Lagoon — In wastewater treatment or livestock facilities, a shallow pond used to store wastewater where sunlight and biological activity decompose the waste.
Lamp — A light source composed of a metal base, a glass tube filled with an inert gas or a vapor, and base pins to attach to a fixture.
Landscaping — Features and vegetation on the outside of or surrounding a building for aesthetics and energy conservation.
Langley — A unit or measure of solar radiation; 1 calorie per square centimeter or 3.69 Btu per square foot.
Lattice — The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.
Latent Cooling Load — The load created by moisture in the air, including from outside air infiltration and that from indoor sources such as occupants, plants, cooking, showering, etc.
Latent Heat — The change in heat content that occurs with a change in phase and without change in temperature.
Latent Heat of Vaporization — The quantity of heat produced to change a unit weight of a liquid to vapor with no change in temperature.
Law(s) of Thermodynamics — The first law states that energy can not be created or destroyed; the second law states that when a free exchange of heat occurs between two materials, the heat always moves from the warmer to the cooler material.
Lead Acid Battery — An electrochemical battery that uses lead and lead oxide for electrodes and sulfuric acid for the electrolyte.
Leading Edge — In reference to a wind energy conversion system, the area of a turbine blade surface that first comes into contact with the wind.
Leaking Electricity — Related to stand-by power, leaking electricity is the power needed for electrical equipment to remain ready for use while in a dormant mode or operation. Electricity is still used by many electrical devices, such as TVs, stereos, and computers, even when you think they are turned "off."
Lethe — A measure of air purity that is equal to one complete air change (in an interior space).
Levelized Life Cycle Cost — A total life cycle cost divided into equal amounts.
Life Cycle Cost — The sum of all the costs both recurring and nonrecurring, related to a product, structure, system, or service during its life span or specified time period.
Lift — The force that pulls a wind turbine blade, as opposed to drag.
Light Quality — A description of how well people in a lighted space can see to do visual tasks and how visually comfortable they feel in that space.
Light-Induced Defects — Defects, such as dangling bonds, induced in an amorphous silicon semiconductor upon initial exposure to light.
Light Trapping — The trapping of light inside a semiconductor material by refracting and reflecting the light at critical angles; trapped light will travel further in the material, greatly increasing the probability of absorption and hence of producing charge carriers.
Line Loss (or Drop) — Electrical energy lost due to inherent inefficiencies in an electrical transmission and distribution system under specific conditions.
Liquid-Based Solar Heating System — A solar heating system that uses a liquid as the heat transfer fluid.
Liquid-To-Air Heat Exchanger — A heat exchanger that transfers the heat contained in a liquid heat transfer fluid to air.
Liquid-To-Liquid Heat Exchanger — A heat exchanger that transfers heat contained in a liquid heat transfer fluid to another liquid.
Lithium-Sulfur Battery — A battery that uses lithium in the negative electrode and a metal sulfide in the positive electrode, and the electrolyte is molten salt; can store large amounts of energy per unit weight.
Live Steam — Steam available directly from a boiler under full pressure.
Load — The power required to run a defined circuit or system, such as a refrigerator, building, or an entire electricity distribution system.
Load Analysis — Assessing and quantifying the discrete components that comprise a load. This analysis often includes time of day or season as a variable.
Load Duration Curve — A curve that displays load values on the horizontal axis in descending order of magnitude against the percent of time (on the vertical axis) that the load values are exceeded.
Load Factor — The ratio of average energy demand (load) to maximum demand (peak load) during a specific period.
Load Forecastt — An estimate of power demand at some future period.
Load Leveling — The deferment of certain loads to limit electrical power demand, or the production of energy during off-peak periods for storage and use during peak demand periods.
Load Management — To influence the demand on a power source.
Load Profile or Shape — A curve on a chart showing power (kW) supplied (on the horizontal axis) plotted against time of occurrence (on the vertical axis) to illustrate the variance in a load in a specified time period.
Load Shedding — Turning off or disconnecting loads to limit peak demand.
Load Shifting — A load management objective that moves loads from on-peak periods to off-peak periods.
Local Solar Time — A system of astronomical time in which the sun crosses the true north-south meridian at 12 noon, and which differs from local time according to longitude, time zone, and equation of time.
Log Law — In reference to a wind energy conversion system, the wind speed profile in which wind speeds increase with the logarithmic of the height of the wind turbine above the ground.
Long Ton — A unit that equals 20 long hundredweight or 2,240 pounds. Used mainly in England.
Long-Wave Radiation — Infrared or radiant heat.
