Greenhouse operators who skim their utility bill may be passing over a line that matters during a grid emergency. On California bills, that entry is the customer's rotating outage group or block, which shows where the site stands in line when electricity supply cannot meet demand.
Every grower holds a place in that sequence, whether or not the utility prints it. Federal reliability standards — NERC's EOP-011 — require grid operators nationwide to maintain emergency plans for cutting load, writes energy analyst Ian Knisely. California is unusual in putting the assignment directly on the bill.
When such plans are triggered, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible; nearly everyone else, greenhouses included, is not. Rolling outages have struck several regions in recent years during both heat waves and winter storms, and for a controlled-environment operation that means fans, pumps, irrigation, heating and control systems going dark at the worst possible moment.
Outage versus curtailment
Knisely locates the difference in control. In an outage, everything stops at once. In a planned curtailment, the grower has already decided which loads drop, by how much, and which stay on to protect the crop. Utilities plan for that day in detail; most greenhouses do not.
Four steps to a written playbook
Most curtailment plans, in his account, come down to four steps.
- Inventory the load. List the major equipment and roughly how much power each piece draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort by criticality. Some loads can be dropped entirely for a few hours without harm to the crop. Some can be trimmed — dimming lights, staggering fans or shifting a setpoint a few degrees. Some must stay on, including controls, alarms and whatever keeps the most sensitive crop alive. The sorting depends on the crop and its stage, so it can shift through the season.
- Treat forecasts as the 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, 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 confirming that backup heat is fueled and tested.
- Assign responsibility. 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.
Where the flexibility has value
Once those steps are complete, a grower should know how many kilowatts can be surrendered, for how long, and at what cost to the crop. That figure, Knisely argues, is what 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, and it exists in most of the country — largely, he notes, so that the outage plan never has to be used.
The practical next step, he concludes, is to ask the utility where a given site falls in its emergency plan and then to start building a curtailment plan of one's own.
Knisely is an energy analyst at Energy Bridge Advisors, which works with controlled-environment agriculture operators to cut utility costs and turn energy flexibility into revenue; he previously worked at BrightFarms and Curaleaf.