DCP161 explained: excess capacity penalty rates, checking headroom, and when a capacity review pays

What DCP161 actually changed

DCP161 is a DCUSA change proposal ("Improved Cost Reflectivity for Excess Capacity Charges") that took effect on 1 April 2018. Before it, a half-hourly metered site on a low voltage or high voltage distribution tariff could draw more than its agreed supply capacity month after month and pay nothing extra. The distribution network operator was carrying capacity on its network that nobody paid for, while neighbouring sites that had bought the right amount of capacity paid in full. The change closed that gap by adding an exceeded capacity charge to the standard distribution tariffs, so any kVA drawn above the agreed level is billed at a separate, higher rate.

Two points are worth fixing in your head before anything else. This only bites on half-hourly settled sites taking a distribution use of system tariff with an agreed supply capacity in kVA, so most single-rate small commercial supplies are untouched. Nor is DCP161 a fine issued by Ofgem or the DNO; it is a line on the distribution charges that your supplier passes through to you, usually shown as "excess capacity" or "exceeded availability" on the bill. The rules sit in the Distribution Connection and Use of System Agreement, which you can read at dcusa.co.uk, and the charging methodology behind it operates under licence conditions overseen by Ofgem.

How the penalty rate is built

Every half-hourly site has an agreed supply capacity, sometimes called available capacity or authorised supply capacity, set in the connection agreement with the DNO. That figure is billed at a capacity rate in pence per kVA per day, every day of the year, used or not.

The exceeded capacity charge works on the same clock but a different basis. The DNO looks at the highest measured demand in kVA in each billing month. If that peak sits above the agreed capacity, the difference becomes "exceeded capacity" and is charged at the exceeded capacity rate, applied per kVA per day across the days in that month. A single bad half hour in week one can therefore generate a charge for the whole month, and a site that peaks over its limit in eleven months of the year effectively pays a second, more expensive capacity bill.

Rates differ by DNO region and by tariff line, they vary between voltage levels, and they change each April. Do not work from a figure quoted in an old article, including this one: pull the current use of system charging statement for the relevant region and find the exceeded capacity rate alongside the capacity rate for that specific tariff line. The statements are published on each network's website, for example Northern Powergrid, UK Power Networks, Electricity North West, National Grid Electricity Distribution and SP Energy Networks. In most published tariffs the exceeded rate sits at a clear premium to the ordinary capacity rate, which is the whole point of the change.

Here is a worked example, using an illustrative rate rather than a real one. Say a site has 200 kVA agreed and peaks at 260 kVA in a 31 day month, and the exceeded capacity rate for its tariff is 3p per kVA per day. That is 60 kVA of excess, times 31 days, times 3p, or about £55.80 for the month. Repeat that pattern across a year and you are into several hundred pounds, before considering that the overshoot may also be pushing up reactive power charges if the site's power factor is poor. On a larger overshoot, say 300 kVA above a 500 kVA agreement, the same arithmetic runs into thousands.

Checking headroom properly

Headroom is the gap between agreed capacity and actual peak demand, measured in kVA. Brokers get this wrong when they compare a kW figure to a kVA agreement, because kVA includes reactive power and is always the larger number where power factor is below one.

The method that stands up to scrutiny:

• Get the agreed supply capacity from the connection agreement, or from the capacity line on twelve months of supplier invoices. If the two disagree, the connection agreement wins and the billing needs correcting.
• Pull twelve months of half-hourly consumption data, ideally with reactive data. Your supplier or data collector can provide it; the settlement framework that governs this data is administered by Elexon.
• Convert to apparent power for each period: kVA equals the square root of kW squared plus kVAr squared. Then multiply by two if your data is in kWh per half hour, since demand is the hourly rate.
• Find the maximum kVA in each calendar month, not just the annual peak. DCP161 charges monthly, so one winter spike matters even if the annual average looks comfortable.
• Express each monthly peak as a percentage of agreed capacity. Below roughly 60 per cent utilisation for twelve straight months, you are probably paying for capacity you do not need. Above about 85 per cent, you are one new compressor or one hot week away from exceeded capacity charges.

One more check: look for growth. A site at 70 per cent today with an electric vehicle charging installation or a new production line in the plan is a very different case from a stable warehouse.

When a capacity review saves money, and when it costs

Since 1 April 2022, following Ofgem's Targeted Charging Review, the residual element of distribution charges for half-hourly sites is recovered through fixed daily charges, with customers placed in bands according to their agreed capacity and voltage. That reform sharpened the economics of a review in both directions. Cutting agreed capacity can lower the capacity charge and, if the reduction crosses a band boundary, cut the fixed residual charge as well, which is often the larger saving.

Reducing capacity looks strongest where twelve months of data show a comfortable margin, the load is stable, and no electrification project is in the pipeline. Savings on a heavily over-specified 500 kVA supply that never passes 250 kVA can run to four figures a year once both the capacity and the band effect are counted.

Against that, weigh the return trip. Giving capacity back is a change to the connection agreement, and getting it later is a new connection application. The DNO may need to reinforce the network, and a connection offer can arrive with a capital contribution attached. Lead times on constrained networks run to months or longer. Reduce too far and you convert a modest saving into an expensive project, plus the exceeded capacity charges you were trying to avoid in the first place. Sites with seasonal peaks, standby loads, on-site generation or plans for charging infrastructure should keep more margin than a spreadsheet suggests.

Increasing capacity is the other half of the review. Where a site sits consistently over its agreed level, an increase usually beats paying the exceeded rate indefinitely, and it also removes a breach of the connection agreement, which is the point most clients have not considered. Ask the DNO for the increase in writing, keep the offer, and check that the supplier updates the capacity on the billing system from the effective date.

What a broker can do this week

• For every half-hourly client, list agreed capacity from the connection agreement and the highest monthly kVA peak over the last twelve months. Flag anything above 85 per cent or below 60 per cent utilisation.
• Scan the last twelve invoices for an excess or exceeded capacity line. Where it appears, price the annual cost at the current regional rate and compare it against the cost of a formal capacity increase.
• Where a reduction looks attractive, check the capacity band thresholds in the current charging statement before quoting a saving, and model the client's growth plans for the next three to five years.
• Fix power factor problems before touching capacity: correcting a poor factor can lower measured kVA and remove the overshoot without any change to the connection agreement.
• Put the request to the DNO in writing, record the effective date, and audit the next two invoices to confirm the change has landed in billing.