Loose Fill Insulation — Insulation made from rockwool fibers, fiberglass, cellulose fiber, vermiculite or perlite minerals, and composed of loose fibers or granules can be applied by pouring directly from the bag or with a blower.
Losses (Energy) — A general term applied to the energy that is converted to a form that can not be effectively used (lost) during the operation of an energy producing, conducting, or consuming system.
Loss of Load Probability (LOLP) — A measure of the probability that a system demand will exceed capacity during a given period; often expressed as the estimated number of days over a long period, frequently 10 years or the life of the system.
Low Btu Gas — A fuel gas with a heating value between 90 and 200 Btu per cubic foot.
Low-E Coatings & (Window) Films — A coating applied to the surface of the glazing of a window to reduce heat transfer through the window.
Low-Emissivity Windows & (Window) Films — Energy-efficient windows that have a coating or film applied to the surface of the glass to reduce heat transfer through the window.
Lower (Net) Heating Value — The lower or net heat of combustion for a fuel that assumes that all products of combustion are in a gaseous state. (See Net Heating Value below.)
Low-Flow Solar Water Heating Systems — The flow rate in these systems is 1/8 to 1/5 the rate of most solar water heating systems. The low-flow systems take advantage of stratification in the storage tank and theoretically allows for the use of smaller diameter piping to and from the collector and a smaller pump.
Low Flush Toilet — A toilet that uses less water than a standard one during flushing, for the purpose of conserving water resources.
Low-Pressure Sodium Lamp — A type of lamp that produces light from sodium gas contained in a bulb operating at a partial pressure of 0.13 to 1.3 Pascal. The yellow light and large size make them applicable to lighting streets and parking lots.
Lumen — An empirical measure of the quantity of light. It is based upon the spectral sensitivity of the photosensors in the human eye under high (daytime) light levels. Photometrically it is the luminous flux emitted with a solid angle (1 steradian) by a point source having a uniform luminous intensity of 1 candela.
Lumens/Watt (lpw) — A measure of the efficacy (efficiency) of lamps. It indicates the amount of light (lumens) emitted by the lamp for each unit of electrical power (Watts) used.
Luminaire — A complete lighting unit consisting of a lamp(s), housing, and connection to the power circuit.
Luminance — The physical measure of the subjective sensation of brightness; measured in lumens.
Lux — The unit of illuminance equivalent to 1lumen per square meter.
Magma — Molten or partially molten rock at temperatures ranging from 1,260 F to 2,880 F (700 C to 1600 C). Some magma bodies are believed to exist at drillable depths within the Earth's crust, although practical technologies for harnessing magma energy have not been developed. If ever utilized, magma represents a potentially enormous resource.
Magnetic Ballast — A type of florescent light ballast that uses a magnetic core to regulate the voltage of a florescent lamp.
Make-Up Air — Air brought into a building from outside to replace exhaust air.
Manual J — The standard method for calculating residential cooling loads developed by the Air-Conditioning and Refrigeration Institute (ARI) and the Air Conditioning Contractors of America (ACCA) based largely on the American Society of Heating, Refrigeration, and Air-Conditioning Engineer's (ASHRAE) "Handbook of Fundamentals."
Marginal Cost — The cost of producing one additional unit of a product.
Masonry — Material such as brick, rock, or stone.
Masonry Stove — A type of heating appliance similar to a fireplace, but much more efficient and clean burning. They are made of masonry and have long channels through which combustion gases give up their heat to the heavy mass of the stove, which releases the heat slowly into a room. Often called Russian or Finnish fireplaces.
Mass Burn Facility — A type of municipal solid waste (MSW) incineration facility in which MSW is burned with only minor presorting to remove oversize, hazardous, or explosive materials. Mass burn facilities can be large, with capacities of 3000 tons (2.7 million kg) of MSW per day or more. They can be scaled down to handle the waste from smaller communities, and modular plants with capacities as low as 25 tons (22.7 thousand kg) per day have been built. Mass burn technologies represent over 75% of all the MSW-to-energy facilities constructed in the United States to date. The major components of a mass burn facility include refuse receiving and handling, combustion and steam generation, flue gas cleaning, power generation (optional), condenser cooling water, residue ash hauling and landfilling.
MCF — An abbreviation for one thousand cubic feet of natural gas with a heat content of 1,000,000 Btus, or 10 therms.
Mean Power Output (of a Wind Turbine) — The average power output of a wind energy conversion system at a given mean wind speed based on a Raleigh frequency distribution.
Mean Wind Speed — The arithmetic wind speed over a specified time period and height above the ground (the majority of U.S. National Weather Service anemometers are at 20 feet (6.1 meters).
