Greenhouse growers should prepare for utility power cuts with a written curtailment plan rather than wait for an emergency notice, according to industry guidance from Ian Knisely, an energy analyst at Energy Bridge Advisors.
In California, utility bills can include a rotating outage group or block that shows where a customer stands if the grid runs short. Knisely notes that every grower has a place in that line, whether or not the information is printed on the bill. Federal reliability standards, specifically NERC's EOP-011, require grid operators nationwide to maintain emergency plans for cutting load.
Utilities across the country keep such plans for times when supply cannot meet demand. When a plan is implemented, 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 affected several regions in recent years during heat waves and winter storms. For a greenhouse, a loss of power can stop fans, pumps, irrigation, heating and controls at the worst possible time.
Knisely distinguishes an outage from a curtailment. 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.
A four-step curtailment playbook
- Inventory major loads. List the main equipment and roughly how much power each piece draws, including supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage.
- Sort loads by priority. Some loads can be dropped entirely for a few hours without harming the crop. Others can be reduced by dimming lights, staggering fans or adjusting a setpoint. 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 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. 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 make sure backup heat is fueled and tested.
- Assign and automate roles. Decide who receives the alert, who makes the decision and who carries it out. If the environmental controller can run the sequence automatically, it should be programmed and tested. Knisely says a plan that depends on one person answering a phone on a Saturday afternoon is not a plan.
Once those steps are complete, a grower should know how many kilowatts can be given up, for how long, and at what cost to the crop. That figure is what the grid is willing to pay for, according to the guidance.
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. That market is demand response. 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 emergency plan, then start making their own. The difference between an outage and a curtailment is control.