Charge of the electric car

The ability of the UK power grid to support the growth of electric cars has been called into question, but as E&T discovers there is more than enough electricity to go around.

One of the key future technologies to green the emissions from car tailpipes is the battery electric vehicle (EV). At present the EV enjoys a niche appeal, but that is set to grow. All the big players are dipping their toes in the water of what is an already crowded pool with offerings such as the Chevy Volt and the iQ PHEV from Toyota. But it is cars from small manufacturers bearing names such as Tango, Kewet, Kurrent and the bizarre looking three-wheeled NmG (no more gas) that are holding sway.

While the maturing technology, battery and drivetrain, is allowing these vehicles to move into mass production there have been concerns raised about the ability of the UK power grid to accommodate a huge explosion of EVs. The results of simulation studies by a consortium including Ricardo, Jaguar-Land Rover, E.ON and Amberjac Projects, have appeased those fears somewhat, indicating that a substantial medium-term rise in the number of electric and plug-in hybrid vehicles would have a much lower impact on the UK national power grid than the earlier, more anxious estimates.

Four vehicle-fleet charging scenarios were simulated, comprising uncontrolled domestic charging, uncontrolled off-peak domestic charging, 'smart' domestic charging and uncontrolled public charging throughout the day - for example, by commuters who recharge their vehicles while at work. Charging was assumed to be single phase AC as this is the most likely near-term solution, but the study also considered fast charging scenarios as for a large number of vehicles the energy demanded over a time period is likely to be the same and distributed evenly.

Assuming a 10 per cent market penetration of plug-in hybrid electric vehicles and pure electric vehicles in the UK, the study showed a daily peak increase in electricity demand of less than two per cent (approximately 1GW) for the scenario of uncontrolled domestic charging - the 'worst case' in terms of peak power demand.

Other scenarios are less challenging: off-peak domestic charging, for example, increases electricity consumption throughout the night, but has no impact on the peak daily demand. Since it will be a number of years before a 10 per cent level of market penetration is achieved, even with the recently announced UK government incentive plans, grid capacity at a national scale should be adequate for this significant electrification of the vehicle fleet. 

"I was reassured because it is not as bad as people think, apart from the more localised regional effects," Corrin Wren, Ricardo chief engineer, says. "I think that is where the challenge is and, not only that, it's making sure that the vehicle technologies are there to support it; it's a blended and coordinated development; that's where the challenge is. I wasn't too surprised but reassured. There are plenty of challenges ahead, and those lie both on the vehicle and the infrastructure side."

Supporting demand

While the national impact is shown to be manageable, as Wren alludes, the research team emphasises that local improvements may nevertheless be necessary - for example, where local network capacity is marginal or where particularly high concentrations of electric or plug-in vehicles occur.

"We have concluded that the grid is capable of supporting that demand," Wren continues. "The issue is about more localised regional effects, so if you can imagine if London in particular took on a massive amount of electric vehicles compared to the whole of the UK, then the localised effect is going to be rather profound. There could be quite a demand on a particular section of the grid."

Further work is ongoing to look at the timeline for reduced power station CO2 emissions, which is the key enabler for electric and plug-in hybrids to reach true ultra-low carbon status. Future reports of the Range Extended Hybrid Electric Vehicle project will look at fast charging infrastructure which would offer significant consumer benefits in the use of electric and plug-in hybrids.

The importance of EVs was established by a pair of government reports late last year. The study undertaken by Arup and Cenex on behalf of the Department for Business Enterprise and Regulatory Reform investigated the scope for the transport sector to switch to vehicles powered through electricity from the grid in the period until 2030. Road-based transport currently accounts for approximately 22 per cent of the UK CO2 emissions and therefore reducing the reliance on carbon-based fuels in this sector is seen as a priority.

The second report, the King Review of Low-Carbon Cars, highlighted the fact that road-based CO2 emissions reductions will come from a number of different sources. However, it concluded that battery EVs and plug-in hybrid electric vehicles (PHEVs) can contribute to the long-term reduction of the UK's CO2 emissions.

"My report has a very positive message," Professor Julia King says, "that major reductions of CO2 emissions from road transport in the years ahead are possible.

"But seizing these opportunities will require action from everyone, with government playing a leading role. Government must coordinate efforts in an international context and provide the leadership to allocate responsibilities among vehicle manufacturers, fuel companies and consumers."

Both studies agree that EVs have the potential to offer significant carbon dioxide and greenhouse gas emissions reductions compared to conventional petrol/diesel fuelled internal combustion engines.

This applies over a full life-cycle, taking account of emissions from power generation and emissions relating to production and disposal. Based on the current UK grid mix there are already significant benefits of the order of approximately 40 per cent reduction; these benefits have the potential to become much greater with further decarbonisation of the UK power mix.

Charging up

At present, most EVs will slow-charge using single-phase power from either home sockets or specially erected charging points in car parks and parking bays - the slow charge will take around six hours.

"It is difficult to say how everything is going to be rolled out and adapted but single-phase is clearly the first point because clearly the grid covers single-phase almost everywhere," Wren says. "Three-phase is more difficult because there is a limited number of transformers that support three-phase, but in terms of fast charging it is considered to be the solution because it runs at a much higher power capability."

For ease of deployment, the short-term solution appears to be single-phase, restraining a daily drive to the distance achieved with a battery charge.

As the industry grows and battery chemistry improves, expect to see fast-charging points spring up at motorway service stations.

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