A new report from ACCURE Battery Intelligence finds that overstated battery availability is putting investor returns at risk, with a 2 percent shortfall in revenue enough to cut a project's debt service coverage ratio from 1.30x to roughly 1.26x and take about a point off what investors actually earn.
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The gap comes down to how availability gets measured. The median battery storage site reports 96.7 percent availability, close to the industry's usual 97 percent target. But only count something as available when it actually responds to a dispatch call, not just when it shows "online," and the median drops to 94.1 percent. That gap averages 2.6 percentage points, and widens to 6 points at the lower end. The report, “Banking BESS: financing lessons for lenders and investors,” draws on 4 GW of power capacity and 10 GWh of energy capacity across ERCOT, CAISO, the UK and Germany, with support from U.S. Bank.
Almost no headroom from day one
Owners typically overbuild capacity by around 20.2 percent above nameplate to absorb conversion losses, usable capacity losses and operational shortfalls. Once those are accounted for, the median project starts commercial operation with just 0.5 percent of headroom left, before any battery ageing even begins. Power conversion systems cause the biggest share of downtime, at 36.4 percent, ahead of balance of system, racks and containers, and most of that, 57.6 percent, comes from small, recurring outages rather than major failures.
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If stranded energy from cell imbalance is factored in, the typical site will deliver 6.9 percent less usable power than its own capacity test says it should, corresponding to about seven battery containers' worth on a top-tier 500 MWh site. On a standard loan, a 2 percent drop in revenue is enough to pull the debt service coverage ratio from 1.30x to about 1.26x, and knock roughly a point off what investors actually earn.
Degradation not the main problem
Batteries in the study aged a bit more slowly than their warranty curves assume, with state of health running 1.8 percentage points above the average curve in early years. But that doesn't mean spare capacity, argues the report. With so little headroom left after conversion, usable capacity and operational losses, a battery ageing more slowly than modelled is simply underused, as opposed to ahead of schedule.
"Lenders and investors rely on contracts, warranties and capacity tests to build their models," said Darya Rüwald, ACCURE's director of battery intelligence and a co-author of the report. "Those documents flatter the asset on availability and capacity, and carry commercial buffers on ageing."
"Every maturing asset class reaches the point where measured field performance, not the contract, sets the baseline for financing," said Kai-Philipp Kairies, ACCURE's chief executive. "Solar and wind made that transition; storage is arriving there now."
