Commercial demand charges: what sets them

A bill that prices your peak, not your volume

Most of a commercial bill scales with consumption: use more kilowatt-hours and you pay more. A demand charge works differently. It is calculated from the highest rate at which the site pulled power during the billing period, averaged over a short interval and billed per unit of that peak. A site that runs a heavy load for twenty minutes and then idles can be billed as though it ran that load all month, while a site using the same number of kilowatt-hours at a steady pace is billed far less. Oncor records this measure as the highest fifteen-minute demand in the billing month, and the account's delivery tariff sets whether it applies and how it is calculated. It is the single most common reason two businesses of the same size see different effective prices.

• Volume charges scale with kilowatt-hours used.
• Demand charges scale with the highest short-interval peak in the period.
• A brief spike can set the charge for the whole month.
• Whether it applies depends on the account's rate class and meter, not on the supplier.

Measured demand and billing demand are not the same number

The meter's measured demand is the highest interval value recorded in the billing cycle. Billing demand is the figure the tariff actually charges, and the tariff may move it first. A demand ratchet keeps billing demand from falling straight to a low current-month peak after a higher one has been set, so the charge can reflect a prior period. A meter multiplier converts the transformed reading from the current and voltage transformers to the customer's true service quantity. And the interval length defines the number itself: a demand meter divides the energy recorded in a window by the window's duration, so the shorter the interval, the sharper the peak it captures. Texas Rule 16 TAC §25.501 governs how transmission and distribution costs flow through to the delivery rate, while the applicable TDU tariff supplies the specific ratchet and minimum-demand provisions for a rate class.

• Measured demand is the highest interval recorded in the cycle; billing demand is what the tariff charges.
• A demand ratchet bills against a prior peak so a low month does not reset the charge.
• A CT/VT meter multiplier scales the transformed reading to the actual service quantity.
• The interval length sets the magnitude: the same energy over a shorter window is a higher peak.

Load factor: the ratio that decides your effective price

Load factor relates how much you used to how much you could have used had your peak run the whole period. Compute it from your own bill: divide the kilowatt-hours consumed in a month by the product of your peak demand in kilowatts and the number of hours in that month, then express the result as a percentage. A site with a sharp peak and modest consumption lands low, and a low load factor is expensive, because the fixed monthly charge and the demand charge are recovered across fewer kilowatt-hours, so each carries more of them. A steady operation of the same size has a high load factor and a lower effective price. This single number explains more about a commercial bill than any headline rate can.

• Load factor = kWh ÷ (peak kW × hours in the period), as a percentage.
• A high load factor spreads fixed and demand costs across more kilowatt-hours.
• A low load factor concentrates them, raising the effective price per kilowatt-hour.
• Calculating your own load factor needs monthly kWh and monthly peak demand.

The four coincident peaks and the transmission access rate

Transmission cost in the ERCOT market is allocated through the four coincident peaks: the single highest fifteen-minute system-wide demand interval in each of June, July, August and September. ERCOT selects the intervals; your account is measured during those exact windows, and the four readings are averaged into your 4CP demand. Under PUCT Substantive Rule §25.192, a transmission service provider's approved annual cost of service is divided by the ERCOT average coincident peak demand to produce the transmission access rate, and each customer's charge follows from that rate applied to its allocated peak. A retail customer meets the cost through the delivery portion of the bill, where the TDU recovers its allocated transmission cost in a PUCT-approved tariff component. The exposure, then, is not your own peak — it is what your meter was doing when the whole system peaked.

• Four intervals: the highest fifteen-minute ERCOT system demand in June, July, August and September.
• Your 4CP demand is the average of your readings at those four intervals.
• The 4CP demand divides the approved transmission cost of service into the access rate.
• The cost reaches you through the TDU's delivery tariff, the following year.

Transmission demand and distribution demand are different questions

A transmission charge asks how much load you contributed when the ERCOT system was at its monthly peak. A distribution demand charge asks how much demand you imposed on the local network, usually measured as your own highest interval in the billing period whether or not the system peaked then. The two can move in opposite directions. A facility that sheds load during the four system intervals can carry a modest 4CP contribution alongside a large distribution demand; a facility that peaks outside those windows can do the reverse. The applicable TDU tariff controls the distribution-demand formula, its ratchet, its minimum billing demand and its voltage-level treatment, so the two determinants should never be collapsed into one demand figure when a bill is read.

