EV charging is not just a numbers game – it’s a grid challenge

Maria Xylia of the Stockholm Environment Institute (SEI) discusses her recent finding that research on EV charging ratios needs deeper interpretation and that utilities must plan for equity, efficiency and flexibility if Europe’s grid is to cope.

Discussions about electric vehicle (EV) charging often centre on a single figure: how many chargers we need. Policymakers and analysts regularly cite the “EVs per charger” ratio, as though there were a universal benchmark.

Yet our recent systematic review, Estimating charging infrastructure demand for electric vehicles: a systematic review, published in Energy Strategy Reviews with funding from the Swedish Energy Agency, shows just how misleading this view can be.

Globally, each public charger today serves on average just 11 EVs. Yet across the literature we synthesized – 140 studies examined in detail from a pool of 12,000 abstracts – the mean charging demand is 135 EVs per charger, with a median of 23. The difference between these figures highlights the extraordinary variability in assumptions, but also reveals a basic truth: chargers can serve far more vehicles than they currently do.

For utilities, this is not a trivial matter of infrastructure efficiency. It raises fundamental questions about how charging is integrated into the power system, how costs are distributed, and how future grids will handle the surge in electrified transport.

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Episode 2: Fitting EVs into Spain’s power system
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No one-size-fits-all

One of the strongest messages from the review is that there is no single charging strategy that fits all contexts. Slow, private charging can spread demand and reduce strain on local networks, while public fast and super-fast charging can serve many more vehicles per unit. Both have a role to play, but the balance matters.

If public charging is overbuilt or underused, it risks becoming economically unsustainable. If too scarce, it risks queues and frustrated drivers. For utilities, the challenge is not choosing one strategy over another, but finding the right mix that aligns with local grid conditions and user needs.

Fast and super-fast charging are particularly underrepresented in research, despite their transformative potential. Our review found that fast chargers can support around 187 EVs per charger, compared with 46 for slow chargers. Super-fast chargers could in theory serve close to 1,000 EVs per unit, but the evidence base remains limited.

Charging equity and the social divide

Another issue is equity. Public charging is consistently more expensive than home charging. Those without access to private driveways or garages (urban renters, low-income households, residents of multi-family blocks) are effectively penalised. They rely on public infrastructure and end up paying more for the same mobility service.

This raises a fundamental fairness question. Should access to affordable charging be treated as a right, or left to market dynamics? If public charging continues to be disproportionately expensive, electrification risks entrenching social divides.

For utilities and regulators alike, this matters not only as a fairness issue but also as a barrier to EV adoption. Unless charging equity is addressed, skepticism about EVs will persist among exactly those groups who cannot afford to be left behind in the transition.

The utility dilemma: income versus efficiency

Utilities find themselves in a peculiar situation. Public charging is a growing source of income: it drives electricity sales, creates demand for grid services, and can open new revenue streams. Yet from a system perspective, an over-reliance on public charging is inefficient and inequitable.

Too few public chargers, and queues deter EV uptake. Too many, and infrastructure sits idle, creating sunk costs and stranded assets. Either scenario is a challenge for distribution system operators. Our findings indicates that this “sweet spot” between sufficiency and profitability is narrower than most assume. For utilities, the dilemma is obvious: short-term profits must be balanced against long-term system resilience.

Towards flexible, smart and bidirectional charging

A way out of this dilemma is to invest in flexible charging strategies, such as smart charging, demand response, and ultimately bidirectional vehicle-to-grid (V2G) solutions. These approaches can transform EVs from a problem for the grid into an asset.

Smart charging allows demand to shift away from peak hours, smoothing the load curve. Bidirectional charging can go further: turning millions of available EV batteries into a distributed energy storage network. For a power system integrating ever higher shares of renewables, this flexibility is invaluable.

Yet here lies a surprising gap. In our review, only 1% of studies addressed V2G in the context of charging demand. Most literature still treats EVs as passive consumers of electricity, rather than potential grid resources. Utilities should not make the same mistake. Future charging investment must prioritise flexibility, not just plug counts.

The problem of unclear definitions

Another barrier highlighted in the review is the lack of clear, harmonised definitions. Terms such as “public” versus “semi-public,” or “slow” versus “fast” charging, are often used inconsistently across studies and jurisdictions. Similarly, the widely cited metric of EVs per charger, which the European Commission has already steered away from, can mask major differences in charging power and user experience.

Without common definitions and transparent reporting, planners and utilities risk misinterpreting demand forecasts, undermining both infrastructure investment and grid planning. For example, one study’s “fast charger” may be another’s “super-fast”, and private workplace chargers may be counted as “public” in some datasets. This ambiguity creates confusion, slows down planning and makes cross-border comparisons unreliable.

Developing harmonised metrics and reporting standards is therefore a critical task for regulators, researchers and industry. Without them, utilities will be left to plan with incomplete or misleading information.

Heavy-duty electrification: the next challenge

These issues are magnified when it comes to heavy-duty vehicles. Our review shows that buses average around five vehicles per charger, and trucks around 14 – much lower figures than for passenger EVs. The reason is simple: duty cycles are longer, charging power needs are far higher, and depot charging remains dominant.

For utilities, the implications are dramatic. A single truck depot may require grid reinforcement on a scale comparable to a new industrial facility. If the planning is not aligned between transport operators and energy providers, the result will be delays, costs and frustration on all sides.

As Europe moves towards electrifying freight corridors and bus fleets, utilities must prepare for megawatt-scale charging within this decade.

A strategic opportunity for utilities

The electrification of transport is often framed as a burden on the grid. In reality, if planned wisely, it can be a strategic opportunity for utilities. By combining different charging strategies, addressing equity gaps, and investing in smart and bidirectional solutions, utilities can ensure that EVs become a cornerstone of a flexible, renewable-powered energy future.

Getting there will require abandoning one-size-fits-all ratios, harmonising definitions across markets, and deepening collaboration between the transport and energy sectors. But the payoff is clear: smarter EV charging is not just about keeping vehicles moving – it is about building the resilient power systems Europe will need for decades to come.

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About the author:

Maria Xylia is a Senior Research Fellow with the Stockholm Environment Institute, working across multidisciplinary projects, from EV charging and transport services to energy system analysis, just transitions in energy and transport and off-grid solutions. She is also affiliated faculty with the KTH Royal Institute of Technology.