Renewable Energy Glossary

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Selectively Reflective Film

A coating with high solar radiation absorptance and low thermal emittance used on the surface of an absorber to increase system efficiency.

Self-Pumped System

A system using a passive pumping method that is similar to a coffee percolator in operation. The collector loops are usually evacuated with a vacuum pump to allow the HTF to boil at a low temperature.

Sensor

A device that changes its electrical resistance according to temperature. Used in the control system of a solar thermal system to measure collector and storage tank temperatures.

Series Connections

Those made between the positive wire of one module and the negative wire of another; voltage is additive while current remains the same.

Series Fusing

Fusing used to protect module interconnections as well as the internal components of the module from other sources of power to which the module is connected.

Shallow Cycle Battery

A battery meant to be discharged only 10 to 20 percent;not suitable for most RE systems.

Sheathing

The structural covering, such as plywood, oriented strandboard, prefabricated panels, etc. that is attached to the exterior of a structure.

SHGC

Solar heat gain coefficient (SHGC) is the fraction of solar radiation admitted through a window, skylight, or door. It is expressed as a number between 0 and 1. The lower a window's SHGC, the less solar heat it transmits.

Short Circuit Current

The current a PV cell or module produces with no resistance or loads in the circuit; this occurs at zero voltage (and thus zero power); also known as Isc.

Short Cycling

A pump repeatedly cycling on and off--often the result of a low on differential on differential controls.

Sight Level

A handheld level used for measuring head on a hydro site.

Single Crystal

PV cells manufactured from a single crystal with perfect silicon lattice structure, making them among the most-efficient commercially available cell technologies; also known as monocrystalline.

Single-Axis Tracker

A tracker at a fixed tilt angle that follows the movement of the sun east to west across the sky (azimuth angle).

Single-Phase AC Electricity

The most common residential service voltage in the U.S., where the two waveforms are offset by 180 degrees.

SIPs

Structural insulated panels (SIPs) are solid wall and roof panels typically made of two faces of oriented strand board with a core of expanded polystyrene foam insulation.

Skylights

Roof windows that are installed in the plane of the roof.

Slip Rings

Rings of bronze (or similar material), which in conjunction with brushes allow the electrical output from the yawing wind generator to be transmitted to the fixed wiring down the tower. Double brushes (on the yawing wind generator) for each of the AC phases or the two DC outputs ride on the rings (on the fixed tower).

SOC

State of charge (SOC) is the percentage representing the amp-hours remaining in the battery bank. 100% SOC indicates a full battery.

Solar Azimuth Angle

The horizontal aspect of the sun's position relative to a defined direction. In the Northern Hemisphere, it is measured in degrees east or west of true south.

Solar Cell

The smallest discrete component of a PV module that, when exposed to sunlight, generates electricity.

Solar Cooking

Cooking food using heat from the sun.

Solar Heat Gain Coefficient

The fraction of solar radiation admitted through a window, skylight, or door. It is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits.

Solar Noon

The time when the sun is at its highest altitude angle for the day, and the solar azimuth angle is 0 degrees (true south).

Solar Rating and Certification Corporation

A not-for-profit corporation that certifies collectors and systems in the U.S. based on testing data from independent test labs.

Solar South

True south--180 degrees on a compass, plus or minus the magnetic declination.

Solar Storage Tank

A vessel used to store quantities of heat, usually liquids, for later use.

Solar Thermal

A technology that harnesses the sun's energy as heat; applications include domestic hot water and space heating.

Solar Thermal Collector

A device designed to absorb incident solar radiation and to transfer the energy to the fluid or air passing through it.

Solar Tubes

Solar tubes have three components: a round, domed plastic skylight that mounts on the roof; a cylindrical metal tube with a highly reflective interior surface; and a diffuser that mounts on the ceiling. Sunlight enters the skylight dome and reflects downward through the reflective tube to the diffuser, which delivers the light below.

Solar Window

The timeframe during which a solar system site is free of shade.

Solstice

Either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21, when the sun reaches its northernmost point on the celestial sphere, and about December 22, when it reaches its southernmost point.

SPD

A surge protection device (SPD) is a voltage-actuated device designed to safeguard equipment from electrical surges and spikes, including those caused by lightning.

Spear Valve

A valve and a nozzle in one fitting that gives continuous control over the flow. A motorized spear valve controlled by logic circuits can maintain constant water level in the intake and maximize energy production.

Split-Phase AC Electricity

The most common residential service voltage in the U.S., where the two waveforms are offset by 180 degrees.

Spray Foam Insulation

Spray foam insulation is a two-component mixture composed of Isocyanate and resin comes together at the tip of a gun, and forms an expanding foam that is sprayed onto roof tiles, concrete slabs, into wall cavities, or through holes drilled in into a cavity of a finished wall.

Stacking Inverters

The output of two or more inverters is coupled to make a higher output voltage.

Stagnation

A state of no flow through a solar collector. Stagnation temperatures are the highest attainable by the collector.

Stall

Aerodynamic stall occurs when the angle of attack becomes too large, and drag increases sharply, either because the blade speed is too low in relation to the wind speed, or the pitch angle has been reduced. The reduced efficiency results in lower speed. Some wind generators are deliberately designed to stall in high winds.

