Vehicle to Grid and Shared Mobility

Vehicle to Grid (V2G) and Shared Mobility are two of the big buzz-phrases rolled out in the transportation sector, as magical solutions to energy storage needs of the grid (V2G) and to all the woes of transport-related climate change. They have both advantages and disadvantages which need to be considered in planning and policy making.

Vehicle to Grid

This is the use of vehicle-mounted batteries to supply peak grid power demand, charging at off-peak times.

  • Some countries’ energy transition plans assume that all the cars in the country, if turned into EVs that are 100% used for grid-connected storage, would account for only a part of the storage needs – they consume similar amounts of energy to the entire electricity grid, with only a 2- 4-hour range, only half of which at most (if the system works flawlessly) would be available to the grid. Therefore it lacks the duration to provide true back-up for renewables.
  • Where they charge from solar power (office, shopping), which is the proffered model, differs from where they would operate as grid-connected batteries, and nobody has proposed a cost-effective model for the financial flows.
  • Most people don’t want their vehicles on less than half charge, which halves (or less) the energy/storage available.
  • The bulk of the need for the storage is in the evening, when vehicles’ charge is lowest, yielding a grossly disproportionate multiplication of point 3.
  • If the 40-60 gigafactories currently planned world-wide are built, they would exhaust the lithium deposits in all current and under-development fields in 2-10 years according to figures from The Economist. Cobalt and other “rare earth metals” are in much shorter supply.
  • To roll out cars-with-solar widely, a high proportion of the parking spaces in the country would have to be fitted with chargers – who would bear the cost of that?
  • Distribution grids need upgrades at enormous cost and ahead of actual demand in order to accommodate variability between forecast and actual EV take-up.

The above-listed challenges would need to be answered for V2G storage services to

be reliable. And it appears that FES 2019 assumes 100% efficiency in V2G services,

which will not be attainable: a perfectly new battery requiring no cooling yields ~96%

efficiency, whereas one approaching its end of life yields ~75%, so a reasonable

assumed average efficiency would be ~85%; then there are converter efficiencies –

90% is reasonable, which has to be applied twice – once for charging and once for discharging. The total round-trip efficiency is therefore .85 x .9 x .9 = 0.6885 or 69%

round trip.

Energy Available from V2G

V2G is supposed to be the “magic bullet” that balances the grid, operating as a mix of battery storage and DSR: the charging of batteries can be displaced to low-demand and/or high-generation periods, while the energy stored in the batteries can also be called upon to support the grid. But can it conceivably provide sufficient energy to achieve this?

  • Vehicles demand about the same energy as the entire electricity grid.
  • Electric vehicles are estimated to be about 5x more efficient at using energy, which reduces available battery capacity to 20% of grid demand.
  • On average, EV batteries will only be half-charged; indeed, as they’ll mostly be called upon at the end of a day’s use, one can only expect them to be quarter-charged on average, reducing battery capacity to 5% of grid demand.
  • And people won’t be happy if their batteries are flat in case they wish/need to pop out in their vehicle, so at least half that charge needs to remain, reducing effective capacity to 2.5% of grid demand.
  • And that assumes that all vehicles will be battery powered, no hydrogen-powered fuel cells: the global shortage of lithium means that no more than one-third of vehicles will be battery powered, and these will be of smaller size and shorter range than the fuel cell vehicles, so the effective capacity is 0.5% of grid demand.

So, no magic bullet.

Shared Mobility

Shared mobility means that, instead of owning vehicles, we call them up. They are fully autonomous, driving themselves to where you are to take you wherever you wish to go.


  1. Fewer vehicles in existence. But that will not be apparent because the greater mileage (see below) will mean that more of them are on the road at any one time.
  2. People will not have to buy a vehicle, they’ll just hire one for the journey like a cheap-rate taxi.
  3. Cheaper than taxis as it’s based on autonomous vehicles.


  1. More vehicles on the road and more mileage driven per annum overall: if privately owned vehicles take 3 people to work, that’s 3 journeys in the morning. A shared vehicle needs to go from work place 1 to home 2, from workplace 2 to home 3, and then from workplace 3 to workplace 1 to take the first guy home. So it doubles the number of journeys – though good scheduling will mean it doesn’t double the mileage, but mileage is still increased substantially. This in turn will lead to much more emissions unless and until the energy system is zero-carbon – and increase the cost of making it so.
  2. Unpredictable vehicle: you won’t know what you’ll get or what condition it’ll be in.
  3. Can’t keep your stuff in the vehicle / pre-load vehicles for journeys / postpone unloading.
  4. Shared vehicles: would you like to share substantial journeys with complete strangers, in close confines? Would you like your children / daughters to? You can’t security vet everyone – and if you could, how would those who fail the vetting get around? And there’s no way at all to vet whether the other guys are nice or obnoxious, sober or drunk, well-washed or not.
  5. Will greatly reduce the use of public transport, thereby increasing emissions and making many services un-viable.

The Challenge

The challenge for policy-makers is to show a viable solution to all these issues; only then can we accept that V2G and Shared Mobility will benefit the system and the population as a whole.

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