Renewable Energy Glossary

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Natural Cooling

A measure of the water vapor content of air.

Natural Ventilation

Optimizes natural convective air flow to distribute warm, cool, or fresh air throughout the house. Properly sized and placed doors, operable windows, and skylights can maximize cross-ventilation and air movement.


In theory only, a unit of power representing an amount of energy saved as the result of energy conservation or increased efficiency. The term was introduced by the chief scientist of the Rocky Mountain Institute, Amory Lovins, in 1989.

Neighborhood Electric Vehicle

A low-speed battery electric vehicle typically limited by law to a maximum speed of 30 mph and capable of recharge by simple household current. They are often used in communities with street plans specifically catering to low-speed community transportation.

Net Head

Early hydro turbines used mechanical governors linked to spear valves to regulate their speed, but they were expensive and troublesome. Modern turbines use electronics to regulate the speed or the voltage using diversion loads (ballast). The controller monitors speed (for synchronous) or voltage (for induction or permanent magnet) alternators.

Net Zero Building

A building that generates as much energy as it uses.


Systems with a single, bi-directional meter that records both consumption and production. True net-metering means that the cost of a kilowatt-hour sold to the utility equals one bought from the utility.

Neutral Conductors

Those that carry AC current and are connected to earth ground.


Neighborhood electric vehicles (NEVs) can include golf carts, a variety of purpose-designed three- and four-wheeled "cart"-type designs, or utility vehicles with a top speed of not more than 30 mph and a simple plug-in recharge capability.


A standard developed by the National Fire Protection Association (NFPA), at OSHA's request, that specifically addresses the hazards related to electrical work and renewable energy systems.


Nickel cadmium (NiCd or Ni-Cad) is a battery chemistry common in early consumer-market rechargeable cells. Using nickel oxide hydroxide and metallic cadmium as electrodes, NiCd has a native voltage of 1.2V, and is stable, relatively inexpensive, has a long cycle life, and is used in many common household applications.

Nickel Cadmium

Also known as NiCd; developed as a rechargeable battery chemistry as early as 1899 by Waldemar Jungner as an alternative to the lead-acid design common at the time. It was made commercially available in the U.S. in 1946, and today remains a common consumer rechargeable cell.

Nickel Metal Hydride

A battery chemistry similar to nickel cadmium but using an alloy that absorbs hydrogen--typically an alloy of nickel and titanium. Inexpensive and safe, these batteries are used in a broad array of consumer applications as well as in electric vehicles.


Nickel metal hydride (NiMH) batteries, developed in the late '60s and brought to market in 1989 as an improved variety of nickel-based cells, provide increased safety, reliability, and lifespan over NiCd cells by introducing a nickel-titanium (TI-NI) alloy in the composition of the cathode.


The pointed piece farthest toward the wind on a wind generator, designed primarily for cosmetic purposes, but also protects the blade attachment points and generator from the weather.

Notched Weir

A specially shaped weir with a V or notch that can be used to easily record the flow. Water level upstream of the notch is directly related to the flow of water through the notch, so observations can be taken quickly on a regular basis.


A plastic or metal orifice that forms a jet for an impulse turbine. The speed of the water in the nozzle depends on the square root of the net head of pressure. So the cross-sectional area of the nozzle(s) determines the flow in the turbine. Nozzles for home-scale hydro turbines may range from 1/8 inch to about 3/4 inch in diameter.

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