Glossary
S-T
Last Updated Monday, July 24, 2000
compiled by Nick Sundt

S, T

S

Sacrificial Anode. A metal rod placed in a water heater tank to protect the tank from corrosion. Anodes of aluminum, magnesium, or zinc are the more frequently metals. The anode creates a galvanic cell in which magnesium or zinc will be corroded more quickly than the metal of the tank giving the tank a negative charge and preventing corrosion. (Source: US Department of Energy, 1999a).

salinity. The degree of salt in water. (Source: Carbon Dioxide Information Analysis Center, 1990a).

salt water intrusion. The invasion of fresh, surface, or groundwater by salt water. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Scheduled Outage. The shutdown of a generating unit, transmission line, or other facility, for inspection or maintenance, in accordance with an advance schedule. (Source: US Energy Information Administration, 1999b)

seasonal variation. The change in a set of meteorological parameters averaged over three months. Seasonal variation is the largest climate variation, and temperature is the most frequently observed meteorological parameter. Often, monthly averaged data are grouped into seasons, according to the prescribed definition. (Source: Carbon Dioxide Information Analysis Center, 1990a).

sea surface temperature. The temperature of the layer of seawater (approximately 0.5 meters deep) nearest the atmosphere. (Source: Carbon Dioxide Information Analysis Center, 1990a).

sea surface temperature anomalies. Temperature of emitted energy from the sea surface. SST anomaly = (SST - SST mean), where SST = sea surface temperature. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Sealed Combustion Heating System. A heating system that uses only outside air for combustion and vents combustion gases directly to the outdoors. These systems are less likely to backdraft and to negatively affect indoor air quality. (Source: US Department of Energy, 1999a).

Seasonal Energy Efficiency Ratio (SEER). A measure of seasonal or annual efficiency of a central air conditioner or air conditioning heat pump. It takes into account the variations in temperature that can occur within a season and is the average number of Btu of cooling delivered for every watt-hour of electricity used by the heat pump over a cooling season. (Source: US Department of Energy, 1999a).

Seasonal Performance Factor (SPF). Ratio of useful energy output of a device to the energy input, averaged over an entire heating season. (Source: US Department of Energy, 1999a).

Seasoned Wood. Wood, used for fuel, that has been air dried so that it contains 15 to 20 percent moisture content (wet basis). (Source: US Department of Energy, 1999a).

Second Law Efficiency. The ratio of the minimum amount of work or energy required to perform a task to the amount actually used. (Source: US Department of Energy, 1999a).

Second Law of Thermodynamics. This law states that no device can completely and continuously transform all of the energy supplied to it into useful energy. (Source: US Department of Energy, 1999a).

Selective Absorber. A solar absorber surface that has high absorbtance at wavelengths corresponding to that of the solar spectrum and low emittance in the infrared range. (Source: US Department of Energy, 1999a).

Selective Surface Coating. A material with high absorbtance and low emittance properties applied to or on solar absorber surfaces. (Source: US Department of Energy, 1999a).

self-generation. A generation facility dedicated to serving a particular retail customer,usually located on the customer's premises. The facility may either be owned directly by the retail customer or owned by a third party with a contractual arrangement to provide electricity to meet some or all of the customer's load. (Source: California Energy Commission, 1999a.)

self-service wheeling. Primarily an accounting policy comparable to net-billing or running the meter backwards. An entity owns generation that produces excess electricity at one site, that is used at another site(s) owned by the same entity. It is given billing credit for the excess electricity (displacing retail electricity costs minus wheeling charges) on the bills for its other sites. (Source: California Energy Commission, 1999a.)

Semiconductor. Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process. (Source: US Department of Energy, 1999a).

Sensible Cooling Effect. The difference between the total cooling effect and the dehumidifying effect. (Source: US Department of Energy, 1999a).

Sensible Cooling Load. The interior heat gain due to heat conduction, convection, and radiation from the exterior into the interior, and from occupants and appliances. (Source: US Department of Energy, 1999a).

sensible heat. The excess radiative energy that has passed from the Earth's surface to the atmosphere through advection, conduction, and convection processes. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Sensible Heat Storage. A heat storage system that uses a heat storage medium, and where the additional or removal of heat results in a change in temperature. (Source: US Department of Energy, 1999a).

Sequestration. See Carbon sequestration.

Series. A configuration of an electrical circuit in which the positive lead is connected to the negative lead of another energy producing, conducting, or consuming device. The voltages of each device are additive, whereas the current is not. (Source: US Department of Energy, 1999a).

service area. any contiguous geographic area serviced by the same electric utility. (Source: California Energy Commission, 1999a.)

Setback Thermostat. A thermostat that can be set to automatically lower temperatures in an unoccupied house and raise them again before the occupant returns. (Source: US Department of Energy, 1999a).

shade screen. A screen affixed to the exterior of a window or other glazed opening, designed to reduce the solar radiation reaching the glazing. (Source: California Energy Commission, 1999a.)

shading. 1) The protection from heat gains due to direct solar radiation; 2) Shading is provided by (a) permanently attached exterior devices, glazing materials, adherent materials applied to the glazing, or an adjacent building for nonresidential buildings, hotels, motels and highrise apartments, and by (b) devices affixed to the structure for residential buildings. (Source: California Energy Commission, 1999a.)

Shading Coefficient. A measure of window glazing performance that is the ratio of the total solar heat gain through a specific window to the total solar heat gain through a single sheet of double-strength glass under the same set of conditions; expressed as a number between 0 and 1. (Source: US Department of Energy, 1999a).

Sheathing. A construction element used to cover the exterior of wall framing and roof trusses. (Source: US Department of Energy, 1999a).

Short Circuit. An electric current taking a shorter or different path than intended. (Source: US Department of Energy, 1999a).

Short Circuit Current. The current flowing freely through an external circuit that has no load or resistance; the maximum current possible. (Source: US Department of Energy, 1999a).

short ton. Common measurement for a ton in the United States. A short ton is equal to 2,000 lbs. or 0.907 metric tons.(Source: US Environmental Protection Agency, 1999a)

shortwave radiation. The radiation received from the sun and emitted in the spectral wavelengths less than 4 microns. It is also called "solar radiation". (Source: Carbon Dioxide Information Analysis Center, 1990a).

Shutter. An interior or exterior movable panel that operates on hinges or slides into place, used to protect windows or provide privacy. (Source: US Department of Energy, 1999a).

side fins. Vertical shading elements mounted on either side of a glazed opening that blocks direct solar radiation from the lower, lateral portions of the sun's path. (Source: California Energy Commission, 1999a.)

Siding. A construction element applied to the outermost surface of an exterior wall. (Source: US Department of Energy, 1999a).

