds the rated current of the equipment or the ampacity of a conductor, resulting from overload, short circuit, or ground fault.

    OVERCURRENT DEVICE
    A safety fuse or breaker designed to open a circuit when an overcurrent occurs.

    PARALLEL CONNECTION
    An electrical circuit with more than one possible path for electron flow. When wiring PV modules, this wiring configuration increases amperage (current), while voltage remains the same. Parallel wiring is positive to positive (+ to +) and negative to negative (- to -). Opposite of a series connection.

    PASSIVE SOLAR
    Any use of the sun's energy in a manner that is found in nature without the use of mechanical aid like pumps or fans. For example, heating a thermal mass (a concrete wall or slab, for instance) during the day with direct sunlight, and using the stored heat in that mass to warm a greenhouse or home at night.

    PAYBACK
    The period of time it takes for an energy generating device or system to pay for itself in fuel savings.

    PEAK LOAD
    The maximum load or electrical power draw occurring in a given period of time.

    PEAK POWER POINT
    Operating point of the IV (current-voltage) curve for a photovoltaic cell or module where the product of the current value times the voltage value is a maximum. Also called the “maximum power point.”

    PEAK SUN HOURS
    The equivalent number of hours per day when solar irradiance averages 1,000 watts per meter squared.

    PELTON WHEEL
    A common impulse turbine runner—the wheel that receives the water, changing the pressure and flow of the water to circular motion to drive an alternator, generator, or machine. Pelton wheels (named after inventor Lester Pelton) are made with a series of cups or “buckets” cast onto a hub.

    PENSTOCK
    The pipe in a hydro system that carries the water from the intake to the turbine.

    PHANTOM LOAD
    A device that consumes energy even when its switch is off, such as the digital clock on a VCR.

    PHOTON
    The actual (physical) particle unit of light, as the electron is a particle of electric charge. Solar-electric modules use photons to generate electricity. Photons not captured by the cell are either reflected, pass through the panel, or are converted to heat in the solar array.

    PHOTOVOLTAIC ARRAY
    A collection of solar modules connected in series, parallel, or series-parallel combination to provide greater voltage, current, or power than can be furnished by a single solar module. Solar-electric arrays can be designed to furnish any desired voltage, current, or power.

    PHOTOVOLTAIC 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, electrons will flow and electrical energy will be available.

    PHOTOVOLTAIC MODULE
    A PV module consists of series and/or parallel wired cells typically made from layered silicon crystals that convert light energy to DC electricity. The number of modules in a given system varies depending on the combined load being powered.

    PIPE LOSS (Frictional head loss)
    The amount of energy or pressure lost due to friction between a flowing liquid and the inside surface of a pipe.

    P-N JUNCTION
    The semiconductor junction in a photovoltaic cell that shunts electrons into a circuit. Electrons are bumped across this junction by photons (light particles).

    POLE MOUNT
    A PV mount that is installed on the top or side of a pole usually set in concrete. Can be fixed or seasonally tilted.

    POLYCRYSTALLINE CELL
    A wafer of silicon with a multi-grained structure. All grains have the same atomic crystal lattice, however, each grain has a unique orientation in space, producing a unique reflection of light, resulting in a "patchy" mottled appearance. AKA multicrystalline cell.

    POST AND BEAM CONSTRUCTION
    A traditional building technique in which post and beam framing units are the basic load-bearing members. Post and beams may be of wood, structural steel, or concrete. In this system, there are fewer framing members, leaving more open space for in-fill. Often used in straw bale construction.

    POWER
    The rate of energy use or generation per unit time, measured in watts. 1 watt = 1 joule per second.

    POWER FACTOR
    The ratio of real power (watts) to apparent power (volt-amps) in an AC circuit. Power factor describes the offset between voltage and amperage peaks in AC. 1 is called “unity” power factor, and is when voltage and amperage peak at the same time—they are then said to be “in phase.” Power factor is calculated by dividing W by VA.

    PRESSURE
    The “push” behind liquid or gas in a tank, reservoir, or pipe. Water pressure is directly related to “head”—the height of the top of the water over the bottom. Every 2.31 feet of vertical head gives 1 psi (pound per square inch) of water pressure.

    PRIMARY CELL
    A primary cell is an electrochemical cell (battery) that cannot be recharged. The chemical process within the primary cell is only one way—discharge. When a primary cell is discharged it is discarded. Common flashlight batteries are primary cells; they are disposable batteries that should be avoided.

