Design and Sizing of Energy Storage for Grid Connected PV Power Plants

By their nature PV power generation can be considered static. This means they do not have inertia as rotating machines do, and thus, they cannot handle transient load demands that go over their instantaneous maximum power point. In addition, when compared to traditional generators their power ramp rate is much steeper, being able to reach values of 90% per minute and higher. Both characteristics have an impact on power system operation, especially in the case of large PV plants. For example, due to their lack of inertia, a PV plant cannot participate in primary frequency regulation, injecting active power during system faults. Further, the rapid power ramp rate exhibit by PV plants can also affect system stability due to the fast increase or decrease in generated power, which usually cannot be compensated by the rest of the generators in the grid. In this regard, it has been shown that these two issues can be mitigated by the addition of energy storage elements to the PV plant power conditioning system. However, to do so proper sizing, interfacing and control of the energy storage is required. To tackle this issue, analysis of energy storage requirements for a grid connected power plant is performed in this paper. As a result, sizing guidelines and a design procedure for the required battery bank are developed. In addition, a control strategy to regulate the power ramp rate of the system is presented and its effectiveness verified through computer simulations.