Utilities across the United States maintain emergency plans for cutting power when supply cannot meet demand, but most greenhouses do not have a matching plan of their own, writes energy analyst Ian Knisely. Federal reliability standards — NERC's EOP-011 — require grid operators nationwide to keep such emergency load-shedding plans. When one is implemented, power is systematically shut off, often with only minutes of warning.
California is unusual in that it prints each customer's rotating outage group or block directly on the utility bill, showing where a site stands in line if the grid runs short. Knisely notes that every grower has a place in that line, whether or not it appears on the bill.
Critical facilities such as hospitals are protected where possible. Almost everyone else, including greenhouses, is at risk. Rolling outages have hit several regions in recent years during both heat waves and winter storms. For a greenhouse, that means fans, pumps, irrigation, heating and controls going dark at the worst possible time.
The difference is control
Knisely separates an outage from a curtailment: 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. A curtailment plan, as he describes it, is a written playbook for the hours when the grid is stressed, and most come down to four steps.
Four steps to a playbook
- Inventory the load. List major equipment and roughly how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort the loads. Some can drop entirely for a few hours with no harm to the crop. Some can be reduced — dimming lights, staggering fans, or moving a setpoint a few degrees. Some must stay on no matter what, such as controls, alarms and whatever keeps the most sensitive crop alive. The sorting depends on what is grown and at what stage, so it can change through the season.
- Set the trigger. An outage order may arrive with only 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, that means pre-cooling in the morning, irrigating early and closing shade curtains before the afternoon peak. In winter, it means heating ahead of the cold peak, closing thermal curtains early and making sure backup heat is fueled and tested.
- Assign the roles. 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. Knisely argues that a plan depending on one person answering a phone at 4 p.m. on a Saturday is not a plan.
What the grid will pay for
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 — the figure the grid is willing to pay for. Before ordering outages, utilities and grid operators 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. It exists in most of the country, largely so the outage plan never has to be used.
Knisely's advice is to ask the utility where a site falls in its plan, and then start making one. He is an energy analyst at Energy Bridge Advisors, which helps controlled-environment agriculture operators cut utility costs and turn energy flexibility into revenue, and he previously worked at BrightFarms and Curaleaf.