First Bus enrols electric bus depots into the balancing mechanism

What happened

On 7 May 2026 First Bus announced it had become the first UK bus operator to enrol electric bus depots into the electricity balancing mechanism, in a trial run with the energy technology firm Optimo Energy. The trial began at the operator's Glasgow depot, with a second site at Great Yarmouth in Norfolk due to join later in the spring.

The scale of the fleet behind the trial is what makes it interesting. First Bus has more than 1,400 zero-emission buses in service, roughly a quarter of its fleet, and has developed 20 electric depots across the UK, with several more due to complete by the end of 2026. The company is committed to a fully zero-emission fleet by 2035.

The technology

The balancing mechanism is the tool used to match electricity supply and demand in close to real time. Generators and, increasingly, flexible consumers offer to raise or lower their output or demand at short notice; the system operator accepts those offers to keep the grid stable.

A depot full of charging buses is, from the grid's perspective, a large and unusually predictable block of demand. Buses follow timetables; their overnight charging windows are long relative to the energy they need; and a depot operator knows exactly which vehicles must be full by which departure time.

That slack is what Optimo Energy's platform trades. It adjusts when buses charge in response to real-time grid signals — pushing demand up when there is excess renewable generation, particularly Scottish wind, and easing off during system peaks, while guaranteeing every bus is charged and ready for service.

The renewables link is the crux. The stated aim of the trial is to minimise curtailed renewable generation — wind power that would otherwise be turned down because the system cannot absorb it. A Glasgow depot that soaks up surplus wind reduces curtailment at one end and peak stress at the other.

Isabel McAllister, First Bus's chief sustainability officer, framed the trial as buses "playing an active role in the UK's energy system... charging when the grid needs us to". Daniel Homoki-Farkas, Optimo's chief executive and co-founder, called electric fleets "a significant opportunity to support the UK's transition to a more flexible energy system".

Why it matters for UK & Ireland

Depot flexibility changes the economics of bus electrification. Electricity is one of the largest operating costs of an electric fleet; balancing mechanism participation turns the depot from a pure cost centre into a revenue-earning grid asset, and First Bus has said it will explore additional flexibility markets for new income streams. For an industry where electrification has depended heavily on public subsidy for vehicles and infrastructure, a recurring revenue line against charging costs matters.

It also matters for the grid. Great Britain needs large volumes of flexible demand to run a renewables-heavy system, and electric fleets are among the biggest new controllable loads being connected — buses today, HGVs and vans behind them.

Bus depots are a natural starting point because their demand is scheduled and professionally managed. First Bus's First Charge offering, which opens its depot infrastructure to third-party fleets, extends the same logic: shared depots aggregating more flexible load per grid connection.

The template travels well. Any wind-heavy grid with an electrifying bus fleet faces the same arithmetic, and operators and system planners in Ireland, where both conditions apply, will find the Glasgow model directly relevant reading.

What to watch

Three markers. First, results: neither First Bus nor Optimo has yet published revenue figures or the volume of flexibility delivered, so the trial's economics remain to be demonstrated in public.

Second, expansion — whether enrolment spreads from Glasgow and Great Yarmouth across the rest of First Bus's 20-plus electric depots, and whether rival operators follow. Third, market design: how the system operator and regulators treat aggregated fleet demand as its volume grows, and which of the additional flexibility markets First Bus chooses to enter next.