The limited autonomy of battery electric vehicles (BEVs) requires the creation of a fairly dense network of charging stations to dissipate the "range anxiety" of users. The dynamic development of a fleet of battery electric vehicles has to be accompanied by an equally dynamic deployment of charging infrastructure.
Electric service stations…
Distributing electricity is not a problem in itself, as the existing networks prove. The major hurdle to be overcome is the time it takes to charge a battery, much longer than the time needed to fill a tank with gasoline. Currently, with a standard household plug, it takes several hours (almost all night) to recharge a 15 kWh battery (the energy equivalent to that of 1.5 liters of diesel). It is crucial to have chargers adapted to the requirements of road transport. Utility companies such as EDF (France) EnBW (Germany) and State Grid (China) presented "smart" charging stations capable of communicating with vehicles (exchanging data with the vehicle) during the 2007 Challenge Bibendum. Electric Vehicle Supply Equipment (EVSE) or chargers use technologies that are already well proven and adapted for this very purpose.
Electrifying streets and roads…
Catenaries have been used to distribute electricity to streetcars or trams for a long time now. Why do we not use this type of network to charge the batteries of EVs while on the move or at a standstill? Imagine for just a moment the forest of pylons and overhead wires, this quickly led to the idea of a ground distribution network with no risk of electrocution. Partnerships between automakers and electricity suppliers have been working on trials for inductive charging. The results of the most advanced trials have been encouraging: they are 90 % efficient with both asphalt and cement. According to the device and the type of current the speed of the vehicle can be from 0 to 70 km/h or on the contrary a minimum of 60 km/h.
The user-subscriber is recognized by means of a code transmitted by the grid.
The possibility of charging the battery by induction while on the move or at a standstill should contribute to eliminating range anxiety. Developing a standard, at least at a continental level, for these networks is highly important.
… or drop and swap battery stations?
Another solution is to replace the depleted battery with a fully-charged one. This however presupposes another proprietary model: that of a returnable battery, just like gas cylinders today. The proponents of this approach maintain that interchangeable batteries overcome the major obstacles to adopting EVs, that is their cost and the distance covered with one cycle. However just like the rental model, this concept needs a dedicated infrastructure to prolong the distances covered by EVs while lowering their purchase price.
Even if this business model is pertinent for certain fleet and given areas, it might prove difficult to deploy on a large scale. This approach would not appear to be justified given the economic advantages and the flexibility of individual chargers. Tests conducted in pilot communities should prove that a fall in the price of electric vehicles associated with a subscription fee will be competitive compared with the alternative of buying outright a traditional electric vehicle and paying charging time.
Normal, fast or rapid charge?
- Normal or standard charge: this is done from a wall box connected to a regular household electrical socket which delivers power of 3.3 kVA single phase voltage (230 V / 16 A). The wall box controls the charging process, avoiding any anomaly and enabling the exchange of information with the future smart grid with its capacity to manage demand for current. The charging time of 6 to 8 hours is the time spent at home (houses or blocks of flats) or in a workplace car park if equipped. The standard charge has no detrimental effect on the battery and its lifespan and should therefore be promoted.
* kVA: kilo volt ampere: unit of apparent power of alternative current which is free from phase shift: 1kVA = 1 kW if the power factor is 1.
- Fast charge: this three-phase power delivers 22 kVA (400 V / 32 A per phase). It is two to three times faster than the standard charge.
- Rapid charge: this is also three-phase power and can deliver 43 kVA (400 V / 63 A per phase) or continuous current is available directly at 50 kW (500 V / 100 A). It takes 20 to 30 minutes to charge to 80 % battery capacity. This type of charging is reserved for emergencies. Note: many of today’s batteries are not consistent with this type of charging power. (Source: Johnson Controls Saft).
Standardization and safety: Two essentials
Unlike the idea of regionalization, that of international standards will quickly have to be made law. As the only guarantors of a sustained investment in public infrastructures (exterior recharge terminals), in private buildings (car parks, for example) or in people's homes, they permit a certain degree of universality in mobility.
Connector standards have not yet been determined for fast and rapid recharging. Since the normal charge involves a large network of consumers, existing standards for domestic appliances have been applied... complete with the differences already established between certain countries (United States and Great Britain, to name but two examples). China, which is very proactive in the field of electric vehicles, has clearly indicated that during the coming decade considerable effort will be expended on standards and regulations.
It goes without saying that all recharging operations should be done in complete safety.
What type of grid will need to be developed?
In cities and suburbs, electric vehicle users will have to acquire new habits and have the "parking-charging" reflex instead of waiting until the battery is completely depleted: and to do this they have to be able to find a charging station where they are going to park their car. Standard or fast charging infrastructure is progressively being deployed in numerous countries according to the growing number of electric or plug-in hybrid vehicles on the roads and under the impetus of public-private partnerships : public car parks, corporate car parks for staff, supermarket and hypermarket car parks.
A fast charging station costs between 35,000 and 40,000 euro. The French government has launched a program to deploy 5,000 public charging stations by delegating the task of managing the network to a public or private operator (ERDF, Bolloré, Véolia, JC Decaud or Vinci) in partnership with hypermarkets, local authorities, companies...
Will the grid be able to meet the demand for energy?
The USA has indicated that their current grid could support the simultaneous overnight charge of 10 % of the electric vehicle automobile fleet. France could go to 20 %... These figures are to be taken with great prudence…
The forecast for France is 2 million electric vehicles by 2020. The simultaneous recharging of this fleet would represent 3 GW or the equivalent of 2 units of an EPR reactor.
The grid operators have to even out the load and then develop smart grids which manage both the electricity supply and demand (charging). On the other hand certain vehicles are only used for several hours per day, they represent an energy reserve that could be exploited the rest of the time. Electric vehicles could therefore be part of an integrated and communicating energy stream.