Greenhouse growers should prepare a written curtailment plan before the grid forces their operations offline, energy analyst Ian Knisely writes in a guidance article on utility outage planning. The warning rests on a simple distinction: an outage stops everything at once, while a planned curtailment lets the grower decide which loads to drop, by how much, and which systems must stay on to protect the crop.
Utilities across the country maintain emergency plans for cutting power when supply cannot meet demand. Federal reliability standards, specifically NERC’s EOP-011, require grid operators nationwide to keep such plans. In California, utility bills also print a customer’s rotating outage group or block, showing where the site stands in line if the grid runs short. Every grower has a place in that line, Knisely notes, whether or not it is printed on the bill.
When an emergency plan is implemented, power is systematically shut off, often with only minutes of warning. Hospitals and other critical facilities are protected where possible, but almost everyone else, including greenhouses, is at risk. Rolling outages have hit several regions in recent years during heat waves and winter storms. For a greenhouse, that can mean fans, pumps, irrigation, heating and controls going dark at the worst possible time.
Four steps to a curtailment playbook
Knisely describes a curtailment plan as a written playbook for hours when the grid is stressed. It comes down to four steps.
- Inventory major equipment and loads. List supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage, along with roughly how much power each draws.
- Sort loads by crop risk. Some equipment can be dropped entirely for a few hours without harm. Some can be reduced, such as 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 the crop and its stage, so it can change through the season.
- Use forecasts and public alerts as triggers. 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 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 roles and automate where possible. 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, Knisely writes.
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 number is what the grid is willing to pay for, according to the article. 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’s advice to growers is to ask their utility where their site falls in its plan and then start making their own.