Comparing energy across multiple business sites

One invoice, several premises: why averaging your sites gives the wrong answer, and how to compare each supply point properly.

One invoice is not one site

If your business runs from more than one premises, you probably get a single invoice covering all of them. That is an accounting convenience, not an energy fact. Each premises is its own supply point, with its own meter, its own network, its own tariff and its own usage shape.

It matters because the cheapest plan is decided per supply point, not per invoice. Two shops in different distribution areas can face genuinely different networks, different tariff structures and different available plans. A warehouse that runs machinery all day and an office that is empty by six have different load shapes, and the plan that suits one may be the wrong shape for the other.

Why averaging is the wrong instinct

The natural approach is to total the kilowatt-hours across the invoice, divide by the number of sites, and compare that. It feels reasonable and it produces a confident answer that is very often wrong.

Averaging destroys exactly the information that determines the best plan. A site with a sharp afternoon peak and a site with a flat overnight load average out to something that resembles neither, and the plan that best suits the average may be optimal for no individual site.

It is worse when demand charges are involved, because demand is not additive at all. Your sites almost certainly do not peak at the same instant, so summing their individual peaks overstates your exposure, while averaging them understates it.

How to do it properly

Split the invoice by supply point. Each premises should have its own NMI (National Metering Identifier) — a ten or eleven character code that uniquely identifies that connection.
Note each site's own network. It is printed on the bill and determines which tariffs and plans are even available there.
Capture each site's own usage, and its own demand figure if it has one. Do not carry one site's peak across to another.
Compare each site independently against the plans available on its network.
Only then add the results up. The total of the best-per-site is the real number — and it is usually better than the best single plan applied everywhere.
Check whether your retailer offers a single account across sites even on different plans. Consolidated billing and per-site optimisation are not mutually exclusive.

What we do with a multi-site invoice

When you upload a business bill covering several premises we split it into one profile per site rather than treating it as one large customer. Each site gets its own comparison on its own network, with its own demand figure priced in.

You confirm the detected sites before anything is stored, so a site the reader mislabelled can be corrected or renamed rather than silently mis-costed. Each confirmed site becomes its own property in your account, with its own bills, comparison history and alerts.

That also means the nightly re-check works per site: if a cheaper plan appears for one premises and not the others, you hear about that one.

Frequently asked questions

What is a NMI and where do I find it?

The National Metering Identifier uniquely identifies an electricity connection point. It is ten or eleven characters, printed on your bill, usually near the supply address or in the usage detail. Each premises has its own.

Can different sites be on different retailers?

Yes. Nothing requires all your sites to be with one retailer, and if they are on different networks with different tariff structures, splitting them can be worth real money. The trade-off is administrative: more accounts and more invoices to manage.

Do my sites' peak demands add together?

For billing, each site is charged on its own peak — they are not summed into one figure. That also means your sites peaking at different times is not something you are rewarded for. Each site is assessed on its own worst moment.

Is one big account cheaper than several small ones?

Not automatically. Larger consumption can unlock better rates in a negotiated contract, but on standard published plans each supply point is priced on its own usage. It is worth comparing both ways rather than assuming scale wins.

General information only, current at the time of writing. Not financial advice. Rebate schemes and rules change; always confirm details with your retailer or state government energy site.