Stand-Alone DC Load-Only System

Systems that include a PV array, charge controller, battery bank, and DC load(s).

Stand-Alone System with AC Loads

Also called “off-grid” systems; these are not connected to the utility and are the primary energy source for the connected electrical loads.

Stand-Alone Systems

Also referred to as an off-grid system; not connected to the utility grid and the only power source for the connected loads.

Stand-Off Mount

A bracket of variable height connected to a roofing system and used to support racking and rails.

Standard Test Conditions

Methods used to test modules and generate their power specifications.

Standby Losses

Heat that is lost from a solar storage tank due to the difference in temperature between the fluid in the tank and the surrounding environment.

Standing-Seam Roofs

Roofs constructed of metal sheets where the seam between the sheets is raised and crimped, keeping moisture from penetrating the surface.

Start-Up Voltage

The lowest DC voltage point at which the inverter turns on and begins inverting power from the PV array.

State of Charge

The percentage representing the amp-hours remaining in the battery bank. 100% SOC indicates a full battery.

Static Head

The measured head (in feet) or pressure (in psi) when no water is moving in the pipe. The total head before friction loss is accounted for.

STC

Standard test conditions (STC) are used to test modules and generate their power specifications.

Storage Tank

A tank use to store solar-heated water.

Straight Vegetable Oil

Vegetable oil that is suitable for fuel in diesel engines or heating oil, a term generally used to distinguish between it and biodiesel. Unlike waste vegetable oil, it is not a waste or byproduct of other industries.

Stratification

The movement of heat by convection in gasses and liquids causes heat to stratify in layers, the warmest being on top. Stratification is caused by gravity, since the warmer gases and liquids are less dense than the cooler layers.

Straw Bale Construction

A building technique using straw bales for the walls. The straw bales can be used as non-structural infill around the building's structural system or used to create the load/roof-bearing walls.

String Inverter

An inverter connected to a PV array where modules are wired together in series “strings” to produce high DC voltage.

String Sizing

Calculating the number of modules per source circuit in order to properly match the modules to a specific inverter.

Structural Insulated Panels

Solid wall and roof panels, typically made of two faces of oriented strand board with a core of expanded polystyrene foam insulation.

Structural Insulated Panels

A composite building material consisting of an insulating layer of rigid polymer foam sandwiched between two layers of structural board.

Stub Tower

A short segment of tower that sits above the highest guy wires and the standard lattice or tubular tower sections to hold the wind generator. This section is designed to attach firmly to the tower and to allow adaptation and mounting for the wind generator.

Stud

A popular term used for a length of wood or steel used in or for wall framing. The area created by a stud is the stud cavity.

Stud Cavity

The width of a wood frame wall, i.e. 2'x4' nominal equals 4' stud cavity and 2'x4' nominal equals 6' stud cavity. The vertical narrow volume of space between typically 16' on center and 24' on center studs.

Sun Charts

Charts that depict the sun's path (altitude and azimuth angles) across the sky at any time of day and any time of year. Many site-evaluation tools use sun charts to predict shading for a site.

Sun Tube

Sun tubes have three components: a round, domed plastic skylight that mounts on the roof; a cylindrical metal tube with a highly reflective interior surface; and a diffuser that mounts on the ceiling. Sunlight enters the skylight dome and reflects downward through the reflective tube to the diffuser, which delivers the light below.

Sun-Tempered Design

By simply orienting the home to the south, adding insulation, and modestly increasing the windows on the south side of the home, a sun-tempered design can provide modest energy savings. This approach includes no additional thermal mass; heat is absorbed by the “incidental” mass within the structure, for example, floors, wall surfaces, and furnishings.

Sunspace

A separate room on the solar side of the house, which is heated by direct gain with thermal mass. The warm air from this space is then circulated to other parts of the home. Circulation can be accomplished through natural convection or with fans and blowers.

Supply-Side Connection

Uses the utility side of the AC service-disconnecting means, between the existing electrical meter and AC service panel to make the grid interconnection for a PV system.

Surge

The increased current draw for a very short time span when certain loads.

Surge Protection Device

A voltage-actuated device designed to safeguard equipment from electrical surges and spikes, including those caused by lightning.

SVO

Straight vegetable oil (SVO), also known as pure plant oil (PPO), is a term used to distinguish unmodified vegetable oil fuel from biodiesel. SVO typically needs to be preheated or blended with diesel fuel to burn in a vehicle efficiently.

Swept Area

The area (in square feet or meters squared) that a wind generator's rotor (blades) sweep. This is the collector area for a wind generator. The larger the collector, the more energy it will capture. Besides the wind itself, this has the largest effect on wind generator production.

Synchronous Generator

An alternator whose output frequency is "synchronous" with the speed of rotation. Often this means a wound-field alternator, used in stand-alone systems, whose voltage can be regulated by an AVR (controlling the field) while the speed is regulated by an electronic load controller (ELC).

System Grounding

Connecting one current-carrying conductor of a system to ground at one point to create a reference to 0 volts.

1 A B C D E F G H I J K L M N O P Q R S T U V W Y

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