    PSI
    See PRESSURE.

    PULSE WIDTH MODULATION (PWM)
    Varying the amount of DC energy sent to a load or other device by changing the length of time a pulse is left on compared to when it is off. The wider the pulse, the greater the energy transfer.

    PURPA
    The Public Utility Regulatory Policies Act, passed in 1978. Requires utilities to purchase excess generation from small-scale generators. However, without net metering, this can amount to a fraction of retail prices.

    PV
    See PHOTOVOLTAIC

    PV ARRAY
    Two or more photovoltaic modules wired in series or parallel.

    PV ARRAY-DIRECT
    The use of electricity directly from a photovoltaic array, without batteries or other electrical storage. Many solar water pumps work this way, using a tank to store water.

    RADIATION
  • The sun's energy that comes to earth in the form of direct, diffuse, and reflected rays.
  • The transfer of heat through electromagnetic waves, without heating the air between objects.
  • RADIOTELEPHONE
    A two-way radio system that enables use of a regular telephone but with radio instead of wires.

    RATED CAPACITY
    The manufacturer's specification for the amount of charge that may be stored in a battery, commonly expressed in amp-hours at a specific rate of discharge.

    RATED WATT
    The manufacturer’s specification for power output of a generating device. In most cases, this is not the most accurate measure to look at, since it predicts output only for ideal circumstances.

    RATE OF CHARGE
    The amount of energy per unit time that is being added to the battery. Rate of charge is commonly expressed as a ratio of the battery or cell’s rated capacity to charge duration in hours. Example: A C/20 rate on a 100 AH battery would be 5 amps, the capacity of the battery divided by 20.

    REGULATOR
    A device that prevents overcharging of batteries by controlling the charge cycle, and usually adjustable to conform to specific battery needs. Regulators do not step the voltage down, but control the rate of charge so the battery stays at a specified voltage. Also called CHARGE CONTROLLER.

    RENEWABLE ENERGY
    Flows of energy that are regenerative or virtually inexhaustible from natural ecological cycles. Most commonly includes solar (electric and thermal), biomass, geothermal, wind, tidal, wave, and hydro power sources.

    RESISTANCE
    Refers to how well a material conducts a flow of electrons, measured in ohms (Ω). Resistance is the property of materials to impede a flow of electrons through the material. All materials have some resistance. Those of low resistance are known as conductors, while those of high resistance are known as insulators. The unit used to measure resistance is the Ohm (Ω).

    RESISTOR
    A device with a known amount of resistance used in electrical circuits.

    REST VOLTAGE
    The voltage of a fully charged cell or battery that is neither being charged or discharged.

    RF (radio frequency)
    Any radiation of a frequency that may be received or radiated by radios. Common usage: RF interference (RFI); refers to the interference of radio frequency radiation with the operation of devices or appliances such as radios, televisions, computers, etc.

    RMS
    Root mean square; defines a time averaged value of a varying sinusoidal parameter, such as AC voltage, amperage, or wattage. The square root of the average of the squares of a set of numbers.

    ROOF MOUNT
    A PV or solar collector rack intended to be installed on a roof. For PVs, its elevation angle can be fixed or seasonally adjustable.

    ROTOR
    The blades of a wind generator, shaped to spin when exposed to wind, harnessing the wind's energy.

    RUNNER
    The part of a hydro turbine that accepts the water and turns its energy into rotating motion.

    R-VALUE
    The measure of a material's resistance to heat flow. The higher the R-value, the greater its insulating capabilities.

    QUARTZ-HALOGEN LIGHT
    An incandescent lamp filled with halogen gas. Somewhat more efficient than standard incandescents.

    SECONDARY CELL
    Secondary cells are batteries (electrochemical cells) that are rechargeable. The chemical reaction within the secondary cell is reversible, allowing the cell to be recharged many times.

    SELF-DISCHARGE
    The tendency of all batteries to lose energy. Self-discharge represents energy lost to internal chemical reactions within the cell. This energy is not and cannot be used from the battery or cell’s output terminals.

    SENSOR (Temperature)
    Sensing device that changes its electrical resistance according to temperature. Used in the control system of a solar thermal system to measure collector and storage tank temperatures.

