Standby charges explained: what utilities bill facilities with on-site generation

You install on-site generation, a cogeneration unit, a solar array, or a backup genset, to cut your utility costs, and then a new line item shows up on the bill: a standby or backup charge. It is there even in months when your generator ran perfectly and you barely touched the grid. For facilities modeling the payback on distributed generation, standby charges are the item most likely to be underestimated, and the one most likely to quietly erode the savings case.

What standby charges are and why utilities levy them

When a site is served partly by its own generation and partly by the grid, it becomes what regulators call a partial-requirements customer. The National Regulatory Research Institute explains that customers pay standby charges so that, if their on-site generator goes offline, planned or unplanned, they retain the guaranteed ability and right to purchase replacement power. The utility has to keep generation and delivery capacity standing ready to serve that load on demand, and standby rates recover the cost of that readiness. The federal Public Utility Regulatory Policies Act underpins the obligation to provide the service.

Standby service is not one charge but several. The EPA CHP Partnership model-tariffs report, prepared with the Regulatory Assistance Project, breaks it into supplemental service for load your generator does not cover, backup or standby service for unscheduled outages of the on-site unit, scheduled maintenance service for planned outages, and economic replacement power when grid energy is cheaper than self-generation. Reading your tariff means knowing which of these components you are being billed for.

How standby charges are calculated

The core of a standby rate is usually a reservation or contract demand charge: a fixed monthly charge tied to the amount of backup capacity you reserve, often based on the nameplate capacity of your on-site generation or a contractually agreed demand. In one tariff documented by the EPA, the reservation demand charge applied only to the demand associated with backup service, at 7.26 dollars per kW-month, plus a 0.66 dollar per kW-day as-used charge when the backup was actually drawn. That split, a fixed reservation piece plus a variable as-used piece, is typical.

Two design features drive the pain. The first is the demand ratchet. The EPA describes a typical ratchet as billing the customer, in each of the 11 months following a peak, for a share of that peak or the current month's peak, whichever is greater. A single outage that forces a brief grid draw can therefore set a demand floor for nearly a year. The second is how the reservation quantity is set: better rate designs tie it to the generator's actual forced outage rate rather than assuming the backup is always needed at the system peak.

Why they can undermine on-site generation economics

Poorly designed standby rates can turn a good project into a bad one. The Great Plains Institute puts it plainly: when standby rates are too high, inflexible, unpredictable, or simply hard to navigate, the extra costs can mean a CHP system fails to provide its needed return and the project does not pencil out. The mechanism is concrete. The EPA notes that if a standby rate has only a demand charge and no energy charge, a single outage can push the facility to its monthly peak for a brief period, so the on-site system achieves no savings that month, and if the rate carries an annual ratchet, that one outage can forgo savings for the entire year.

The magnitudes are not trivial. In EPA's modeling, a contract-demand-only standby structure accounted for more than 7 percent of total electricity cost in the distributed-generation case. As a rule of thumb, the same analysis found that tariffs yielding avoided costs above 90 percent of the full-service retail rate generally provide enough savings to support on-site generation, and rates that fall well below that threshold are where projects get into trouble. Standby charges can run into the thousands or tens of thousands of dollars per month for larger systems, which is enough to swing a payback calculation on its own.

How to audit your standby charges

A standby audit compares what you reserve against what you actually use, and checks the rate design for the features that erode value. The EPA CHP Partnership and the Regulatory Assistance Project's best-practice work point to a consistent checklist.

• Compare reserved or contract demand against your actual backup draws. If you reserve far more capacity than a realistic outage requires, you are overpaying.
• Check whether the reservation quantity reflects your generator's forced outage rate rather than assuming backup is always needed at the system peak.
• Look for demand ratchets. Prefer rates with no more than a 30-day ratchet, or daily as-used demand charges rather than monthly.
• Confirm maintenance service is discounted and can be scheduled in low-demand periods.
• Make sure you are not charged for shutdowns caused by events on the utility side of the meter.
• Check small-system exemptions. NREL notes some jurisdictions exempt on-site generators below a contract demand of 50 kW from standby tariffs.

Standby charges rarely sit alone on the bill, so audit them alongside the rest of your tariff. The same discipline used in utility rate and tariff optimization applies here, and if your on-site generation is solar, the crediting mechanics in commercial solar and your electricity bill interact with what you owe under standby service.

The data you need to audit standby charges

You cannot audit a reservation charge without knowing your actual demand behavior. That means interval demand data showing when and how hard you drew from the grid during outages, a full bill history to see how ratchets carried a peak forward, and your generator's outage record to test whether the reserved capacity is justified. Standardized, aligned billing and interval data turns a standby audit from a guessing exercise into a straightforward comparison of reserved versus used, month by month.