Energy Storage

As long as there has been an electrical grid, companies have sought ways to safely and efficiently store energy so that it can be consumed on demand, output can be meticulously controlled and the exact frequency of the energy distributed can be tightly regulated. Today, a wide variety of technologies have been developed and deployed to ensure that the grid can meet our everyday energy needs – from scalable banks of advanced chemistry batteries and magnetic flywheels, to pumped hydro-power and compressed air storage.

Perhaps most importantly, energy storage is resource neutral and allows us to use electricity from any power source more efficiently. Whether the energy produced comes from a solar power plant or a field of wind turbines, energy storage technologies capture that energy to be used on demand when it is needed most.

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Energy Storage Definitions

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.

C Rate – A charge rate that, under ideal conditions, is equal to the energy storage capacity of an electricity storage device divided by 1 hour. For example, a storage device that can store 5 kilowatt-hours of electric energy has a C rate of 5 kilowatts, also known as a C rate of 1.

Charge Rate – The rate at which storage can be charged.

Days of Storage – The number of consecutive days a stand-alone system will meet a defined load without energy input.

Depth of Discharge – The portion of energy discharged from a storage system relative to the amount of extractable stored energy.

End of Discharge Voltage – For electrochemical batteries, the voltage of the battery that has been fully discharged.

Energy Density – The ration of available energy per pound; usually used to compare storage batteries.

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.

Frequency Regulation – The injection and withdrawal of power on a second-by-second basis to maintain grid frequency (60 Hz).

Gel-type Battery – Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

Load Leveling – A method for reducing fluctuations in customer electricity demand. It usually involves storing power during periods of light loading on the system and delivering it during periods of high demand.

Peak Shaving – The process of reducing the amount of energy purchased from the utility company during peak hours when the charges are highest.

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