Utilities across the U.S. maintain detailed emergency plans for cutting power when supply cannot meet demand, but most greenhouse operations have no matching plan of their own. Ian Knisely, an energy analyst at Energy Bridge Advisors, argues that growers should write a curtailment playbook before the grid forces the issue.
Every grower holds a place in the utility's outage order, whether or not it appears on the bill. In California, bills print a customer's rotating outage group or block, the position a site occupies if the grid runs short. Nationwide, federal reliability standards (NERC's EOP-011) require grid operators to keep emergency load-shedding plans, but printing that detail directly on the bill is unusual to California.
When such a plan is triggered, power is shut off systematically, often with only minutes of warning. Critical facilities such as hospitals are protected where possible; almost everyone else, greenhouses included, is at risk. Rolling outages have hit several regions in recent years during both heat waves and winter storms, and for a greenhouse that means fans, pumps, irrigation, heating and controls going dark at the worst possible moment.
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. Knisely lays out four steps.
Four steps to a curtailment plan
Inventory the load. List the major equipment and roughly how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
Sort the loads. Some can be dropped entirely for a few hours with no harm to the crop. Some can be trimmed, such as dimming lights, staggering fans or shifting a setpoint a few degrees. Others must stay on regardless, including controls, alarms and whatever keeps the most sensitive crop alive. The sorting depends on what is grown and at what stage, so it can change through the season.
Treat forecasts as the 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. 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 fuelled and tested.
Assign roles and automate. Decide who receives the alert, who makes the decision and who carries it out. If the environmental controller can run the sequence automatically, program it and test it. A plan that depends on one person answering a phone on a Saturday afternoon is not a plan.
Once those steps are done, a grower should know how many kilowatts can be given up, for how long and at what cost to the crop.
That figure matters beyond emergencies. 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. The market is known as demand response and exists across most of the country, largely so that outage plans never have to be used.
Knisely's advice is to ask the utility where a site falls in its plan, and then start making one.