Study: EV Charging Patterns and Emissions Impact

When and where you charge an EV matters more than you think. Charging during off-peak hours when the UK grid is less carbon-intensive can drastically reduce emissions. Fleet managers must rethink their strategies to align charging schedules with cleaner energy periods, especially as EV adoption grows.

Key points:

• Grid Carbon Intensity Fluctuates: Charging during low-demand periods (22:00–07:00) reduces emissions compared to peak times.
• Home Charging Dominates: 77% of UK EV users rely on home chargers, yet workplace and public stations still account for 35% of energy use.
• Large Fleets Face Challenges: High, simultaneous demand from fleets can strain the grid and increase emissions.
• Cost Differences: Home charging is taxed at 5% VAT, while public charging faces a 20% VAT rate, making it significantly more expensive.

Fleet operators should focus on:

1. Scheduling charging during off-peak hours.
2. Using tools like telematics to monitor and optimise charging.
3. Prioritising home and workplace charging for cost and emissions savings.

Conclusion: Timing and location of charging are just as critical as switching to EVs. Smarter charging strategies are key to reducing emissions and managing costs effectively.

What Impact Do EV Charging Stations Have On The Electrical Grid? - Earth Science Answers

How Charging Time Affects Emissions

Charging time plays a crucial role in determining the emissions associated with electric vehicles (EVs). While EVs are often seen as a cleaner alternative to traditional vehicles, their environmental impact can vary significantly depending on when they are charged.

The UK electricity grid doesn't maintain a consistent carbon intensity throughout the day. Instead, it fluctuates based on the mix of energy sources feeding into the grid at any given time. During periods of high demand, fossil fuels like gas are often used to meet the extra load, leading to higher carbon intensity. Conversely, during low-demand periods, renewable energy sources such as wind and solar dominate, resulting in lower emissions.

For fleet operators, this variability is a game-changer. Charging the same EV during a high-carbon period produces more emissions than charging it during a low-carbon period. This highlights the importance of carefully planning charging schedules to align with times when the grid is cleaner.

The UK's electricity grid has made significant strides in reducing carbon emissions. A major milestone was the October 2024 closure of Ratcliffe-on-Soar, the country's last coal-fired power station. Between 2023 and 2024, the electricity supply sector accounted for 41% of the UK's year-on-year emissions reductions. While EV charging is becoming cleaner overall as the grid decarbonises, strategic timing can further amplify these environmental benefits.

Peak vs Off-Peak Charging

Peak and off-peak charging times present distinct opportunities and challenges for fleet operators.

Peak demand typically occurs during the early morning and evening when households and businesses are most active. To meet this demand, the grid often relies on gas-fired power plants, increasing the carbon intensity of electricity. In contrast, off-peak periods - usually late at night and early morning (22:00 to 07:00) - see lower demand. During these hours, renewable energy sources often make up a larger share of the grid, reducing emissions per kilowatt-hour.

For fleet operators, this creates a clear advantage: charging vehicles during off-peak hours can significantly lower their carbon footprint. However, operational requirements may complicate this strategy. For example, a vehicle that needs to be ready for an early morning shift might not have the flexibility to delay charging until late evening. The challenge lies in identifying which vehicles can shift their charging schedules without disrupting day-to-day operations.

Seasonal and Weather-Driven Variations

Grid carbon intensity doesn't just fluctuate by time of day - it also changes with the seasons and weather conditions. During summer, increased solar generation can lead to lower carbon intensity during daylight hours. In winter, while solar output decreases, wind generation often rises, depending on weather patterns. These seasonal shifts mean that optimal charging times are not fixed but vary throughout the year based on the availability of renewable energy.

Surface transport electrification is a major focus, as this sector accounts for nearly 30% of the emissions reductions needed during this decade. For fleet operators, this adds another layer of complexity. Rather than charging vehicles as soon as they return to the depot, operators can schedule charging sessions to coincide with periods of high renewable energy generation. This requires monitoring grid carbon intensity forecasts and adjusting schedules accordingly. For instance, windy nights might provide an ideal opportunity for charging, while calm evenings with high demand could be the worst time, even during traditional "off-peak" hours.