    SERIES CONNECTION
    A wiring configuration used to increase voltage from more than one supply. Series wiring is positive to negative (+ to -) or negative to positive (- to +). Opposite of parallel connection. Series circuits have only one possible path for electron flow.

    SERIES REGULATOR
    A device that prevents overcharging of a battery by disconnecting the charging source as the battery voltage approaches some upper limit.

    SERIES STRING
    A group of PV modules or batteries wired in series.

    SHORT CIRCUIT
    A circuit in which two source leads of opposite polarity or dissimilar potential are connected directly to each other with no regulation or load in between, allowing the full energy potential of the source to flow through the circuit. A short circuit will trip the breaker or fuse, and may damage components, or even cause a fire.

    SHORT CIRCUIT CURRENT (ISC)
    The current between two points in a circuit when the points are electrically connected with a conductor with essentially zero resistance. Normally applied to PV modules, which can be short circuited safely because they are limited current devices.

    SHUNT (noun)
    1. A resistive load through which electron flow is diverted, typically used to heat air or water.

    2. A component with a precise, known resistance used to determine amperage by measuring the voltage across it and using Ohm's law (I = V/R).

    SHUNT (verb)
    To divert electrical current to a separate circuit or load.

    SHUNT REGULATOR
    A device that prevents overcharging of a battery by diverting some (or all) of the charging current to a resistive load when the battery voltage reaches a preset upper limit.

    SIDE-OF-POLE MOUNT
    A PV mount installed on the side of a pole. May be fixed or seasonally adjustable.

    SILICON
    A nonmetallic element, which 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.

    SINGLE CRYSTAL CELL
    A wafer of silicon that has a perfect, continuous, crystal lattice (on the atomic level).

    SITE EVALUATION
    An estimation of a location for its potential for solar, hydro, or wind power.

    SOLAR THERMAL COLLECTORS
    A solar collector is a device designed to absorb incident solar radiation and to transfer the energy to the fluid or air passing through it.

    SOLAR COOKER
    A device that converts the sun's energy into heat energy, which is then used to cook food.

    SOLAR-ELECTRIC CELL
    See PHOTOVOLTAIC CELL

    SOLAR-ELECTRIC MODULE
    See PHOTOVOLTAIC MODULE

    SOLAR ENERGY
    Energy coming directly from the Sun.

    SOLSTICE (SUMMER & WINTER
    The longest and shortest days of the year. The longest day (Summer Solstice) is about June 21st in the Northern Hemisphere. The shortest day (Winter Solstice) is about December 21st in the Northern Hemisphere.

    STAND-ALONE SYSTEM
    A system that operates independently of the utility lines. It may draw supplementary electricity from the utility, but is not capable of providing electricity to the utility.

    STANDARD TEST CONDITIONS (STC)
    The standardized conditions of 1,000 watts per meter squared of solar insolation at 25°C (77°F) for testing PV module ratings.

    STATE OF CHARGE (SOC)
    A ratio, expressed in percent, of the energy remaining in a battery in relation to its capacity when fully charged.

    STORAGE BATTERY
    See BATTERY and SECONDARY CELL.

    STRATIFICATION
    The movement of heat by convection in gasses and liquids causes heat to stratify in layers, the warmest being on top. Stratification is caused by gravity, since the warmer gases and liquids are less dense than the cooler layers.

    STRAW BALE CONSTRUCTION
    A building technique using straw bales for the walls. See POST AND BEAM CONSTRUCTION.

    STRUCTURAL INSULATED PANELS (SIPs)
    A no-cavity solid building system of wall and roof panels "sandwiching" polystyrene insulation between an outer and inner sheathing panel (typically oriented strand board (OSB) or metal).

    SUSTAINABLE
    A material or energy source, which if managed carefully, will provide at current levels indefinitely.

    SULFATION
    The formation of lead-sulfate crystals on the plates of a lead-acid battery, which decreases battery capacity by impeding the opportunity for chemical reaction within a cell. Sulfation can be caused by leaving the battery in a discharged state for long periods of time.

    SURGE CAPACITY
    The maximum amount of AC power an inverter may deliver to a load (or loads) for a short period of time, such as when starting a motor.

    SWEPT AREA
    The area (in square feet or meters^2) that a wind generator’s rotor (blades) sweep. This is the collector area for a wind generator. The larger the collector, the more energy it will capture.

