Industry Glossary

Activated Shelf Life

The period of time, at a specified temperature, that a charged battery can be stored before its capacity falls to an unusable level.

Activation Voltage(s)

The voltage(s) at which a charge controller will take action to protect the batteries.

Adjustable Set Point

A feature allowing the user to adjust the voltage levels at which a charge controller will become active.

Alternating Current (AC)

A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission networks use AC because>voltage can be controlled with relative ease.

Ampere (amp)

A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere.

Ampere-Hour(Ah/AH)

A measure of the flow of current (in) over one hour; used to measure battery capacity

Anemometer

An instrument used to measure the velocity, or speed, of the wind..

Anode

The positive electrode in a battery.

Availability Factor

The percentage of time that a wind turbine is able to operate and is not out commission due to maintenance or repairs.

Base Load

The average amount of electric power that a utility must supply in any period.

Battery

Two or more electrochemical cells enclosed in a container and electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term battery also applies to a single cell if it constitutes the entire electrochemical storage system.

Battery Available Capacity

The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, initial state of charge, age, and cut-off voltage.

Battery Capacity

The maximum total electrical charge, expressed in ampere-hours, which a battery can deliver to a load under a specific set of conditions.

Battery Cell

The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, an electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, and a container for all the above.

Battery Cycle Life

The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

Battery Energy Capacity

The total energy available, expressed in watt-hours kilowatt-hours, which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut-off voltage. This term is more common to system designers than it is to the battery industry where capacity usually refers to ampere-hours.

Battery Energy Storage

Energy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter.

Battery Life

The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.

Blades

The flat panels on a wind turbine that are connected to a center shaft that converts the push of the wind into a circular motion in a wind turbine.

Capacity Factor

A measure of the productivity of a wind turbine, calculated by the amount of power that a wind turbine produces over a set period of time, divided by the amount of power that would have been produced if the turbine had been running at full capacity during that same time interval.

Cell (battery)

A single unit of an electrochemical device capable of producing direct voltage by converting chemical energy into electrical energy. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably).

Charge

The process of adding electrical energy to a battery.

Charge Controller

A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

Charge Factor

A number representing the time in hours during which a battery can be charged at a constant current without damage to the battery. Usually expressed in relation to the total battery capacity, i.e., C/5 indicates a charge factor of 5 hours. Related to charge rate.

Charge Rate

The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.

Conductor

The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line.

Converter

A unit that converts a direct current (dc) voltage to another dc voltage.

Cut-in Speed

The wind speed at which the turbine blades begin to rotate and produce electricity, typically around 10 miles per hour.

Cut-out Speed

The wind speed at which the turbine automatically stops the blades from turning and rotates out of the wind to avoid damage to the turbine, usually around 55 to 65 miles per hour.

Cutoff Voltage

The voltage levels (activation) at which the charge controller disconnects the energy source from the battery or the load from the battery.

Cycle

The discharge and subsequent charge of a battery.

DC-to-DC Converter

Electronic circuit to convert direct current voltages (e.g., photovoltaic module voltage) into other levels (e.g., voltage). Can be part of a maximum power point tracker.

Deep-Cycle Battery

A battery with large plates that can withstand many discharges to a low state-of-charge.

Deep Discharge

Discharging a battery to 20% or less of its full charge capacity.

Depth of Discharge (DOD)

The ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. Under certain conditions, such discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%

Direct Current (DC)

A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to alternating current, its opposite.

Discharge

The withdrawal of electrical energy from a battery.

Discharge Rate

The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

Distributed Energy Resources (DER)

A variety of small, modular power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.

Distributed Generation

A popular term for localized or on-site power generation.

Distributed Power

Generic term for any power supply located near the point where the power is used. Opposite of central power.

Distributed Systems

Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids.

Electric Circuit

The path followed by electrons from a power source (generator or battery), through an electrical system, and returning to the source.

Electric Cooperative

A form of utility in which all users own shares. Electric cooperatives are common in rural areas that are expensive to serve because of the long distances between users. Frequently, the government contributes in various ways to rural cooperatives to reduce costs to individual owner/users.

Electric Current

The flow of electrical energy (electricity) in a conductor, measured in amperes.

Electrical grid

An integrated system of electricity distribution, usually covering a large area

Energy Audit

A survey that shows how much energy used in a home, which helps find ways to use less energy.

Energy Density

The ratio of available energy per pound; usually used to compare storage batteries.

Energy Policy Act of 1992 (EPAct)

A federal statute that, among other things, established additional forms of non-utility generators. It also permitted non-generator-owning municipalities to purchase wholesale electricity, thus opening the door to municipalization.

Environmental Impact Statement (EIS)

A thorough study of each proposed electric utility project with potential for significant environmental impacts, including evaluation of alternatives and mitigation.

Equalization

The process of restoring all cells in a battery to an equal state-of-charge. Some battery types may require a complete discharge as a part of the equalization process.

Float Charge

The voltage required to counteract the self-discharge of the battery at a certain temperature.

