Look closely at a California utility bill and there is a number many growers pass over: the rotating outage group or block assigned to the site. It marks where the operation stands in line if the grid runs short — a line every grower is in, whether or not it appears on the bill.
Why the outage block matters
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 the utility bill. When such a plan is implemented, power is shut off systematically, often with only minutes of warning. Hospitals and similar critical facilities are protected where possible; almost everyone else, greenhouses included, is not.
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 moment.
Outage versus curtailment
Utilities plan for that day in detail; most greenhouses do not. The difference between an outage and a curtailment is control. 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.
Four steps to a written playbook
A curtailment plan is a written playbook for the hours when the grid is stressed. Most 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 the loads. Some can drop entirely for a few hours without harm to the crop. Some can be reduced, by dimming lights, staggering fans or moving a setpoint a few degrees. Some must stay on regardless, 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.
- 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, 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. 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.
What that number is worth
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. That number 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; it exists in most of the country, largely so the outage plan never has to be used.
The recommendation from Ian Knisely, an energy analyst at Energy Bridge Advisors who previously worked at BrightFarms and Curaleaf, is to ask the utility where a site falls in its plan — and then start building a plan of one's own.