Sigma Heat. The sum of sensible heat and latent heat in a substance above a base temperature, typically 32 degrees Fahrenheit. (Source: US Department of Energy, 1999a).

signal-to-noise ratio. A quantitative measure of the statistical detectability of a signal, expressed as a ratio of the magnitude of the signal relative to the variability. For first detection of a CO2-induced climate change, the model signal is the mean change or anomaly in some climatic variable, usually surface air temperature, attributed by a numerical model to increased concentrations of carbon dioxide. Observed noise is the standard deviation or natural variability computed from observations of that variable and adjusted for sample size, autocorrelation, and time averaging. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Silicon. A chemical element, of atomic number 14, that is semi-metallic, and an excellent semiconductor material used in solar photovoltaic devices; commonly found in sand. (Source: US Department of Energy, 1999a).

silviculture. Management of forest land for timber. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Simple CS (Caulk and Seal). A technique for insulating and sealing exterior walls that reduces vapor diffusion through air leakage points by installing pre-cut blocks of rigid foam insulation over floor joists, sheet subfloor, and top plates before drywall is installed. (Source: US Department of Energy, 1999a).

Sine Wave. The type of alternative current generated by alternating current generators, rotary inverters, and solid-state inverters. (Source: US Department of Energy, 1999a).

Single-Crystal Material. In reference to solar photovoltaic devices, a material that is composed of a single crystal or a few large crystals. (Source: US Department of Energy, 1999a).

Single Glaze or Pane. One layer of glass in a window frame. It has very little insulating value (R-1) and provides only a thin barrier to the outside and can account for considerable heat loss and gain. (Source: US Department of Energy, 1999a).

Single-phase. A generator with a single armature coil, which may have many turns and the alternating current output consists of a succession of cycles. (Source: US Department of Energy, 1999a).

sink. A reservoir that uptakes a pollutant from another part of its cycle. Soil and trees tend to act as natural sinks for carbon. (Source: US Environmental Protection Agency, 1999a)

Sizing. The process of designing a solar system to meet a specified load given the solar resource and the nominal or rated energy output of the solar energy collection or conversion device. (Source: US Department of Energy, 1999a).

Skylight. A window located on the roof of a structure to provide interior building spaces with natural daylight, warmth, and ventilation. (Source: US Department of Energy, 1999a).

Slab. A concrete pad that sits on gravel or crushed rock, well-compacted soil either level with the ground or above the ground. (Source: US Department of Energy, 1999a).

Slab on Grade. A slab floor that sits directly on top of the surrounding ground. (Source: US Department of Energy, 1999a).

Small Power Producer (SPP). Under the Public Utility Regulatory Policies Act (PURPA), a small power pro duction facility (or small power producer) generates electricity using waste, renewable (water, wind and solar), or geothermal energy as a primary energy source. Fossil fuels can be used, but renewable resource must provide at least 75 percent of the total energy input. (See Code of Federal Regulations, Title 18, Part 292.) (Source: US Energy Information Administration, 1999b)

Smart Window. A term used to describe a technologically advanced window system that contains glazing that can change or switch its optical qualities when a low voltage electrical signal is applied to it, or in response to changes in heat or light. (Source: US Department of Energy, 1999a).

smog. Air pollution associated with oxidants. (Source: Carbon Dioxide Information Analysis Center, 1990a).

smoke. Particles suspended in air after incomplete combustion of materials. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Sodium Lights. A type of high intensity discharge light that has the most lumens per watt of any light source. (Source: US Department of Energy, 1999a).

Soffit. A panel which covers the underside of an roof overhang, cantilever, or mansard. (Source: US Department of Energy, 1999a).

soil. Complex mixture of inorganic minerals (i.e., mostly clay, silt, and sand), decaying organic matter, water, air, and living organisms. (Source: US Environmental Protection Agency, 1999a)

soil carbon. A major component of the terrestrial biosphere pool in the carbon cycle. Organic soil carbon estimates, rather than total soil carbon, are generally quoted. The amount of carbon in the soil is a function of historical vegetative cover and productivity, which in turn is dependent upon climatic variables. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Solar Access or Rights. The legal issues related to protecting or ensuring access to sunlight to operate a solar energy system, or use solar energy for heating and cooling. (Source: US Department of Energy, 1999a).

Solar Altitude Angle. The angle between a line from a point on the earth's surface to the center of the solar disc, and a line extending horizontally from the point. (Source: US Department of Energy, 1999a).

Solar Air Heater. A type of solar thermal system where air is heated in a collector and either transferred directly to the interior space or to a storage medium, such as a rock bin. (Source: US Department of Energy, 1999a).

Solar Array. A group of solar collectors or solar modules connected together. (Source: US Department of Energy, 1999a).

Solar Azimuth. The angle between the sun's apparent position in the sky and true south, as measured on a horizontal plane. (Source: US Department of Energy, 1999a).

Solar Cell. A solar photovoltaic device with a specified area. (Source: US Department of Energy, 1999a).

Solar Collector. A device used to collect, absorb, and transfer solar energy to a working fluid. (Source: US Department of Energy, 1999a).

solar constant. The rate at which solar energy is received just outside the Earth's atmosphere on a surface that is normal to the incident radiation and at the mean distance of the Earth from the sun. The current value is 0.140 watt/cm2. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Solar Cooling. The use of solar thermal energy or solar electricity to power a cooling appliance. There are five basic types of solar cooling technologies: absorption cooling, which can use solar thermal energy to vaporize the refrigerant; desiccant cooling, which can use solar thermal energy to regenerate (dry) the desiccant; vapor compression cooling, which can use solar thermal energy to operate a Rankine-cycle heat engine; and evaporative coolers ("swamp" coolers), and heat-pumps and air conditioners that can by powered by solar photovoltaic systems. (Source: US Department of Energy, 1999a).

solar cycle. The periodic change in sunspot numbers. It is the interval between successive minima and is about 11.1 years. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Solar Declination. The apparent angle of the sun north or south of the earth's equatorial plane. The earth's rotation on its axis causes a daily change in the declination. (Source: US Department of Energy, 1999a).

Solar Distillation. The process of distilling (purifying) water using solar energy. Water can be placed in an air tight solar collector with a sloped glazing material, and as it heats and evaporates, distilled water condenses on the collector glazing, and runs down where it can be collected in a tray. (Source: US Department of Energy, 1999a).

Solar Energy. Electromagnetic energy transmitted from the sun (solar radiation). The amount that reaches the earth is equal to one billionth of total solar energy generated, or the equivalent of about 420 trillion kilowatt-hours. It also includes indi-rect forms of energy such as wind, falling or flowing water (hydropower), ocean thermal gradients, and biomass, which are produced when direct solar energy interact with the Earth. (Source: US Department of Energy, 1999a and US Environmental Protection Agency, 1999a).

