| 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. |
| Tail Boom Or Vane Boom | The strut that holds the (vane) to the generator frame. |
| Tail/Vane Deflection | A spring loaded vane that folds in a horizontal plane to turn the machine out of the wind as it increases velocity. |
| Tailrace | The pipe, flume, or channel in a hydroelectric system that carries the water from the turbine runner back to the stream or river. |
| Take-Out Point | The metering points at which a metered entity takes delivery of energy. |
| Taking | Reducing the value of someone’s property through government action without just compensation. |
| Tame (Tertiary Amyl Methyl Ether) | another oxygenate that can be used in reformulated gasoline. It is an ether based on reactive C5 olefins and methanol. |
| Tar Sands | Sedimentary rocks containing heavy oil that cannot be extracted by conventional petroleum recovery methods. |
| Tare Loss | Loss caused by a charge controller. One minus tare loss, expressed as a percentage, is equal to the controller efficiency. |
| 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. |
| Task Lighting (Task-Oriented Lighting) | Lighting designed specifically to illuminate one or more task locations, and generally confined to those locations. |
| Tax Credits | Credits established by the federal and state government to assist the development of the alternative energy industry. |
| Tebbad | The “fever wind” of Turkestan. |
| Temperature | Degree of hotness or coldness measured on one of several arbitrary scales based on some observable phenomenon (such as the expansion). |
| Temperature Compensation | A circuit that adjusts the charge controller activation points depending on battery temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from ambient temperature. |
| Temperature Factors | Are used to decrease battery capacity at cold temperatures, to decrease PV module voltage at high temperatures and to increase the resistance of wire at high temperatures. |
| Therapeutic | the treatment of disease or other disorder; something that may benefit health. (Geothermal) hot springs are often thought of as therapeutic. |
| Therm | One hundred thousand (100,000) British thermal units (1 therm = 100,000 Btu). |
| Thermal | Of, using, producing, or caused by heat. |
| Thermal (Energy) Storage | A technology that lowers the amount of electricity needed for comfort conditioning during utility peak load periods. A buildings thermal energy storage system might, for example, use off-peak power to make ice or to chill water at night, later using the ice or chilled water in a power saving process for cooling during the day. See THERMAL MASS. |
| 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 Break (Thermal Barrier) | An element of low heat conductivity placed in such a way as to reduce or prevent the flow of heat. Some metal framed windows are designed with thermal breaks to improve their overall thermal performance. |
| Thermal Electric | Electric energy derived from heat energy, usually by heating a working fluid, which drives a turbogenerator. |
| Thermal Energy | The energy derived from heat. |
| 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. |
| Thermal Power Plant | any stationary or floating electrical generating facility using any source of thermal energy, with a generating capacity of 50 megawatts or more, and any facilities appurtenant thereto. Exploratory, development, and production wells, resource transmission lines, and other related facilities used in connection with a geothermal exploratory project or a geothermal field development project are not appurtenant facilities for the purposes of this division. Thermal powerplant does not include any wind, hydroelectric, or solar photovoltaic electrical generating facility. |
| Thermal Storage Walls | A thermal storage wall that is glazed on the outside . Solar heat strikes the glazing and is absorbed into the wall and slowly heats the room behind the wall. |
| Thermally Enhanced Oil Recovery (Teor) | Injection of steam to increase the amount of petroleum that may be recovered from a well. |
| Thermodynamics | A study of the transformation of energy into other manifested forms and of their practical applications. The three laws of thermodynamics are: 1) Law of Conservation of Energy-energy may be transformed in an isolated system, but its total is constant. 2) Heat cannot be changed directly into work at constant temperature by a cyclic process. 3) Heat capacity and entropy of every crystalline solid becomes zero at absolute zero (0 degrees Kelvin). |
| Thermophotovoltaic (TPV) Device | A device in which solar energy is concentrated on to a radiator which reaches a high temperature and emits the energy in a different part of the spectrum, better matched to the bandgap of the matched solar cell. This approach should enable high cell efficiencies to be obtained. |
| Thermophotovoltaic Cell (Tpv) | 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. |
| Thermostat | An automatic control device designed to be responsive to temperature and typically used to maintain set temperatures by cycling the HVAC system. |
| Thermostat, Setback | A device, containing a clock mechanism, which can automatically change the inside temperature maintained by the HVAC system according to a preset schedule. The heating or cooling requirements can be reduced when a building is unoccupied or when occupants are asleep. |
| 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. |
| Thick Cells | Conventional solar cells in most types of PV modules, such as crystalline silicon cells, which are typically from 200-400 micrometers thick. In contrast, thin-film cells are several microns thick. |
| Thick-Crystalline Materials | Semiconductor material, typically measuring from 200-400 micromterers thick, that is cut from boules, ingots or ribbons. |
| Thin Film | A layer of semiconductor material, such as copper indium diselenide, cadmium telluride, gallium arsenide, or amorphous silicon, a few microns or less in thickness, used to make photovoltaic cells. |
| Thin Film Photovoltaic Module | A photovoltaic module constructed with sequential layers of thin film semiconductor materials. See amorphous silicon. |
