Greenhouse operations are being urged to prepare for the moment the power grid runs short rather than wait for a utility to switch off the lights. Writing for Greenhouse Grower, Ian Knisely, an energy analyst at Energy Bridge Advisors, argues that most growers have no written plan for a rotating outage, even though the utilities serving them do.
Knisely points growers to a detail usually buried on California utility bills: the rotating outage group or block assigned to each account, which shows where a site stands in line if the grid cannot meet demand. Every grower holds a place in that queue whether or not it is printed, he notes. Federal reliability standards, specifically NERC's EOP-011, require grid operators nationwide to keep emergency plans for cutting load; California is unusual in printing the assignment directly on customer bills.
Under such plans, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible, but almost everyone else, greenhouses included, is exposed. Rolling outages have hit several regions in recent years during both heat waves and winter storms, which for a greenhouse means fans, pumps, irrigation, heating and environmental controls going dark at the worst possible moment.
Outage versus curtailment
The distinction Knisely draws comes down to control. An outage stops everything at once; in a planned curtailment the grower decides in advance which loads are dropped, by how much, and which stay on to protect the crop. He describes a curtailment plan as a written playbook for the hours when the grid is stressed, assembled from four steps.
- Inventory the loads. List the major equipment, including supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage, with a rough figure for how much power each one draws.
- Sort what can go. Some loads can be shed entirely for a few hours without harming the crop; others can be trimmed by dimming lights, staggering fans or shifting a setpoint a few degrees; a third group, covering controls, alarms and whatever keeps the most sensitive crop alive, must stay on regardless. The sorting depends on what is grown and at which stage, so it can change through the season.
- Act on the forecast. 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 first. Growers with a plan treat those signals as the trigger: pre-cooling in the morning, early irrigation and closed shade curtains before an afternoon summer peak, or heating ahead of a winter cold peak, closing thermal curtains early and confirming backup heat is fueled and tested.
- Assign 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, Knisely writes.
Completing those steps produces a number growers can take to their utility: how many kilowatts they can give up, for how long, and at what cost to the crop. That figure, he argues, is what the grid is willing to pay for. 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, demand response, exists across most of the country, largely so the outage plan never has to be used.
His advice is to ask the utility where a site falls within its emergency plan, then begin drafting a matching plan for the greenhouse.