Solar Film. A window glazing coating, usually tinted bronze or gray, used to reduce building cooling loads, glare, and fabric fading. (Source: US Department of Energy, 1999a).

Solar Fraction. The percentage of a building's seasonal energy requirements that can be met by a solar energy device(s) or system(s). (Source: US Department of Energy, 1999a).

Solar Furnace. A device that achieves very high temperatures by the use of reflectors to focus and concentrate sunlight onto a small receiver. (Source: US Department of Energy, 1999a).

Solar Gain. The amount of energy that a building absorbs due to solar energy striking its exterior and conducting to the interior or passing through windows and being absorbed by materials in the building. (Source: US Department of Energy, 1999a).

Solar Irradiation. The amount of solar radiation, both direct and diffuse, received at any location. (Source: US Department of Energy, 1999a).

solar radiation. Energy from the Sun. Also referred to as short-wave radiation. Of importance to the climate system, solar radiation includes ultra-violet radiation, visible radiation, and infrared radiation.(Source: US Environmental Protection Agency, 1999a)

Solarium. A glazed structure, such as greenhouse or "sunspace." (Source: US Department of Energy, 1999a).

Solar Mass. A term used for materials used to absorb and store solar energy. (Source: US Department of Energy, 1999a).

Solar Module (Panel). A solar photovoltaic device that produces a specified power output under defined test conditions, usually composed of groups of solar cells connected in series, in parallel, or in series-parallel combinations. (Source: US Department of Energy, 1999a).

Solar Noon. The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky; equal to true or due, geographic south. (Source: US Department of Energy, 1999a).

Solar Pond. A body of water that contains brackish (highly saline) water that forms layers of differing salinity (stratifies) that absorb and trap solar energy. Solar ponds can be used to provide heat for industrial or agricultural processes, building heating and cooling, and to generate electricity. (Source: US Department of Energy, 1999a).

Solar Power Satellite. A solar power station investigated by NASA that entailed a satellite in geosynchronous orbit that would consist of a very large array of solar photovoltaic modules that would convert solar generated electricity to microwaves and beam them to a fixed point on the earth. (Source: US Department of Energy, 1999a).

Solar Panel. See Solar Module. (Source: US Department of Energy, 1999a).

Solar Radiation. A general term for the visible and near visible (ultraviolet and near-infrared) electromagnetic radiation that is emitted by the sun. It has a spectral, or wavelength, distribution that corresponds to different energy levels; short wavelength radiation has a higher energy than long-wavelength radiation. (Source: US Department of Energy, 1999a).

Solar Simulator. An apparatus that replicates the solar spectrum, and used for testing solar energy conversion devices. (Source: US Department of Energy, 1999a).

Solar Space Heater. A solar energy system designed to provide heat to individual rooms in a building. (Source: US Department of Energy, 1999a).

Solar Spectrum. The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter). About 99 percent of solar radiation is contained in a wavelength region from 300 nm (ultraviolet) to 3,000 nm (near-infrared). The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation. (Source: US Department of Energy, 1999a).

Solar Thermal Electric Systems. Solar energy conversion technologies that convert solar energy to electricity, by heating a working fluid to power a turbine that drives a generator. Examples of these systems include central receiver systems, parabolic dish, and solar trough. (Source: US Department of Energy, 1999a).

Solar Thermal Systems. Solar energy systems that collect or absorb solar energy for useful purposes. Can be used to generate high temperature heat (for electricity production and/or process heat), medium temperature heat (for process and space/water heating and electricity generation), and low temperature heat (for water and space heating and cooling). (Source: US Department of Energy, 1999a).

Solar Time. The period marked by successive crossing of the earth's meridian by the sun; the hour angle of the sun at a point of observance (apparent time) is corrected to true (solar) time by taking into account the variation in the earth's orbit and rate of rotation. Solar time and local standard time are usually different for any specific location. (Source: US Department of Energy, 1999a).

Solar Transmittance. The amount of solar energy that passes through a glazing material, expressed as a percentage. (Source: US Department of Energy, 1999a).

Solenoid. An electromechanical device composed of a coil of wire wound around a cylinder containing a bar or plunger, that when a current is applied to the coil, the electromotive force causes the plunger to move; a series of coils or wires used to produce a magnetic field. (Source: US Department of Energy, 1999a).

Solenoid Valve. An automatic valve that is opened or closed by an electromagnet. (Source: US Department of Energy, 1999a).

Solid Fuels. Any fuel that is in solid form, such as wood, peat, lignite, coal, and manufactured fuels such as pulverized coal, coke, charcoal, briquettes, pellets, etc. (Source: US Department of Energy, 1999a).

Solidity. In reference to a wind energy conversion device, the ratio of rotor blade surface area to the frontal, swept area that the rotor passes through. (Source: US Department of Energy, 1999a).

Solstice. The two times of the year when the sun is apparently farthest north and south of the earth's equator; usually occurring on or around June 21 (summer solstice in northern hemisphere, winter solstice for southern hemisphere) and December 21 (winter solstice in northern hemisphere, summer solstice for the southern hemisphere). (Source: US Department of Energy, 1999a).

Southern Oscillation. A large-scale atmospheric and hydrospheric fluctuation centered in the equatorial Pacific Ocean. It exhibits a nearly annual pressure anomaly, alternatively high over the Indian Ocean and high over the South Pacific. Its period is slightly variable, averaging 2.33 years. The variation in pressure is accompanied by variations in wind strengths, ocean currents, sea-surface temperatures, and precipitation in the surrounding areas. El Nino occurrences are associated with the phenomenon. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Southern Oscillation Index. An indicator based on the pressure gradient between the quasi-stationary low pressure region and the center of a subtropical high pressure cell. A positive index corresponds to an anomalously high pressure difference between the two centers of action. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Space Heater. A movable or fixed heater used to heat individual rooms. (Source: US Department of Energy, 1999a).

Spacer (Window). Strips of material used to separate multiple panes of glass within the windows. (Source: US Department of Energy, 1999a).

Specific Heat. The amount of heat required to raise a unit mass of a substance through one degree, expressed as a ratio of the amount of heat required to raise an equal mass of water through the same range. (Source: US Department of Energy, 1999a).

Specific Heat Capacity. The quantity of heat required to change the temperature of one unit weight of a material by one degree. (Source: US Department of Energy, 1999a).

Specific Humidity. The weight of water vapor, per unit weight of dry air. (Source: US Department of Energy, 1999a).

Specific Volume. The volume of a unit weight of a substance at a specific temperature and pressure. (Source: US Department of Energy, 1999a).

Spectral Energy Distribution. A curve illustrating the variation or spectral irradiance with wavelength. (Source: US Department of Energy, 1999a).