Infrastructure and Accessibility

The infrastructure to support strategic charging is growing quickly. In 2024, public charge point installations increased by 39.7% year-on-year. However, the location of these charge points matters just as much as their overall number. According to UK Power Networks, by 2025, 91% of charging sessions will occur at home, work, or en-route, with only 9% happening at destination chargers. This distribution pattern influences when and where fleet vehicles can charge, which in turn affects the carbon intensity of those sessions.

Fleet operators who actively manage charging schedules based on grid carbon intensity can achieve emissions reductions that go beyond the benefits of simply switching to EVs. As the grid continues to decarbonise and renewable energy capacity grows, the importance of timing optimisation will only increase. By understanding these fluctuations and integrating them into their operations, fleet managers can make substantial progress toward sustainability goals while maintaining efficiency.

Scaling Challenges for Fleet Charging

Managing charging for a handful of electric vehicles (EVs) is a completely different ballgame compared to handling a large fleet. What works for an individual EV owner or a small fleet often falls apart when scaled up. The main issue? Large fleets can create demand surges that overwhelm the grid, forcing it to rely on additional - and often fossil fuel-based - generation. This reveals why traditional charging strategies don’t translate well to large-scale operations.

Why Small-Scale Methods Don’t Work for Large Fleets

For individual EV owners or small fleet operators, reducing charging emissions can be as simple as plugging in during off-peak hours. A few vehicles charging overnight barely register on the grid’s radar, blending smoothly into its baseline demand. Under these conditions, using average emissions factor (AEF) calculations to estimate emissions works reasonably well because the added demand is minimal compared to the grid’s overall capacity.

But things shift dramatically with larger fleets. Imagine a fleet of 200 vehicles, each requiring 50 kWh for a full charge. That’s a massive 10,000 kWh demand spike, forcing the grid to fire up gas-powered peaking plants to meet the load. Fleet vehicles also tend to follow predictable schedules. For instance, many return to their depots around 5 p.m., just as the grid is already under strain from peak household and business demand. This synchronised charging creates a perfect storm, with emissions per kilowatt-hour shooting up far beyond what AEF calculations predict. These methods simply don’t account for the grid’s reactive measures to handle such concentrated demand.

Large Fleet Considerations

The charging needs of large fleets are fundamentally different from those of individual EV users. While an individual can rely on a 7 kW home charger to fully recharge their vehicle overnight in 6–8 hours, fleet operators don’t have the luxury of waiting that long. Lengthy charging times can disrupt operations and drive up costs.

Fleet charging is also far from dispersed. When dozens - or even hundreds - of vehicles return to a depot at the same time, the demand becomes highly concentrated. To keep operations running smoothly, large fleets increasingly depend on rapid charging infrastructure. These chargers, which can deliver up to 350 kW, can replenish a battery to 80% in around 20 minutes. However, as of September 2025, rapid chargers account for just 11% of the UK’s charging capacity.

The emissions impact of rapid charging is significant. A single 350 kW charger running for 20 minutes creates a 116 kWh demand spike. Now imagine 50 vehicles charging simultaneously - that’s a staggering 17,500 kW surge. This kind of load forces the grid to rely on less efficient, carbon-intensive peaking plants. By contrast, individual EV users charging overnight at 7 kW create a much smoother demand curve that the grid’s baseline generation can handle. Additionally, only about 9% of UK battery EV drivers travel more than 20,000 kilometres a year, meaning that home charging typically meets their needs. Fleet vehicles, however, cover greater distances and require faster charging, creating a tension between operational efficiency and lower emissions.

Geography adds another layer of complexity. The UK’s charging infrastructure is unevenly distributed, with rural areas lagging behind urban centres. While small fleets can operate in areas with better infrastructure, larger fleets working across multiple regions face infrastructure gaps and variability. This inconsistency makes it hard to implement standardised charging protocols. Instead, fleet operators often have to create region-specific strategies, adding complexity and reducing operational efficiency.

