EV charging 108: Vehicle to Grid

Electric Vehicle (EV) is more than a just a vehicle, it is readily available energy storage. In that sense, an EV is an asset to the grid, and being smart about charging is important as we saw in the previous article. We all know that uncontrolled charging is a problem that needs to be fixed. Now the question is can I also use the EV as a grid resource? Can I use my EV to offer support to the uptake of renewable energy? Can I use my EV when it is parked to earn money through the support I am offering to the power grid? Can I use my EV as backup storage for my home? Can EV act as Energy storage and help balance the load in my building? Can my EV give power to another EV? In case of emergency can I run a load with my EV? Can I use my EV to give power to my neighbor?

EV as a grid resource

As you might have expected the answer to all of the above is yes. With the advancement of Information and Communication Technology, EV charging is much more than charging a battery. One can plan to charge more when a large amount of Solar is available or when the rate of power is cheap. But in charging there is only one direction of power transfer from Grid to Vehicle. We can also plan for a bi-directional power flow system, where the Vehicle can also supply electricity stored in the battery. Adding battery discharge into the mix will change the value streams completely. This means the ability to do more with an EV, and we can supply electricity from

• Vehicle to Grid (V2G)
• Vehicle to Building (V2B)
• Vehicle to Load (V2L)
• Vehicle to Home (V2H)
• Vehicle to Vehicle (V2V)

Overall, the vehicle to any demand power transfer can be termed as V2X. Even in the case of battery swapping, where the batteries are charged outside the vehicle, the stack of batteries being charged can act as a grid resource. We can call this B2G or B2X. The conclusion here is that there can be many versions of Vehicle Grid Interactions. We only need to remember that two-directional power flow (V2X) implies additional possibilities than one-way of V1G or G2V. This is explained in the diagram below.

In the case of unidirectional power flow, with only control on charging the benefits I can obtain from the EV stops once the battery gets fully charged. However, if we are thinking of both charging and discharging, then the EV continues to be a valuable resource till the time the vehicle departs from the charging point. This brings us to the important point that V2G is applicable in cases where EVs are parked for a long period of time, definitely longer than the time it takes to charge the battery. An example of this could be an Electric Car that is parked during work hours in a parking lot.

Connecting Vehicle to Home

Connecting a Vehicle to a Home is not rocket science. One of the ways to V2H is using the charger in the car itself. In this case, the charger power is typically 7 kW, which makes it perfectly suitable to connect to a home. All you need to do is to ensure that the charger in the car is bi-directional. Recently many manufacturers including Volkswagen have announced that their EVs will come equipped with bidirectional chargers. Another way to do it using DC Wall box chargers which also help create a microgrid in a home or a building. This DC power can be easily interlinked with the Distributed Solar generation also. As most of the home appliances are DC in nature it is possible for this DC microgrid to handle all the demand from a home. The below video explains how the vehicle to home works.

Supplying to the Grid

Supplying power back to the grid is not as easy as supplying an isolated demand. The power generated from the system, in this case, should match the specifications of grid power. The requirements can be compared to a Grid-Connected Inverter in a Solar Rooftop System. This inverter converts the DC power generated by a solar panel to an AC wave that is fed into the grid. The arrangement from feeding battery power into the grid is a little different as it needs another inverter design. While Solar Panels are current sources, batteries are voltage sources. So we cannot connect a battery to the grid using the Solar Grid Connection Inverter. But we can use a different design of an inverter or a hybrid inverter to achieve this. This kind of system can also be part of net metering or feed-in arrangement.

V2G for linking Solar and EVs

V2G is a great method to encourage Solar EV charging or creating local microgrids with Solar and EVs. Europe is one of the happening places for V2G pilots in the world. One of the projects that are making waves recently is a Local Solar Microgrid at a Train Station in France. Here Electric Vehicles are used to?balance local “microgrids” at?the train?station. The energy is stored in the Vehicles during times of excess solar generation. Energy from the vehicles is used when Solar generation is lesser than demand.?This project is quite interesting because of the application of blockchain technology for the project. Find more about this.

Bidirectional Charging Technology pilots and trends

CHAdeMO and Nissan Leaf need to be recognized as the early proponents of V2G. The other popular Charging protocol is CCS is only catching up. A large number of early V2G pilots are focused on electric cars. However electric buses with large batteries are also good candidates for V2G. In Europe, electric power utilities are also interested in V2G. One of the popular V2G projects by Engie is explained in the Video below

Battery life, aggregation, and other challenges ahead

There are multiple challenges in using EVs as a grid resource. One of the debates is the impact of V2G on batteries. Many manufactures feared that discharges would lead to battery degradation, and took the call that the battery warranty is made void if the vehicle is used for V2G. Though battery prices are coming down, it is still the most expensive component in a vehicle. And naturally, without proper incentives which can outweigh the costs, the market will not be viable. EV manufacturers have become a critical part of the V2G value chain, and recent trends appear favourable. The application also matters a lot, for example, frequency support from EV with shallow charge-discharge cycles should have a lesser impact on the battery life. Needless to say that there is a need for further R&D in the area.

An EV in itself is too small in size to offer benefits when compared to standalone battery storage. However, when a large number of EVs are integrated through an aggregator, it can offer the same benefits as any large energy storage system. This aggregator can offer services locally or in the electricity markets. Even with aggregation, it is imperative to recognize the value of EVs is not limited to the energy it can offer in kWh. It is more sensible to value the energy from these fast-acting storages in terms of their capabilities. One such important case is the quick support they can offer to the grid for controlling frequency. Here the value comes in terms of the load that can be increased or decreased quickly in terms of kW/min or kW/sec.

There is no doubt that in the big picture of Decarbonisation of transport, Vehicle to grid interaction is important. Though there is a significant value from Vehicle to Grid interaction, there are many challenges ahead. You can read more about V2G pilots and the challenges in AEEE's report on Vehicle to Grid Integration.

Link to other articles in the series

Link to Part 1:?EV Charging 101

Link to Part 2:?EV Charging 102

Link to Part 3:?EV charging 103

Link to Part 4:?EV Charging 104

Link to Part 5:?EV Charging 105

Link to Part 6:?EV Charging 106

Link to Part 7: EV Charging 107

Note: I am an electrical and electronics engineer and not an expert in EV or batteries. However, my current area of research is EV charging, and my auto-didactic tendencies are lately on overdrive with my focused reading. The article is a summary of my notes from multiple sources. A fellow EV enthusiast may find it useful, though caution is advised. As this article intended to help me in improving my writing skills, please do let me know how I am doing in the comments section.