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EARTH Synonymous with “ground.”

EFFICIENCY (PV modules) The ratio of power output of a photovoltaic cell to the incident power from the sun or simulated sun sources under specified standard insulation conditions. A solar cell that converts 1/10 of the sun’s energy that strikes its surface to electricity has an efficiency of 10 percent.

EFFICIENCY The effectiveness of a device to convert energy from one form to another, or to transfer energy from one body to another. An electric pump that is 60 percent efficient converts 60 percent of the input energy into work—pumping water. The remaining 40 percent becomes waste heat.

ELECTRICAL POTENTIAL Same as VOLTAGE.

ELECTRIC CURRENT The rate at which electrons flow through an electrical conductor, usually measured in amperes (amps).

ELECTRICITY Energy flow resulting from the flow of charged particles, such as electrons or ions.

ELECTROLYSIS The breaking down of a chemical compound into simpler compounds or elements by the passage of electricity through the chemical compound. Commonly used to describe the extraction of hydrogen (and oxygen) from water.

ELECTROLYTE The fluid in a battery, which is the medium of ion transport within an electrochemical cell. It provides a path for electron transfer between the anode and cathode of a battery cell.

ELECTROMAGNETIC RADIATION (EMR) Magnetic radiation produced by a changing electrical current, such as alternating current (AC).

ELECTRON A negatively charged particle. The movement of electrons in an electrical conductor constitutes an electric current.

EMBODIED ENERGY The energy consumed by all of the processes associated with the production of a material. This includes the energy required in mining, transport, manufacturing, administration, use, disposal, etc.

ENERGY The amount of work that a system or entity can do (potential energy) or is doing (kinetic energy), measured in joules. The product of power and time, measured in watt-hours. 1,000 watt-hours = 1 kilowatt-hour (KWH).

ENERGY DENSITY A ratio of a battery or cell’s capacity to either its volume or weight. Volumetric energy density is expressed in watt-hours per cubic inch. Weight energy density is expressed in watt-hours per pound.

ENGINE A machine that converts energy into mechanical force or motion. Sources of energy include heat, chemical reaction, potential energy of elevated water, etc.

EQUALIZATION The process of restoring all cells in a battery to an equal state-of-charge. For lead-acid batteries, this is a charging process designed to bring all cells to 100 percent state-of-charge.

EQUALIZING CHARGE A continuation of normal battery charging, at a voltage level slightly higher than the normal end-of-charge voltage, in order to provide cell equalization within a battery.

EQUINOX (SPRING & FALL) The time when the sun crosses the plane of the earth’s equator, making night and day of equal length all over the earth, occurring about March 21st and September 21st.

EVAPORATION The process of a liquid changing its state into a gas when heat is added. In the most common occurrence on earth, water evaporation requires 970 BTUs per pound (pint).