Lastly, grid stability is a major concern. The UK grid must balance supply and demand in real time. The predictable, simultaneous charging patterns of large fleets during peak hours can strain the system, forcing the activation of reserve generation capacity - usually fossil fuel-based peaking plants. This reliance on high-emission energy sources during demand spikes explains why emissions reductions achieved by small-scale operations don’t scale up linearly to larger fleets. This grid strain highlights the urgent need for smarter strategies, which will be explored in the next section on cascading marginal emissions.

Cascading Marginal Emissions Strategies

Managing emissions for large-scale fleet charging demands a fresh perspective. Traditional methods that calculate emissions on a per-vehicle basis simply don’t scale when dealing with thousands of vehicles. That’s where the Cascading Marginal Emissions Factor (MEF) methodology steps in. Designed specifically for large fleet operations, it offers a structured, tiered approach to handle the complexities of fleet-wide charging.

How Cascading MEF Works

Cascading MEF organises charging demand into tiers, starting from individual chargers and scaling up to regional grids and even the national grid. Each layer applies a marginal emissions factor that reflects the unique dynamics of that level.

Here’s the idea: as more vehicles charge, the grid’s response evolves. For instance, the first vehicle plugging in during off-peak hours might draw power from lower-carbon sources in the grid’s baseline generation. But as demand increases - say, when hundreds or thousands of vehicles charge simultaneously - the grid must activate additional, often higher-emission generation. Cascading MEF captures these changes, ensuring that emissions are calculated accurately at every level of aggregation.

This approach is especially critical for large fleets. The emissions impact of the 1,000th vehicle charging at a given time can differ dramatically from that of the 1,000,001st vehicle. Instead of relying on a static emissions factor, Cascading MEF maintains detailed granularity, making it possible to track these variations across scales.

In the UK, fleet operators must integrate real-time data on grid carbon intensity with detailed charging profiles, including start times, duration, power draw, and location. Regional grid data - showing different energy mixes and renewable availability - also plays a key role in applying this methodology effectively.

Different charging setups add another layer of complexity. For example:

• Home charging, which accounts for about 77% of charging among UK battery electric vehicle users, often takes place during evenings and nights when lower-carbon generation is more prevalent.
• Workplace charging typically occurs during daytime hours, which can align with solar energy availability.
• Rapid public chargers provide energy quickly but at unpredictable times, requiring statistical models to assess their emissions impact.

By layering these variables, Cascading MEF not only captures the grid’s dynamic responses but also lays the groundwork for optimising charging based on location and timing.

Cascading MEF Benefits for Fleet Operators

One of the standout advantages of Cascading MEF is its ability to scale without losing accuracy. Whether managing 100 vehicles or 100,000, the methodology maintains a clear connection between charging behaviour and the grid’s response. This avoids the common pitfall of averaging emissions, which can obscure the true benefits of strategic charging decisions.

Fleet operators can use this methodology to compare various charging scenarios with precision. For instance, they might assess the emissions impact of charging 1,000 vehicles at 18:00 - when demand and emissions are high - versus charging the same number at 02:00 during off-peak hours. Aggregating these decisions across the fleet allows operators to calculate the total emissions reductions achievable through optimised scheduling.

Cascading MEF also aligns with the ongoing decarbonisation of the UK grid. As renewable energy capacity grows, fleet operators can update their marginal emissions factors to reflect cleaner grid conditions. For example, with EVs now making up 28% of new vehicle sales in 2024, off-peak charging still offers significant emissions savings because peak periods often rely on fossil fuel plants. However, as renewables expand, operators can shift towards strategies that prioritise real-time renewable generation, such as charging during periods of high wind output.

This adaptability is crucial for long-term planning. Instead of sticking to a fixed charging strategy, operators can evolve their approach as grid conditions change - moving from simply avoiding peak hours to actively targeting times when renewable energy is abundant. Cascading MEF supports this transition by incorporating updated grid forecasts and renewable generation predictions.

