Greenhouse growers who receive a utility bill may have noticed a line that rarely gets attention: the rotating outage group or block. In California, that number shows where a site falls in the queue when the grid runs short. Federal reliability standards, including NERC's EOP-011, require grid operators nationwide to maintain emergency plans for cutting load, even if most utilities do not print the customer's place in the plan on the bill.
Those plans can matter to controlled-environment agriculture. When supply cannot meet demand, utilities may shut off power systematically, sometimes with only minutes of warning. Hospitals and other critical facilities are protected where possible. Greenhouses are generally not, leaving fans, pumps, irrigation, heating and environmental controls exposed during heat waves or winter storms. Rolling outages have affected several regions in recent years.
Utilities prepare detailed plans for such days; many greenhouses do not. The distinction between an outage and a curtailment is control. In an outage, equipment stops at once. In a planned curtailment, the grower decides ahead of time which loads to drop, how much to reduce them and which systems must remain on to protect the crop.
A curtailment plan is a written playbook for hours when the grid is stressed. The guidance outlines four steps:
- Inventory loads. List major equipment and estimate its approximate power draw, including supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage.
- Sort by crop need. Some loads can be shut off for a few hours without harm. Others can be reduced by dimming lights, staggering fans or adjusting a setpoint by a few degrees. Controls, alarms and systems that keep the most sensitive crop alive may need to stay on. The ranking depends on the crop and its growth stage, so it can change through the season.
- Use forecasts as triggers. An outage order may arrive with little notice, but heat waves and cold snaps are forecast days in advance, and grid operators usually issue public alerts before an emergency. In summer, growers can pre-cool in the morning, irrigate early and close shade curtains before the afternoon peak. In winter, they can heat ahead of the cold peak, close thermal curtains early and confirm backup heat is fueled and tested.
- Assign roles and automate where possible. Decide who receives the alert, who makes the decision and who carries it out. If an environmental controller can run the sequence automatically, program and test it. A plan that depends on one person answering a phone on a Saturday afternoon is not a plan.
Completing those steps gives a grower a clearer estimate of how many kilowatts can be shed, for how long and at what cost to the crop. That estimate also matters in demand-response markets, where utilities and grid operators pay customers to reduce load on request. A megawatt that disappears on request is cheaper than one bought at emergency prices, and such programs exist in most of the country, largely to reduce the need to use outage plans.
Growers can ask their utility where a site falls in its emergency plan, then build a curtailment plan of their own. The aim is not to avoid every disruption, but to enter the hardest hours with operating margin and a clear sequence for protecting the crop.