How to test photovoltaic energy storage cabinet batteries

This report describes development of an effort to assess Battery Energy Storage System (BESS) performance that the U.S. Department of Energy (DOE) Federal Energy Management Program (FEMP) and others can employ to evaluate performance of deployed BESS or solar photovoltaic (PV) +BESS systems.

Avoid risks, enhance market access An Energy Storage System (ESS) battery, incorporates one or more cells, modules or battery packs which is controlled by a battery management system (BMS). These batteries are typically encased in one with terminals to connect to other products. Some ESS batteries may also have cooling and heating units within.

Efficiency is the sum of energy discharged from the battery divided by sum of energy charged into the battery (i.e., kWh in/kWh out). This must be summed over a time duration of many cycles so that initial and final states of charge become less important in the calculation of the value.

For battery systems, Efficiency and Demonstrated Capacity are the KPIs that can be determined from the meter data. Efficiency is the sum of energy discharged from the battery divided by sum of energy charged into the battery (i.e., kWh in/kWh out).

That method compared actual metered PV system energy delivery with that of a computer model. The computer model used was the National Renewable Energy Laboratory's (NREL's) System Advisor Model (SAM). The KPIs reported are Availability (% up-time) and Performance Ratio (PR).

The computer model used was the National Renewable Energy Laboratory's (NREL's) System Advisor Model (SAM). The KPIs reported are Availability (% up-time) and Performance Ratio (PR). If the PV system output was zero or less than 5% of the model estimate, then the time interval was counted as “unavailable.”