On a practical level, the methodology also helps tackle operational challenges faced by large fleets. For example, it can guide location-based charging strategies, such as prioritising public chargers in areas with higher renewable energy penetration or encouraging home charging in regions with cleaner grids. This allows operators to balance operational demands with environmental goals while maintaining accurate emissions modelling across both individual vehicles and the entire fleet.

Finally, the computational efficiency of Cascading MEF reduces complexity without sacrificing precision, making it a practical tool for real-world fleet management. It empowers operators to make informed, data-driven decisions that align with both operational needs and sustainability targets.

Charging Infrastructure and Location

When it comes to electric vehicles (EVs), where they are charged can significantly influence both emissions and costs. Charging at home, work, or public locations each comes with its own set of benefits and challenges. For fleet managers, understanding these differences is key to making informed decisions about optimising charging schedules and locations.

Workplace, Home, and Public Charging

In the UK, most EV users prefer charging at home. In fact, 77% of battery electric vehicle (BEV) users rely on private home chargers - well above the European average of 66% and the global average of 64%. However, home charging only accounts for about 65% of the total energy delivered, meaning a significant portion of charging still happens at workplaces or public stations.

For fleet operators, this distribution presents both opportunities and obstacles. Home charging often occurs overnight during off-peak hours, which not only reduces costs but also aligns with lower grid carbon intensity. On the other hand, workplace charging tends to happen during the day, when demand on the grid is higher, though it may coincide with solar energy availability. Public charging, especially in the UK, leans heavily on rapid DC chargers, reflecting a growing preference for fast charging infrastructure compared to other European markets.

Charging patterns reveal that by 2025, 91% of sessions will take place at home, work, or en-route locations, with only 9% occurring at destination points. For fleet vehicles without off-street parking, on-street home charging is crucial, accounting for 22% of sessions in residential areas.

Cost is another critical factor. Nearly half of UK BEV users find public charging too expensive. This is largely due to differences in VAT rates: home electricity is taxed at 5%, while public charging carries a 20% VAT rate. This disparity significantly raises public charging costs. For fleet managers, this means prioritising home and workplace charging can lead to substantial savings. A GRIDSERVE study revealed that half of non-EV drivers would consider switching to EVs if public charging VAT matched the lower 5% rate.

Workplace charging offers a practical middle ground. It provides predictability and allows for charging schedules to be aligned with periods of lower grid carbon intensity. Unlike public rapid chargers, which prioritise speed, workplace chargers - typically AC - can optimise charging rates based on grid conditions and vehicle needs. While public charging infrastructure has expanded rapidly in the UK, with a 40% increase in installations in 2024, coverage remains uneven. This means fleet operators must carefully plan charging schedules around the available infrastructure to maintain efficiency and meet emissions targets.

Charging Speed Effects

The speed of charging also plays a role in emissions and operational efficiency. Slow AC charging (3–7 kW) and fast AC charging (7–22 kW) are generally more energy-efficient than rapid DC charging (50 kW and above), which tends to lose more energy during the conversion process. However, rapid DC chargers are essential for fleets needing quick vehicle turnaround.

The UK has seen significant growth in rapid DC charger installations, reflecting the demand for faster charging cycles, especially for vehicles that cannot afford downtime. However, from an emissions perspective, the timing of charging is often more important than the speed. Slow charging during off-peak hours is more efficient and environmentally friendly, while rapid charging during peak periods can lead to higher emissions. Fleet managers should reserve rapid charging for urgent situations and schedule routine charging during off-peak hours to minimise emissions.

Looking at future trends, the City of London’s infrastructure plans highlight these trade-offs. By 2025, they aim to have 26 rapid chargers and 65 standard chargers (7 kW+), with each standard charger capable of serving two vehicles simultaneously. This approach balances the need for speed with efficiency.

Emerging 800V battery technology could help address the speed-versus-emissions dilemma, allowing vehicles to charge quickly while maintaining efficiency. Until this technology becomes widely available, fleet managers will need to carefully weigh operational demands against emissions when choosing charging solutions.