Spectral Irradiance. The monochromatic irradiance of a surface per unit bandwidth at a particular wavelength, usually expressed in Watts per square meter-nanometer bandwidth. (Source: US Department of Energy, 1999a).

Spectral Reflectance. The ratio of energy reflected from a surface in a given waveband to the energy incident in that waveband. (Source: US Department of Energy, 1999a).

Spectrum. see Solar Spectrum above. (Source: US Department of Energy, 1999a).

Spectrally Selective Coatings. A type of window glazing films used to block the infrared (heat) portion of the solar spectrum but admit a higher portion of visible light. (Source: US Department of Energy, 1999a).

Spillway. A passage for surplus water to flow over or around a dam. (Source: US Department of Energy, 1999a).

Spinning Reserve. Electric power plant or utility capacity on line and running at low power in excess of actual load. (Source: US Department of Energy, 1999a).

Split Spectrum Photovoltaic Cell. A photovoltaic device where incident sunlight is split into different spectral regions, with an optical apparatus, that are directed to individual photovoltaic cells that are optimized for converting that spectrum to electricity. (Source: US Department of Energy, 1999a).

Split System Air Conditioner. An air conditioning system that comes in two to five pieces: one piece contains the compressor, condenser, and a fan; the others have an evaporator and a fan. The condenser, installed outside the house, connects to several evaporators, one in each room to be cooled, mounted inside the house. Each evaporator is individually controlled, allowing different rooms or zones to be cooled to varying degrees. (Source: US Department of Energy, 1999a).

Spot Purchases. A single shipment of fuel or volumes of fuel, purchased for delivery within 1 year. Spot purchases are often made by a user to fulfill a certain portion of energy requirements, to meet unanticipated energy needs, or to take advantage of low-fuel prices. (Source: US Energy Information Administration, 1999b)

Squirrel Cage Motors. This is another name for an induction motor. The motors consist of a rotor inside a stator. The rotor has laminated, thin flat steel discs, stacked with channels along the length. If the casting composed of bars and attached end rings were viewed without the laminations the casting would appear similar to a squirrel cage. (Source: US Department of Energy, 1999a).

Stability (power system). The property of a system or element by virtue of which its output will ultimately attain a steady state. The amount of power that can be transferred from one machine to another following a disturbance. The stability of a power system is its ability to develop restoring forces equal to or greater than the disturbing forces so as to maintain a state of equilibrium. (Source: US Energy Information Administration, 1999b)

Stack. A smokestack or flue for exhausting the products of combustion from a combustion appliance. (Source: US Department of Energy, 1999a).

Stack (Heat) Loss. Sensible and latent heat contained in combustion gases and vapor emitted to the atmosphere. (Source: US Department of Energy, 1999a).

Stagnation Temperature. A condition that can occur in a solar collector if the working fluid does not circulate when sun is shining on the collector. (Source: US Department of Energy, 1999a).

Stand-Alone Generator. A power source/generator that operates independently of or is not connected to an electric transmission and distribution network; used to meet a load(s) physically close to the generator. (Source: US Department of Energy, 1999a).

Stand-Alone Inverter. An inverter that operates independent of or is not connected to an electric transmission and distribution network. (Source: US Department of Energy, 1999a).

Standard Air. Air with a weight of 0.075 pounds per cubic foot with an equivalent density of dry air at a temperature of 86 degrees Fahrenheit and standard barometric pressure of 29.92 inches of mercury. (Source: US Department of Energy, 1999a).

Standard Conditions. In refrigeration, an evaporating temperature of 5 degrees Fahrenheit (F), a condensing temperature of 86 degrees F., liquid temperature before expansion of 77 degrees F., and suction temperature of 12 degrees F. (Source: US Department of Energy, 1999a).

Standard Cubic Foot. A column of gas at standard conditions of temperature and pressure (32 degrees Fahrenheit and one atmosphere). (Source: US Department of Energy, 1999a).

Standard Industrial Classification (SIC) Code. Standardized codes used to classify businesses by type of activity they engage in. (Source: US Department of Energy, 1999a).

Standby Facility. A facility that supports a utility system and is generally running under no-load. It is available to replace or supplement a facility normally in service. (Source: US Energy Information Administration, 1999b)

Standby losses (water heater terminology). Storage water heaters constantly loose heat by conduction through the walls of the tank, and through the first few feet of water pipes. To reduce standby losses, insulate the tank, the first two feet of the cold water inlet pipe, and the first three feet of the hot water outlet pipe. (Source: Lawrence Berkeley Laboratory, 1999)

Standby Service. Support service that is available, as needed, to supplement a consumer, a utility system, or to another utility if a schedule or an agreement authorizes the transaction. The service is not regularly used. (Source: US Energy Information Administration, 1999b)

Static Pressure. The force per unit area acting on the surface of a solid boundary parallel to the flow. (Source: US Department of Energy, 1999a).

steady state efficiency. A performance rating for space heaters; a measure of the percentage of heat from combustion of gas which is transferred to the space being heated under specified steady state conditions. (Source: California Energy Commission, 1999a.)

Steam. Water in vapor form; used as the working fluid in steam turbines and heating systems. (Source: US Department of Energy, 1999a).

Steam Boiler. A type of furnace in which fuel is burned and the heat is used to produce steam. (Source: US Department of Energy, 1999a).

Steam-Electric Plant (Conventional). A plant in which the prime mover is a steam turbine. The steam used to drive the turbine is produced in a boiler where fossil fuels are burned. (Source: US Energy Information Administration, 1999b)

Steam Turbine. A device that converts high-pressure steam, produced in a boiler, into mechanical energy that can then be used to produce electricity by forcing blades in a cylinder to rotate and turn a generator shaft. (Source: US Department of Energy, 1999a).

Stirling Engine. A heat engine of the reciprocating (piston) where the working gas and a heat source are independent. The working gas is compressed in one region of the engine and transferred to another region where it is expanded. The expanded gas is then returned to the first region for recompression. The working gas thus moves back and forth in a closed cycle. (Source: US Department of Energy, 1999a).

Stoichiometry. Chemical reactions, typically associated with combustion processes; the balancing of chemical reactions by providing the exact proportions of reactant compounds to ensure a complete reaction; all the reactants are used up to produce a single set of products. (Source: US Department of Energy, 1999a).

