Renewable Energy Glossary

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R-Value

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

Radiant Barrier

A thin, reflective foil sheet that exhibits low radiant energy transmission and under certain conditions can block radiant heat transfer; installed in attics to reduce heat flow through a roof assembly into the living space.

Radiant Heating

Heating by transferring heat by radiation through space from warm building surfaces such as floors, walls, or ceilings.

Radiation

The transfer of heat through electromagnetic waves, without heating the air between objects.

Rammed Earth

A building technique in which earth is tamped into forms, defining the walls.

Reaction Turbine

A hydro-electric turbine with a submerged runner. Examples include Francis and Kaplan. Suction below the runner can increase the head in this type of turbine, so we measure the head from intake to tailrace surface levels.

RECs

Renewable energy certificates (RECs) are the financial mechanism whereby the renewable “attributes” of an electricity source are sold by the producer to a customer who wishes to claim the attributes for policy mandates or marketing objectives.

Rectifier

An electronic assembly of one-way valves called diodes that converts alternating current (AC) into direct current (DC). Most wind turbines use alternators to generate 3-phase AC electricity that must be converted to DC for the battery and/or inverter. The rectifier can be included in the turbine but more often is housed in the controller.

Rectifier

A grouping of diodes (one-way electrical valves) that changes alternating current (AC) output to direct current (DC) output.

Redbook

A compilation of solar and other climate data for hundreds of locations in the U.S. Can be found at http://rredc.nrel.gov/solar/pubs/redbook/.

Refractometer

Used to determine the concentration of glycol in a solution.

Regenerative Braking

A system that captures the energy from a vehicle's forward momentum to recharge the battery system when braking. Rather than the energy being dissipated by heat by the brakes, the energy is converted to an electric current by the motor and motor controller.

Relative Humidity

A measure of the degree of saturation of the air at a given dry-bulb temperature.

Renewable Energy

Energy generated from natural resources--such as the sun, wind, and water--that are inexhaustible or replaceable.

Renewable Energy Certificates

The financial mechanism whereby the renewable “attributes” of an electricity source are sold by the producer to a customer who wishes to claim the attributes for policy mandates or marketing objectives.

Renewable Portfolio Standard

Specifies the minimum percentage of total generation that a utility is required to meet from renewable sources.

Resistance

The opposition to electrical current flow based on material type, diameter, length, and ambient temperature. It is measured in ohms and written either as either the Greek letter Omega or R.

Riser

A channel or tube in a flat plate or pool collector that transports the heat transfer fluid in the absorber.

Rotor

The blades and hub of a wind generator, shaped to spin when exposed to wind, harnessing the wind's energy. (The same term is also used to refer to the moving part(s) in the alternator.)

RPS

A renewable portfolio standard (RPS) specifies the minimum percentage of total generation that a utility is required to meet from renewable sources.

RTD

A resistance thermal device (RTD) is a device that changes resistance with temperature. Used on most European-manufactured controls.

Runner

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

1 A B C D E F G H I J K L M N O P Q R S T U V W Y

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