Greenhouse growers who watch their energy bills for usage and demand may be overlooking another number: the rotating outage group or block printed on California utility bills. That detail indicates where a site stands in line when the grid runs short. Every grower occupies a place in that queue, whether or not the utility prints it.
The backdrop is a national system of emergency load-cutting plans. Federal reliability standards, including NERC’s EOP-011, require grid operators across the country to maintain plans for shedding load when supply cannot meet demand. California is unusual in printing outage-group information directly on utility bills, but the underlying risk is not limited to one state.
When such a plan is activated, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible. Almost everyone else, including greenhouses, is exposed. Rolling outages have struck several regions in recent years during heat waves and winter storms. For a greenhouse, the consequence can be fans, pumps, irrigation, heating and environmental controls going dark at the worst possible time.
Outage versus curtailment
Utilities plan for those emergencies in detail; most greenhouses do not. Ian Knisely, an energy analyst at Energy Bridge Advisors, 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 systems must stay on to protect the crop.
A curtailment plan is a written playbook for the hours when the grid is stressed. Knisely outlines four basic steps.
- Inventory the loads. List major equipment and estimate how much power each item draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort by criticality. Some loads can be shut off entirely for a few hours without harming the crop. Others can be reduced, such as dimming lights, staggering fans or adjusting a setpoint by a few degrees. Controls, alarms and whatever keeps the most sensitive crop alive must remain on. The ranking depends on the crop and its growth stage, so it can change during the season.
- Use 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.
- 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 on a weekend afternoon is not a plan, Knisely argues.
After those steps, a grower should know how many kilowatts can be surrendered, for how long and at what cost to the crop. That number is what the grid may be willing to pay for.
Demand response as a buffer
Before ordering outages, utilities and grid operators will pay customers that agree in advance to cut load. A megawatt that disappears on request is cheaper than one bought at emergency prices. That market is demand response, and it exists in most of the country, largely so the outage plan never has to be used.
The practical advice is twofold: ask the utility where a site falls in its emergency plan, then build a site-specific plan. For greenhouse operators, the difference is control over which systems stop, which keep running and how much crop risk the operation is prepared to accept.