Greenhouse growers who receive a utility bill may overlook a small line item that matters during a grid emergency: the rotating outage group or block assigned to their site. In California, that information is printed on the bill, showing where a customer stands if electricity supply falls short. Elsewhere, the assignment may not appear on the bill, but it still exists.
Federal reliability standards, including NERC’s EOP-011, require grid operators nationwide to maintain emergency plans for cutting load. Utilities use those plans when supply cannot meet demand, systematically shutting off power, often with only minutes of warning. Hospitals and other critical facilities are protected where possible; most other customers, including greenhouses, remain exposed.
Outage versus curtailment
Rolling outages have affected several regions in recent years during heat waves and winter storms. For a greenhouse, an outage can stop fans, pumps, irrigation, heating and environmental controls at the worst moment. The article draws a distinction between an outage and a planned curtailment: in an outage, everything stops at once; in a curtailment, the grower decides in advance which loads to drop, how much to reduce them and which must stay on to protect the crop.
That decision-making can be organized as a written playbook. The first step is to list major equipment and estimate its power draw, including supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage.
The second is to sort loads. Some can be shut off entirely for a few hours without harming the crop. Others can be reduced—by dimming lights, staggering fans or shifting a temperature setpoint by a few degrees. A third group must remain on, such as controls, alarms and equipment needed to keep the most sensitive crop alive. The sorting depends on the crop and its growth stage, so it can change during the season.
Use forecasts as a trigger
The third step is to act on weather and grid alerts. 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, that can mean pre-cooling in the morning, irrigating early and closing shade curtains before the afternoon peak. In winter, it can mean heating ahead of the cold peak, closing thermal curtains early and making sure backup heat is fueled and tested.
The fourth step is to assign responsibility: 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 at 4 p.m. on a Saturday is not a plan, according to the article.
Completing those steps gives a grower an estimate of how many kilowatts can be given up, for how long and at what cost to the crop. That estimate is also the basis for demand response, a market in which utilities and grid operators pay customers to cut load on request. It exists in most of the country, largely to reduce the need to use emergency outage plans.
Growers can ask their utility where their site falls in the outage plan, then begin drafting their own curtailment plan.