Float Life

The number of years that a battery can keep its stated capacity when it is kept at float charge.

Gigawatt (GW)

A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.

Grid-Connected System

A residential electrical system such as solar panels or wind turbines which act like a central generating plant, supplying power to the commercial grid.

Hub

The central part of the wind turbine, which supports the turbine blades on the outside and connects to the low-speed rotor shaft inside the nacelle.

Hybrid System

The combination of multiple energy producing technologes such as photovoltaic systems combined with small wind turbine systems.

Input Voltage

This is determined by the total power required by the alternating current loads and the voltage of any direct current loads. Generally, the larger the load, the higher the inverter input voltage. This keeps the current at levels where switches and other components are readily available.

Inverter

A device that converts direct current electricity toalternating current either for stand-alone systems or to supply power to an electricity grid.

Kilowatt (kW)

A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

Kilowatt-Hour (kWh)

1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.

Lead-Acid Battery

A general category that includes batteries with plates made of pure lead, lead-antimony, or lead-calcium immersed in an acid electrolyte.

Life

The period during which a system is capable of operating above a specified performance level.

Life-Cycle Cost

The estimated cost of owning and operating an energy system for the period of its useful life.

Line-Commutated Inverter

An inverter that is tied to a power grid or line. The commutation of power (conversion from direct current to alternating current) is controlled by the power line, so that, if there is a failure in the power grid, the energy system cannot feed power into the line.

Liquid Electrolyte Battery

A battery containing a liquid solution of acid and water. Distilled water may be added to these batteries to replenish the electrolyte as necessary. Also called a flooded battery because the plates are covered with the electrolyte.

Load

The demand on an energy producing system; the energy consumption or requirement of a piece or group of equipment. Usually expressed in terms of amperes or watts in reference to electricity.

Load Circuit

The wire, switches, fuses, etc. that connect the load to the power source.

Low Voltage Cutoff (LVC)

The voltage level at which a charge controller will disconnect the load from the battery.

Low Voltage Disconnect

The voltage at which a charge controller will disconnect the load from the batteries to prevent over-discharging.

Low Voltage Warning

A warning buzzer or light that indicates the low battery voltage set point has been reached.

Maintenance-Free Battery

A sealed battery to which water cannot be added to maintain electrolyte level.

Megawatt (MW )

1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.

Megawatt-Hour

1,000 kilowatt-hours or 1 million watt-hours.

Met Tower

A group of instruments (including anemometers and wind vanes) that collectively measure various meteorological parameters such as wind speed, wind direction, and temperature at various heights above the ground. met is short for meteorological.

Modularity

The use of multiple inverters connected in parallel to service different loads.

Multi-Stage Controller

A charging controller unit that allows different charging currents as the battery nears full state_of_charge.

Nacelle

The structure at the top of the wind turbine tower just behind (or in some cases, in front of) the wind turbine blades that houses the key components of the wind turbine, including the rotor shaft, gearbox, and generator.

National Electrical Code (NEC)

Contains guidelines for all types of electrical installations. The 1984 and later editions of the NEC contain Article 690, "Solar Photovoltaic Systems" which should be followed when installing a PV system.

National Electrical Manufacturers Association (NEMA)

This organization sets standards for some non-electronic products like junction boxes.

National Renewable Energy Laboratory (NREL)

A U.S. Department of Energy research facility funded to research renewable energy technologies such as wind, solar, biomass, hydro and geothermal energy.

Net Metering

A term used to describe grid connected installations in which the local electrical source such as a wind turbine or solar panels are connected to the electrical meter so that when excess electricity is generated it is passed to the grid causing the meter to run backwards.

Nickel Cadmium Battery

A battery containing nickel and cadmium plates and an alkaline electrolyte.

Nominal Voltage

A reference voltage used to describe batteries, >modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).

Ohm

A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

Overcharge

Forcing current into a fully charged >battery. The battery will be damaged if overcharged for a long period.

Peak Demand/Load

The maximum energy demand or load in a specified time period.

Plates

A metal plate, usually lead or lead compound, immersed in the electrolyte in a battery.

Power Conditioning

The process of modifying the characteristics of electrical power (for e.g., inverting direct current to alternating current).

Power Conversion Efficiency

The ratio of output power to input power of the inverter.

Power Density

The ratio of the power available from a battery to its mass (W/kg) or volume (W/l).

Power Factor (PF)

The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes.

Production Tax Credit (PTC)

The result of the Energy Policy Act of 1992, a commercial tax credit that applies to whole-sale electrical generators of wind energy facilities based upon the amount of energy generated in a year.

Pulse-Width-Modulated (PWM) Wave Inverter

A type of power inverter that produce a high quality (nearly sinusoidal) voltage, at minimum current harmonics.

Rated Battery Capacity

The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. See battery capacity.

Rated Power

Rated power of the inverter. However, some units can not produce rated power continuously.

Rated Wind Speed

The wind speed at which the turbine is producing its nameplate-rated power production. For most small wind turbines this is around 30 to 35 miles per hour.

