When a California utility bill arrives, most growers skip past one line: the rotating outage group or block that shows where a site sits in the queue if the grid runs short. According to Ian Knisely, an energy analyst at Energy Bridge Advisors, every grower occupies a place in that line whether or not it appears on the bill.
Federal reliability standards — NERC's EOP-011 — require grid operators nationwide to maintain emergency plans for cutting load, Knisely notes. California stands out by printing the relevant information directly on utility bills. When such plans are triggered, power is systematically shut off, often with only minutes of warning. Critical facilities such as hospitals are protected where possible, but nearly everyone else, including greenhouses, is at risk.
What an outage means for a greenhouse
Rolling outages have struck several regions in recent years during both heat waves and winter storms. For a greenhouse, that can mean fans, pumps, irrigation, heat and controls going dark at the worst possible moment. The difference between an outage and a curtailment, Knisely writes, is control: in an outage everything stops at once, while 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 curtailment plan
Knisely describes a curtailment plan as a written playbook for the hours when the grid is stressed, built around four steps.
- Inventory the major equipment and estimate how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort loads into three groups: those that can drop entirely for a few hours without harming the crop, those that can be reduced (dimming lights, staggering fans, adjusting a setpoint a few degrees), and those that must stay on, such as controls, alarms and whatever keeps the most sensitive crop alive. The sorting depends on the crop and its stage, so it can change through the season.
- Treat forecasts and public grid alerts as triggers. In summer, growers with a plan pre-cool in the morning, irrigate early and close shade curtains before the afternoon peak; in winter, they heat ahead of the cold peak, close thermal curtains early and make sure backup heat is fueled and tested.
- Assign who receives the alert, who makes the decision and who carries it out. If an environmental controller can run the sequence automatically, it should be programmed and tested. A plan that depends on one person answering a phone at 4 p.m. on a Saturday, Knisely says, is not a plan.
Turning flexibility into a market signal
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, Knisely writes, is what the grid is 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, and it exists in most of the country, largely so the outage plan never has to be used.
Knisely advises growers to ask their utility where their site falls in its plan, then to start making their own.