What Is a Demand Charge?
A demand charge is a fee on your electric bill based on the highest rate of power your facility draws at any single moment during the billing period, measured in kilowatts (kW). It is separate from the energy charge, which is based on the total electricity you use over the month, measured in kilowatt-hours (kWh). On many commercial bills, the demand charge is 30 to 70 percent of the total amount due.
Energy is the shaded area. Demand is the single highest point.
Demand (kW) versus energy (kWh)
Your utility bills you on two different things. Energy is how much electricity you use over the month. Demand is how fast you use it at your busiest instant. A useful comparison is a car trip: energy is the total distance you drove, and demand is your top speed along the way. You can drive a short distance at a high top speed, or a long distance gently, and the bill treats those very differently.
This is why two facilities that use the exact same number of kilowatt-hours can pay very different bills. The one with sharp, spiky power use pays more, because its peak demand is higher even though its total energy is the same.
How demand is measured
Most utilities measure demand in short windows, often 15 minutes. The meter records your average power in every window across the billing period, and your demand charge is set by the single highest window. One brief spike, on one afternoon, can set the charge for the whole month.
Some utilities go further with a ratchet clause, where your billed demand for a given month cannot fall below a set percentage of your highest peak from the past several months. Under a ratchet, a summer spike can keep your demand charge elevated well into the winter. It is worth checking your tariff for this, because it changes the value of trimming your peak.
Why utilities charge for demand
The grid has to be built to meet your highest possible draw, not your average one. The wires, transformers, and generation capacity that serve your peak sit ready even when you are not using them. The demand charge is how the utility recovers the cost of standing that capacity up for you. The higher and spikier your peak, the more capacity you require, and the more you pay.
How much demand charges cost
Demand is priced as a rate per kilowatt of peak, often somewhere from a few dollars to more than twenty dollars per kW each month, depending on your utility and tariff. Multiply that rate by your peak kW and by twelve months, and the annual figure gets large fast. A facility with a 400 kW peak on a $20/kW tariff pays around $96,000 a year in demand charges alone.
How to find the demand charge on your bill
Look for a line measured in kW rather than kWh. It may be labeled demand, billing demand, peak demand, or maximum demand, and it usually sits near a separate per-kW rate. If you see a kW figure with its own dollar amount, that is your demand charge. If your bill shows only kWh, you are likely on a smaller rate without demand charges, in which case storage has less to work with.
Why demand charges drive battery storage savings
Because the charge is set by your single highest spike, you do not have to lower your usage all day to save money. You only have to shave the peak. A battery charges during quiet hours and discharges during your spike, so the meter never records the full peak. Your billed demand drops, and so does the charge, without changing how you run the building.
This is the largest and most reliable way storage earns its keep for most commercial and industrial facilities. It is also why a sharp, repeatable peak makes a facility a strong candidate, and a flat load makes it a weak one. If you want to know whether your peak is worth shaving, that is exactly what a Storage Decision Report figures out from your own bill.
Ways to reduce demand charges
Battery storage. Discharges during your peak to cap the billed demand. The biggest and most dependable lever for facilities with a real peak.
Staggering equipment. Avoid starting large motors, compressors, or chillers at the same moment. Sequencing startups can trim the spike at no capital cost, though the effect is limited.
Shifting flexible loads. Moving non-urgent, heavy loads to off-peak hours lowers the peak, where your operation allows it.
Operational changes help at the margins, but they depend on the building tolerating disruption to its schedule. Storage is the option that lowers the peak without asking you to change how you operate, which is why it carries most of the savings.
Common questions about demand charges
What is the difference between a demand charge and an energy charge?
An energy charge is based on the total electricity you use over the month, measured in kilowatt-hours. A demand charge is based on the highest rate of power you draw at any single moment, measured in kilowatts. You pay both, and on many commercial bills the demand charge is the larger surprise.
How is billing demand measured?
Utilities measure your average power in short windows, often 15 minutes, across the billing period. Your billed demand is set by the single highest window. One brief spike can set the charge for the entire month.
Why do I pay a demand charge if I only hit that peak once?
Because the grid must be built and maintained to serve your highest possible draw, even if you reach it briefly. The demand charge recovers the cost of holding that capacity ready for you.
How much can battery storage reduce demand charges?
It depends on how much of your peak the system can shave, which depends on your load shape and the system size. For a facility with a sharp, repeatable peak, storage can trim a meaningful share of the peak and recover a large part of the demand charge, often paying back in a few years. A flat load benefits much less.
What is a demand charge ratchet?
A ratchet clause sets a floor under your billed demand based on your highest peak over the past several months. Under a ratchet, a single high peak can keep your demand charge elevated long after the spike, which makes shaving the peak even more valuable.
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