With reference too


A thin sheet of semiconductor (photovoltaic material) made by cutting it from a single crystal or ingot.


A vertical structural element that holds up a roof, encloses part or all of a room, or stands by itself to hold back soil.

Wall Orientation

The geographical direction that the primary or largest exterior wall of a building faces.

Water Jacket

A heat exchanger element enclosed in a boiler. Water is circulated with a pump through the jacket where it picks up heat from the combustion chamber after which the heated water circulates to heat distribution devices. A water jacket is also an enclosed water-filled chamber in a tankless coiled water heater. When a faucet is turned on water flows into the water heater heat exchanger. The water in the chamber is heated and transfers heat to the cooler water in the heat exchanger and is sent through the hot water outlet to the appropriate faucet.

Water Source Heat Pump

A type of (geothermal) heat pump that uses well (ground) or surface water as a heat source. Water has a more stable seasonal temperature than air thus making for a more efficient heat source.

Water Turbine

A turbine that uses water pressure to rotate its blades; the primary types are the Pelton wheel, for high heads (pressure); the Francis turbine, for low to medium heads; and the Kaplan for a wide range of heads. Primarily used to power an electric generator.

Water Wall

An interior wall made of water filled containers for absorbing and storing solar energy.

Water Wheel

A wheel that is designed to use the weight and/or force of moving water to turn it, primarily to operate machinery or grind grain.


The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of Voltage and Current (amperage).


A unit of electricity consumption of one Watt over the period of one hour.


A device for measuring power consumption.

Wave Form

The shape of the phase power at a certain frequency and amplitude.


The distance between similar points on successive waves.

Wave Power

The concept of capturing and converting the energy available in the motion of ocean waves to energy.


Caulking and weatherstripping to reduce air infiltration and exfiltration into/out of a building.


A material used to seal gaps around windows and exterior doors.


The process of transmitting electricity over one or more separately owned electric transmission and distribution systems. (See Wholesale and Retail Wheeling.)

Whole House Fan

A mechanical/electrical device used to pull air out of an interior space; usually located in the highest location of a building, in the ceiling, and venting to the attic or directly to the outside.

Wholesale Wheeling

The wheeling of electric power in amounts and at prices that generally have been negotiated in long term contracts between the power provider and a distributor or very large power customer.

Wind Energy

Energy available from the movement of the wind across a landscape caused by the heating of the atmosphere, earth, and oceans by the sun.

Wind Energy Conversion System (WECS) or Device

An apparatus for converting the energy available in the wind to mechanical energy that can be used to power machinery (grain mills, water pumps) and to operate an electrical generator.

Wind Generator

A WECS designed to produce electricity.


A WECS that is used to grind grain, and that typically has a high-solidity rotor; commonly used to refer to all types of WECS.


A generic term for a glazed opening that allows daylight to enter into a building and can be opened for ventilation.

Windpower Curve

A graph representing the relationship between the power available from the wind and the wind speed. The power from the wind increases proportionally with the cube of the wind speed.

Wind Power Plant

A group of wind turbines interconnected to a common power provider system through a system of transformers, distribution lines, and (usually) one substation. Operation, control, and maintenance functions are often centralized through a network of computerized monitoring systems, supplemented by visual inspection. This is a term commonly used in the United States. In Europe, it is called a generating station.

Windpower Profile

The change in the power available in the wind due to changes in the wind speed or velocity profile; the windpower profile is proportional to the cube of the wind speed profile.

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 the wind undisturbed by obstacles.

Wind Speed Duration Curve

A graph that indicates the distribution of wind speeds as a function of the cumulative number of hours that the wind speed exceeds a given wind speed in a year.

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 with height above the surface of the ground or water.

Wind Turbine

A term used for a wind energy conversion device that produces electricity; typically having one, two, or three blades.

Wind Turbine Rated Capacity

The amount of power a wind turbine can produce at its rated wind speed, e.g., 100 kW at 20 mph. The rated wind speed generally corresponds to the point at which the conversion efficiency is near its maximum. Because of the variability of the wind, the amount of energy a wind turbine actually produces is a function of the capacity factor (e.g., a wind turbine produces 20% to 35% of its rated capacity over a year).

Wind Velocity

The wind speed and direction in an undisturbed flow.


A building structural element that is built onto a building’s exterior along the inner edges of all the windows, and extending from the ground to the eaves. Wingwalls help ventilate rooms that have only one exterior wall which leads to poor cross ventilation. Wingwalls cause fluctuations in the natural wind direction to create moderate pressure differences across the windows. They are only effective on the windward side of the building.

Wire (Electrical)

A generic term for an electrical conductor.

Wood Stove

A wood-burning appliance for space and/or water heating and/or cooking.

Working Fluid

A fluid used to absorb and transfer heat energy.

Wound Rotor Motors

A type of motor that has a rotor with electrical windings connected through slip rings to the external power circuit. An external resistance controller in the rotor circuit allows the performance of the motor to be tailored to the needs of the system and to be changed with relative ease to accommodate system changes or to vary the speed of the motor.