The Signal Report // ENERGY STORAGE
Energy Storage.
Grid batteries, chemistry, and controls, from someone who helps build the AI that cycles them. All reports →
31 in this beat · page 1 of 4
Why a burned battery can catch fire again
On 18 September, about 1,200 still-charged modules at Moss Landing caught fire on their own, twenty months after the 2025 blaze. A fire doesn't drain a battery. The NTSB found responders can't measure or remove that stranded energy from a wrecked pack, and salt-water discharge corrodes terminals and lets voltage rebound.
Read the report → Report 174 · Energy Storage · 2026-10-03 · 6 minWhat a 20,000-cycle battery claim means
Hithium's launch release for its grid sodium-ion cell measured 94.2% capacity after 4,000 cycles and said it was expected to pass 20,000 at 70% health. A straight line through that one point lands right on 20,000. Nine months later the claim read simply 'over 20,000 charge cycles.' How to read any five-digit cycle count.
Read the report → Report 168 · Energy Storage · 2026-09-30 · 6 minWhat a 409 Wh/kg battery test proves
Finland's VTT measured a Donut Lab cell at 409.3 Wh/kg. The seven-page report shows one cell, two cycles, a ten-hour discharge in a voltage window the customer supplied, and no chemistry determination at all. A real number, and a narrow one, plus five questions to ask of any "independently tested" battery claim.
Read the report → Report 162 · Energy Storage · 2026-09-26 · 7 minHow a 4-hour microgrid ran a town for 6 days
After Helene washed out its substation, Hot Springs, N.C. kept its downtown lit for 143.5 hours on a solar-and-battery microgrid designed for 4 to 6 hours of full load. The battery did not do it alone: flood damage cut demand, the sun refilled it daily, and outlying circuits were rationed. Those are the three questions to ask of any backup quote.
Read the report → Report 156 · Energy Storage · 2026-09-22 · 8 minWhat clipping recapture is actually worth
DC-coupled batteries are sold on catching the solar an inverter clips. NREL modelled it across about 55,000 US sites: at the typical 1.3 DC/AC ratio the recoverable energy averages 0.2% of the array's output, and 80% of new hybrid plants in 2024 were AC-coupled anyway.
Read the report → Report 150 · Energy Storage · 2026-09-19 · 9 minState of charge is not a measurement
The percentage on a battery app is charge inferred by summing current readings, divided by a capacity number fixed at the factory. A DOE handbook chapter says 100 percent is defined by a charging procedure, not measured. The DOE test protocol meters the energy and merely records what the battery management system claims.
Read the report → Report 144 · Energy Storage · 2026-09-12 · 10 minWhen a battery warranty actually ends
A home battery is sold with a number of years on it. I read the current published warranties from Tesla and Enphase, and in neither document does the calendar end the coverage on its own. One closes on 37.8 MWh of aggregate throughput, one on 6,000 discharged cycles, and both define success as a battery that has lost a large share of its capacity. The same Powerwall is also guaranteed to 80 percent in nine European countries and 70 percent in the United States.
Read the report → Report 138 · Energy Storage · 2026-09-09 · 8 minWhere the code says a home battery can go
Residential code caps a single storage unit at 20 kWh and the whole installation at 40 or 80 kWh depending on where it sits, keeps units three feet apart unless a fire test report says otherwise, and never in a bedroom. The catch is that the model code is not the law: the edition your jurisdiction adopted, and the amendments it made, are.
Read the report → Report 132 · Energy Storage · 2026-09-06 · 10 minWhat a battery cost per kWh actually includes
Nearly every grid-battery article quotes a dollars-per-kilowatt-hour figure, and most trace back to one NREL report. It assumes a four-hour system, puts interconnection upgrades outside the fence, and builds its low and high cases from the minimum and maximum of a literature survey rather than a confidence interval. The catalog abstract also quotes six figures that appear nowhere in the PDF.
Read the report → Report 126 · Energy Storage · 2026-09-03 · 10 minMost of the Battery Queue Never Gets Built
Berkeley Lab's annual count found 749 gigawatts of storage waiting to connect to the grid. That number keeps getting reported as a pipeline. Of everything that entered these queues from 2000 to 2020, 13 percent of the capacity has come online, the median project now takes 61 months, and the storage line actually got 16 percent shorter last year.
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