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Distributed Energy Resources

DOE Lab Introduces Tool to Analyze Performance of Solar-Battery Backup Systems

Lawrence Berkeley National Laboratory has released a digital tool to analyze the ability of a photovoltaic energy storage system to provide backup power during short-duration interruptions.

Berkeley Lab’s Power Reliability Event Simulator Tool is a publicly available model that can simulate the occurrence of short-duration power interruptions in any county in the continental United States.

PRESTO simulates the occurrence of interruption events over a large number of simulation years, up to 20,000, and, in each simulation year, produces a time-series of interruption events with stochastic frequency, duration, and timing. The model then uses a set of probabilistic functions trained on historical hourly power interruption data at the county level obtained from PowerOutage.US for the years 2017 through 2021. As a result, the Berkeley researchers said, statistical properties of simulated power interruption events match the statistical properties of actual historical power interruptions for the selected county.

Berkeley Lab said PRESTO is primarily designed for use in Monte Carlo or other probabilistic analyses of the impacts of short-duration power interruptions. One application is to assist in evaluating the backup power capabilities and customer reliability value of onsite photovoltaic energy storage systems or other strategies for mitigating short-duration power interruptions.

When a county is selected for analysis, PRESTO loads default average interruption duration and frequencies based on power reliability data from the Energy Information Administration, which the user can either use or override. Berkeley Lab said the user can then visualize the statistical properties of the produced dataset, including distributions of duration and frequency as well as seasonal and time-of-day profiles, and download the results.

To demonstrate the tool’s use, Berkeley Lab developed a case study analysis that explored several key determinants of photovoltaic energy storage systems backup power performance for representative single-family homes in three regions of the United States.

The case study highlights how photovoltaic energy storage systems backup performance is affected by how a customer operates the battery under normal day-to-day conditions and how that affects the battery’s state of charge when a power interruption occurs.

The case study found that backup performance is especially low for interruptions occurring during the evening hours when the customer is assumed to be taking service under a utility’s residential time-of-use rates, which has a peak period extending from 4 p.m. to 8 p.m.

The rates incentivize customers to discharge their batteries during those peak times, but that leaves little charge remaining for any power interruption that might occur soon thereafter, Berkeley Lab said.

The case study also illustrated how photovoltaic energy storage system backup performance is impacted by system sizing, backup load configuration, whether or not the customer is able to charge from the grid, and regional variations in heating and cooling demand.

Berkeley Lab is hosting a free webinar on November 7 at 11:00 a.m. Pacific Time at which it will present its PRESTO tool and the case study.