Flexibility vs cheap tariffs: where the real savings are

It’s easy to get excited about earning money from the grid and lose sight of where the real savings sit. For almost every depot, the priorities are clear — and flexibility income is the smallest of them.

The big win: cheap charging

The largest, most reliable saving comes from charging on a time-of-use tariff in the cheap overnight hours. Shifting the fleet’s charging into the low-price window can roughly halve the energy cost versus charging at peak — and it applies to every kWh, every night. This is the foundation.

The second win: avoiding a grid upgrade

Close behind is using smart charging (and a battery where needed) to fit within your connection and dodge an expensive grid reinforcement. Avoiding a large one-off cost — potentially tens or hundreds of thousands of pounds — dwarfs what flexibility trading returns.

The bonus: flexibility income

Flexibility and DSR then sit on top as a modest, steady supplement — real, worth having, but the icing rather than the cake. Chasing it should never distort the core design.

Keep the order right

The trap is over-investing to maximise a small revenue stream while under-investing in the tariff strategy and grid design that deliver the big savings. Get the cheap-charging and grid-fit basics right first; make sure the infrastructure can also participate in flexibility; then treat any income as a welcome extra. Priorities in that order keep the economics honest — the running-cost tool shows where the real numbers land.