On many California utility bills, a line lists the customer’s rotating outage group or block. The detail is easy to skip, but it shows where a site stands in line when the grid runs short. Every grower has a place in that line, whether or not it appears on the bill.
Federal reliability standards, including NERC’s EOP-011, require grid operators nationwide to keep emergency plans for cutting load. California is unusual because it prints this information directly on utility bills, according to Ian Knisely, an energy analyst at Energy Bridge Advisors. When an emergency plan is used, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible. Most other customers, including greenhouses, remain at risk.
Rolling outages have hit several regions in recent years during heat waves and winter storms. For a greenhouse, a sudden loss can stop fans, pumps, irrigation, heating and controls at the worst possible time.
Utilities plan for such days in detail. Most greenhouses do not. Knisely draws the difference between an outage and a curtailment: 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 curtailment playbook
- List the load. Identify major equipment and roughly how much power each piece draws, including supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage.
- Sort the loads. Some can drop entirely for a few hours without harming the crop. Some can be reduced by dimming lights, staggering fans or shifting 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.
- Use forecasts as 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. In summer, growers can pre-cool in the morning, irrigate early and close shade curtains before the afternoon peak. In winter, they can heat ahead of the cold peak, close thermal curtains early and confirm backup heat is fueled 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 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 number is what the grid is willing to pay for.
Before ordering outages, utilities and grid operators 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.
Growers should ask their utility where their site falls in its plan, then start making their own.