    SWITCH
    A device that breaks an electrical circuit, halting the flow of electrons through the circuit.

    TAIL
    The part of a wind generator that makes the rotor face into the wind. Often the tail is also involved in governing the machine, by folding down or sideways to swing the rotor out of the wind.

    TAILRACE
    The pipe, flume, or channel in a hydroelectric system that carries the water from the turbine runner back to the stream or river.

    THERMAL BREAK
    A material of low thermal conductivity placed in such a way as to reduce the flow of heat between two materials of high thermal conductivity.

    THERMAL MASS
    A material that has the ability to absorb, store, and release heat energy. The more heat energy that is required to change the temperature of high-density materials (concrete, bricks, tiles), the more thermal mass the materials have.

    THERMOSYPHON
    Passive solar hot water systems that rely on the natural convection of liquids to collect energy. Designed with the tank above the collection surface.

    THIN FILM
    A PV manufacturing technique where silicon is vapor deposited, a few molecules thick, onto another material.

    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, the optimum angle will vary.

    TILT-UP TOWER
    A nonclimbable wind generator tower that tilts up and down to allow installation and servicing of the turbine on the ground. Normally these employ a gin pole—a horizontal lever arm that helps raise and lower the tower.

    TOP-OF-POLE MOUNT
    See POLE MOUNT.

    TRACKER
    A mounting rack for a PV array that automatically tilts to follow the daily path of the sun through the sky. A “tracking array” will produce more energy through the course of the day than a “fixed array” (nontracking), particularly during the long days of summer. Some trackers are single-axis while others are dual-axis.

    TRANSFORMER
    An electrical device that steps up voltage and steps down current proportionally (or vice-versa). Transformers work with AC only.

    TRASH RACK
    A large strainer at the input to a hydro system. Used to remove debris from the water before it enters the pipe.

    TURBINE
    An engine that produces rotary motion through reaction or impulse, or both, with moving fluid or gas. The resultant rotary motion is usually used to drive an alternator generator.

    TURGO
    In hydroelectric systems, a type of impact hydro runner optimized for lower heads and higher volumes than a Pelton runner.

    UNINTERRUPTIBLE POWER SUPPLY (UPS)
    A power supply providing continuous, uninterruptible service—commonly used in telecommunications and computer networks.

    UPWIND
    In relation to a wind turbine, toward the wind. An upwind turbine has its blades on the upwind side of the tower.

    UTILITY GRID
    Commercial electrical energy distribution system. Synonyms: Mains, Grid.

    UTILITY-INTERTIE (UI) SYSTEM
    See GRID-TIE SYSTEM.

    VOLT (V)
    The volt is the unit used in the measurement of electromotive force (electrical “pressure”). A standard electrical definition of the volt is: an electromotive force of 1 volt is necessary to move a current of 1 ampere through a 1 Ω resistor. It is often also referred to as electrical potential difference or potential difference.

    VOLTAGE
    A measure of the force or "push" given the electrons in an electrical circuit; a measure of electrical potential. Analogy: pressure in a water pipe. AKA Potential.

    VOLTAGE DROP
    Loss of voltage (electrical pressure) caused by the resistance in wire and electrical devices. Proper wire sizing will minimize voltage drop, particularly over long distances. Voltage drop is determined by four factors: wire size, current (amps), voltage, and length of wire. Water analogy: friction loss in pipe.

    VOLTAGE, NOMINAL
    A way of naming a range of voltage to a standard. Example: A “12 volt nominal” system may operate in the range of 10 to 20 Volts. We call it “12 volts” for simplicity.

    VOLTAGE, OPEN CIRCUIT
    See OPEN CIRCUIT VOLTAGE

    VOLTAGE, PEAK POWER POINT (Vpp)
    The voltage at which a photovoltaic module or array generates at the highest power (watts). A “12 volt nominal” PV module will typically have a peak power voltage of around 17 volts. A PV array-direct solar pump should reach this voltage in full sun conditions. In a higher voltage array, it will be a multiple of this voltage.

    VOLTMETER
    A device for measuring the voltage difference between any two points in an electrical circuit.

    WATT
    Unit of power. Power is the rate of generating or using energy. One watt is the power developed or dissipated in a one volt circuit in which there is a current of one ampere (6.28 million million electrons per second). Watts = amps X volts.

    WATT-HOUR
    A unit of measurement quantifying an amount of energy used or generated. A load that consumes 1 watt for 10 hours uses 10 watt-hours.

