Optimal Integration of Distributed Energy Storage Devices in Smart Grids

Energy storage is traditionally well established in the form of large scale pumped-hydro systems, but nowadays is finding increased attraction in medium and smaller scale systems. Such expansion is entirely complementary to the forecasted wider integration of intermittent renewable resources in future electrical distribution systems (Smart Grids). This paper is intended to offer a useful tool for analyzing potential advantages of distributed energy storages in Smart Grids with reference to both different possible conceivable regulatory schemes and services to be provided. The Smart Grid Operator is assumed to have the ownership and operation of the energy storage systems, and a new cost-based optimization strategy for their optimal placement, sizing and control is proposed. The need to quantify benefits of both the Smart Grid where the energy storage devices are included and the external interconnected grid is explored. Numerical applications to a Medium Voltage test Smart Grid show the advantages of using storage systems related to different options in terms of incentives and services to be provided.

I. Nomenclature

Cost for building branch .

Cost of installation of capacitors.

Cost of installation of DESSs.

Cost of losses.

Cost of energy for price arbitrage.

Cost of reactive power imported from HV grid.

Cost of reactive power provided by DG units.

Cost of network upgrading.

Cost for upgrading branch .

Energy stored in the DESS located at node and at the end of the th time interval of the th year.

Cost of branch maintenance.

Number of days of the th year characterized by a specified load and generation level at the th interval.

Number of time intervals at the th year.

Number of years of the planning period.

Size of DESS base unit.

Active power of DESS at th node and th time interval of the th year.

Total DESSs active power at th time interval of the th year (sum of on all grid nodes).

Distribution system active power losses at th interval of the th year.

Installation price of capacitor base unit.

Installation price of DESS base unit.

DG reactive power price at th time interval of the th year.

Losses price at th time interval of the th year.

HV reactive power price at th time interval of the th year.

Active energy price at the th time interval of the th year.

Size of capacitor base unit.

DG total reactive power at th time interval of the th year.

Reactive power imported from HV grid at th time interval of the th year.

Specified value of .

Residual value of branch .

Number of DESS base units at node .

Number of capacitor base units at node .

Total number of nodes.

Total number of nodes where capacitors are installed.

Total number of nodes where DESSs are installed.

Total number of branches in the network.

Discount rate.

Rate of change of .

Rate of change of .

Rate of change of .

Rate of change of .

DESSs charging efficiency.

DESSs discharging efficiency.

Duration of the th time interval of the th year.