Interruptible and Curtailable Rate Options: How They Work
By Illinois Commercial Energy editorial team
Reviewed by JakenEnergy commercial energy team
Interruptible and Curtailable Rate Options: How They Work
Most electricity pricing rewards you for how much and when you use power. Interruptible and curtailable options add a different lever: they reward you for your willingness to stop using power on request. In exchange for a pricing concession, you agree to reduce your load to a committed level when the grid or a program operator calls an event. For a facility with flexible load, that can be a sensible trade. For one that cannot cut power without harming its core operation, it can be a poor fit. This guide explains the mechanics, the trade-off, and how to judge whether the arrangement suits your facility.
The Basic Bargain
An interruptible or curtailable rate is built on a simple exchange. The system needs the ability to shed load at moments of stress — hot afternoons, tight supply, grid emergencies. Load that can be reduced on demand has value to the grid, and these programs pay for it in the form of a pricing concession. You accept that concession up front, and in return you commit to curtailing to an agreed level when you are called.
The concession is the compensation for flexibility. The commitment is the obligation to perform. Everything worth understanding about these options lives in the space between those two things: how much you are paid or credited, what exactly you must do when called, and what happens if you cannot.
How an Event Works
The details vary by program and by rate schedule, but the shape is consistent. The operator determines that load reduction is needed and issues a signal. You receive notice — the amount of lead time is a defining feature, ranging from substantial advance warning to something much shorter. You then reduce your load to the level you committed to and hold it there for the duration of the event. When the event ends, you return to normal operation.
Several parameters define how demanding this is in practice:
- Notice. How much warning you get before you must curtail. Longer notice is easier to plan around.
- Frequency. How many events can occur in a season or a year.
- Duration. How long a single event can last.
- Depth. How much load you must shed, or what level you must curtail to.
- Season and hours. When events are most likely, often aligning with peak demand periods.
Two programs offering a similar concession can be very different to live with once these parameters are compared. A program with generous notice and rare, short events asks far less of an operation than one with little warning and frequent, long ones.
The Operational Trade-Off
The concession is money on the table. The cost is operational: you are giving up some control over when you can run at full load, and you are taking on the obligation to cut when called. The central risk is non-performance. If you commit to curtailing and then cannot — because a critical order is running, because the equipment you planned to shed turns out to be essential that day — programs generally define a consequence, which can include penalties or the loss of the concession you were counting on.
That is why the honest question is not "how large is the concession?" but "can I reliably perform when called, given how my facility actually runs?" A commitment you can only meet in theory is worse than no commitment at all, because you have priced in a benefit you may have to give back.
Where These Options Fit
Interruptible and curtailable rates are one long-standing form of demand response, and they sit alongside broader demand-response programs, including those coordinated through the regional grid operator. In northern Illinois that operator is PJM; in central and southern Illinois it is MISO. The common thread across all of them is that a facility is compensated for the ability to reduce load during periods of grid stress. The specific rate schedules, program rules, and eligibility differ by utility and by operator, so the starting point is understanding which programs your account can access. Our overview of /commercial-electricity/ and the utility detail at /utilities/comed/ give context on how the supply and delivery pieces fit together.
Importantly, participating does not change who delivers your power or your underlying reliability of service. Your delivery utility still owns the wires, meter, and outages. A curtailment during an event is a planned reduction you agreed to, not an unplanned outage — a distinction worth keeping clear when weighing the option.
Judging Fit for Your Facility
Whether the trade is worthwhile comes down to your load and your tolerance for the commitment. A practical way to assess it:
- Inventory your flexible load. Identify equipment and processes you could pause, shift, or shed on short notice without harming core output. The size of that flexible block sets the ceiling on what you can commit.
- Map your critical load. Be honest about what cannot be interrupted. Continuous processes, safety systems, and anything tied directly to product quality generally should not be on the table.
- Stress-test the parameters. Walk through the worst realistic case: shortest notice, longest duration, peak season, during a busy production run. If you could still perform, the commitment is realistic. If not, reconsider the depth you commit to.
- Weigh the concession against the risk. Compare the value of the concession to the cost of a missed event and the operational friction of curtailing. A smaller, reliable commitment often beats a larger one you might fail to meet.
- Read the performance terms. Confirm exactly what you must do, how performance is measured, and what happens if you fall short. Get it in writing.
For facilities with genuine, dependable flexibility, these options can turn idle operational slack into value. For facilities whose load is essentially all critical, the risk usually outweighs the concession. The demand response for Illinois businesses guide goes deeper on building a curtailment playbook, and /commercial-energy-procurement/ covers how these options fit a broader energy strategy.
Sources
This guide is educational and does not promise any specific savings or outcome. The value and obligations of any interruptible, curtailable, or demand-response option depend on the program rules, your load, and your ability to perform; confirm the exact terms with the program operator and the primary sources above.
Frequently Asked Questions
QWhat is an interruptible or curtailable rate?
It is a pricing arrangement in which a customer accepts a pricing concession in exchange for agreeing to reduce electrical load when called upon. When the grid or program operator signals an event, the customer curtails to a committed level. The concession compensates the customer for the operational flexibility it provides.
QHow is that different from demand response?
They overlap. Interruptible and curtailable rates are one long-standing form of demand response tied to a rate schedule. Broader demand-response programs, including those run through the regional grid operator, can compensate a facility for reducing load during grid stress. The common thread is being paid or given a concession for the ability to cut load on request.
QWhat happens if I cannot curtail when called?
That is the central risk. Programs generally define what you commit to and what happens if you fall short, which can include penalties or loss of the concession. Before enrolling, understand the notice you will get, how often events can occur, how long they last, and the consequence of not performing so the commitment is realistic for your operation.
QDoes this affect my delivery service or reliability?
Participating in an interruptible or demand-response option does not change who delivers your power. Your delivery utility, ComEd or Ameren Illinois, still owns the wires, meter, and outages. Curtailment during an event is a planned reduction you agree to, not an unplanned outage, and it is distinct from ordinary reliability of service.
QWhich facilities are the best fit?
Facilities with flexible or non-critical load that can be reduced on short notice tend to fit best, such as operations that can shift, pause, or shed certain equipment without harming core output. Facilities with continuous critical loads that cannot be interrupted are usually a poorer fit and should weigh the operational risk carefully.