Stoichiometric Ratio. The ratio of chemical substances necessary for a reaction to occur completely. (Source: US Department of Energy, 1999a).

stoma, plant stomata. A minute pore in the epidermis of plant leaves or stems. Stoma, which are bordered by guard cells that regulate the size of the opening, function in gas exchange between the plant and the external environment. The stomatal apparatus or stomate consists of the stoma plus guard cells. (Source: Carbon Dioxide Information Analysis Center, 1990a).

storm surge. A rise of the sea, preceding a storm (usually a hurricane) due to the winds of the storm and low atmospheric pressure.  (Source: National Weather Service, 1999a.)

straight line winds. Thunderstorm winds most often found with the gust front. They originate from downdrafts and can cause damage which occurs in a "straight line", as opposed to tornadic wind damage which has circular characteristics. (Source: National Weather Service, 1999a.)

stranded benefits. Public interest programs and goals which could be compromised or abandoned by a restructured electric industry. These potential "stranded benefits" might include: environmental protection, fuel diversity, energy efficiency, low-income ratepayer assistance, and other types of socially beneficial programs. (Source: California Energy Commission, 1999a.)

stranded costs/stranded assets. See embedded Costs Exceeding Market Prices. (Source: California Energy Commission, 1999a.)

stratification. Separating into layers. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Storage Capacity. The amount of energy an energy storage device or system can store. (Source: US Department of Energy, 1999a).

Storage Hydropower. A hydropower facility that stores water in a reservoir during high-inflow periods to augment water during low-inflow periods. Storage projects allow the flow releases and power production to be more flexible and dependable. Many hydropower project operations use a combination of approaches. (Source: US Department of Energy, 1999a).

Storage Tank. The tank of a water heater. (Source: US Department of Energy, 1999a).

Storage Water Heater. A water heater that releases hot water from the top of the tank when a hot water tap is opened. To replace that hot water, cold water enters the bottom of the tank to ensure a full tank. (Source: US Department of Energy, 1999a).

Storm Door. An exterior door that protects the primary door. (Source: US Department of Energy, 1999a).

Storm Windows. Glass, plastic panels, or plastic sheets that reduce air infiltration and some heat loss when attached to either the interior or exterior of existing windows. (Source: US Department of Energy, 1999a).

Stranded Investment (Costs and Benefits). An investment in a power plant or demand side management measures or programs, that become uneconomical due to increased competition in the electric power market. For example, an electric power plant may produce power that is more costly than what the market rate for electricity is, and the power plant owner may have to close the plant, even though the capital and financing costs of building the plant have not been recovered through prior sales of electricity from the plant. This is considered a Stranded Cost. Stranded Benefits are those utility investments in measures or programs considered to benefit consumers by reducing energy consumption and/or providing environmental benefits that have to be curtailed due to increased competition and lower profit margins. (Source: US Department of Energy, 1999a).

stratosphere. Second layer of the atmosphere, extending from about 19 to 48 kilometers (12 to 30 miles) above the Earth’s surface. It contains small amounts of gaseous ozone (O 3 ), which filters out about 99 percent of the incoming harmful ultraviolet (UV) radiation. Most commercial airline flights operate at a cruising altitude in the lower stratosphere. See ozone layer, ultraviolet radiation.(Source: US Environmental Protection Agency, 1999a)

stratospheric ozone. See ozone layer. (Source: US Environmental Protection Agency, 1999a)

Stud. A popular term used for a length of wood or steel used in or for wall framing. (Source: US Department of Energy, 1999a).

subbituminous coal. A dull, black coal of rank intermediate between lignite and bituminous coal.(Source: US Environmental Protection Agency, 1999a)

Subsidiary Body for Implementation (SBI). (UN Framework Convention on Climate Change). Makes recommendations on policy and implementation issues to the Climate Convention's Conference of the Parties and, if requested, other bodies. (Source: UN Climate Change Secretariat, 1999a)

Subsidiary Body for Scientific and Technological Advice (SBSTA) (UN Framework Convention on Climate Change). Serves as the link between the information and assessments provided by expert sources (such as the IPCC) on the one hand, and the policy-oriented needs of the Climate Convention's Conference of the Parties on the other. (Source: UN Climate Change Secretariat, 1999a)

Substation. An electrical installation containing power conversion (and sometimes generation) equipment, such as transformers, compensators, and circuit breakers. (Source: US Department of Energy, 1999a).

Substrate. The physical material upon which a photovoltaic cell is applied. (Source: US Department of Energy, 1999a).

sulfur cycle. Cyclic movement of sulfur in different chemical forms from the environment, to organisms, and then back to the environment. (Source: US Environmental Protection Agency, 1999a)

sulfur dioxide (SO 2 ). A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes is changed in a complex series of chemical reactions in the atmosphere to sulfate aerosols. These aerosols are believed to result in negative radiative forcing (i.e., tending to cool the Earth’s surface) and do result in acid deposition (e.g., acid rain). See aerosols, radiative forcing, acid deposition, acid rain. (Source: US Environmental Protection Agency, 1999a)

sulfur hexafluoride (SF 6 ). A colorless gas soluble in alcohol and ether, slightly soluble in water. A very powerful greenhouse gas used primarily in electrical transmission and distribution systems and as a dielectric in electronics. The global warming potential of SF 6 is 23,900. See global warming potential. (Source: US Environmental Protection Agency, 1999a)

Sun Path Diagram. A circular projection of the sky vault onto a flat diagram used to determine solar positions and shading effects of landscape features on a solar energy system. (Source: US Department of Energy, 1999a).

sunk cost. In economics, a sunk cost is a cost that has already been incurred, and therefore cannot be avoided by any strategy going forward. (Source: California Energy Commission, 1999a.)

Sunspace. A room that faces south (in the northern hemisphere), or a small structure attached to the south side of a house. (Source: US Department of Energy, 1999a).

Sun Tempered Building. A building that is elongated in the east-west direction, with the majority of the windows on the south side. The area of the windows is generally limited to about 7% of the total floor area. A sun-tempered design has no added thermal mass beyond what is already in the framing, wall board, and so on. Insulation levels are generally high. (Source: US Department of Energy, 1999a).

sunspot. A relatively dark, sharply defined region on the solar disk, marked by an umbra approximately 2000K cooler than the effective photospheric temperature, surrounded by a less dark but also sharply bounded penumbra. The average spot diameter is about 3700 km, but can range up to 245,000 km. Most sunspots are found in groups of two or more, but they can occur singly. Sunspots are cyclic, with a period of approximately 11 years. The quantitative description of sunspot activity is called the Wolf sunspot number, denoted R. The Wolf sunspot number is also referred to as Wolfer sunspot number, Zurich relative sunspot number (Rz), or relative sunspot number. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Super Insulated Houses. A type of house that has massive amounts of insulation, airtight construction, and controlled ventilation without sacrificing comfort, health, or aesthetics. (Source: US Department of Energy, 1999a).

Super Window. A popular term for highly insulating window with a heat loss so low it performs better than an insulated wall in winter, since the sunlight that it admits is greater than its heat loss over a 24 hour period. (Source: US Department of Energy, 1999a).

Supplementary Heat. A heat source, such as a space heater, used to provide more heat than that provided by a primary heating source. (Source: US Department of Energy, 1999a).

