Dynamic District Heating plant. DDH power plant is a multi-unit CHP plant that includes engines, boilers and pump modules.

A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another.

DC injection braking is a method of slowing AC electric motors.

A DC connector (or DC plug) is an electrical connector for supplying direct current power.

Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight (direct or indirect) can provide effective internal lighting.

Daylight saving time (DST) is the practice of advancing clocks (typically by one hour) during warmer months so that darkness falls at a later clock time.

Daylight harvesting systems use daylight to offset the amount of electric lighting needed to properly light a space, in order to reduce energy consumption.

Daylight is the combination of all direct and indirect sunlight during the daytime.

A datum reference is some important part of an object, (such as a point, line, plane, hole, set of holes, or pair of surfaces) that serves as a reference in defining the geometry of the object and (often) in measuring aspects of the actual geometry

A data sheet is a document that summarizes the performance and other characteristics of a product, machine, component (e.g., an electronic component), material, subsystem (e.g., a power supply), or software in sufficient detail that allows a buyer to understand what the product is and a design engineer to understand the role of the component in the overall system.

A data logger is an electronic device that records data over time or in relation to location either with a built in instrument or sensor or via external instruments and sensors.

Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer.

Efficient "egg beater" VAWT wind turbine invented by Frenchman Georges Darrieus.

A dam constructed in a valley relies on the natural topography to provide most of the basin of the reservoir.

Dam removal is the process of demolishing a dam, returning water flow to the river.

A dam failure or dam burst is a catastrophic type of failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release.

A dam is a barrier that stops or restricts the flow of water or underground streams. Hydropower is often used in conjunction with dams to generate electricity.

Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.

Changes in electricity demand through a normal day.

A variation of the Giromill, in which each blade can rotate around its own vertical axis producing constant torque loads.