Most electric utilities keep detailed emergency plans for cutting power when supply falls short of demand. Far fewer greenhouses have a plan for those same hours, writes Ian Knisely, an energy analyst at Energy Bridge Advisors, in an article urging controlled-environment growers to prepare their own curtailment playbook.
Federal reliability standards, specifically NERC's EOP-011, require grid operators nationwide to maintain emergency plans for shedding load, Knisely notes. When such a 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, greenhouses included, is not. California is unusual in printing a customer's rotating outage group or block directly on the utility bill, telling a grower where it stands in line, but every grower holds a place in that line whether or not it appears on paper.
Rolling outages have hit several regions in recent years during both heat waves and winter storms. For a greenhouse, the consequence is fans, pumps, irrigation, heating and controls going dark at the worst possible moment.
Outage versus 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.
Four steps to a written plan
- Inventory the load. List major equipment and roughly how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort by priority. Some loads can be dropped entirely for a few hours without harm to the crop. Others 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 what is grown and at which stage, so it can change through the season.
- Act on forecasts. The 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 first. Growers with a plan treat those signals as the trigger: in summer, pre-cooling in the morning, irrigating early and closing shade curtains before the afternoon peak; in winter, heating ahead of the cold peak, closing thermal curtains early and confirming 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, and program and test the environmental controller if it can run the sequence automatically. A plan that depends on one person answering a phone at 4 p.m. on a Saturday is not a plan.
Completing those steps tells a grower how many kilowatts it can give up, for how long and at what cost to the crop, which is the number the grid is willing to pay for.
Utilities and grid operators will pay customers that agree in advance to cut load, Knisely writes, because 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, he says, so the outage plan never has to be used. His advice: ask the utility where a site falls in its plan, then start making one.