California utility bills carry a detail that many greenhouse growers overlook: the customer's rotating outage group or block. It shows where a site stands in line if the grid runs short, writes Ian Knisely, an energy analyst at Energy Bridge Advisors. Every grower has a place in that line, whether or not the information is printed on the bill.
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. California is unusual in printing the rotating outage information directly on the utility bill. When an emergency plan is implemented, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible. Almost everyone else, including greenhouses, remains at risk.
Rolling outages have hit several regions in recent years during heat waves and winter storms. For a greenhouse, an outage can stop fans, pumps, irrigation, heating and controls at the worst possible time. Utilities plan for that day in detail, Knisely writes, but most greenhouses do not.
Outage versus curtailment
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. A curtailment plan is a written playbook for the hours when the grid is stressed. Knisely describes four main steps.
1. Inventory loads
First, list the major equipment and roughly how much power each piece draws. The list should include supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls, and any cold storage.
2. Sort by crop need
Next, sort the loads. Some can be dropped entirely for a few hours with no harm to the crop. Some can be reduced, such as by dimming lights, staggering fans, or adjusting a setpoint by a few degrees. Some must stay on no matter what, including controls, alarms, and whatever keeps the most sensitive crop alive. The sorting depends on what is grown and the crop's stage, so it can change through the season.
3. Use forecasts as triggers
The 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. Growers with a plan treat those signals as the trigger. In summer, they 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. The crop then enters the hard hours with some margin.
4. Assign decisions and automate
Finally, decide who receives the alert, who makes the decision, and who carries it out. If the environmental controller can run the sequence automatically, it should be programmed and tested. A plan that depends on one person answering a phone at 4 p.m. on a Saturday is not a plan, according to Knisely.
Know the number and the market
Once those steps are complete, the 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 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. It exists in most of the country, largely so the outage plan never has to be used.
Knisely advises growers to ask their utility where their site falls in its plan, then start making their own.