Supply Duct. The duct(s) of a forced air heating/cooling system through which heated or cooled air is supplied to rooms by the action of the fan of the central heating or cooling unit. (Source: US Department of Energy, 1999a).

Supply Side. Technologies that pertain to the generation of electricity. (Source: US Department of Energy, 1999a).

surface air temperature. The temperature of the air near the surface of the Earth, usually determined by a thermometer in an instrument shelter about 2 meters above the ground. The true daily mean, obtained from a thermograph, is approximated by the mean of 24 hourly readings and may differ by 1.0 degree C from the average based on minimum and maximum readings. The global average surface air temperature is 15 degrees C. (Source: Carbon Dioxide Information Analysis Center, 1990a).

surface albedo. The fraction of solar radiation incident on the Earth's surface that is reflected by it. Reflectivity varies with ground cover, and during the winter months it varies greatly with the amount of snow cover (depth and areal extent). Roughness of terrain, moisture content, solar angle, and angular and spectral distribution of ground-level irradiations are other factors affecting surface albedo. (Source: Carbon Dioxide Information Analysis Center, 1990a).

surface mining. Removal of soil, sub-soil, and other strata and then extracting a mineral deposit found fairly close to the Earth’s surface. See strip mining. (Source: US Environmental Protection Agency, 1999a)

surface water. All water naturally open to the atmosphere. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Sustainability. The capacity to last or continue to operate indefinitely. (Source: Global Environment Facility, 2000a).

Sustainable development. There is probably no fully agreed definition of sustainable development. However, most people agree that sustainable development means undertaking development activities while improving and maintaining the well-being of people and ecosystems into the future. Such development is likely to be sustainable if it improves the quality of human life while conserving the Earth’s vitality and diversity. (Source: Global Environment Facility, 2000a).

Sustainable use. Making use of a resource or product indefinitely, usually because of sound environmental management. (Source: Global Environment Facility, 2000a).

sustained winds. The wind speed obtained by averaging the observed values over a one minute period. (Source: National Weather Service, 1999a.)

swamp. A type of wetland that is dominated by woody vegetation and does not accumulate appreciable peat deposits; it may be fresh- or saltwater, and tidal or nontidal. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Swamp Cooler. A popular term used for an evaporative cooling device. (Source: US Department of Energy, 1999a).

Synchronous Generator. An electrical generator that runs at a constant speed and draws its excitation from a power source external or independent of the load or transmission network it is supplying. (Source: US Department of Energy, 1999a).

Synchronous Inverter. An electrical inverter that inverts direct current electricity to alternating current electricity, and that uses another alternating current source, such as an electric power transmission and distribution network (grid), for voltage and frequency reference to provide power in phase and at the same frequency as the external power source. (Source: US Department of Energy, 1999a).

Synchronous Motor. A type of motor designed to operate precisely at the synchronous speed with no slip in the full-load speeds (rpm). (Source: US Department of Energy, 1999a).

synthetic fertilizer. Commercially prepared mixtures of plant nutrients such as nitrates, phosphates, and potassium applied to the soil to restore fertility and increase crop yields. See organic fertilizer.(Source: US Environmental Protection Agency, 1999a)

synthetic natural gas (SNG). A manufactured product chemically similar in most respects to natural gas, resulting from the conversion or reforming of petroleum hydrocarbons. It may easily be substituted for, or interchanged with, pipeline quality natural gas.(Source: US Environmental Protection Agency, 1999a)

System Capacity. (Heating, Ventilation and Cooling Terminology). System capacity is a measurement of the total amount of heat or cooling your furnace, heat pump or air conditioner can produce in one hour. This amount is reported in Btu/hr on the nameplate of your equipment. (Source: Lawrence Berkeley Laboratory, 1999)


T

take-out point. The metering points at which a metered entity takes delivery of energy. (Source: California Energy Commission, 1999a.)

Tankless Water Heater. A water heater that heats water before it is directly distributed for end use as required; a demand water heater. (Source: US Department of Energy, 1999a).

tariff. A document, approved by the responsible regulatory agency, listing the terms and conditions, including a schedule of prices, under which utility services will be provided. (Source: California Energy Commission, 1999a.)

Task Lighting. Any light source designed specifically to direct light a task or work performed by a person or machine. (Source: US Department of Energy, 1999a).

Telecommuting. Using a personal computer that is connected by a modem to a site outside the housing unit where a member of the household is employed. Instead of commuting to a place of employment, the household member works at home using a personal computer. (Source: US Energy Information Administration, 1998a).

temperature . Measure of the average speed of motion of the atoms or molecules in a substance or combination of substances at a given moment. See heat. (Source: US Environmental Protection Agency, 1999a)

Temperature Coefficient (of a solar photovoltaic cell). The amount that the voltage, current, and/or power output of a solar cell changes due to a change in the cell temperature. (Source: US Department of Energy, 1999a).

Temperature Humidity Index. An index that combines sensible temperature and air humidity to arrive at a number that closely responds to the effective temperature; used to relate temperature and humidity to levels of comfort. (Source: US Department of Energy, 1999a).

Temperature/Pressure Relief Valve. A component of a water heating system that opens at a designated temperature or pressure to prevent a possible tank, radiator, or delivery pipe rupture. (Source: US Department of Energy, 1999a).

Temperature Zones. Individual rooms or zones in a building where temperature is controlled separately from other rooms or zones. (Source: US Department of Energy, 1999a).

Tempering Valve. A valve used to mix heated water with cold in a heating system to provide a desired water temperature for end use. (Source: US Department of Energy, 1999a).

terrestrial. Pertaining to land. (Source: US Environmental Protection Agency, 1999a)

terrestrial radiation. The total infrared radiation emitted by the Earth and its atmosphere in the temperature range of approximately 200-300K. Because the Earth is nearly a perfect radiator, the radiation from its surface varies as the fourth power of the surface's absolute temperature. Terrestrial radiation provides a major part of the potential energy changes necessary to drive the atmospheric wind system and is responsible for maintaining the surface air temperature within limits for livability. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Therm. A unit of heat containing 100,000 British thermal units (Btu). (Source: US Department of Energy, 1999a).

Thermal Balance Point. The point or outdoor temperature where the heating capacity of a heat pump matches the heating requirements of a building. (Source: US Department of Energy, 1999a).

Thermal break (window efficiency Terminology). A material that doesn't transmit heat well, such as plastic, sandwiched inside the metal parts of the frame. This reduces the heat being transferred through the frame.Thermal breaks can be used in the spacer between panes of glass in multi-pane windows as well as in the main body of the frame. (Source: Lawrence Berkeley Laboratory, 1999)

Thermal Efficiency. A measure of the efficiency of converting a fuel to energy and useful work; useful work and energy output divided by higher heating value of input fuel times 100 (for percent). (Source: US Department of Energy, 1999a).