Different types of vehicles also have unique charging needs. For instance, taxis under high-uptake scenarios could require 32 rapid chargers to meet a daily demand of 524 vehicles. Light commercial vehicles, which saw their electric market share rise to 8.3% in Q1 2025 (up from 6.3% in 2024), often benefit from workplace charging setups that allow for longer charging times and predictable schedules.

The decarbonisation of the UK’s electricity grid, including the closure of the Ratcliffe-on-Soar coal station in October 2024, has improved the emissions profile of all charging locations, especially public rapid chargers. While the emissions impact of rapid charging during peak hours is expected to decrease over time, strategic timing will remain essential for reducing carbon output.

Fleet operators should adopt a mixed approach to charging infrastructure. Combining rapid chargers for time-sensitive situations with standard 7 kW chargers for routine charging can maximise flexibility while keeping emissions in check. Scheduling slower, more efficient charging during off-peak periods is a practical way to balance operational needs with environmental goals.

Recommendations for Fleet Operators

Fleet managers aiming to cut emissions and save on costs need a well-thought-out approach to EV charging. By combining smart scheduling with data-driven strategies, it's possible to optimise operations. With the UK's charging network expected to grow from 18,000 chargers in 2020 to over 55,000 by 2025, the infrastructure is rapidly expanding. The following recommendations translate insights into practical strategies for fleets.

Optimising Charging Schedules

To make the most of the grid's changing carbon intensity, fleet operators should focus on charging during off-peak hours. This approach not only reduces emissions but also lowers costs. Smart charging technology can automate this process, adjusting charging rates in real time based on grid demand and taking advantage of dynamic pricing.

For fleets with predictable return schedules, collaborating with energy suppliers can help identify the best charging windows. Vehicles that require charging during the day present a different challenge. In such cases, workplace charging facilities should align with periods of high renewable energy generation. Adjusting charging times to match renewable output ensures vehicles are powered when the grid is at its cleanest.

Depot-based charging offers another advantage, as it benefits from lower VAT rates. For drivers relying on public charging, route planning should prioritise ultra-rapid chargers, which have seen a 51% growth year-on-year. These chargers can replenish a battery to 80% in roughly 20 minutes. However, rapid charging should primarily be used for urgent situations, with routine charging scheduled during off-peak hours.

Using Telematics for Charging Data

After optimising charging schedules, telematics can validate these plans using real-time data. Telematics transforms EV charging into a strategic advantage by tracking key metrics like vehicle usage patterns, battery levels, charging duration, energy consumption, and location-specific charging opportunities. This data highlights inefficiencies and supports informed decisions about infrastructure and scheduling.

GRS Fleet Telematics, for example, offers real-time tracking and optimisation tools. Its features include route planning, fuel efficiency monitoring, and vehicle location tracking, all of which can inform charging strategies. Additionally, driver monitoring tools, such as speed tracking and eco-driving analytics, encourage behaviours that reduce energy consumption.

Integrating telematics data with real-time grid carbon intensity allows systems to recommend optimal charging times, aligning schedules with periods of lower emissions. Look for solutions that provide real-time alerts for charging anomalies, predictive maintenance insights, and seamless integration with energy management systems. These tools ensure that operational adjustments are both cost-effective and environmentally conscious.

Tracking energy consumption on a per-vehicle and per-kilometre basis can help calculate emissions for each journey. Breaking down these figures by vehicle type, route, and charging location reveals where changes can lead to the biggest reductions in emissions. Regularly comparing actual charging patterns against optimised schedules quantifies potential improvements and supports further investment in infrastructure.

The UK government requires smart grid technologies to be integrated into charging infrastructure, offering fleet operators access to standardised and efficient systems. Ensure that your telematics solution is compatible with smart charging equipment to enable automated scheduling based on real-time grid conditions and renewable energy availability.

