Evaluating the Technical and Economic Performance of PV Plus Storage Power Plants by National Renewable Energy Laboratory

Posted: August 31, 2017 - 11:20 / NREL / Reports
Executive Summary
The decreasing costs of both PV and energy storage technologies have raised interest in the creation of combined “PV plus storage” power plants. In this study, we examine the tradeoffs among various PV plus storage configurations and discuss an approach to quantify the impact of configuration on system net value.
 
We consider the four system configurations listed in Table ES-1.
We use benefit/cost (B/C) ratio, measured here by the ratio of the sum of Year 1 energy and capacity value and the Year 1 (levelized) capital and operating costs, as our primary performance metric, as levelized cost of energy does not consider the difference in value between various PV plus storage configurations. Coupling PV and storage can change both the benefits (energy revenue and capacity value) and costs. Coupling PV and storage can increase the revenue by utilizing otherwise clipped energy. Coupling can also decrease revenue by restricting storage operation during periods of high solar output because of the shared inverter. Coupling can also reduce costs by sharing components.
 
To evaluate these tradeoffs, we consider a case study of different PV plus storage systems located in Southern California. Figure ES-1 shows the results for our base system, which consists of a 50-megawatt (MW) fixed-tilt PV system with an inverter loading ratio of 1.3 and 30 MW/120 megawatt-hours (MWh) of storage. At historical (2014) electricity prices (when PV penetration in California was about 6%), and 2016 estimated costs for PV and battery components, the B/C ratio of PV without storage is greater than a system with added storage. However, because of the decrease in system capital cost associated with coupling, DC-coupled PV plus storage systems have higher B/C ratios than PV and storage deployed independently. The plant with the highest B/C ratio is the plant that stores only solar due to eligibility for the investment tax credit (ITC). While forcing the plant to store only solar reduces energy revenue, the decrease in cost due to the ITC is greater than the loss in revenue.