Key Terms
Descriptions are taken from Works Cited.
Active Solar: Stores electricity. A charge controller keeps the battery charged.
Battery System: Use of solar energy (such as for radiant heat) that requires mechanical equipment (such as solar collectors, pumping systems, and storage batteries).
Biosphere: The part of the Earth’s crust, waters, and atmosphere that supports life. The ecosystem comprising the entire Earth and the living organisms that inhabit it.
Bureau of Land Management (BLM): U.S. government agency that manages public lands. Balances the needs of many people AND protects the land and resources. Considers social, economic, and environmental impacts of activities that occur on specific public lands. (see also Land Use Plan)
Carbon Cycle: The circulation of carbon between living organisms and their surroundings. Carbon dioxide from the atmosphere is synthesized by plants into plant tissue, which is ingested and metabolized by animals and converted to carbon dioxide again during respiration and decay.
Carbon Dioxide (CO2) Gas: Created from the hydrosphere through degassing, or from land animals and soil through respiration, or from the lithosphere through the combustion of fossil fuels.
Carbon Footprint: A measure of the amount of carbon dioxide released into the atmosphere by a single endeavor or by a company, household, or individual through day-to-day activities over a given period.
Concentrated Solar Power (CSP): A solar system that uses mirrors (or other reflecting devices) to collect solar energy. Solar radiation must be very concentrated to generate electricity. Requires a continuous supply of strong sunlight.
Conversion Efficiency: The proportion of radiant energy that the cell converts into electrical energy relative to the amount of radiant energy that is available and striking the PV cell. Improving conversion efficiency is vital to making PV energy more competitive.
Dopant: A doping agent used to alter electrical properties. One layer of a PV cell is diffused with a negative tendency (“n-layer”) dopant such as phorphorous while another layer is diffused with a positive tendency (“p-layer”) dopant such as boron. Dopants create an electrical field to motivate electrons when light strikes the PV cell.
Electricity Measurement: The following are typical measurements and formulas.
- Electrical Current (I): measured in Amps (A)
Current is the number of electrons flowing past a fixed point.
Electrical current = electrons flowing between two points having a difference in voltage.
- Electrical Energy (E): measured in Watt-Hours (Wh) or Kilowatt-Hours (kWh)
1000 Watt-Hours (Wh) = 1 Kilowatt-Hour (1 kWh)
Energy = Power x Time
E = P x t
E = W x h = Wh
Introduces the concept of time to electrical power (see description below). Determine the electrical energy a device consumes if you know how long (time) a device consumes electrical power at a specific rate (power).
- Electrical Power (P): measured in Watt-Hours (Wh)
Power = Voltage x Current
P = V x I
W = V x A
Power is the measure of the rate of doing work or the rate at which energy is converted. Electrical power is the rate at which electricity is produced or consumed. Electric power is combination of pressure (voltage) and rate of flow (current) that results in ability to do work.
- Ohm’s Law: Voltage = Current x Resistance
V = I x R
V = A x Ω
In many materials, especially metals, the current that flows through a material is proportional to voltage. Double the voltage, the current is doubled. Resistance of the material remains the same.
- Resistance (R): measured in Ohms (Ω)
A property that slows the flow of electrons. Resistance of a conducting wire depends on properties of metal used to make the wire and the wire diameter. Common conducting wire—copper, aluminum, silver. Resistors (with set resistances) can be placed in circuits to reduce or control current flow.
- Voltage: measured in Volts (V)
Pressure that pushes electrons in a circuit. A measure of pressure applied to electrons to make them move. Measurement of the strength of the current in a circuit.
- Wattage: measured in Watts (W)
Wattage = Current x Voltage
W = I x V
W = A x V
Electron Flow: Flow through wire depends on electrical pressure pushing electrons.
Energy: Can exist in a variety of forms, such as electrical, mechanical, chemical, thermal, or nuclear, and can be transformed from one form to another. It is measured by the amount of work done, usually in joules or watts.
Federal Land Policy and Management Act of 1976: States that the Bureau of Land Management (BLM) manages public lands for multiple uses. Charters the BLM with balancing the needs of many people AND protecting the land and resources.
Fossil Fuels: Any combustible organic material, as oil, coal, or natural gas, derived from the remains of former life. Made up of hydrocarbon molecules.
- Paleozoic Era: 570 million years ago
Vast seas teamed with microscopic plants, plankton, trilobites, corals, crinoids, and brachiopods. When these carbon-contained organisms died, their remains sank to the sea floor.
- Mesozoic Era: 320 million years ago
Layer upon layer on the sea floor plus evaporation and earthquakes dried up half of the great sea. This heat and pressure changed dead organic matter into hydrocarbons and inorganic matter into sedimentary rock.
