Commercial greenhouses depend on a long list of electrical loads—fans, pumps, irrigation, heating, cooling and controls—and those systems can go dark together when a utility orders a rolling outage. Energy analyst Ian Knisely argues that growers should not leave their place in that queue to chance. Utilities maintain emergency plans for cutting power when supply cannot meet demand, and almost every customer, including a greenhouse, can be affected.
Federal reliability standards, specifically NERC's EOP-011, require grid operators nationwide to keep emergency plans for shedding load. California stands out because utilities print a customer's rotating outage group or block directly on the bill, giving growers a visible indication of where they sit if the grid runs short. Every grower has a place in that line, whether or not it appears on the bill.
Utilities plan for such days in detail; most greenhouses do not, according to Knisely. In recent years, rolling outages have struck several regions during heat waves and winter storms. Hospitals and other critical facilities are protected where possible, but most other customers remain exposed. For a greenhouse, an unexpected shutdown can interrupt ventilation, pumping, irrigation, heating and environmental controls at a critical moment.
Outage versus curtailment
The key difference between an outage and a curtailment is control. When an outage begins, equipment stops at once. Under a planned curtailment, the grower decides in advance which loads to drop, how much to reduce them and which systems must remain on to protect the crop. Knisely describes a curtailment plan as a written operating guide for hours when the grid is under stress; most such plans, he says, come down to four steps.
Four planning steps
- Inventory the load. List major equipment and estimate its approximate power draw. The list should cover supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and any cold storage.
- Sort equipment by priority. Some loads can be shut off entirely for a few hours without harming the crop. Others can be reduced—by dimming lights, staggering fans or shifting 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 during the season.
- Use forecasts 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. Growers with a plan can pre-cool in the morning, irrigate early and close shade curtains before the summer afternoon peak. In winter, they can heat ahead of the cold peak, close thermal curtains early and confirm that 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 a single person answering a phone on a Saturday afternoon is not a real plan, Knisely writes.
From readiness to revenue
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 calculation matters beyond emergency preparation. Before ordering outages, utilities and grid operators will pay customers that agree in advance to cut load, because a megawatt that disappears on request is cheaper than one bought at emergency prices. The market is known as demand response and exists in most of the country, largely so that the outage plan never has to be used.
Knisely advises growers to ask their utility where a site falls in its outage plan, then to begin drafting their own. The aim is not to predict every grid emergency, but to enter the most constrained hours with a prepared sequence, tested equipment and a clear sense of which crop-protection loads must stay energized.