Look closely at a California utility bill and one line is easy to miss: the rotating outage group or block. It indicates where a customer stands in line if the grid runs short. Every grower has a place in that line, whether or not it is printed on the bill. Federal reliability standards, including NERC’s EOP-011, require grid operators nationwide to maintain emergency plans for cutting load. California is unusual in putting the group directly on the bill.
The distinction matters because utilities plan for supply emergencies in detail; most greenhouses do not. When an emergency plan is implemented, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible. Almost everyone else, including a greenhouse, is exposed. Rolling outages have hit several regions in recent years during heat waves and winter storms. For a greenhouse, that can mean fans, pumps, irrigation, heating and controls going dark at the worst possible time.
An outage is not a curtailment
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 drop, by how much, and which stay on to protect the crop. A curtailment plan is therefore a written playbook for the hours when the grid is stressed. It does not prevent the utility from acting. It gives the operation a pre-agreed sequence for protecting the crop while reducing demand.
Four steps to a usable playbook
The first step is an equipment inventory. List the major loads and roughly how much power each draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage. Rough estimates are enough to start; the point is to know what can be switched, dimmed, staggered or kept running.
The second step is to sort loads by consequence. Some can drop entirely for a few hours without harming the crop. Some can be reduced, such as dimming lights, staggering fans or adjusting a setpoint by a few degrees. Others must stay on regardless, including controls, alarms and whatever keeps the most sensitive crop alive. The sorting is not fixed. It depends on what is grown and the crop’s stage, so the priority list can change through the season.
The third step is to act on advance signals. 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 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 crop then enters the hardest hours with some margin rather than starting from the wrong temperature or moisture level.
The fourth step is to assign decisions and execution. Decide who receives the alert, who makes the call and who carries it out. If an 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.
A written plan also turns a general concern into a repeatable routine. The inventory identifies what can be switched; the ranking establishes what may be switched without unacceptable crop risk; the trigger list sets when to act; and the roles determine who acts. Together they reduce the chance that a brief warning produces an improvised response. Because the ranking can shift with crop stage and season, the plan should be reviewed as the production cycle changes rather than treated as a one-time document.
From preparedness to a paid resource
Once those steps are complete, a grower should know how many kilowatts the operation can give up, for how long, and at what cost to the crop. That number is also what the grid may be willing to pay for. Before ordering outages, utilities and grid operators will pay customers who 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 exists in most of the country, largely so the outage plan never has to be used.
Demand response does not remove the need for curtailment planning. A grower still has to know which loads can be shed, for how long and with what crop impact before agreeing to reduce demand. The same load inventory and priority list therefore serve both emergency preparedness and any compensated demand-response arrangement.
The practical conclusion is narrow but consequential. A greenhouse should ask its utility where the site falls in the emergency plan, then build its own curtailment plan around the equipment, crop and season. Utilities already have an outage plan. The greenhouse needs one too, with the difference being that the grower can decide what stays on.