When a California utility bill arrives, one line is easy to overlook: the rotating outage group or block. It shows where a site sits in the queue if the grid runs short. Every grower has a place in that sequence, whether or not the bill prints it. 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 information directly on the utility bill.
Utilities across the country keep plans for shutting off power when supply cannot meet demand. When such a plan is implemented, service is cut systematically, often with only minutes of warning. Critical facilities such as hospitals 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, the result can be fans, pumps, irrigation, heating and controls going dark at the worst possible time.
Energy analyst Ian Knisely argues that utilities plan for that day in detail, while most greenhouses do not. 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. The plan does not prevent the grid emergency; it changes who has made the operating decisions before the emergency arrives. That distinction matters because the utility’s sequence sets the timing, but the grower’s playbook sets the response.
A playbook in four steps
Knisely describes a curtailment plan as a written playbook for the hours when the grid is stressed. Most such plans come down to four steps.
- List the loads. Identify major equipment and roughly how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort what can be cut. Some loads can drop entirely for a few hours without harming the crop. Some can be reduced by dimming lights, staggering fans or adjusting a setpoint a few degrees. Controls, alarms and whatever keeps the most sensitive crop alive must stay on. The sorting depends on the crop and its stage, so it can change through the season.
- Set a trigger. 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 the trigger. In summer, that means pre-cooling in the morning, irrigating early and closing shade curtains before the afternoon peak. In winter, it means heating ahead of the cold peak, closing thermal curtains early and making sure backup heat is fueled and tested. Either way, the crop enters the hard hours with some margin.
- Assign roles. Decide who receives the alert, who makes the decision 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.
After those steps, a grower should know how many kilowatts can be given up, for how long and at what cost to the crop. That figure becomes the basis for what the grid will pay. 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. It exists in most of the country, largely so the outage plan never has to be used.
The four steps also expose the limits of a generic plan. Load priorities depend on the crop and its growth stage, and they can shift as the season changes. Triggers rely on weather forecasts and public alerts, not only on the outage notice. Roles must survive weekends, vacations and shift changes. Automation can help, but only if the sequence is programmed and tested. These are operational conditions, not guarantees that a crop will be spared.
For a greenhouse, the operating boundary is biological as well as electrical. The equipment on the list—lighting, fans, cooling, heating, pumps, dehumidification, controls and cold storage—supports the crop environment in different ways. A short reduction in one load may be tolerable; an unplanned loss across several loads at once leaves less room to respond. That is why the plan separates loads that can be dropped, reduced or must remain on, and why the grower, rather than the utility alone, has to set the cost to the crop.
The practical conclusion is twofold. Growers should ask their utility where a site falls in its emergency plan. They should also start making their own plan, because the utility’s sequence determines when power may go; the curtailment playbook determines what the greenhouse does before and during that window. The two documents answer different questions: when the grid may act, and how the greenhouse will act.