- Cenozoic Era: 250 million years ago until today
Heat and pressure formed many layers of sedimentary rock and deep source rock (where oil and natural gas form).
Gamma Rays: Transformed into visible light when they reach sun’s surface (photosphere).
Greenhouse Gasses: Any of the atmospheric gases that contribute to the greenhouse effect by absorbing infrared radiation produced by solar warming of the Earth's surface.
Grid-Connected PV System: Photovoltaic (PV) system that operates in parallel and interconnected with national utility grid. Primary component—inverter or power conditioning unit (PCU) that converts DC into AC power. No battery storage is needed.
Heat Energy: Not transmitted from sun (because space between sun an Earth is a vacuum). Radiant energy transforms into thermal (heat) energy when it strikes molecules in the atmosphere or on Earth’s surface.
Hydrosphere: The oceans or masses of water on Earth. Carbon dioxide molecules are produced from the ocean through photosynthesis.
Inverter: (see Power Inverter)
Land Use Plan: Detailed guide prepared by the Bureau of Land Management (BLM) that explains what activities are allowed on public land. Describes how activities are managed and monitored. Meets all governing laws and regulations.
Light Consumption
- Efficacy: Ratio of light produced to energy consumed. It's measured as the number of lumens produced divided by the rate of electricity consumption (lumens per watt).
Light Quality
- Color Rendition: How colors appear when illuminated by a light source. Color rendition is generally considered to be a more important lighting quality than color temperature. Most objects are not a single color, but a combination of many colors. Light sources that are deficient in certain colors may change the apparent color of an object. The Color Rendition Index (CRI) is a 1–100 scale that measures a light source's ability to render colors the same way sunlight does. The top value of the CRI scale (100) is based on illumination by a 100-watt incandescent light bulb. A light source with a CRI of 80 or higher is considered acceptable for most indoor residential applications.
- Color Temperature: Color of the light source. By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature. Confusingly, higher Kelvin temperatures (3600–5500 K) are what we consider cool and lower color temperatures (2700–3000 K) are considered warm. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing. A color temperature of 2700–3600 K is generally recommended for most indoor general and task lighting applications.
- Glare: Excessive brightness from a direct light source that makes it difficult to see what one wishes to see. A bright object in front of a dark background usually will cause glare. Bright lights reflecting off a television or computer screen or even a printed page produces glare. Intense light sources—such as bright incandescent lamps—are likely to produce more direct glare than large fluorescent lamps. However, glare is primarily the result of relative placement of light sources and the objects being viewed.
Light Quantity
- Footcandle: Measurement of the intensity of illumination. A footcandle is the illumination produced by one lumen distributed over a 1-square-foot area. For most home and office work, 30–50 footcandles of illumination is sufficient. For detailed work, 200 footcandles of illumination or more allows more accuracy and less eyestrain. For simply finding one's way around at night, 5–20 footcandles may be sufficient.
- Flux: Luminous power.
- Illumination: Distribution of light on a horizontal surface. The purpose of all lighting is to produce illumination.
- Lumen: Unit of luminous power (flux); a measure of the total “amount” of visible light emitted by a source (lamp). As reference, a 100-watt incandescent lamp emits about 1600 lumens. (see also Luminous Power and Radiant Power)
Lighting
- Accent Lighting: Draws attention to special features or enhances the aesthetic qualities of an indoor or outdoor environment.
- Ambient Lighting: Provides general illumination indoors for daily activities, and outdoors for safety and security.
- Luminaire: A complete lighting unit.
- Task Lighting: Facilitates particular tasks that require more light than is needed for general illumination, such as under-counter kitchen lights, table lamps, or bathroom mirror lights.
Lithosphere: Rigid outermost shell of Earth (or any planet). Fossil fuels are found in the lithosphere.
Load: Something that uses electricity. Any device placed in a circuit to do work. Every load has resistance.
Lumen (lm): Unit of luminous power (flux); a measure of the total “amount” of visible light emitted by a source. (see also Luminous Power and Radiant Power)
Luminous Power (or Luminous Flux): Measurement of the perceived power of light. Measurements reflect the varying sensitivity of the human eye to different wavelengths of light. (see also Lumen and Radiant Power)
National Environmental Policy Act: Protection of environment became national goal.
Nonrenewable Resource: A natural resource which cannot be produced, regrown, regenerated, or reused on a scale which can sustain its consumption rate. Examples are coal, petroleum/oil, and natural gas.
