Greenhouse growers who receive a utility bill may already have a place in their local grid operator’s emergency load-shedding plan—whether or not they know it. In California, the bill can include a rotating outage group or block that shows where a customer sits in line if the grid runs short. Federal reliability standards, including NERC’s EOP-011, require grid operators nationwide to maintain emergency plans for cutting load. California is unusual in printing the group information directly on utility bills, according to Ian Knisely, an energy analyst at Energy Bridge Advisors.
Those plans are designed to protect critical facilities such as hospitals where possible. Other customers, including greenhouses, can still lose power, often with only minutes of warning. Rolling outages have affected several regions in recent years during heat waves and winter storms. For a greenhouse, the consequence is that fans, pumps, irrigation, heating and environmental controls can go dark at the worst possible time.
Knisely draws a distinction between an outage and a curtailment. In an outage, equipment stops at once. In a planned curtailment, the grower decides in advance which loads to drop, how much to reduce and which systems must remain on to protect the crop. That difference is control. A curtailment plan is a written playbook for the hours when the grid is stressed, and Knisely says most plans come down to four steps.
Inventory and rank greenhouse loads
The first step is to list major equipment and estimate how much power each item draws. The list should cover supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
The second step is to sort those loads into three groups. Some can be shut off entirely for a few hours without harming the crop. Some can be reduced—by dimming lights, staggering fans or adjusting a setpoint by a few degrees. Others must stay on no matter what, 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.
Use forecasts and assign responsibility
An outage order may arrive with only 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 a trigger. In summer, Knisely recommends pre-cooling in the morning, irrigating early and closing shade curtains before the afternoon peak. In winter, growers can heat ahead of the cold peak, close thermal curtains early and make sure backup heat is fueled and tested. In either case, the crop enters the hard hours with some margin.
The plan also needs clear responsibility: who receives the alert, who makes the decision and who carries it out. If the environmental controller can run the sequence automatically, it should be programmed and tested. A plan that depends on one person answering a phone at 4 p.m. on a Saturday is not a plan, Knisely writes.
Know the number—and the market
After completing those steps, a grower should know how many kilowatts the operation can give up, for how long and at what cost to the crop. That number matters beyond emergency preparation. Before ordering outages, utilities and grid operators will 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, and it exists in most of the country, largely so the outage plan never has to be used.
Knisely advises growers to ask their utility where their site falls in its emergency plan, then start making their own. The aim is to move from a utility’s outage sequence to a grower-controlled curtailment sequence.