Wednesday, 15 April 2015

V2G : The Cons

Well, now since you know about what V2G is and that you can make some extra bucks by providing the service, you should now also know about the drawbacks of using your electric vehicle (EV) to provide the service.

But first you need to about the aggregator

Like I wrote in my previous post, your vehicle does not have a battery large enough to impact the electricity grid significantly. To provide any service of value, a number of vehicles have to be aggregated. And this is precisely the responsibility of an aggregator (who is an entity just like your electric utility). The role of an aggregator is to collect a sufficient number of vehicles (say all the vehicles in a parking lot) and manage them most according to the needs of the grid, i.e, when the grid operator requires the vehicles to supply energy, the operator will send a signal to the aggregator and the aggregator will in turn decide which vehicles from the aggregation of vehicles will provide the energy needed.And he will do in a way that utilizes the fleet of the vehicles most efficiently.

So, where is the problem ?

To enroll in an aggregation, you might have to give up some freedom on mobility, i.e, you may have to get into a contract which binds you from using your EV in some specified hours. In most cases, this is not a problem, because V2G service is provided generally during office hours when the car is parked. But in cases of emergency, you may be unable to use your vehicle. In other cases, you may have to enter your driving patterns the day ahead, so that the aggregator can plan accordingly. You may not know your own schedule in advance sometimes, so dealing with such situations might be cumbersome.All such constraints depend totally on the aggregator and the kind of contract you have signed.

Is that the only drawback ? Unfortunately, NO.

You brought your electric vehicle for a huge amount, and that is because the batteries that power the EV are very expensive. Batteries are the most costly component of an EV and till the time improvements in technology come about, the prices of batteries are going to stay that high. The important thing for you to know as an EV owner is that these batteries have a specified lifetime, just like any other device, after which it is no longer considered suitable to be used in a EV. You may have noticed, laptop batteries are able to power your laptop for much longer times initially, but as they age, they are able to power your laptop for lesser and lesser time for the same charge. This is because the ability of any battery to hold charge (or energy) decreases with time. And for EVs, batteries are considered unusable when they can hold less than 80% of the charge that new batteries can hold. Battery life is also dependent on other factors such as depth of discharge and operating temperature. If you discharge your battery more, it wears out faster. Each battery also has a specified number of charge/discharge cycles, i.e, say you can charge and discharge your battery about 1000 times. So the faster you finish the cycle count, the sooner you will have to replace your battery.

How does V2G impact your EV battery ?

V2G needs to draw energy from your battery and supply that energy to the grid, and this means it is using up some of the charge/discharge cycles of your battery. This will cause the battery to age faster. Also, if the aggregator discharges your battery completely or nearly completely, the chances are higher that your battery can suffer damage. Most of the car manufacturers don't cover V2G in their warranty which means you pay the cost of replacing the battery. However, on the positive side of things, aggregators ensure that they manage your batteries in such a way that it causes minimal or zero impact on the batteries. Some of the grid services may not even require energy to be drawn out of the battery, they just need you to postpone charging during times of high energy demand. Such services can give you benefits of V2G without impacting battery life.

So, moral of the story is to talk to your aggregator and car manufacturer before signing up for an aggregation. In this way you can ensure that you can make the most out of V2G without harming your EV. 


  1. Great work !! Critical ideas presented in a lucid manner.
    Can you comment on the impact of partial cycles on the battery life. Say the impact of one complete cycle Vs 10 partial cycles of 10 % depth

    1. Each battery has a number of charge/discharge cycles at a specific depth of discharge. The curve looks something like this
      So, it is difficult to accurately determine the tradeoff between the depth of discharge and the number of charge discharge cycles.
      A general rule of thumb is that deeper depth of discharge is more detrimental to the battery than more cycles of charge/discharge at a low depth of discharge. So I would say, one complete cycle would cause more impact than 10 partial cycles at 10% depth.

  2. If the storage technology advances (which is supposed to help V2G), then I suppose that storage could be directly used up in storing energy produced in the night rather than taking it through a vehicle which will certainly decrease the efficiency.

    1. Your statement holds merit. The only point to be noted is that storage prices will have to drop much more significantly for it to be used directly in the grid. Using storage through V2G does not require such a significant decrease in storage prices because what it lacks in price, it makes up in the sheer number of electric vehicles on the road.

    2. Thats true. I would say that there is only a window of some years when V2G would be a big thing before the coming of very cheap storage.

    3. That is true. Cheap Storage has the possibility of changing the entire scenario of the energy sector.