Is Grid Scale DC-Coupled PV and Energy Storage Plant Really a Good Idea?

It is now widely accepted that a coupled PV and Battery Energy Storage System (BESS) hybrid power plant behind a common point of interconnection provides many cost and performance benefits over two separate stand-alone plants. The “DC-coupled” design approach where the PV and BESS share a common DC bus and power electronics is widely considered as an optimal, more efficient solution. The alternate “AC-coupled” design, where both the resources share a common AC bus, require separate inverters and step-up transformers, thus adding costs and incurring additional transformation losses. However, in practice, the AC-coupled design is preferred for large grid scale plants for a variety of reasons including the undesirable distribution of storage on a vast PV field, grounding concerns, maturity of dual-port utility-scale inverters, and flexibility of grid operations. In this presentation a quantification of these tradeoffs based on our grid-scale hybrid plant development experience is provided.