cstjnodLaboratory notebook

Technical memorandum

File
TM-26-1018
From
Charlie O'Donoghue
Date
Reading
5 min
Subject
Electric vehicles · Energy · Systems thinking

EVs are home energy's gateway drug

In 2023 I wrote that an EV nearly doubles a home's electricity. That held. What changed is where I think the flexibility is, and who can sell it.

AI-forward: Claude drafted this from my notes and checked every source against its claim. The argument, the cuts and the edit are mine.

In September 2023 I wrote a piece about EV charging and demand side response. Its standfirst said EVs are a gateway drug into home energy. I would now rewrite one part: where the flexibility is.

What held up

The stick held. A typical UK home uses about 2,500 kWh a year, 6.8 kWh a day. The average car covers about 19.5 miles a day, which at 3.3 miles per kWh takes about 5.9 kWh: 86% more than the house uses. A full charge is about nine and a half days of home use. Nothing else a household buys comes close, so you start reading tariffs, then pricing solar, batteries and heat pumps.

The carrot held too. A car needing 6 kWh, parked twelve hours on a 7 kW charger, charges in under an hour. The grid pays for that slack, which I called demand side response and most people now call flexibility.

What changed

More cars. Zapmap counts over 2.28 million fully electric cars on UK roads at the end of September 2026, about 3.5 million with plug-in hybrids. In 2023 I quoted 850,000.

The 2030 date. Days before my 2023 piece, Rishi Sunak pushed the end of new petrol and diesel car sales from 2030 to 2035. The next government moved it back. Since April 2025, new purely petrol or diesel cars end in 2030 and hybrids in 2035, when all new cars and vans must be zero emission. The ZEV mandate wants 33% of each maker’s new cars zero emission in 2026 and 80% in 2030. A consultation on those yearly targets, not the dates, runs from August 2026 to 23 October.

Tax. Since 1 April 2025 electric cars pay vehicle excise duty: £10 the first year for a new car, then the £200 standard rate. The government plans a per-mile charge, eVED, from April 2028.

The operator. National Grid ESO became the government-owned National Energy System Operator (NESO) on 1 October 2024, independent of National Grid.

Flexibility became a market. The Demand Flexibility Service began as a winter contingency in 2022. Nearly 2 million households and businesses signed up for winter 2024/25, and NESO has made it year-round. In July 2024 Ofgem made Elexon the market facilitator for local and national flexibility. In March 2025 it chose Elexon to build a common register for flexible assets like EV chargers, heat pumps and home batteries, due in 2027.

The charger rules settled in. Since 30 June 2022 every home charger sold must take signals and change when and how fast it charges. It must offer default off-peak hours and a random delay, and keep charging if it loses its connection.

The charger is the join

The charger is the only device on both sides of the plug. On one is the car. On the other is the site: main fuse, cooker, heat pump, solar, second car, tariff.

Each session tells the charger when the car arrived, what it took and when it left. The car never learns the site. It knows its battery, often better than the charger, but not the fuse, the kettle or the other car. Tariffs that steer charging through the car maker’s cloud work for price, never for a limit the car can’t see.

Site side of the plug Car side of the plug Flex market NESO, networks, suppliers The house other loads The charger on both sides The car knows its battery The grid local network Car maker its cloud energy main fuse energy energy load, if metered arrived, took, left buys firmness offer, how firm schedule from price, never the limit energy information readings, records limit
The charger is the only device on both sides of the plug. It can learn the car and the house; the car never learns the site.

Flex is only as firm as what you know

A flexibility offer promises to draw no more than this, between these times. NESO, a network operator or a supplier buys how sure that promise is. A broken one can cost money.

Plugged in is a guess. A departure time makes it a plan, energy needed a schedule, a known site limit a promise.

illustrative most homes a depot a guess a plan a schedule a promise how firm the promise plugged in + departure time + energy needed + site limit what the charger knows
Flex firmness as a function of what the charger knows. Illustrative, not measured.

A home charger knows the least. Unless the driver tells the app, it has no departure time. On basic AC it often cannot read state of charge. It may not see the house. So home flex is a forecast, pooled across thousands of homes until guesses average out. Useful, not firm.

Which is why depots are the market

Depot vans return after one shift and leave for the next. The operator plans routes, so it knows what each van needs. One team runs the chargers, vans and building, behind one connection of known capacity. What a home charger guesses, a depot has written down.

That is firm flex in bulk, with one person to say yes. I think flexibility becomes a business there first. Homes will follow as chargers learn more and drivers share departure times.

In 2023 I thought opt-in was the hard part. More than 2.4 million homes and businesses have signed up to NESO’s Demand Flexibility Service, typically through a supplier or aggregator. The hard part is knowing enough to make the promise worth buying.

What I would tell a product manager now

In 2023 I asked who owns the deal. Now I ask who holds the information. Whoever has it makes firm promises. Everyone else resells guesses.

At home, close the gaps without burdening the driver: learn the routine, ask for a departure time once, read the house where you can. A fleet already has the information. Get it to the charger.

The car got people into home energy. The charger is where they stay.

Sources