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SECONDARY CELL Secondary cells are batteries (electrochemical cells) that are rechargeable. The chemical reaction within the secondary cell is reversible, allowing the cell to be recharged many times.

SELF-DISCHARGE The tendency of all batteries to lose energy. Self-discharge represents energy lost to internal chemical reactions within the cell. This energy is not and cannot be used from the battery or cell’s output terminals.

SENSOR (Temperature) Sensing 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 CONNECTION A wiring configuration used to increase voltage from more than one supply. Series wiring is positive to negative (+ to -) or negative to positive (- to +). Opposite of parallel connection. Series circuits have only one possible path for electron flow.

SERIES REGULATOR A device that prevents overcharging of a battery by disconnecting the charging source as the battery voltage approaches some upper limit.

SERIES STRING A group of PV modules or batteries wired in series.

SHORT CIRCUIT A circuit in which two source leads of opposite polarity or dissimilar potential are connected directly to each other with no regulation or load in between, allowing the full energy potential of the source to flow through the circuit. A short circuit will trip the breaker or fuse, and may damage components, or even cause a fire.

SHORT CIRCUIT CURRENT (ISC) The current between two points in a circuit when the points are electrically connected with a conductor with essentially zero resistance. Normally applied to PV modules, which can be short circuited safely because they are limited current devices.

SHUNT (noun)

1. A resistive load through which electron flow is diverted, typically used to heat air or water.
2. A component with a precise, known resistance used to determine amperage by measuring the voltage across it and using Ohm’s law (I = V/R).

SHUNT (verb) To divert electrical current to a separate circuit or load.

SHUNT REGULATOR A device that prevents overcharging of a battery by diverting some (or all) of the charging current to a resistive load when the battery voltage reaches a preset upper limit.

SIDE-OF-POLE MOUNT A PV mount installed on the side of a pole. May be fixed or seasonally adjustable.

SILICON A nonmetallic element, which when specially treated, is sensitive to light and capable of transforming light into electricity. Silicon is the basic material of most beach sand, and is the raw material used to manufacture most photovoltaic cells.

SINGLE CRYSTAL CELL A wafer of silicon that has a perfect, continuous, crystal lattice (on the atomic level).

SITE EVALUATION An estimation of a location for its potential for solar, hydro, or wind power.

SOLAR THERMAL COLLECTORS A solar collector is a device designed to absorb incident solar radiation and to transfer the energy to the fluid or air passing through it.

SOLAR COOKER A device that converts the sun’s energy into heat energy, which is then used to cook food.

SOLAR-ELECTRIC CELL See PHOTOVOLTAIC CELL

SOLAR-ELECTRIC MODULE See PHOTOVOLTAIC MODULE

SOLAR ENERGY Energy coming directly from the Sun.

SOLSTICE (SUMMER & WINTER) The longest and shortest days of the year. The longest day (Summer Solstice) is about June 21st in the Northern Hemisphere. The shortest day (Winter Solstice) is about December 21st in the Northern Hemisphere.

STAND-ALONE SYSTEM A system that operates independently of the utility lines. It may draw supplementary electricity from the utility, but is not capable of providing electricity to the utility.

STANDARD TEST CONDITIONS (STC) The standardized conditions of 1,000 watts per meter squared of solar insulation at 25˚C (77˚F) for testing PV module ratings.

STATE OF CHARGE (SOC) A ratio, expressed in percent, of the energy remaining in a battery in relation to its capacity when fully charged.

STORAGE BATTERY See BATTERY and SECONDARY CELL.

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. See POST AND BEAM CONSTRUCTION.

STRUCTURAL INSULATED PANELS (SIPs) A no-cavity solid building system of wall and roof panels "sandwiching" polystyrene insulation between an outer and inner sheathing panel (typically oriented strand board (OSB) or metal).

SUSTAINABLE A material or energy source, which if managed carefully, will provide at current levels indefinitely.

SULFATION The formation of lead-sulfate crystals on the plates of a lead-acid battery, which decreases battery capacity by impeding the opportunity for chemical reaction within a cell. Sulfation can be caused by leaving the battery in a discharged state for long periods of time.

SURGE CAPACITY The maximum amount of AC power an inverter may deliver to a load (or loads) for a short period of time, such as when starting a motor.

SWEPT AREA The area (in square feet or meters^2) 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.

SWITCH A device that breaks an electrical circuit, halting the flow of electrons through the circuit.