Cold-Chain Backup Bank

Frigoríficos Sarrión runs a 41,000 m² frozen distribution centre on the PLAZA platform west of Zaragoza, holding 62,000 pallet positions at −24 °C for retail and export customers. Its exposure was never a long blackout. It was the 200-millisecond voltage dips that arrive on the regional 45 kV network a few times a month, drop the DC bus on the ammonia plant's screw compressor drives, and drag the contactors out with them. Each event started a 45-minute staged restart. Chamber temperature rose about 0.4 °C an hour with the compressors down, and two dips in one shift put the building inside the temperature thresholds its customers audit against.

A 1.6 MVA diesel standby set was already on site and it had never once helped: fifteen seconds to accept load is fifteen seconds too late when the trip has already happened. What the site needed was a supply the refrigeration plant never sees fail, rated to carry 3.2 MW of continuous load plus the inrush of a 900 kW screw compressor restarting into a warming chamber. Space was the second constraint. The only free ground sat between the ammonia machinery room and the lorry apron, and the separation distance required between a lithium installation and an ammonia charge of that size consumed most of it.

The solution

Eight megawatt-hours of usable LFP capacity — CATL EnerOne+ racks in three liquid-cooled containers — feed a dedicated refrigeration switchboard through two 2 MVA Sungrow bidirectional inverters running in grid-forming mode. A solid-state tie switch sits between that switchboard and the 15 kV incomer and opens in under 2 milliseconds once the dip detector sees any phase fall below 0.85 pu. The compressors carry on. When the network settles, the switch resynchronises and recloses on a phase match, and recharge is rate-limited so the recovery does not write a new peak into the monthly demand record. The containers stand behind a 4 m reinforced wall that also serves as the ammonia separation barrier — one structure doing two jobs, which is what made the footprint work.

At full refrigeration load the bank holds the site for 2 hours 20 minutes, against a worst recorded outage of 41 minutes. State of charge never drops below 60 per cent; the top 40 per cent is cycled daily against the day-ahead spread and used to trim the contracted capacity under the 6.1TD tariff, which pays for the asset between events. Twenty-two months on, the plant has ridden through 31 dips and two full outages with no interruption to the compressors, no staged restart, and no product written off. The diesel set remains in place and has not been called on since handover.