For fleets where not all drivers have access to home charging, telematics data becomes even more critical. While around 65% of energy is delivered through home charging, understanding when and where drivers charge can guide infrastructure planning and help negotiate better rates with charging network operators.

Conclusion

When it comes to cutting emissions, the timing of EV charging is just as important as the shift to electrification itself. Fleet operators who view charging as a strategic decision, rather than merely a logistical task, stand to achieve substantial savings and emission reductions.

The UK's progress in EV infrastructure reflects this potential. Ranked fourth in the 2025 EV Charging Index, the nation has seen a nearly 40% rise in public charge point installations in 2024 and recorded its tenth consecutive year of emissions reductions, totalling 10.8 MtCO₂e. However, the true environmental impact hinges on how effectively this infrastructure is utilised.

Home charging remains the most common option in the UK, giving fleet operators the flexibility to charge during off-peak hours when grid carbon intensity is lower. This approach directly ties emissions reductions to the specific power plants supplying energy at different times.

To thrive in this evolving landscape, fleet operators must focus on three key elements: diversified charging, intelligent scheduling, and telematics integration. A well-rounded strategy includes charging options spread across home, workplace, and public locations, scheduling aligned with grid carbon intensity, and the use of advanced telematics tools to monitor and optimise performance. For instance, platforms like GRS Fleet Telematics (https://grsft.com) provide real-time insights that help operators fine-tune their charging strategies. With 92% of UK BEV users considering another BEV as their next vehicle, the momentum for electrification is undeniable.

That said, public charging costs remain a barrier for many. While two-thirds of users find BEV fuelling cheaper overall, nearly half consider public charging prohibitively expensive. This underscores the need for strategic planning - prioritising home and workplace charging for cost efficiency while using public charging selectively to maintain operational flexibility.

Sustainability in fleet electrification isn’t just about adopting EVs; it’s about integrating charging into broader fleet management practices. By combining disciplined scheduling, expanding infrastructure, and leveraging powerful data tools, fleet operators can achieve both environmental gains and a competitive edge in the rapidly electrifying transport sector. Together, these strategies position fleets for long-term success in a changing landscape.

FAQs

How can fleet operators optimise EV charging to reduce environmental impact?

Fleet operators have the opportunity to make their EV charging schedules more environmentally friendly by focusing on off-peak hours, such as late at night or early in the morning. During these times, the electricity grid tends to draw more heavily on renewable energy sources, which can help cut down on overall emissions.

By leveraging real-time grid carbon intensity data, operators can pinpoint the best times to charge with minimal environmental impact. On top of that, smart charging systems can take the guesswork out of the process. These systems can automate charging schedules, ensuring vehicles are powered up efficiently while keeping their carbon footprint as low as possible.

What are the advantages and challenges of using the Cascading Marginal Emissions Factor method for managing large fleets?

The Cascading Marginal Emissions Factor (CMEF) methodology provides a smarter way to measure the carbon footprint of charging electric vehicles (EVs). By factoring in how electricity grid emissions fluctuate throughout the day, CMEF enables large fleet operators to fine-tune their charging schedules to cut down on carbon emissions while staying aligned with their sustainability targets.

That said, putting CMEF into practice isn't straightforward. It demands access to detailed grid emissions data, sophisticated tracking systems, and strategic planning to ensure charging remains both eco-friendly and practical. For businesses managing extensive fleets, tools like telematics solutions can make this process easier. These systems offer valuable insights, helping companies strike the right balance between reducing emissions and keeping costs in check.

How does the VAT difference between charging an EV at home and at public stations impact fleet costs?

The VAT rate for electricity used to charge electric vehicles (EVs) at home is just 5%, whereas public charging points usually come with a 20% VAT rate. This disparity can have a noticeable effect on operational costs, particularly for businesses that depend on public charging facilities.

To cut expenses, fleet operators can encourage drivers to charge their vehicles at home or at company locations where the lower VAT rate is applied. Additionally, adopting smart charging strategies and leveraging telematics systems to track and analyse charging habits can help manage costs more effectively while also reducing environmental impact.

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