The electricity price behind this quarter's figures
A compressor's running cost is built from two numbers: how much power it draws, and what that power costs per unit. The second number does not hold still. The unit rate UK businesses pay for electricity moves from one quarter to the next, and a running-cost or leak-cost figure worked out last spring can be wrong by the time the same compressor is still running in autumn.
Where the price comes from
The Department for Energy Security and Net Zero (DESNZ) publishes a non-domestic electricity price as part of its quarterly energy statistics, covering the unit rate paid by UK businesses in pence per kilowatt-hour (kWh). It can be shown including VAT or excluding it, and a running-cost figure that does not say which basis it uses cannot be checked against the table it was taken from.
Why the VAT basis matters
Most workshops pay VAT on their electricity at the standard rate, so a figure quoted excluding VAT understates what actually leaves the account, while a figure quoted including VAT will not line up against a rate a supplier quotes net. Stating the basis next to the price is what lets the two be matched up.
What moves when the price moves
A change in the unit rate carries through to everything priced from it: the yearly cost of running a compressor at full load, the cost of an air leak that has been sitting there since the last service, and the saving from turning the working pressure down by a bar. None of these need working out again from scratch when the rate changes. They need the new rate put through the same arithmetic, which is what the running costs guide and the leak costs guide set out step by step.
Three things worth re-pricing each quarter
Each of these is worked out from a different set of figures, but all three move when the electricity price does. Use whichever matches the question you're actually asking.
| What you're re-pricing | What drives the cost | What changes each quarter | How to recalculate it |
|---|---|---|---|
| A single leakA leak left unrepaired costs the same air whatever the price, so the pound figure moves with the rate alone | Hole size, system pressure and the hours the system runs under pressure | Only the electricity price changes; the air lost through the hole stays the same | Re-run the leak size and hours you already have through the current price |
| A pressure setting changeEven half a bar off the setting shows up across every hour the compressor runs, so it is worth checking after any price change | The bar the compressor is set to cut in and cut out at | The saving from running at a lower pressure scales directly with the new rate | Re-run the compressor's rated power and hours at the current price |
| A workshop's running costWorth doing at the start of each quarter, since the rate behind last quarter's figure has moved on | Motor power, duty cycle and hours run across the year | The whole annual figure moves up or down with the quarterly rate | Re-run the compressor's rated power and your logged hours at the current price |
This sets out what changes in each calculation. The figures behind each row come from your own compressor's rating plate and running hours, worked through the leak costs guide and the running costs guide.
Where a price change lands on your running cost
A change in the electricity rate doesn't change how your compressor runs. It changes what every hour under load now costs you, and that lands hardest on whichever part of the system already draws the most power for the least return.
Which parts of the system feel it most
A compressor that runs long hours at a high duty cycle (the proportion of time it spends running under load rather than idling) carries more of any price movement than one that cycles on and off through a quiet day, because the change applies to every kilowatt-hour drawn, not to a fixed standing charge. A two-shift workshop is exposed to a rate change in a way a single-shift one isn't, purely through the extra hours of power it draws at that rate.
Where to check first
None of the things that cost you money changed when the price did; the air still leaks at the same rate, the pressure is still set where it was, and the compressor still cycles the way it always has. What changed is what each of those now costs, which makes this the point to look again.
- Leaks: a hole in a hose or fitting draws power continuously, whether or not a tool is in use, so its cost moves in step with the rate.
- Working pressure: running the system a bar or two higher than the tools actually need means the compressor works harder for every litre delivered, at whatever the current rate happens to be.
- Duty cycle: a compressor sized well above current demand spends more of its time compressing air nobody is using yet, and that idle running still shows up on the meter.
Re-checking a leak or a pressure setting against the current rate takes the same arithmetic it always did; only the number you multiply by has moved. The leak costs guide works through that arithmetic for a hole of a given size, and the running costs guide does the same for pressure settings and duty cycle. If the figures point to buying differently, get compressor quotes sets out what to send a distributor to make the comparison mean something.
Convert, recalculate, act
A price change only means something once it's been run through your own numbers.