Thermal Energy. The energy developed through the use of heat energy. (Source: US Department of Energy, 1999a).

Thermal Energy Storage. The storage of heat energy during utility off-peak times at night, for use during the next day without incurring daytime peak electric rates. (Source: US Department of Energy, 1999a).

Thermal Envelope Houses. An architectural design (also known as the double envelope house), sometimes called a "house-within-a-house," that employs a double envelope with a continuous airspace of at least 6 to 12 inches on the north wall, south wall, roof, and floor, achieved by building inner and outer walls, a crawl space or sub-basement below the floor, and a shallow attic space below the weather roof. The east and west walls are single, conventional walls. A buffer zone of solar-heated, circulating air warms the inner envelope of the house. The south-facing airspace may double as a sunspace or greenhouse. (Source: US Department of Energy, 1999a).

Thermal Mass. Materials that store heat. (Source: US Department of Energy, 1999a).

Thermal Storage Walls (Masonry or Water). A thermal storage wall is a south-facing wall that is glazed on the outside. Solar heat strikes the glazing and is absorbed into the wall, which conducts the heat into the room over time. The walls are at least 8 in thick. Generally, the thicker the wall, the less the indoor temperature fluctuates. (Source: US Department of Energy, 1999a).

Thermal Resistance (R-Value). This designates the resistance of a material to heat conduction. The greater the R-value the larger the number. (Source: US Department of Energy, 1999a).

thermocline. A transition layer of water in the ocean, with a steeper vertical temperature gradient than that found in the layers of ocean above and below. The permanent thermocline separates the warm mixed surface layer of the ocean from the cold deep ocean water, and is found between 100- and 1000-meter depths. The thermocline first appears at the 55 - 60 degrees N and S latitudes, where it forms a horizontal separation between temperate and polar waters. The thermocline reaches its maximum depth at mid-latitudes and is shallowest at the equator and at its northern and southern limits. The thermocline is stably stratified, and transfer of water and carbon dioxide across this zone occurs very slowly. Thus, the thermocline acts as a barrier to the downward mixing of carbon dioxide. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Thermocouple. A device consisting of two dissimilar conductors with their ends connected together. When the two junctions are at different temperatures, a small voltage is generated. (Source: US Department of Energy, 1999a).

Thermodynamic Cycle. An idealized process in which a working fluid (water, air, ammonia, etc) successively changes its state (from a liquid to a gas and back to a liquid) for the purpose of producing useful work or energy, or transferring energy. (Source: US Department of Energy, 1999a).

Thermodynamics. A study of the transformation of energy from one form to another, and its practical application. (see Law(s) of Thermodynamics above). (Source: US Department of Energy, 1999a).

Thermoelectric Conversion. The conversion of heat into electricity by the use of thermocouples. (Source: US Department of Energy, 1999a).

Thermography. A building energy auditing technique for locating areas of low insulation in a building envelope by means of a thermographic scanner. (Source: US Department of Energy, 1999a).

thermohaline. Refers to the combined effects of temperature and salinity that contribute to density variations in the oceans. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Thermophotovoltaic Cell. A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation. (Source: US Department of Energy, 1999a).

Thermopile. A large number of thermocouples connected in series. (Source: US Department of Energy, 1999a).

Thermostat. A device used to control temperatures; used to control the operation of heating and cooling devices by turning the device on or off when a specified temperature is reached. (Source: US Department of Energy, 1999a).

Thermosyphon. The natural, convective movement of air or water due to differences in temperature. In solar passive design a thermosyphon collector can be constructed and attached to a house to deliver heat to the home by the continuous pattern of the convective loop (or thermosyphon). (Source: US Department of Energy, 1999a).

Thermosyphon (Solar) Systems. Thermosyphon systems use a separate storage tank located above the collector. Liquid warmed in the collector rises naturally above the collector, where it is kept until it is needed. The liquid can be either water or a glycol solution. If the fluid is water, freeze protection is provided by electric heat. If the fluid is glycol, the heat from the glycol is transferred to water in the storage tank. (Source: US Department of Energy, 1999a).

Thin Film. A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make solar photovoltaic cells. (Source: US Department of Energy, 1999a).

Three-phase Current. Alternating current in which three separate pulses are present, identical in frequency and voltage, but separated 120 degrees in phase. (Source: US Department of Energy, 1999a).

tidal marsh. Low, flat marshlands traversed by channels and tidal hollows and subject to tidal innundation; normally, the only vegetation present are salt-tolerant bushes and grasses. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Tilt Angle (of a Solar Collector or Module). The angle at which a solar collector or module is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection. (Source: US Department of Energy, 1999a).

Timer. A device that can be set to automatically turn appliances (lights) off and on at set times. (Source: US Department of Energy, 1999a).

Timer (Water Heater). This device can automatically turn the heater off at night and on in the morning. (Source: US Department of Energy, 1999a).

Ton (of Air Conditioning). A unit of air cooling capacity; 12,000 Btu per hour. (Source: US Department of Energy, 1999a).

Topping-cycle. A means to increase the thermal efficiency of a steam electric generating system by increasing temperatures and interposing a device, such as a gas turbine, between the heat source and the conventional steam-turbine generator to convert some of the additional heat energy into electricity. (Source: US Department of Energy, 1999a).

Total Heat. The sum of the sensible and latent heat in a substance or fluid above a base point, usually 32 degrees Fahrenheit. (Source: US Department of Energy, 1999a).

Total Incident Radiation. The total radiation incident on a specific surface area over a time interval. (Source: US Department of Energy, 1999a).

Total Internal Reflection. The trapping of light by refraction and reflection at critical angles inside a semiconductor device so that it cannot escape the device and must be eventually absorbed by the semiconductor. (Source: US Department of Energy, 1999a).

trade winds. Persistent tropical winds that blow from the subtropical high pressure centers towards the equatorial low.  (Source: National Weather Service, 1999a.)

trace gas. A minor constituent of the atmosphere. The most important trace gases contributing to the greenhouse effect are water vapor, carbon dioxide, ozone, methane, ammonia, nitric acid, nitrous oxide, ethylene, sulfur dioxide, nitric oxide, dichlorofluoromethane or Freon 12, trichlorofluoromethane or Freon 11, methyl chloride, carbon monoxide, and carbon tetrachloride. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Tracking Solar Array. A solar energy array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy. (Source: US Department of Energy, 1999a).

