Energy analyst Ian Knisely is urging greenhouse operators to prepare their own power-curtailment plans, warning that utility emergency procedures are designed to protect the grid, not to protect crops. Federal reliability standards such as NERC’s EOP-011 require grid operators to maintain plans for cutting load when supply cannot meet demand. California is unusual in printing a customer’s rotating outage group directly on the utility bill, but every grower still has a place in the queue.
When such a plan is used, power is shut off systematically, often with only minutes of warning. Hospitals and other critical facilities are protected where possible; a greenhouse is generally not. Rolling outages have affected several regions in recent years during heat waves and winter storms, leaving fans, pumps, irrigation, heating and controls dark at the worst possible time.
A plan, not a scramble
Knisely draws a distinction between an outage and a curtailment: an outage stops everything at once, while a planned curtailment gives the grower advance control over which loads drop, by how much and which remain on to protect the crop. He describes a curtailment plan as a documented sequence for the hours when the grid is stressed, built around four steps.
- List the loads. Inventory major equipment and estimate its power draw, including supplemental lighting, fans, evaporative cooling, heating, pumps, dehumidification, controls and cold storage.
- Rank by criticality. Some loads can be shut off for a few hours without harm. 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 remain on. The ranking depends on crop and growth stage and can change through the season.
- Use forecasts as triggers. An outage order may arrive with little notice, but heat waves and cold snaps are forecast days ahead, and grid operators often issue public alerts. 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 confirm 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 relies on a single person being reachable by phone is not reliable.
Once those steps are complete, a grower should know how many kilowatts can be shed, for how long and at what cost to the crop. That figure also underpins demand response, a market in which utilities and grid operators pay customers to reduce load on request. Such payments are generally cheaper than buying power at emergency prices, and demand-response programs operate in most of the country largely to reduce the need for outage plans.
Knisely’s advice is to ask the utility where a site falls in its emergency plan and then build a greenhouse-specific plan. The objective is not to keep every system running through a grid emergency, but to enter the constrained hours with a deliberate sequence and a buffer for the crop.