    Thursday, September 17, 2009

    What is a Solar Water Tempering Valve?

    Tempering ValveTempering Valve
    AKA: mixing valve

    On a sunny day, the water in your collectors can reach scalding temperatures. A tempering valve can save you from a 160°F (70°C) shower. Ouch! The tempering valve goes at the very end of the chain, right after the backup water and before the faucet. If the water coming out of the backup heater is too hot, the tempering valve opens to mix cold water back in and prevent scalding. The temperature of the hot water can be set by the user on most valves. For instance, a popular valve allows a temperature setting between 120°F and 160°F (49°C-71°C).

    Wednesday, September 16, 2009

    What is a Solar Water Backup Water Heater?

    Backup Water HeaterTank Water Heater
    AKA: natural gas, propane, electric, or wood water heater

    The backup water heater ensures that hot water is at the tap whether the sun shines or not. On a sunny, hot day, if the sun has preheated the water to 140°F (60°C) or more, the backup water heater uses no energy at all because the solar preheat temperature is greater than the typical 120°F (49°C) thermostat setting. On a day when the solar preheat is 85°F (29°C), the backup heater boosts the temperature the remaining 35°F (19°C). Since incoming cold-water temperatures are at ground temperature (usually about 50°F; 10°C), 85°F represents 50 percent of the energy needed to bring the water from 50°F to 120°F.

    Not all backup water heaters use a tank. Keeping a tank of water warm between uses can account for 15 percent or more of the total energy expended for hot water. Tankless water heaters eliminate this standby loss. Solar hot water systems and tankless water heaters are a winning combination. If you´re in Seattle, for instance, and can reduce your water heating cost by 60 percent using solar energy, and save another 15 percent by going tankless, this results in a 75 percent total savings. The household that used to spendTankless Water Heater $300 per year to heat water now only spends $75. In sunnier climates, this number can approach zero. However, not all tankless heaters can be used as a backup heater for solar. Check with the manufacturer.

    Tuesday, September 15, 2009

    What is a Solar Water Isolation Valve?

    Isolation ValveIsolation Valve
    AKA: solar bypass

    An isolation valve should be a part of every solar water heater to isolate the solar tank in case of a problem, while still allowing the backup water heater to remain in service. The isolation valve is a manual valve or valves placed in both the incoming and outgoing potable water lines to the solar tank. It can be a three-valve configuration, or a three-port and two-port valve. Manually turning the valve or valves will place the solar tank "on line" or "off line." It works by directing the flow either through or past the solar tank. These valves can also be plumbed to bypass the backup gas or electric water heater, allowing them to be turned off (eliminating standby heat loss) during the seasons when the SHW system can supply 100 percent of the household´s hot water.

    Monday, September 14, 2009

    What are Solar Water Controls?

    ControlsControls
    AKA: differential controls, PV module

    In active systems using pumps, whenever the collector is hotter than the storage tank, the pump should be on and the system circulating. When the tank is hotter than the collector, the pump should be off. This function is performed by either a differential thermostat control system or the use of a PV-powered pump. The differential thermostat controller compares heat sensor readings from the storage tank and collectors and switches the pump accordingly.

    With a PV-powered pump, a solar-electric panel is connected directly to the pump. It´s a simple setup—when the sun comes out, the pump comes on. The brighter the sun, the faster it pumps. Controls are not needed in batch heater systems, where energy is moved by simple water pressure, or in thermosyphon systems, where energy is moved naturally by heat rising.

    Sunday, September 13, 2009

    What is a Solar Water Expansion Tank?

    Expansion TankClosed-loop systems require an expansion tank. An expansion tank has a chamber in which air is locked inside a bladder or diaphragm. It screws into standard 1/2-inch or 3/4-inch threaded plumbing fittings. When pipes are filled with heat-transfer fluid (water and glycol) and the operating pressure of the system is set, the fluid will occupy a given volume based on the temperature. As the fluid is heated by the sun, it expands. This is where the expansion tank is critical. Without it, something would blow!

    The expansion tank allows the fluid to safely expand by compressing the air in the chamber. The size of the expansion tank needed depends on the total volume of fluid, which is determined by the number and size of collectors, and the length and diameter of the pipes in the solar loop.

