California utility bills carry a detail many greenhouse growers skip past: the rotating outage group, or block, assigned to the site. The line shows where a customer stands in line if the grid runs short. Ian Knisely, an energy analyst at Energy Bridge Advisors, points out that California is unusual in printing that information directly on the bill — but every grower holds a place in the queue whether or not it is written down anywhere.
Federal reliability standards, specifically NERC's EOP-011, require grid operators across the country to maintain emergency plans for cutting load. When such a plan is invoked, power is shut off systematically, often with only minutes of warning. Hospitals and similar critical facilities are protected where possible. Nearly everyone else, greenhouses included, is not. Rolling outages have hit several regions in recent years, during heat waves as well as winter storms, and for a growing operation the loss lands on fans, pumps, irrigation, heating and controls at the worst possible moment.
The difference between an outage and a curtailment is control. In an outage everything stops at once. In a planned curtailment the grower has decided in advance which loads drop, by how much, and which stay on to keep the crop alive. Knisely describes a curtailment plan as a written playbook for the hours when the grid is stressed, and most such plans come down to four steps.
Four steps to a workable plan
- Inventory the load. List major equipment and roughly how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort what can go. Some loads can be dropped entirely for a few hours without harm to the crop. Others can be trimmed — dimming lights, staggering fans, shifting a setpoint a few degrees. A third group must stay on regardless, including controls, alarms and whatever keeps the most sensitive crop alive. The sorting depends on the crop and its growth stage, so it can change through the season.
- Set the trigger. An outage order may arrive with minutes of notice, but heat waves and cold snaps are forecast days ahead, and grid operators usually issue public alerts before an emergency. Growers with a plan treat those signals as the starting point. In summer that means pre-cooling in the morning, irrigating early and closing shade curtains before the afternoon peak; in winter, heating ahead of the cold peak, closing thermal curtains early and confirming backup heat is fueled and tested.
- Assign the roles. Decide who receives the alert, who makes the call and who carries it out. If the environmental controller can run the sequence automatically, program it and test it. A plan that depends on one person answering a phone at 4 p.m. on a Saturday is not a plan.
Completing those steps leaves a grower with a number the grid is willing to pay for: how many kilowatts can be surrendered, for how long, and at what cost to the crop. Before ordering outages, utilities and grid operators pay customers that agree in advance to cut load, because a megawatt that disappears on request is cheaper than one bought at emergency prices. That market is demand response. It operates in most of the country and exists largely so the outage plan never has to be used.
Knisely's advice is to ask the utility where a site falls in its plan and then to start writing a plan of one's own. He is an energy analyst at Energy Bridge Advisors, which works with controlled-environment agriculture operators on utility costs and on turning energy flexibility into revenue, and he previously worked at BrightFarms and Curaleaf.