| Wafer | A thin sheet of crystalline semiconductor material either made by mechanically sawing it from a single-crystal boule or multicrystalline ingot or block, or made directly by casting. The wafer is "raw material" for the solar cell. |
| Water Heater | An appliance for supplying hot water for purposes other than space heating or pool heating. |
| Water Phases | the change of water from one state to another. The change from ice to liquid is melting; the reverse process is freezing. The change from liquid to gas is evaporation and the product is water vapor; the change from water vapor to liquid is called condensation. Evaporation and condensation are both important functions in geothermal phenomena and in geothermal technology. |
| Waterspout | A tornado occurring over water. Sometimes it is a lesser whirlwind over water, comparable in intensity to a dust devil over land. |
| Watsco | The Western Association for Transmission System Coordination. |
| Watt | A unit for measuring electric power, eg. 1 horse power = 746 watts. One Kilowatt = 1000 watts. One Megawatt = 1,000,000 watts. |
| Watt (W) | the measure of the amount of current flowing through a wire at a given time. |
| Watt (W) | The unit of electrical power commonly used to define the electricity consumption of an appliance. The power developed when a current of one ampere flows through a potential difference of one volt; 1/746 of a horsepower. 1 Watt = 1 Joule/s. |
| Watt Hour (Wh) | A unit of energy equal to one Watt of power being used for one hour. |
| Watt Hours | A unit of energy equivalent to the power of one watt operating for one hour. |
| Watt Peak (Technical Definition) | The Watt Power output of a Solar module is the number of Watts Output when it is illuminated under standard conditions of 1000 Watts/meter2 intensity, 25°C ambient temperature and a spectrum that relates to sunlight that has passed through the atmosphere (AM or Air Mass 1.5). |
| Watt Peak (User Friendly Definition) | Is the Direct Current Watts output of a Solar Module as measured under an Industry standardized Light Test before the Solar Module leaves the Manufacturers facility. |
| 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. |
| Watt-Hour (Wh) | A unit of electricity consumption of one watt over the period of one hour. |
| Waveform | The shape of a wave or pattern representing a vibration. The shape characterizing an AC current or voltage output. |
| Weatherstripping | Specially designed strips, seals and gaskets installed around doors and windows to limit air leakage. |
| Wet Shelf Life | The period of time that a charged battery, when filled with electrolyte, can remain unused before dropping below a specified level of performance. |
| Wet-Bulb Temperature | The temperature at which water, by evaporating into air, can bring the air to saturation at the same temperature. Wet-bulb temperature is measured by a wet-bulb psychrometer. |
| Wheeling | The transmission of electricity by an entity that does not own or directly use the power it is transmitting. Wholesale wheeling is used to indicate bulk transactions in the wholesale market, whereas retail wheeling allows power producers direct access to retail customers. This term is often used colloquially as meaning transmission. |
| Whole House Fan | A system capable of cooling a house by exhausting a large volume of warm air when the outside air is cool. |
| Wholesale Competition | A system whereby a distributor of power would have the option to buy its power from a variety of power producers, and the power producers would be able to compete to sell their power to a variety of distribution companies. |
| Wholesale Power Market | The purchase and sale of electricity from generators to resellers (who sell to retail customers) along with the ancillary services needed to maintain reliability and power quality at the transmission level. |
| Williwaw | Violent gusts of cold air that blow off the mountainous coasts into the oceans in the Aleutian Islands of Alaska and the Straits of Magellan, near the south end of South America. |
| Willy-Willy | The name for a hurricane that occurs in the seas north of Australia. |
| Wind | Moving air. |
| Wind Energy | Also see "Wind Power" Energy available from the movement of the wind across a landscape. The wind’s movement is caused by the sun, which heats the atmosphere, the earth, and the oceans, forcing air to rise and fall in cycles. |
| Wind Energy Conversion System (WECS) | An apparatus for converting wind energy to mechanical energy, making it available for powering machinery and operating electrical generators. |
| Wind Farm | A piece of land on which wind turbines are sited for the purpose of electricity generation. |
| Wind Generator | A system that captures the force of the wind to provide rotational motion and transfers that power to an alternator or generator. |
| Wind Power | Also see "Wind Energy." Energy available from the movement of the wind across a landscape. The wind’s movement is caused by the sun’s heat, the earth, and the oceans, forcing air to rise and fall in cycles. |
| Wind Power Plant | A group of wind turbines interconnected to a common utility system. |
| Wind Resource Assessment | The process of characterizing the wind resource and its energy potential for a specific site or geographical area. |
| Wind Rose | A diagram that indicates the average percentage of time that the wind blows from different directions, on a monthly or annual basis. |
| Wind Speed | The rate of flow of wind when it blows undisturbed by obstacles. |
| Wind Speed Frequency Curve | A curve that indicates the number of hours per year that specific wind speeds occur. |
| Wind Speed Profile | A profile of how the wind speed changes at different heights above the surface of the ground or water. |
| Wind Turbine | A machine that captures the energy of the wind and transfers the motion to a generator shaft. |
| Wind Turbine Rated Capacity | The amount of power a wind turbine can produce at its rated wind speed. |
| Wind Turbines | use the wind’s energy to generate electricity. |
| Wind Velocity | The wind speed and direction in an undisturbed flow. |
| Windmill | A wind energy conversion system that is used to grind grain. However, the word windmill is commonly used to refer to all types of wind energy conversion systems. |
| Window | A wide band gap material chosen for its transparency to light. Generally used as the top layer of a photovoltaic device, the window allows almost all of the light to reach the semiconductor layers beneath. |
| Windpower Profile | The change in the power available in the wind due to changes in the wind speed or velocity. |
| Wire Types | See Article 300 of National Electric Code for more information. |
| Wires Charge | A broad term which refers to charges levied on power suppliers or their customers for the use of the transmission or distribution wires. |
| Work Function | The energy difference between the Fermi level and vacuum zero. The minimum amount of energy it takes to remove an electron from a substance into the vacuum. |
| WRTA | The Western Regional Transmission Association, an RTG. |
| WSSCC | The Western System Coordinating Council. A voluntary industry association created to enhance reliability among western utilities. |
| WSSP | The Western Systems Power Pool. A FERC approved industry institution that provides a forum for short-term trades in electric energy, capacity, exchanges and transmission services. The pool consists of approximately 50 members and serves 22 states, a Canadian province and 60 million people. The WSSP is headquarter in Phoenix, Arizona. |
