I’ve recently written about some of the issues with scaling up battery-electric vehicle production and why hydrogen is not the answer. In this article, I will explain why electric road systems are a much better solution. These allow vehicles to charge as they are driving, giving electric vehicles unlimited range, including heavy trucks. All roads don’t need to be fully electrified since vehicles are still expected to have batteries. There just needs to be charging zones along major highways and busy bottlenecks in cities. This is the only current electrification system suitable for heavy trucks. Although heavy trucks are only a small percentage of the vehicles on the road, they produce about one-third of the emissions because they travel long distances at sustained power outputs. Electric roads also make a lot of sense for private cars because they allow smaller batteries to be used, greatly reducing vehicle cost while also reducing weight and, therefore, performance. The capital cost of road electrification may initially seem quite high but is surprisingly cheap when compared to the alternatives.
Issues with Battery Electric Vehicles
A major issue with battery electric vehicles (BEV) is their limited range. Although the energy density of batteries has improved, it remains far lower than hydrocarbon fuels. For private cars, this means a choice between a much shorter range or a larger and much heavier vehicle. For heavy trucks, it simply isn’t possible to use batteries and achieve the required range.
Battery technologies are being developed to increase energy density and reduce critical metal content. However, industry experts do not expect the fundamental limitations to change. There is also likely to be a degree of compromise. To achieve very low levels of critical metal content, energy density will be sacrificed.
The Problem with Hydrogen
Hydrogen is often seen as the answer to the poor energy density of batteries. Roadmaps to decarbonizing transport often see hydrogen as the solution for vehicles that must be able to cover long distances at high power outputs, such as heavy trucks and luxury cars. The cost of hydrogen fuel cell electric vehicles (FCEV) is currently very high but is expected to fall. However, the really big issue with hydrogen is its inefficiency as an energy vector in an electrified world. Solar panels and wind turbines produce electricity, and vehicles generally require electricity to power their motors. The hydrogen must, therefore, be produced from electricity, compressed, transported and used to generate electricity again. Each stage involves significant losses, adding up to mean that a typical fuel cell vehicle is four or five times less efficient than a battery vehicle. Even with the most optimistic forecasts for the technology, fuel call vehicles powered by renewable electricity generation will still be less than half as efficient in 2050.
This inefficiency means that we would need to build considerably more wind and solar generation capacity. This has very significant capital cost. In a recent study I carried out for the Society of Automotive Engineers, I estimated the increased electrical demand required if heavy-goods vehicles were converted to hydrogen instead of being directly electrified. The cost of installing the additional wind and solar capacity would be $180 billion for the United Kingdom alone, almost a quarter of the country’s total annual government spending.
Types of Electric Road Systems
Electric road systems (ERS) provide a way of powering and charging a vehicle as it is driving along a road. There are three main types of ERS:
- Overhead lines, also known as a catenary system: These are often used for electric railways and trams. They may also be used along highways to power heavy commercial vehicles.
- Conductive track: These are simply conductive metal tracks installed in or on the surface of a road or sometimes along the side of the road.
- Inductive track: These are buried conductive coils below the surface of the road. An electric current is induced in a coil on the bottom of the car.
This would not require all roads to be electrified. Instead, charging zones would be included on long stretches of highways and in busy areas of urban road systems.
Overhead lines are the cheapest form of ERS to install. They are also the most technically mature due to their similarity to systems used by railways, trams and trolley buses. Two conductive lines are suspended over the road at a height of approximately 5meters. This height means that relatively long stretches of over 1km can be safely electrified. Vehicles require a pantograph that makes the connection while compensating for lateral and vertical movements of the vehicle. This means the system is only suited to large commercial vehicles. These systems have been in trial operation since 2016, with testing on public highways in Sweden and Germany.
Although overhead lines are cheap and mature, they have significant disadvantages. The pylons along the roadside are a danger in road traffic accidents and fallen cables may endanger pedestrians. The public may also object to the visual impact of overhead cables, especially in areas of natural beauty. Perhaps most significantly, this system is not compatible with the majority of vehicles, such as private cars.
Conductive tracks work in essentially the same way as the classic toy Scalextric. A retractable pick-up, mounted underneath the vehicle, establishes an electrical connection by sliding contact. Safety is ensured by dividing the tracks into short segments that are only energized when a vehicle is passing over them. An additional layer of safety may be provided by presenting an earth rail at the road surface with the live rail within a deep and narrow slot. Extensive tests of conductive track systems are being carried out in Sweden. Because conductive tracks can be used by both heavy and light vehicles, they appear to have the lowest overall cost.
Inductive tracks, or road bound inductive systems, use an energized coil buried within the road surface to induce a current in a coil on the underside of a vehicle. Inductive charging of buses has been in operation in Korea since 2010, and the Dongwon online electric vehicle (OLEV) is now a mature technology although it is a low-speed system for city buses. Recent trials carried out on highways in France and Italy found efficiency depends on the accuracy of alignment with the coils and is at best 80 percent. The major advantage of inductive tracks over conductive ones is that they should require far less maintenance and cleaning. However, when maintenance is required, it may be more expensive requiring the road surface to be dug up.
An Economical Solution
While there is clearly a significant capital cost in electrifying the road network, it is surprisingly cheap when compared to the alternatives. Elonroad estimate the installation cost of electrifying two lanes of a road at $1.7 million per mile. For the UK’s 7,330 miles of trunk roads, this comes to approximately USD$14.2 billion (EUR£13 billion). When compared to the $180 billion required for the additional electricity capacity that hydrogen would require, that really isn’t very much. Even this stark comparison doesn’t fully capture the benefit of using electric road systems since it only considers the energy savings for heavy vehicles. If an electric road system is used that is also compatible with private cars, then smaller batteries can be used. This would significantly reduce the cost of purchasing electric cars, accelerating uptake, reducing the critical metals used to produce them and saving consumers money. A small increase in road tax could, therefore, easily pay for an electric road system while still leaving the taxpayer much better off overall.
An additional benefit of reduced battery capacity is that alternative battery chemistries can be selected that have far lower critical metal content. This will make ramping-up electric vehicle production much easier.
Cost analysis suggests that if most vehicles use an electrified road system, the cost savings from the smaller batteries will be greater than the cost of installing the ERS. This compares the cost of BEVs driving on normal roads with smaller capacity BEVs driving on various types of electrified roads. Considering the full societal cost, the most expensive option is overhead electrification since it can only be used by large commercial vehicles. Conductive and inductive tracks both result in a lower societal cost than BEVs without any roadway electrification. They provide the same level of vehicle cost savings, but conductive tracks have greater efficiency and lower infrastructure costs, making them the most economical solution. Although inductive tracks are the most expensive in terms of infrastructure, they still cost less than the additional battery capacity required without a dynamic charging system.
Electric roads offer a way of electrifying road transport that is technically simple and economically sound. The big challenge now is agreeing on a common standard and rolling it out at the federal or continental level.