Commercial greenhouse growers often focus on crop schedules and energy prices, but a number printed on a California utility bill can reveal how their operation would fare if the grid runs short. That number identifies the site’s rotating outage group or block, placing it in line for forced power cuts. Every grower has such a place, whether or not the utility prints it.
Utilities and grid operators maintain emergency plans for cutting load when supply cannot meet demand. Federal reliability standard NERC EOP-011 requires such plans nationwide. California is unusual in putting the rotating outage group directly on customer bills. When an emergency plan is activated, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible; most other customers, including greenhouses, are not.
Rolling outages have affected several regions during heat waves and winter storms. For a greenhouse, a sudden loss of power can stop fans, pumps, irrigation, heating and environmental controls at the worst possible time. Utilities plan for that day in detail. Many greenhouses do not.
Curtailment gives the grower control
The difference between an outage and a curtailment is control. In an outage, everything stops at once. In a planned curtailment, the grower decides in advance which loads to drop, how much to reduce them and which systems must stay on to protect the crop. A curtailment plan is a written playbook for the hours when the grid is under stress.
Most plans begin with four steps. First, list major equipment and estimate its power draw: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage. Second, sort each load. Some can be shut off for a few hours without harming the crop. Some can be reduced by dimming lights, staggering fans or shifting a temperature setpoint a few degrees. Controls, alarms and systems that keep the most sensitive crop alive may need to remain on. The sorting depends on the crop and its growth stage, so it can change through the season.
Third, use advance signals as triggers. 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 can pre-cool in the morning, irrigate early and close shade curtains before the afternoon peak in summer. In winter, they can heat ahead of the cold peak, close thermal curtains early and confirm that backup heat is fueled and tested. The crop then enters the critical hours with some margin.
Fourth, assign roles. The plan should specify who receives the alert, who makes the decision and who carries it out. If an environmental controller can run the sequence automatically, it should be programmed and tested. A plan that depends on one person answering a phone on a Saturday afternoon is not a plan.
Know the number the grid will pay for
After 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 figure is what the grid is willing to pay for. 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. This market is called demand response and exists in most of the country, largely so the outage plan never has to be used.
Growers can ask their utility where their site falls in the emergency plan, then start writing their own. The exercise turns an unexpected shutdown into a controlled reduction, with the grower deciding what stays on and what can wait.