DigesterAn airtight vessel or enclosure in which bacteria decomposes biomass in water to produce biogas.
Digester (Anaerobic)A device in which organic material is biochemically decomposed (digested) by anaerobic bacteria to treat the material and/or to produce biogas.
DimmerA light control device that allows light levels to be manually adjusted. A dimmer can save energy by reducing the amount of power delivered to the light…
DiodeAn electronic device that allows current to flow in one direction only.
DioriteA coarse-grained intrusive (or plutonic) igneous rock, less mafic than gabbro, but more mafic than granite and granodiorite; the plutonic equivalent of…
DioxinA family of compounds, some of which are hazardous, that result from combustion of carbon materials.
DipThe angle that a planar geologic surface, for example, a fault, is inclined from the horizontal.
Dip TubeA tube inside a domestic water heater that distributes the cold water from the cold water supply line into the lower area of the water heater where…
direct accessThe ability of an electric power consumer to purchase electricity from a supplier of their choice without being physically inhibited by the owner of the…
Direct CurrentA type of electricity transmission and distribution by which electricity flows in one direction through the conductor; usually relatively low voltage and…
Direct current (DC)A steady current that flows in one direction only. The current from batteries is an example of direct current.
Direct effectsEffects on the environment which occur at the same time and place as the initial cause or action.
Direct impactsImpacts occurring at the place of origin and at the time of the proposed activity.
Direct Normal Insolation (DNI)Sunlight that directly strikes a surface. DNI does not include refracted sunlight that strikes clouds, dust, or the ground first.
Direct Solar Water HeaterThese systems use water as the fluid that is circulated through the collector to the storage tank. Also known as "open-loop" systems.
Direct Vent HeaterA type of combustion heating system in which combustion air is drawn directly from outside and the products of combustion are vented directly outside.
Direct Water HeaterA type of water heater in which heated water is stored within the tank. Hot water is released from the top of the tank when a hot water faucet is turned.
Direct-GainThe process by which sunlight directly enters a building through the windows and is absorbed and stored in massive floors or walls.
Directional drillingThe practice of drilling non-vertical wells. Also called slant drilling.
disaccharidesThe class of compound sugars that yields two monosaccharide units upon hydrolysis; examples are sucrose, maltose, and lactose.
Discharge(DIS-charj) In medicine, a fluid that comes out of the body. Discharge can be normal or a sign of disease.
Discount rateThe discount rate is the interest rate the Federal Reserve charges on loans it makes to banks and other financial institutions.
DiscountingA method of financial and economic analysis used to determine present and future values of investments or expenses.
Dish engineThe dish engine is a concentrating solar power (CSP) technology that produces electricity, typically in the range of 3 to 25 kilowatts, by using a…
Dispatchable power (dispatchability)The ability of a power-producing facility to provide required amounts of power (at or below the facility's nameplate rating) on demand of the grid…
DispatchingTo schedule and control the generation and delivery of electric power.
Displacement PowerA source of power (electricity) that can displace power from another source so that source's power can be transmitted to more distant loads.
DisposalA term used in some countries, including the U.S., to mean that an application has been abandoned, denied (rejected) or allowed (granted).
Distance zonesA subdivision of the landscape as viewed from an observer position. The BLM defined zones include foreground, middleground, background, and seldom seen.
distillateThe portion of a liquid that is removed as vapor and condensed during a distillation process.
Distillate fuel oilProducts of refinery distillation sometimes referred to as middle distillates; kerosene, diesel fuel, and home heating oil. No.
Distillate oilAny distilled product of crude oil. A light petroleum product used for home heating and most machinery.
distillationThe process of heating a mixture to separate the more volatile from the less volatile parts, and then condensing fractions of the resulting vapour so as…
distillers dried grains (DDG)The dried grain byproduct of the grain fermentation process, which may be used as a high-protein animal feed.
Distillers´ dried grains (DDG)The dried byproduct of the grain fermentation process. Typically used as a high-protein animal feed.
Distributed GenerationA term used by the power industry to describe localized or on-site power generation.
DistributionThe sale of securities. Also refers to a sum payable to shareholders representing their share of profits.
