How will energy compression technology for fast charging of Electric Vehicles affect the future power grid?
The number of Electric Vehicles (EV) on the road is growing, propelled in part by fast-charging battery technology. Imagine if fast inductive EV charging stations become reality. What will that mean for the power grid? We need to start thinking ahead to prepare for how it will affect the future power grid.
To understand the implications we must look at the requirements for both power (measured in kW) and energy (measured in kWh). It is also important to recognize that energy is the sum of power over time (or, mathematically, the area under the power-curve). The figure displays two power-curves that produce the same amount of energy.
Assume that in the near future it’s possible to charge a battery with 15kWh in one minute. With this amount of energy you can drive approximately 75–100km. From an energy perspective, it is not a problem for the MV/LV substation feeding the fast charging station, as 10 fillings per hour equals an average load of 150kW. Typical urban MV/LV substations in Europe have a capacity of 400–1000kVA and most of the existing substations can accommodate this additional energy demand. However, charging a 15kWh battery in one minute calls for 900kW, which means that charging only two EVs creates a serious problem, even for a large MV/LV substation.
It seems like the obvious solution would be to increase the size of the MV/LV distribution substation for each fast-charging location, but that’s not economically sensible. However, the solution could be found in changing the power paradigm “adapt the generation to match the load”, as that concept is already being used to help cope with variable renewable generation where the load adapts to the generation instead (Renewable integration: Is it time for a second paradigm shift?). Unfortunately, for fast charging we have to find another solution, as it is not possible to reduce the power while increasing charging time.
What we need to do is decouple generation and load. This can be achieved with an (electrical) storage system, but not a “normal” battery system because of the high current demand. When fast charging is done with an industrial AC voltage in the range of 400V to 690V a current in the order of 1000A is needed. For these applications, a storage system based on supercapacitors is suitable, and there are already containerized solutions on the market today, capable of delivering 1000kW for 60 seconds. For fast-charging stations, this capability needs to be increased because we want to be able to fast charge more than one EV simultaneously. Although capable of fast energy discharge the supercapacitor system can be (much) “slower recharged” from existing MV/LV distribution substations.
To conclude, specifically for fast charging EVs, the power paradigm has to be changed to “decoupling of generation and load.” This requires energy compression technology, where slowly accumulated energy is released on MW-scale in minutes. Compare this with pulsed power technology where GWs and more are needed in micro- or even nano-seconds.
The example of fast charging illustrates a developing trend in power systems that both load and generation become increasingly “spiky” nature. Notice, for example, the development that more and more residential equipment enter the market with high power ratings which have a relatively short time of operation, like hot-water taps, coffee machines and microwave ovens.
In general, the development for suitable energy compression technology for different power levels could be very beneficial to complement (aggregated) demand response and cope with peaks and coincidence, providing better utilization and avoiding the need for significant grid reinforcements.