Greenhouse growers who track energy costs may overlook a small item on a California utility bill: the rotating outage group or block that determines where a site stands when the grid runs short. That detail matters because utilities nationwide maintain emergency plans to cut power when supply cannot meet demand, and a greenhouse can lose fans, pumps, irrigation, heating and controls with little warning.
Federal reliability standards, including NERC’s EOP-011, require grid operators to keep emergency load-shedding plans. California is unusual in printing a customer’s outage position on the bill. When such plans are used, power is shut off systematically, often with minutes of notice. Hospitals and other critical facilities are protected where possible, but most other customers, including greenhouses, remain exposed. Rolling outages have hit several regions in recent years during heat waves and winter storms.
From outage to controlled 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 remain on to protect the crop.
A curtailment plan is a written playbook for hours when the grid is stressed. It can be organized around four steps.
- Inventory the load. List major equipment and estimate how much power each item draws: supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage.
- Sort by priority. Some loads can be dropped entirely for a few hours without harming the crop. Others can be reduced by dimming lights, staggering fans or adjusting a setpoint by a few degrees. Controls, alarms and whatever keeps the most sensitive crop alive must stay on. The ranking depends on the crop and its growth stage, so it can change through the season.
- Use the forecast as a 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, growers with a plan can pre-cool in the morning, irrigate early and close shade curtains before the afternoon peak. In winter, they can 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 an environmental controller can run the sequence automatically, it should be programmed and tested. A plan that depends on one person answering a phone on a Saturday afternoon is not a plan.
What the flexibility is worth
After those steps, 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 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.
The practical next step is to ask the utility where a site falls in its emergency plan, then build a curtailment plan of its own.