Nuclear Fusion: A process in which the sun uses gases and makes energy in its inner core. During nuclear fusion, high pressure and temperature force hydrogen (H) atoms to come apart and produce radiant—solar—energy. Nuclear fusion produces gamma rays which are constantly and re-emitted. (see also Gamma Rays and Radiant Energy)
Passive Solar: Use of solar energy (such as for radiant heat) that does not require mechanical equipment. The building acts as a solar collector.
Photons: Bundles of radiant energy. Photons strike a PV cell and may be reflected, absorbed, or transmitted through the cell. Only absorbed photons generate electricity.
Photosphere: Visible surface of the sun.
Photosynthesis: (in plants) The synthesis of organic compounds from carbon dioxide and water (with the release of oxygen) using light energy absorbed by chlorophyll.
Photovoltaic (PV): (photo means light, volt is a measurement of electricity) PV cells generate electricity directly from electrons freed by the interaction of radiant energy with the semiconductor materials in the PV cells. Residential PV system offsets power usage at an individual home. Commercial PV system is designed to offset power usage at a business or industrial site. Utility PV system is employed by energy companies to produce base-load or peak-load power for sale to consumers. (see also Grid-Connected PV System, Standalone PV System, and Photovoltaic Technology)
- PV Cell: Cell that converts sunlight into electricity. Conversion is silent and instantaneous without the use of mechanical parts. Typical PV cell provides 0.5 V of electricity.
- PV Module: PV cells connected together for more power. Connected in series and/or parallel circuits. Produce higher voltages, currents, and power levels. PV module is smallest PV component sold commercially. Range in power output from 10 watts to 300 watts.
- PV Array: One or more PV modules assembled as a pre-wired field-installable unit. Complete power-generating unit.
Photovoltaic Effect: Basic physical process through which a PV cell converts sunlight directly into electricity. More electricity when light is more intense, when light strikes PV modules directly.
Photovoltaic Technology: The following is a summary of how a PV cell is made.
- Silicon: Commonly used semiconductor (to absorb).
- n-Layer: Thin layer of silicon on a PV cell to which phosphorous typically is added to give it extra electrons. The n-layer gives up electrons as a negative tendency.
- p-Layer: Thin layer of silicon on a PV cell to which boron typically is added to create a positive tendency to attract electrons.
- p-n Junction: Point of contact and barrier.
- Electric Field: Formed when the electrons interact between the n-layer and p-layer (at the p-n junction). This provides voltage needed to drive current through the circuit and power an external load.
- Circuit: Formed when a wire connects the n-layer and p-layer to create a connecting circuit through which electricity travels. Wire provides path for electrons to move away from each other. This flow of electrons is an electric current that can power a load.
Power Inverter: Converts DC current (current flows in single direction) to AC current (flow reverses direction at intervals). AC is used by most appliances/devices.
Radiant Energy (Solar Energy): Produced during nuclear fusion in the sun when four hydrogen (H) nuclei (centers of the atoms) fuse to form one helium (He) atom. Matter converts to energy during nuclear fusion. Converted matter is emitted into space as radiant energy. 15% is reflected back into space, 30% powers the water cycle (evaporation–condensation–precipitation), and some energy is absorbed by plants, land, oceans. The rest is reflected and can be used to supply our energy needs.
Radiant Power (Radiant Flux): Measurement of the total power of light emitted, independent of the eye’s ability to perceive it. (see also Lumen and Luminous Flux)
Renewable Resource: Any natural resource that can be replenished naturally with the passage of time. Examples are solar, wind, hydro, geothermal, and biomass.
Solar Collector: Captures sunlight and changes it into heat energy that can be trapped, stored, and used.
Solar Electriciy: Electricity produced by solar energy. Two types are concentrated solar power (CSP) and photovoltaics. (see also Concentrated Solar Power and Photovoltaics)
Solar Energy: Energy derived from the sun in the form of solar radiation.
Solar Panel: A panel that, when exposed to radiation from the sun, is used to heat water. When mounted with solar cells, it is used to produce electricity directly.
Solar Space Heating: Heating the inside of a building using solar energy. Two types are passive solar and active solar. (see also Passive Solar and Active Solar)
Solar Water Heating: Active system that collects sunlight and converts it to heat. Pump circulates water through collector until it reaches desired temperature (the set point). Water is pumped to storage tank where it is used in a heat exchanger to heat water. (see also Passive Solar and Active Solar)
Standalone PV System: Photovoltaic (PV) system that is independent of national electric utility grid. Supplies electricity to a single system. Includes one or more batteries to store electricity. Used for water pumping, highway lighting, weather stations, remote homes, areas away from power lines.
Sun: A ball of gar made up mostly of hydrogen (H) and helium (He) atoms.
Sustainable Energy: The provision of energy such that it meets the needs of the present without compromising the ability of future generations to meet their needs.