Vehicle-to-grid · techno-economic analysis

Should Berlin's e-buses power the grid?

Berlin's operator BVG is electrifying its bus fleet and has to build depot chargers anyway. This proposal asks whether it should pay extra for bidirectional chargers, so parked buses can charge when power is cheap and sell energy back at evening peaks (Bus-to-Grid).

Team Billriz Condor, Carlos Andrés Villamar Martínez, Kien Long van HoSupervisor Bence Bróní Bereczk

Run the scenarios Read the proposal (PDF) See the code

A day at the depot

Most buses leave between 05:00 and 08:00 and return between 16:00 and midnight. That leaves a cheap night-charging window and a pool of parked buses during the morning and evening price peaks.

Charging window, 00:00–05:00 · 50% of the fleet Discharging at peaks, 06:00–09:00 and 16:00–21:00 · 15–30% of the fleet Most buses on the road

Day-ahead prices in Germany range from about €20–50/MWh in low-demand hours to €150–200/MWh at peaks (SMARD, 2025). The model assumes charging at €10–30/MWh in the optimised window and selling at €150/MWh.

E-bus fleet roll-out

Battery-electric buses in service (BVG targets)

Investment 2025–2030

CAPEX in millions of euros

Baseline operating costs 2025–2030

OPEX before any smart charging, in millions of euros (charging at €90/MWh)

Scenario explorer

Benefit in OPEX is savings from cheaper charging, plus discharging revenue in the bidirectional case, as a share of baseline OPEX (€482M). Move the sliders to compare the two charger types.

Charging price in the night window Share of fleet discharging at peaks

Benefit in OPEX for every scenario in the report

Rows: charging price. Columns: charger type and share of the fleet discharging at peaks. The cell matching the sliders is outlined.

Key findings

Arbitrage alone doesn't pay backSelling energy at peaks can't recover the full cost of bidirectional chargers. That's expected for a public operator that isn't run for profit.

A small premium for a big upgradeBidirectional chargers cost 30% more per kW, which adds only about €41M (+6%) to a €699M electrification programme.

Benefit rises from 16–21% to 22–33%Discharging revenue of €29–58M over 2025–2030 lifts the benefit in OPEX well above what smart charging achieves on its own.

Value for the whole gridA 1,250-bus fleet could avoid up to about 101 t of CO₂ a day by replacing fossil peaker plants. It can also defer transformer and grid upgrades.

Roadmap

PilotOne depot with a few bidirectional chargers, run for a full seasonal cycle to test winter and summer loads.

Scale-upMore depots and a growing share of V2G chargers, with automated charge-scheduling software.

Grid integrationFormal grid-support contracts with the grid operator (DSO), locked-in prices, and depots used as planned flexibility assets.

Main risks and mitigation

Risk	Mitigation
Battery degradation	Battery-life management with proper cycling and charging strategies
Charger reliability	Redundant chargers and spare charging capacity at depots
Back-end/cyber vulnerability	Robust, secure energy-management back end
Electricity price volatility	Long-term price contracts for charging and discharging
Technology costs	Fixed-price contracts for chargers and installation
Lagging V2G regulation	Engage early in policy-making with local and EU regulators

How it's calculated

This Python model rebuilds the CAPEX and bus O&M figures from the proposal's assumptions, then runs the full charging-price × discharge-availability sensitivity matrix. The explorer above uses the same equations.

analysis/b2g_financial_model.pyOpen on GitHub →

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