| Thin Film PV Module | A solar PV module constructed with sequential layers of thin film semiconductor materials usually only micrometers thick. Currently, thin film technologies account for around 12% of all solar modules sold around the world. This share is expected to increase, since thin film technologies represent a potential route to lower costs. |
| Tidal Power | Energy obtained by using the motion of the tides to run water turbines that drive electric generators. |
| 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. |
| Time-Of-Use (Tou) Rates | The pricing of electricity based on the estimated cost of electricity during a particular time block. Time-of-use rates are usually divided into three or four time blocks per twenty-four hour period (on-peak, mid-peak, off-peak and sometimes super off-peak) and by seasons of the year (summer and winter). Real-time pricing differs from TOU rates in that it is based on actual (as opposed to forecasted) prices which may fluctuate many times a day and are weather-sensitive, rather than varying with a fixed schedule. |
| Time-Of-Use Meter | A measuring device that records the times during which a customer uses various amounts of electricity. This type of meter is used for customers who pay time-of-use rates. |
| Time-Of-Use Rates | Electricity prices that vary depending on the time periods in which the energy is consumed. In a time-of- use rate structure, higher prices are charged during utility peak-load times. Such rates can provide an incentive for consumers to curb power use during peak times. |
| Tin Oxide | A wide band-gap semiconductor similar to indium oxide; used in heterojunction solar cells or to make a transparent conductive film, called NESA glass when deposited on glass. |
| Ton Of Cooling | A useful cooling effect equal to 12,000 Btu hours. |
| Top-Of-Pole Mount | See POLE MOUNT. |
| Total AC Load Demand | The sum of the AC loads; its value is important to select the correct Inverter. |
| Total Harmonic Distortion | The measure of closeness in shape between a waveform and it’s fundamental component. |
| 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. |
| 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. |
| Tracking Array | A photovoltaic (PV) 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. |
| Trade Wind | The consistent system of prevailing winds occupying most of the tropics. They constitute the major component of the general circulation of the atmosphere. Trade winds blow northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere. The trades, as they are sometimes called, are the most persistent wind system on earth. |
| Trading Day | The 24-hour period beginning at midnight and ending at the following midnight. |
| Trailing Edge | The blade edge that faces away from the direction of rotation. |
| Transfer (Electric Utility) | To move electric energy from one utility system to another over transmission lines. |
| Transformer | A device that raises or lowers the voltage or force of AC electricity. |
| Transistor | A semiconductor device that is used as a switch in a circuit. |
| Transition Costs | See Embedded Costs Exceeding Market Prices. |
| Transmission | Transporting bulk power over long distances. |
| Transmission Lines | The wires for getting high voltage electricity from one place to another. |
| Transmission Owner | An entity that owns transmission facilities or has firm contractual right to use transmission facilities. |
| Transmission-Dependent Utility | A utility that relies on its neighboring utilities to transmit to it the power it buys from its suppliers. A utility without its own generation sources, dependent on another utility’s transmission system to get its purchased power supplies. |
| Transmittance | The time rate of heat flow per unit area under steady conditions from the air (or other fluid) on the warm side of a barrier to the air (or fluid) on the cool side, per unit temperature difference between the two sides. |
| Transmitting Utility (Transco) | This is a regulated entity which owns, and may construct and maintain, wires used to transmit wholesale power. It may or may not handle the power dispatch and coordination functions. It is regulated to provide non-discriminatory connections,comparable service and cost recovery. According to EPAct, any electric utility, qualifying cogeneration facility, qualifying small power production facility, or Federal power marketing agency which owns or operates electric power transmission facilities which are used for the sale of electric energy at wholesale. (See also "Generation Dispatch & Control" and "PowerPool.") |
| Transpired Solar Collectors | use solar energy to preheat ventilation air. |
| Trash Rack | A large strainer at the input to a hydro system. Used to remove debris from the water before it enters the pipe. |
| Tray Cable (Tc) | may be used for interconnecting balance-of-systems. |
| Trickle Charge | A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition. |
| Tsr | Tip Speed Ratio. The ratio of how much faster the blade tips are moving compared to the speed of the wind. |
| Tunneling | Quantum mechanical concept whereby an electron is found on the opposite side of an insulating barrier without having passed through or around the barrier. |
| Turbine | a machine with blades that are rotated by the forceful movement of liquid or gas, such as air, steam or water or a combination. |
| Turbine Generator | A device that uses steam, heated gases, water flow or wind to cause spinning motion that activates electromagnetic forces and generates electricity. |
| Turbine-Generator | A machine in which the energy of a moving fluid, such as water or steam, is converted to mechanical power that drives an electric generator. |
| Turbulence | A swirling motion of the atmosphere that interrupts the flow of wind. |
| Turbulent | Violently agitated or disturbed. |
| Turgo | In hydroelectric systems, a type of impact hydro runner optimized for lower heads and higher volumes than a Pelton runner. |
| Two-Axis Tracking | A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal). |
| Typhoon | The name for a hurricane that occurs in the Pacific Ocean, west of the International Dateline (180 degrees longitude). |
