Build or Flex? Why Smart EV Charging Is Becoming Grid Infrastructure
Under Ofgem's ED3 price control, a DNO must show flexibility couldn't resolve a constraint before it can reinforce. That shifts smart EV charging from optional add-on toward grid infrastructure.
For most of the last decade, the industry conversation about electric vehicles and the grid has had one shape: more EVs mean more load, more load means more strain, more strain eventually means more copper in the ground. That framing isn't wrong, but it's no longer the whole story — and under Ofgem's ED3 price control methodology, it's not even the first question a network operator is required to ask.
The new default is "flex before build." Before a distribution network operator can put physical reinforcement — a new transformer, a bigger cable, an upgraded substation — into its regulated investment plan, it increasingly has to show that flexibility couldn't have done the job instead. That single procedural shift turns smart EV charging, batteries and demand-side response from optional add-ons into something closer to grid infrastructure in their own right.
This is the strategic context the rest of this series sits inside. Understanding it first makes everything that follows — microgrids, V2G, standards, reliability, fairness — legible as parts of one transition, not six unrelated trends.
What "build and flex" means under ED3
ED3 doesn't ban reinforcement — it reorders the decision. A DNO facing a forecast constraint now has to evidence that it has genuinely considered whether flexible resources, deployed intelligently, can relieve or defer the problem before capital investment is approved into the price control. Flexibility isn't a nice-to-have sitting alongside the traditional plan; for many constraints, it's the plan, with reinforcement as the fallback when flexibility runs out of road.
Figure 1. The test isn't "is flexibility cheaper" in the abstract — it's whether a specific, evidenced flexible solution can resolve this specific constraint, at this location, in time.
When delayed or modulated charging relieves a constraint
Most local network constraints aren't permanent — they're peaky. A feeder or a secondary substation can sit comfortably under its rating for twenty-two hours a day and brush against its limit for two. If the thing pushing it over that limit is a cluster of EVs charging at 6pm when everyone gets home, then shifting even a modest share of that charging by two or three hours can be the difference between a constraint and a non-event.
Modulated charging works the same way at finer resolution — instead of delaying the whole session, an aggregator or charger throttles the rate of charge during the narrow window when the local network is under pressure, then lets it resume at full rate once the constraint passes. Done well, the driver barely notices; the network sees a shaved peak instead of a breach.
Why flexibility can't eliminate every reinforcement need
Flexibility manages a peak. It doesn't create headroom that isn't there.
Some constraints are structural rather than peaky — a network that's genuinely undersized for the baseline load it now carries, growing steadily as electrification continues, isn't going to be solved by shifting charging times indefinitely. Flexibility also has physical and behavioural limits: customers will tolerate a delayed charge occasionally, not as a permanent condition; weather-dependent resources like solar and batteries have their own constraints on when and how much they can contribute; and every flexible asset has a duration limit on how long it can hold a reduced state before something has to give.
The honest way to think about flexibility is as a tool for buying time and shaving peaks — sometimes for years, sometimes indefinitely for a constraint that was always going to be marginal. It's not a substitute for capacity that a growing network genuinely doesn't have.
How DNOs weigh flexibility against reinforcement
Figure 2. Neither option is categorically cheaper or better — the comparison has to be made constraint by constraint, against a specific forecast, not as a general policy preference.
What this means for CPOs, fleets, developers and aggregators
If a DNO now has to actively seek out flexibility before it can reinforce, that creates real commercial opportunity for anyone who can offer a genuinely dispatchable, evidenced service — charge-point operators with smart-charging capability, fleet operators with predictable dwell times, aggregators who can pool smaller assets into something a DNO can contract with confidence.
It also creates new obligations. A DNO can't build a flexibility-first investment plan around assets that might respond — it needs assets that reliably will, and that can prove it after the fact. That shifts the commercial relationship from "connect and consume" toward something closer to a service contract, with the accountability that implies.
Evidence, not just intent
Availability
How often the resource can genuinely be called on, not just its theoretical maximum capability.
Location
Flexibility only helps a specific constraint if it sits on the right part of the network — aggregate national capacity doesn't relieve a single feeder.
Response
How quickly the asset can actually change its behaviour once instructed, and how that's verified.
Persistence
Whether the response can be sustained for as long as the constraint lasts, not just for a few minutes.
DNO ED3 business plans are due in December 2026, which makes the balance between anticipatory investment and flexibility an immediate, live issue rather than a future one. The operators who treat smart charging as infrastructure — measurable, contractable, accountable — will be the ones shaping those plans, not just responding to them.
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Chris Gales
Chris Gales leads CEHG. He converts complex technical and commercial choices into clear decisions and dependable outcomes for utilities running connected device estates at scale.
He writes these field notes from the practice — on bearer migration, smart metering architecture, procurement and operations — to help estates start counting down early.