Background

Current work involves combining battery-based Energy Storage (ES) with PV to mitigate ramping and to shift generation to better align with load. These PV + ES systems typically have separate inverters to convert DC output from batteries and solar arrays to AC (sometimes referred to as AC coupled). Some systems utilize a shared inverter, with a common DC bus and a single AC output (sometimes referred to as DC coupled). This could potentially reduce capital cost.

A separate trend in PV systems is an increase in plant DC:AC ratios. This can be due to relatively low panel prices, interconnection constraints, and long-term degradation of panels. The result can be an “optimal” plant from an economic perspective, but with sometimes significant amounts of energy being wasted due to inverter AC “clipping”, where the inverter capacity is below the DC output of the array, sometimes for only minutes at a time.

Project Objectives

Georgia Power (GPC), Southern Company Services, Inc. (SCS) and EPRI collaboratively demonstrated PV plus Energy Storage (PV+ES) technology in Athens, GA to capture solar energy that would have been clipped due to oversizing the PV array compared to inverter AC output rating. The goal of this project was to understand the impact of DC/AC ratio on energy clipping loss; promote the technology deployment; and evaluate the performance of MW-scale application of this PV+ES concept through the energy clipping loss comparison, cost-benefit analysis, and other potential performance benefits investigation. The evaluation entailed:

• Technology assessment and performance analysis of a small-scale field demo at GPC’s 1MW PV Demo facility in Athens, GA (~15kWdc/10kWac PV array with battery for this project, separate from existing 1MW arrays)
• A feasibility study to look at value of MW-scale implementation of this technology