Vehicle to Grid – even for older cars

For most people an EV is the largest battery they will ever possess. And it is idle 90% of the day even if there are useful things for it to do. If you have a solar system, you can store energy in your car’s battery during the day and take it out again after the sun set (or is hidden behind clouds).

In the future (and in some countries even today), it will be possible to draw excess energy from the grid (for example the noon-peak of PV power) and sell it for a higher price when it is needed.

Trouble is, that older cars and even cars on the market right now either do not support taking energy out of the battery at all or are only able to supply loads directly, without grid connection.

Until now at least. Most cars have a CCS quick charge port which is nothing else than a direct connection to the car’s high voltage battery. We “only” need to convince the car to close the relays that normally separate the charge port from the battery.

And exactly that has been achieved by the openinverter community. So far we have successfully tested the following cars:

  • Hyuanday Ioniq classic 28 kWh
  • Polestar
  • MG4
  • Tesla Model Y
  • BYD Atto3

Next comes the task of actually taking the battery voltage to the grid. This is not a big issue, as battery inverters already exist for home storage systems. They take for example 100-500V input voltage and feed it to the grid.

Also there are multiple implementations of energy management systems that control the charging and discharging of the battery. Many of them are open source but also commercial vendors like SMA offer this functionality – for obvious reasons.

So, an upcoming project is to tie all these building blocks together. A device will communicate with the car’s CCS controller and convince it to close its charge port relays. On the other side it will talk to the battery inverter and energy meter to achieve a zero grid power exchange (i.e. prevent drawing or feeding energy to/from the grid).

Finally, should you be worried about impeding the longevity or your battery you can relax. When the battery is only cycled around half-full, say 30-70%, this does not drive degradation as many studies confirm.

We will update you here when things are progressing.

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