Uranium dioxide or uranium oxide, also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite.

Uranium is a chemical element with the symbol U and atomic number 92.

Turbines where the blades are upwind of the tower.

On the same side from where the wind is blowing from.

The oil and gas industry is usually divided into three major sectors: upstream, midstream and downstream.

Unstable stratification of fluids occurs when each layer is more dense than the one below it.

The proces of disconnecting a generator or plant from the grid in a controlled manner.

The Universe of Energy was a pavilion located on the eastern side of Future World at Epcot, a theme park at the Walt Disney World Resort in Bay Lake, Florida.

As energy is defined via work, the SI unit of energy is the same as the unit of work – the joule (J).

United States customary units (U.S. customary units) are a system of measurements commonly used in the United States since it was formalized in 1832, developed from English units which were in use in the British Empire before the U.S. became an independent country.

The UNFCCC secretariat (UN Climate Change) is the United Nations entity tasked with supporting the global response to the threat of climate change.

A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity.

The unit commitment problem (UC) in electrical power production is a large family of mathematical optimization problems where the production of a set of electrical generators is coordinated in order to achieve some common target, usually either match the energy demand at minimum cost or maximize revenues from electricity production.

An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails.

A common source of unintentional backfeeding is an electrical generator (typically a portable generator) that is improperly connected to a building electrical system.

The term "unglazed air collector" refers to a solar air heating system that consists of a metal absorber without any glass or glazing over top.

"Undervoltage" occurs when the nominal voltage drops below 90% for more than 1 minute.

A method to transmit electricity through insulated cables that are buried underground.

A method of seasonal thermal energy storage that utilises the earths starta or aquifers.

An underground storage tank is, according to United States federal regulations, a storage tank, not including any underground piping connected to the tank, that has at least 10 percent of its volume underground.