Sizing Of Energy Storage For Microgrid

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Microgrid is a Small Scale Power Supply Network to provide Power for a Small Community. It is used for local Power Generation for local loads. It uses highly Flexible and efficient Small Power Generating sources. It is connected to both the local generating units and the utility grid thus preventing power outages. Excess power can be sold to the utility grid. Size of the Microgrid may range from housing estate to municipal regions.

Need Of Microgrid

Microgrid could be the answer to our energy crisis. Transmission losses gets highly reduced. Microgrid results in substantial savings and cuts emissions without major changes to lifestyles. Provide high quality and reliable energy supply to critical loads. Various microgrid components are 

Wind Turbine - Wind pushes the fan blades of wind turbine and produce energy output. No control over the energy output.

Micro Turbine - Single staged combustion turbine. Usually powered by biogas, natural gas, propane.

Photovoltaic system - PV cell is a self-contained electricity producing device consist of semiconducting material. Light striking on the semiconducting material in PV cell, creating dc.

Fuel cell - FC uses an electrochemical process  to turn hydrogen and oxygen to electricity. Energy storage system - ESS include electrochemical battery, super capacitor, compressed air energy storage, super conducting energy storage, flywheel energy storage etc. Lithium ion is commonly used because best energy to weight ratio and slow loss of charge when not in use. ESS store energy at the time of surplus and re-dispatch it when needed.  ESS plays an important role in microgrid. Sizing of ESS to be considered first when considering ESS in MG. ESS increase the reliability of power system. The cost of ESS includes one time ESS cost and the annual maintenance cost. The battery storage system made up of small battery blocks.

Microgrid

Microgrid Operating Modes

Microgrid Island Mode

Island Mode - Utility grid is not supplying power. Static switch is open. Feeder A, B, C are being supplied by Microsources.Feeder D (not sensitive) is dead. 

Microgrid Grid ConnectedMode

Grid Connected Mode - Utility grid is active. Static switch is closed. All the feeders are being supplied by utility grid.

ESS in islanded microgrid

Sizing of a suitable battery bank in terms of power and energy help in shaving the peak demand. Stores excess renewable energy and supply load when renewable energy is low. When ESS discharges its energy to power grid its generating positive real power. The upstream grid can be treated as bidirectional generator which generate  positive power  when power is transferred from the MG and generate negative power when the power transferred from the MG to upstream grid. The output of bidirectional generator is limited by the capacity of transmission line between the MG and upstream grid.   

Conclusion

BESS for MG decrease the schedule cost of MG in islanded MG and increase  benefit of MG. As the size  of BESS increases, the benefit increases. The TCPD increases in a constant rate and when the size of BESS is greater than optimal size TC will increase  in islanded MG and TB will reduce in grid connected MG.

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