The most expensive mistake in solar cold storage is buying a battery big enough to run the compressors flat-out all night. It doubles the project cost and pushes payback beyond the contract. Here is how we size batteries so the room holds temperature and the numbers still work.
Key facts
- Rule of thumb: overnight load is 60–70% of daytime load once the room is pre-cooled and the doors stay shut.
- A 10 MT frozen store typically needs ~150 kWh of usable battery; a 20–50 MT multi-room site 250–500 kWh.
- A 2–2.5 MWh battery for full overnight autonomy on a standard site costs US$490,000–615,000 — more than the rest of the site — and pushes payback to 9–10 years.
- Cycle life matters more than capacity: cold rooms cycle the battery every day, so 8,000–15,000-cycle LFP beats cheaper chemistry.
Pre-cool, then coast
Solar is strongest from 10 a.m. to 3 p.m. We run the compressors hard then, pulling the room a few degrees below set-point. Insulated 150 mm panels and the thermal mass of frozen product then carry the room through the evening with the compressors cycling far less. The battery only has to cover that reduced overnight load.
The two-number sizing method
First, the overnight energy: overnight hours (about 12) multiplied by 60–70% of the daytime average load. Second, the power: the largest compressor start-up surge the inverter must deliver at 3 a.m. Buy the battery for the first number and the inverter for the second, and add 10–15% for cloudy days if there is no grid.
Chemistry and cycles
A cold room cycles its battery once or twice every day — 365 to 730 cycles a year. Over an 8-year contract that is up to 6,000 cycles. A 15,000-cycle graphene LFP battery does the whole contract on one set; a cheaper 4,000-cycle battery is replaced twice, which costs more than buying right the first time.
Want the battery sized for your room, not a sales target?
Talk to Frontières BayFrequently asked
What about a week of cloud?
Grid tops up where it exists; at fully off-grid sites a gas generator is fitted as last-resort backup. Alarms warn long before product is at risk.
Lead-acid or lithium?
Lithium (LFP). Lead-acid cannot handle daily deep cycling in 40 °C rooms and is replaced every two to three years.