Distribution LineOne or more circuits of a distribution system on the same line or poles or supporting structures' usually operating at a lower voltage relative to the…
Distribution SystemThat portion of an electricity supply system used to deliver electricity from points on the transmission system to consumers.
District EnergyA district energy system consists of a central plant that produces steam, hot water, or chilled water, to provide space heating, domestic hot water…
District HeatingA heating system in which steam or hot water for space heating or hot water is piped from a central boiler plant or electric power/heating plant to a…
District heating or coolingA system that involves the central production of hot water, steam, or chilled water and the distribution of these transfer media to heat or cool buildings.
DiversionThe process of removing some minor criminal, traffic or juvenile cases from the full judicial process, on the condition that the accused undergo some sort…
DiversityThe distribution and abundance of different plants and animals within an area.
Diversity FactorThe ratio of the sum of the noncoincidental maximum demands of two or more loads to their coincidental maximum demands for the same period.
Domestic water useWater used for household purposes such as drinking; food preparation; bathing; washing clothes, dishes, and dogs; flushing toilets; and watering lawns and…
DonorIn a solar photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band…
DopantA chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material.
Double Wall Heat ExchangerA heat exchanger in a solar water heating system that has two distinct walls between the heat transfer fluid and the domestic water, to ensure that there…
Double-Pane or Glazed WindowA type of window having two layers (panes or glazing) of glass separated by an air space.
Downdraft gasifierA gasifier in which the product gases pass through a combustion zone at the bottom of the gasifier.
Downwind Wind TurbineA horizontal axis wind turbine in which the rotor is downwind of the tower.
DownzoningA change in zoning classification to less intensive use and/or development.
DraftA signed, written order by which one party (the drawer) instructs another party (the drawee) to pay a specified sum to a third party (the payee), at sight…
Draft DiverterA door-like device located at the mouth of a fireplace chimney flue for controlling the direction and flow of the draft in the fireplace as well as the…
Draft environmental impact statement (DEIS)A draft statement of environmental effects. Section 102 of the National Environmental Policy Act requires a DEIS for all major federal actions.
Draft HoodA device built into or installed above a combustion appliance to assure the escape of combustion byproducts, to prevent backdrafting of the appliance, or…
DragDevice on fishing reels that allows line to pay out under pressure, even though the reel is engaged; set correctly, it ensures against line breakage.
Drainback (Solar) SystemsA closed-loop solar heating system in which the heat transfer fluid in the collector loop drains into a tank or reservoir whenever the booster pump stops…
Draindown (Solar) SystemsAn open-loop solar heating system in which the heat transfer fluid from the collector loop and the piping drain into a drain whenever freezing conditions…
DrawdownLowering a lake level for a specific purpose.
DrillAn oblong tool made of flaked stone used in drilling holes in wood, leather or hides.
Drop structureAn in-stream structure of various materials designed to reduce the energy and force of stream flow.
Dry Bulb TemperatureThe temperature of the air as measured by a standard thermometer.
Dry cooling systemAlso known as dry closed-loop cooling; a technology for rejecting heat from the steam condensate of a thermoelectric plant.
Dry lakeAn ephemeral lake of an arid or semiarid region, typically found at low elevation points in desert valleys.
Dry Steam Geothermal PlantsConventional turbine generators are used with the dry steam resources. The steam is used directly, eliminating the need for boilers and boiler fuel that…
Dry Ton2,000 pounds of material dried to a constant weight.
Dry washA natural drainage channel that is typically dry, but conveys water following significant rainfall events and is subject to rapid flow during flash…
dryingMoisture removal from biomass to improve serviceability and utility.
Dual Duct SystemAn air conditioning system that has two ducts, one is heated and the other is cooled, so that air of the correct temperature is provided by mixing varying…
Dual-fueled (or dual-fired) unitA generating unit that can produce electricity using two or more fuels. In some of these units, only the primary fuel can be used continuously; the…
Duct FanAn axial flow fan mounted in a section of duct to move conditioned air.
Duct(s)The round or rectangular tube(s), generally constructed of sheet metal, fiberglass board, or a flexible plastic-and-wire composite, located within a wall…