Mechanical Systems — Those elements of building used to control the interior climate.
Median Wind Speed — The wind speed with 50 percent probability of occurring.
Medium Btu Gas — Fuel gas with a heating value of between 200 and 300 Btu per cubic foot.
Medium Pressure — For valves and fittings, implies that they are suitable for working pressures between 125 to 175 pounds per square inch.
Megawatt — One thousand kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.
Megawatt-hour — One thousand kilowatt-hours or 1 million watt-hours.
Mercury Vapor Lamp- A high-intensity discharge lamp that uses mercury as the primary light-producing element. Includes clear, phosphor coated, and self-ballasted lamps.
Met — An approximate unit of heat produced by a resting person, equal to about 18.5 Btu per square foot per hour.
Metal Halide Lamp — A high-intensity discharge lamp type that uses mercury and several halide additives as light-producing elements. These lights have the best Color Rendition Index (CRI) of the High-Intensity Discharge lamps. They can be used for commercial interior lighting or for stadium lights.
Methane — A colorless, odorless, tasteless gas composed of one molecule of Carbon and four of hydrogen, which is highly flammable. It is the main constituent of "natural gas" that is formed naturally by methanogenic, anaerobic bacteria or can be manufactured, and which is used as a fuel and for manufacturing chemicals.
Methanol (CH3OH; Methyl alcohol or wood alcohol) — A clear, colorless, very mobile liquid that is flammable and poisonous; used as a fuel and fuel additive, and to produce chemicals.
Metric Ton (Tonne) — A unit of mass equal to 1,000 kilograms or 2,204.6 pounds.
Microclimate — The local climate of specific place or habitat, as influenced by landscape features.
Microgroove — A small groove scribed into the surface of a solar photovoltaic cell which is filled with metal for contacts.
Micrometer — One millionth of a meter (10-6 m).
Mill — A common monetary measure equal to one-thousandth of a dollar or a tenth of a cent.
Minority Carrier — A current carrier, either an electron or a hole, that is in the minority in a specific layer of a semiconductor material; the diffusion of minority carriers under the action of the cell junction voltage is the current in a photovoltaic device.
Minority Carrier Lifetime — The average time a minority carrier exists before recombination.
Mixing Valve — A valve operated by a thermostat that can be installed in solar water heating systems to mix cold water with water from the collector loop to maintain a safe water temperature.
Modified Degree-Day Method — A method used to estimate building heating loads by assuming that heat loss and gain is proportional to the equivalent heat-loss coefficient for the building envelope.
Module — The smallest self-contained, environmentally protected structure housing interconnected photovoltaic cells and providing a single dc electrical output; also called a panel.
Moisture Content — The water content of a substance (a solid fuel) as measured under specified conditions being the: Dry Basis, which equals the weight of the wet sample minus the weight of a (bone) dry sample divided by the weight of the dry sample times 100 (to get percent); Wet Basis, which is equal to the weight of the wet sample minus the weight of the dry sample divided by the weight of the wet sample times 100.
Moisture Control — The process of controlling indoor moisture levels and condensation.
Monolithic — Fabricated as a single structure.
Monoculture — The planting, cultivation, and harvesting of a single species of crop in a specified area.
Motor — A machine supplied with external energy that is converted into force and/or motion.
Motor Speed — The number of revolutions that the motor turns in a given time period (i.e. revolutions per minute, rpm).
Movable Insulation — A device that reduces heat loss at night and during cloudy periods and heat gain during the day in warm weather. A movable insulator could be an insulative shade, shutter panel, or curtain.
MTBE — Methyl Tertiary Butyl Ether (MTBE) is an ether compound used as a gasoline blending component to raise the oxygen content of gasoline. MTBE is made by combining isobutylene (from various refining and chemical processes) and methanol (usually made from natural gas).
Multijunction Device — A high-efficiency photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.
Multi-Zone System — A building heating, ventilation, and/or air conditioning system that distributes conditioned air to individual zones or rooms.
Municipal Solid Waste (MSW) — Waste material from households and businesses in a community that is not regulated as hazardous.
Municipal Waste — As defined in the Energy Security Act (P.L. 96-294; 1980) as "any organic matter, including sewage, sewage sludge, and industrial or commercial waste, and mixtures of such matter and inorganic refuse from any publicly or privately operated municipal waste collection or similar disposal system, or from similar waste flows (other than such flows which constitute agricultural wastes or residues, or wood wastes or residues from wood harvesting activities or production of forest products)."
Municipal Waste to Energy Project (or Plant) — A facility that produces fuel or energy from municipal solid waste.
Air Conditioning Units