Transformer. An electromagnetic device that changes the voltage of alternating current electricity. It consists of an induction coil having a primary and secondary winding and a closed iron core. (Source: US Department of Energy, 1999a).

transient tracers. Chemical elements (often radioactive) or compounds that have finite lifetimes. Atmospheric testing of nuclear weapons from the mid-1950s to the early 1960s released large quantities of radionuclides to the atmosphere. Atmosphere-ocean exchange processes have transferred some of these elements to the oceans. Studying the behavior and distribution of these specific isotopes and other chemical tracers in the ocean will provide information on: (1) residence times of the water and its dissolved components in gyres, basins, etc. (2) the mode and rate of formation and the subsequent spreading rates of specific water types, such as the polar water of the Norwegian and Greenland Seas, (3) deep-ocean circulation and ocean-mixing processes, such as advection and upwelling, and (4) the flux of anthropogenic carbon dioxide into the ocean through its correlation with several different transient tracers. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Transmission. The process of sending or moving electricity from one point to another; usually defines that part of an electric utility's electric power lines from the power plant buss to the last transformer before the customer's connection. (Source: US Department of Energy, 1999a).

Transmission and Distribution Losses. The losses that result from inherent resistance in electrical conductors and transformation inefficiencies in distribution transformers in a transmission and distribution network. (Source: US Department of Energy, 1999a).

Transmission Lines. Transmit high-voltage electricity from the transformer to the electric distribution system. (Source: US Department of Energy, 1999a).

transpiration. The process in plants by which water is taken up by the roots and released as water vapor by the leaves. The term can also be applied to the quantity of water thus dissipated. (Source: Carbon Dioxide Information Analysis Center, 1990a).

transportation sector. Consists of private and public passenger and freight transportation, as well as government transportation, including military operations.(Source: US Environmental Protection Agency, 1999a)

tree rings. Annual growth increments of trees that indicate, among other factors, the climatic conditions that enhance or limit growth. Tree ring widths and indexes have been used to search for solar-terrestrial relationships and climatic cycles and to reconstruct past climates. See also dendroclimatology and dendrochronology. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Trellis. An architectural feature used to shade exterior walls; usually made of a lattice of metal or wood; often covered by vines to provide additional summertime shading. (Source: US Department of Energy, 1999a).

Trickle (Solar) Collector. A type of solar thermal collector in which a heat transfer fluid drips out of header pipe at the top of the collector, runs down the collector absorber and into a tray at the bottom where it drains to a storage tank. (Source: US Department of Energy, 1999a).

Triple Pane (Window). This represents three layers of glazing in a window with an airspace between the middle glass and the exterior and interior panes. (Source: US Department of Energy, 1999a).

Trombe Wall. A wall with high thermal mass used to store solar energy passively in a solar home. The wall absorbs solar energy and transfers it to the space behind the wall by means of radiation and by convection currents moving through spaces under, in front of, and on top of the wall. (Source: US Department of Energy, 1999a).

trophic level. A segment of the food chain in which all organisms obtain food and energy in, basically, the same manner (e.g., photosynthesis, herbivory, or carnivory) and in which all organisms are the same number of links from the photosynthetic segment. (Source: Carbon Dioxide Information Analysis Center, 1990a).

tropical depression. Tropical mass of thunderstorms with a cyclonic wind circulation and winds between 20 and 34 knots. (Source: National Weather Service, 1999a.)

tropical disturbance. An organized mass of tropical thunderstorms, with a slight cyclonic circulation, and winds less than 20 knots. (Source: National Weather Service, 1999a.)

tropical storm. An organized cyclone in the tropics with wind speed between 35 and 64 knots. (Source: National Weather Service, 1999a.)

tropopause. The boundary between the troposphere and the stratosphere (about 8 km in polar regions and about 15 km in tropical regions), usually characterized by an abrupt change of lapse rate. The regions above the troposphere have greater atmospheric stability than those below. The tropopause marks the vertical limit of most clouds and storms. (Source: Carbon Dioxide Information Analysis Center, 1990a).

troposphere. The inner layer of the atmosphere below about 15 km, within which there is normally a steady decrease of temperature with increasing altitude. Nearly all clouds form and weather conditions manifest themselves within this region, and its thermal structure is caused primarily by the heating of the Earth's surface by solar radiation, followed by heat transfer by turbulent mixing and convection. (Source: Carbon Dioxide Information Analysis Center, 1990a).

tropospheric ozone precursor. See ozone precursor. (Source: US Environmental Protection Agency, 1999a)

tropospheric ozone. See ozone.(Source: US Environmental Protection Agency, 1999a)

Truck size classifications. U.S. Bureau of the Census has categorized trucks by gross vehicle weight (gvw) as follows: (Source: Center for Transportation Analysis, 1999a)

Light - Less than 10,000 pounds gvw (Also see Light Truck.)
Medium - 10,001 to 20,000 pounds gvw
Light-heavy - 20,001 to 26,000 pounds gvw
Heavy-heavy - 26,001 pounds gvw or more.


True Power. The actual power rating that is developed by a motor before losses occur. (Source: US Department of Energy, 1999a).

True South. The direction, at any point on the earth that is geographically in the northern hemisphere, facing toward the South Pole of the earth. Essentially a line extending from the point on the horizon to the highest point that the sun reaches on any day (solar noon) in the sky. (Source: US Department of Energy, 1999a).

Tube (Fluorescent Light). A fluorescent lamp that has a tubular shape. (Source: US Department of Energy, 1999a).

Tube-In-Plate-Absorber. A type of solar thermal collector where the heat transfer fluid flows through tubes formed in the absorber plate. (Source: US Department of Energy, 1999a).

Tube-Type Collector. A type of solar thermal collector that has tubes (pipes) that the heat transfer fluid flows through that are connected to a flat absorber plate. (Source: US Department of Energy, 1999a).

tundra. A type of ecosystem dominated by lichens, mosses, grasses, and woody plants. It is found at high latitudes (arctic tundra) and high altitudes (alpine tundra). Arctic tundra is underlain by permafrost and is usually very wet. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Tungsten Halogen Lamp. A type of incandescent lamp that contains a halogen gas in the bulb, which reduces the filament evaporation rate increasing the lamp life. The high operating temperature and need for special fixtures limits their use to commercial applications and for use in projector lamps and spotlights. (Source: US Department of Energy, 1999a).

Turbine. A device for converting the flow of a fluid (air, steam, water, or hot gases) into mechanical motion. (Source: US Department of Energy, 1999a).

turnover rate. The fraction of the total amount of mass (e.g., carbon) in a given pool or reservoir that is released from or that enters the pool in a given length of time. The turnover rate of carbon is often expressed as GtC/year. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Two-Tank Solar System. A solar thermal system that has one tank for storing solar heated water to preheat the water in a conventional water heater. (Source: US Department of Energy, 1999a).

Two-Axis Tracking. A solar array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal). (Source: US Department of Energy, 1999a).

typhoon. A hurricane that forms in the Western Pacific Ocean. (Source: National Weather Service, 1999a.)