The Grid Capacity Trap: Why buying the EVs is the easy part

If you are a fleet manager or sustainability director, the first phase of decarbonisation feels like a procurement challenge. You audit your vehicles, select the electric replacements (e-Transits, Vivaros), and calculate the TCO.

Then comes the “Grid Trap.”

You submit a connection request to your DNO (Distribution Network Operator) for the chargers required to power those vans, and you get a letter back. It says your depot—which has run happily on a 60kVA or 100kVA supply for decades—now needs 500kVA to support your new fleet.

The quote for reinforcement is six figures. The lead time is 18 months. And just like that, your 2030 net-zero target hits a brick wall.

This scenario is playing out at council depots, logistics hubs, and bus garages across the UK. But often, the problem isn’t the grid. The problem is the math.

The Flaw of “Nameplate” Engineering

The reason DNO quotes are so high is that they are often based on “Nameplate Capacity”—the worst-case scenario where every charger you install is running at full power, simultaneously, forever.

If you install ten 22kW chargers, the traditional calculation says you need 220kW of headroom.

But in reality, fleets don’t behave like that.

• Vehicles arrive at different times.
• They have different states of charge (SOC).
• They dwell for 12 hours overnight but only need 4 hours to charge.

This gap between Maximum Possible Demand and Actual Diversified Demand is where the opportunity lies.

Bridging the Gap with Simulation

You cannot solve this problem with a spreadsheet. To avoid a £500k grid upgrade, you need rigorous, physics-based simulation.

At Thoughtful Electron, we model these constraints using high-resolution operational data. Instead of asking “How much power do we need if everything turns on at once?”, we ask:

“What is the minimum grid connection required if we optimize the charging schedule against the vehicle dwell times?”

By layering in Solar PV, Battery Energy Storage Systems (BESS), and Smart Load Management, we can often fit a fleet requiring “theoretical” 300kVA into a “constrained” 70kVA connection.

The Role of V2G and Smart Control

This is where the engineering reality meets the commercial vision.

For sites with severe constraints, Vehicle-to-Grid (V2G) moves from a “nice to have” pilot to a critical infrastructure asset. By allowing vehicles to discharge back into the depot microgrid during morning heating peaks (when the depot offices are warming up and the fleet is prepping to leave), you can shave the peak demand that dictates your grid connection cost.

Discover, Diagnose, Design

We approach these projects in three phases:

1. Discover: We integrate your half-hourly billing data, PV generation profiles, and fleet duty cycles to build a baseline model.
2. Diagnose: We stress-test your current grid limit. We find out exactly where the breaker trips—is it 8:00 AM in December? Is it 5:00 PM in July?
3. Design: We use Python and Golang optimisation algorithms to model the “No-Reinforcement” scenario. We simulate the exact mix of battery storage and smart control needed to keep you within your DNO cap.

The Outcome

The result is a Decarbonisation Roadmap that is actually deliverable.

We recently modelled a scenario for a commercial depot facing a restrictive <70kVA limit. The traditional advice was to upgrade the substation. Our simulation proved that by combining 64kWp of Solar PV with a smart-managed charging strategy, the site could support its EV transition without digging up the road.

Buying the vans is easy. Keeping them charged without breaking the bank is the real engineering challenge.

Facing a grid constraint on your site? Book a Strategy Call to discuss how simulation can unlock your capacity.