Rectifier

A device that converts alternating current to direct current. See inverter.

Regulator

Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs.

Reserve Capacity

The amount of generating capacity a central power system must maintain to meet peak loads.

Resistance (R)

The property of a conductor, which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms.

Resistive Voltage Drop

The voltage developed across a cell by the current flow through the resistance of the cell.

Rotor

Comprises the spinning parts of a wind turbine, including the turbine blades and the hub.

Sealed Battery

A battery with a captive electrolyte and a resealing vent cap, also called a valve-regulated battery. Electrolyte cannot be added.

Secondary Battery

A battery that can be recharged.

Self-Discharge

The rate at which a battery, without a load, will lose its charge.

Shallow-Cycle Battery

A battery with small plates that cannot withstand many discharges to a low state-of-charge.

Shelf Life of Batteries

The length of time, under specified conditions, that a battery can be stored so that it keeps its guaranteed capacity.

Short-Circuit Current

The current flowing freely through an external circuit that has no load or resistance; the maximum current possible.

Sine Wave

A waveform corresponding to a single-frequency periodic oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.

Sine Wave Inverter

An inverter that produces utility-quality, sine wave power forms.

Single-Stage Controller

A charge controller that redirects all charging current as the battery nears full state-of-charge.

Specific Gravity

The ratio of the weight of the solution to the weight of an equal volume of water at a specified temperature. Used as an indicator of battery state-of-charge.

Spinning Reserve

Electric power plant or utility capacity on-line and running at low power in excess of actual load.

Square Wave

A waveform that has only two states, (i.e., positive or negative). A square wave contains a large number of harmonics.

Square Wave Inverter

A type of inverter that produces square wave output. It consists of a direct current source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency.

Stand-Alone System

An autonomous or hybrid electrical system not connected to a grid. May or may not have storage, but most stand-alone systems require batteries or some other form of storage.

Standby Current

This is the amount of current (power) used by the inverter when no load is active (lost power). The efficiency of the inverter is lowest when the load demand is low.

State-of-Charge (SOC)

The available capacity remaining in the battery, expressed as a percentage of the rated capacity.

Storage Battery

A device capable of transforming energy from electric to chemical form and vice versa. The reactions are almost completely reversible. During discharge, chemical energy is converted to electric energy and is consumed in an external circuit or apparatus.

Stratification

A condition that occurs when the acid concentration varies from top to bottom in the battery electrolyte. Periodic, controlled charging at voltages that produce gassingwill mix the electrolyte.

Sulfation

A condition that afflicts unused and discharged batteries; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge.

Surge Capacity

The maximum power, usually 3-5 times the rated power, that can be provided over a short time.

Temperature Compensation

A circuit that adjusts the charge controller activation points depending on battery temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from ambient temperature.

Total AC Load Demand

The sum of the >alternating current loads. This value is important when selecting an inverter.

Total Harmonic Distortion

The measure of closeness in shape between a waveform and it's fundamental component.

Transformer

An electromagnetic device that changes the voltage of alternating current electricity.

Trickle Charge

A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

Tower

The base structure that supports and elevates a wind turbine rotor and nacelle. .

Uninterruptible Power Supply (UPS)

The designation of a power supply providing continuous uninterruptible service. The UPS will contain batteries.

Utility-Interactive Inverter

An inverter that can function only when tied to the utility grid, and uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the energy source's output is fully synchronized with the utility power.

Vented Cell

A battery designed with a vent mechanism to expel gases generated during charging.

Volt (V)

A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.

Voltage

The amount of electromotive force, measured in volts, that exists between two points.

Voltage Protection

Many inverters have sensing circuits that will disconnect the unit from the battery if input voltage limits are exceeded.

Voltage Regulation

This indicates the variability in the output voltage. Some loads will not tolerate voltage variations greater than a few percent.

Watt

The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).

Waveform

The shape of the phase power at a certain frequency and amplitude.

Wet Shelf Life

The period of time that a charged battery, when filled with electrolyte, can remain unused before dropping below a specified level of performance.

Wind Monitoring System

Also termed met tower, a group of instruments (including anemometers and wind vanes) that collectively measure various meteorological parameters such as wind speed, wind direction, and temperature at various heights above the ground..

Wind Powering America (WPA)

A U.S. Department of Energy initiative designed to promote the use of wind energy across the country, with the goal of quadrupling U.S. wind capacity by 2010.

Wind Power Class

A system designed to rate the quality of the wind resource in an area, based on the average annual wind speed. The scale ranges from 1 to 7 with 1 being the poorest wind energy resources and 7 representing exceptional wind energy resources

Wind Resource

The wind energy available for use based on historical wind data, topographic features, and other parameters.

Wind Rose

A circular plot used to define certain characteristics about wind speed and direction observed at a monitoring location.

Wind Speed

The rate at which air particles move through the atmosphere, commonly measured with an anomometer.

Wind Vane

A device used to measure wind direction.