    In most cases, a total of 3 to 6 gallons (11-23 l) of fluid is in a solar loop. A #15 (2 gal; 7.6 l) expansion tank is usually adequate. It never hurts to go larger, especially for systems with more than 60 square feet (5.6 m2) of collectors. A #30 has twice the expansion capability. With the proper expansion tank in place, the fluid can go from 0 to 200°F (-18-93°C) with the pressure in the solar loop remaining the same.

    Saturday, September 12, 2009

    What is a Solar Water Heat Exchanger?

    Heat ExchangerHeat exchangers are used in closed-loop solar hot water systems. They enable the transfer of heat from one fluid to another without the two mixing. Internal heat exchangers are inside the tank and not visible. They can be as simple as a coil of pipe resting in the bottom of the tank, or wrapped around the outside beneath the insulation and cover. As the heated fluid from the solar collector travels through the coil, the heat is passed from the hotter fluid to the cooler potable water.


    An external heat exchanger is usually a pipe within a pipe. The solar fluid and potable water flow counter to one another, and heat is transferred within the heat exchanger pipe. Fluid may be moved with pumps, thermosyphoning, or a combination of the two.

    Friday, September 11, 2009

    What is a Solar Water Pump?

    Water PumpWater Pump
    AKA: circulating pump, circulator

    Pumps are used in active systems, but are not required in batch or thermosyphon systems. They circulate water or antifreeze between the solar collector and the storage tank. The right pump for the job depends on the size of the system and the distance and height between the collector(s) and the storage tank. AC pumps plug into a wall outlet while DC pumps are powered from a DC source, such as a photovoltaic panel. Good pumps can last as long as 20 years with heavy use.

    We Will NEVER Forget!

    Thursday, September 10, 2009

    What is a Solar Storage Tank?

    Solar Storage TankSolar Storage Tank
    AKA: solar water tank, solar tank

    A solar water tank is an insulated water storage tank. Cold water that used to go directly to your conventional water heater enters the solar tank and solar-heated water exits. In closed-loop systems, the water is heated by contact with a coil of pipe containing the water or antifreeze that circulates through the collectors. In open-loop systems, the potable water is directly circulated through the collectors.

    The preheated solar water is then plumbed back to the cold side of your existing heater, which now functions as a backup. Whenever hot water is turned on in the house, preheated solar hot water is moved from the solar tank to the backup heater.

    Sunday, September 6, 2009

    What are Solar Water Collector Mounting Systems?

    Collector Mounting Systems
    AKA: mounts, racks

    The three most common mounting systems for solar collectors are the roof mount, ground mount, and awning mount. Roof-mounted collectors are held by brackets, usually parallel to and a few inches above the roof. Ground-mount systems can be as simple as four or more posts in the ground, lengths adjusted to affect optimal tilt. An awning mount attaches the collectors to a vertical wall. Horizontal supports push the bottoms of the collectors out to achieve the desired tilt.

    When choosing a mounting system, roof mounts are usually the cheapest option, provided tilt and orientation are within acceptable parameters. If weight is an issue, ground mounts can be a good choice. Wall mounts are another solution that can work well in some situations.

    Find the sunniest spot for your collectors. Generally, you want no shading between 9 AM and 3 PM. Facing collectors up to 30 degrees east or west of true south and at your site's latitude plus 15 degrees tilt, generally will still yield results within 15 percent of optimum. Any nominal losses from tilt, orientation, or even shading can usually be overcome by adding more collector area.

    Saturday, September 5, 2009

    What are Solar Water Collectors?

    Solar CollectorsFlat Plate CollectorEvacuated Tube Collector
    AKA: Solar thermal panels

    A solar collector consists of a network of pipes through which water (or in colder climates, antifreeze) is heated. Collectors come in various sizes, with 4 by 8 feet (1.2 x 2.4 m) the most common.

    On a typical summer day (sunny and warm), the fluid in the collectors reaches 140°F to 180°F (60°C-80°C). On a clear winter day (sunny and cold), it can reach 120°F to 150°F (50°C-65°C). When it´s cloudy and warm, collectors can reach 70°F to 90°F (20°C-30°C), and when it´s cloudy and cold, 50°F to 60°F (10°C-15°C). As long as the temperature in the collector is greater than that of your incoming cold water (usually about 50°F; 10°C), your solar hot water system is saving you energy.

