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Solar Technology related terms beginning with D.

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  • Dangling Bonds : A chemical bond associated with an atom on the surface layer of a crystal. The bond does not join with another atom of the crystal, but extends in the direction of exterior of the surface.

  • Days of Storage : The number of consecutive days the stand-alone system will meet a defined load without solar energy input. This term is related to system availability.

  • DC : See direct current.

  • DC-to-DC Converter : Electronic circuit to convert direct current voltages (e.g., photovoltaic module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker.

  • Deep-Cycle Battery : A battery with large plates that can withstand many discharges to a low state-of-charge.

  • Deep Discharge : Discharging a battery to 20% or less of its full charge capacity.

  • Depth of Discharge (DOD) : The ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%.

  • Dendrite : A slender threadlike spike of pure crystalline material, such as silicon.

  • Dendritic Web Technique : A method for making sheets of polycrystalline silicon in which silicon dendrites are slowly withdrawn from a melt of silicon whereupon a web of silicon forms between the dendrites and solidifies as it rises from the melt and cools.

  • Depletion Zone : Same as cell barrier. The term derives from the fact that this microscopically thin region is depleted of charge carriers (free electrons and hole).

  • Design Month : The month having the combination of insolation and load that requires the maximum energy from the photovoltaic array.

  • Diffuse Insolation : Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.

  • Diffuse Radiation : Radiation received from the sun after reflection and scattering by the atmosphere and ground.

  • Diffusion Furnace : Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.

  • Diffusion Length : The mean distance a free electron or hole moves before recombining with another hole or electron.

  • Diode : An electronic device that allows current to flow in one direction only. See blocking diode and bypass diode.

  • Direct Beam Radiation : Radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7 to transcribe the solar disc.

  • Direct Current (DC) : A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to alternating current, its opposite.

  • Direct Insolation : Sunlight falling directly upon a collector. Opposite of diffuse insolation.

  • Discharge : The withdrawal of electrical energy from a battery.

  • Discharge Factor : A number equivalent to the time in hours during which a battery is discharged at constant current usually expressed as a percentage of the total battery capacity, i.e., C/5 indicates a discharge factor of 5 hours. Related to discharge rate.

  • Discharge Rate : The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

  • Disconnect : Switch gear used to connect or disconnect components in a photovoltaic system.

  • Distributed Energy Resources (DER) : A variety of small, modular power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.

  • Distributed Generation : A popular term for localized or on-site power generation.

  • Distributed Power : Generic term for any power supply located near the point where the power is used. Opposite of central power. See stand-alone systems.

  • Distributed Systems : Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system.

  • Donor : In a photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.

  • Donor Level : The level that donates conduction electrons to the system.

  • Dopant : A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).

  • Doping : The addition of dopants to a semiconductor.

  • Downtime : Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours per year or that percentage.

  • Dry Cell : A cell (battery) with a captive electrolyte. A primary battery that cannot be recharged.

  • Duty Cycle : The ratio of active time to total time. Used to describe the operating regime of appliances or loads in photovoltaic systems.

  • Duty Rating : The amount of time an inverter (power conditioning unit) can produce at full rated power.

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