• Transmission demand is measured at the four ERCOT system peaks.
• Distribution demand follows the local tariff, usually the account's own peak.
• One facility can be high on one measure and low on the other.
• The TDU tariff, not the supplier, sets both.

Power factor: when the tariff adjusts the demand it bills

Power factor compares the real power a site uses, measured in kilowatts, with the apparent power it draws, measured in kilovolt-amperes. A lagging power factor below the tariff's threshold means the site pulls more apparent power for the same useful load, and a tariff can respond by adjusting billed demand upward or by billing on kVA rather than kW. Oncor's tariff permits an adjustment of billing demand where power factor is below ninety-five per cent, applied using the average power factor during the fifteen-minute peak-demand interval of the month. Where a utility publishes a formula, it typically scales the measured demand by the ratio of the threshold to the actual power factor. Because the treatment differs by utility, rate schedule and demand component, the exact tariff section matters — and the remedy, correction equipment on the customer's side of the meter, is an engineering decision rather than a procurement one.

• Power factor = kW ÷ kVA; below the tariff threshold the site draws more apparent power.
• A tariff may adjust billed demand upward or bill on kVA instead of kW.
• The adjustment is applied at the peak interval, not across the month.
• Correction is customer-side equipment, not a supply-contract term.

Interval data is the prerequisite for any of this

None of it can be managed from a monthly bill. You need the interval data — the fifteen-minute readings a demand-metered account already records — to see when your peaks fall and how they line up with the system's. Oncor requires an interval data recorder, or IDR, for premises that exceed seven hundred kilowatts at least twice in a twelve-month period, and treats those interval-metered premises differently from non-IDR premises profiled from other data. Accounts with IDR meters can pull fifteen-minute data from Oncor's IDR portal; accounts on standard advanced meters can retrieve interval data through Smart Meter Texas. Ask for the interval history rather than the summary, and use it for two things: finding the hours where your load coincides with system peaks, and re-measuring after each change to confirm it worked.

• Request fifteen-minute interval data for each demand-metered account.
• IDR metering applies above the tariff threshold; non-IDR premises are profiled.
• Interval data comes from the utility's portal, not a monthly summary.
• Re-measure after each change, or you cannot tell whether it worked.

Reduction happens inside the interval, not across the month

Because the basis is a coincident demand, lowering consumption at other times does not change it. What lowers it is reducing load during the specific fifteen-minute windows that set it — an operational problem, not a procurement one, which is why the work usually sits with whoever runs the building rather than whoever buys the energy. The approaches are the same ones used for a monthly peak: shed discretionary load, shift production, pre-cool the space, or run on-site generation or storage through the window. Because the interval is not announced in advance, the response has to be a rehearsed protocol rather than an improvised one. Assign an owner and test the protocol before the summer, not during it.

• Only reductions inside the coincident interval affect the calculation.
• Approaches: shed discretionary load, shift production, pre-cool, run on-site generation or storage.
• The interval is not announced ahead of time, so the response has to be a rehearsed protocol.
• Assign an owner and test the protocol before the summer, not during it.

Where this meets your supply contract

Demand also shapes what a supplier will offer. Supply agreements can carry a minimum usage or ratchet provision that bills against a floor or a historical peak, which matters when your peak falls after a change in operations — the contract may still reflect the old one. That is a clause question rather than a delivery question, and it belongs alongside the end-of-term provisions when an agreement is read. A site that has genuinely changed its load profile should ask, in writing, how the contract treats the change before it signs, because the meter will show the new peak and the contract may not.

• Minimum usage and ratchet provisions can bill against a historical peak.
• Check whether a load change is reflected in the contract or only in the meter.
• Ask for the treatment in writing before signing.

What this does not change

Delivery and transmission are the half of the bill a business cannot shop: they are set by tariff and are identical whichever supplier bills the supply line. Demand management therefore reduces what you pay for something you were going to pay regardless — it does not replace competing your supply, and competing your supply does not reduce a demand charge. Eligibility for any of this still depends on the service address, the meter and the utility territory; municipal utilities, cooperatives and some jurisdictions offer no retail choice at all. HighGround Exchange may receive compensation from providers on completed purchases, and an inquiry places no order and switches no supplier.

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