    Several types of solar collectors are on the market. Flat-plate are thin (3-4 in.; 7-10 cm), black, and covered with glass to hold in the sun´s energy.Batch Collector/StorageThermosyphon Collector/Storage

    In evacuated tube collectors, a glass tube surrounds each individual pipe in a vacuum. This nearly eliminates the influence of ambient air temperature. Evacuated tubes perform better than flat-plate collectors in cloudy weather, and can achieve higher temperatures compared to other collector types, but are typically more expensive. All active systems and some thermosyphon systems may use either flat plate collectors or evacuated tube collectors.

    A third type, called integrated collector storage (ICS) or batch, combines the solar collector and storage tank into one unit. An ICS panel can resemble a flat-plate collector with greater depth (6 in.; 15 cm). A simple batch heater can be a tank within a glazed box.

    Friday, September 4, 2009

    Solar Hot Water System Components

    Understanding the basic components of an RE system and how they function is not an overwhelming task. Here are some brief descriptions of the common equipment used in solar hot water systems. Systems vary—not all equipment is necessary for every system type.

    • Solar Collectors

    • Collector Mounting System

    • Solar Storage Tank

    • Water Pump

    • Heat Exchanger
    • Expansion Tank
    • Controls

    • Isolation Valve

    • Backup Water Heater
    • Tempering Valve
    Check back every day for an explanation of each of these terms... Until tomorrow....

    Thursday, September 3, 2009

    Solar Water Heater Closed-Loop Drainback Systems

    The closed-loop drainback system requires perhaps the least routine service of any active system. The heat-transfer fluid is distilled water, which seldom has to be changed. When the system is at rest (not pumping), the solar collector is empty and the distilled water is stored in a 10-gallon (38 l) reservoir tank, usually located just above the solar storage tank. Higher capacity reservoir tanks are typically required in large systems.

    When the pump turns on, the distilled water is circulated from the reservoir back through the collector and heat exchanger, passing heat to the potable water in the solar tank. When the pump shuts off again, the distilled water drains back into the reservoir. The collector must therefore always be higher than the storage tank, and there must be sufficient continuous slope in the piping to ensure against freezing.

    Drainback systems are effective and reliable. They work great, even on the hottest and coldest days of the year, and can operate twenty years without needing service. The only downside is that larger pumps usually have to be used, especially if you´re pumping water two stories or more, since the drainback pump has to lift the distilled water to the height of the solar collectors.

    One way around the height problem is to place the reservoir in the attic, reducing the height the pump has to lift. However, if it's located in a place where the pipes going to and from the reservoir could freeze, glycol must be added. This is also done when long, horizontal pipe runs do not allow drainback to occur quickly.

    The following illustration includes the primary components of any closed-loop drainback system.

    Drainback System


    Wednesday, September 2, 2009

    Solar Water Heater Pressurized Glycol Systems

    In this active, closed-loop system, incoming potable water is routed to the solar storage tank, but never into the collectors. A water and antifreeze mixture circulates from the collectors through a coil of pipe in the solar tank, and then is pumped back through the collectors. (In most climates, a 50/50 propylene glycol and water mixture will keep collectors from freezing.) The potable water is warmed by heat transfer through contact with the pipe.

    These systems require an expansion tank and a few other auxiliary components for filling, venting, and maintaining the system. A definite advantage to antifreeze systems is that the collectors can be mounted anywhere. These systems are pretty much the only choice in very cold climates.

    The following illustration includes the primary components of any pressurized glycol system.

    Pressurized Glycol System

    Tuesday, September 1, 2009

    Solar Water Heater Open-Loop Direct Systems

    Used in tropical settings where freezing never occurs, this is the simplest of the active systems. A standard, 52-gallon (200 l) electric tank can be used, teamed with a 40-square-foot (3.7 m2) solar thermal collector. Normally the electric element is not hooked up, so this tank becomes a storage tank only, for preheated water feeding an existing backup water heater.

    An air vent, automatic or manual, is installed at the high point of the solar thermal collector to initially purge air. The pump, a small circulator pump using as little as 10 watts, can be powered directly by a 10-watt PV module, or a thermostatically controlled AC pump can be used. A snap-switch sensor can be installed to limit the temperature the solar tank reaches. Standard snap-switch sensors are available for 160°F or 180°F (71 or 82°C).

    The following illustration includes the primary components of any open-loop direct system.

    Open Loop Direct System