Assuming some future state where (nearly) all cars are going to be electric, we will have a very large number of big batteries on wheels mostly standing around mostly under-utilized and already paid for by their owners.

As we have seen in this previous post, there would be a significant imbalance on a weekly timescale between load and generation in a primarily wind & PV based power grid. Given the large amount of already paid for storage capacity, it would be temping to use it as grid storage (V2G vehicle-to-grid) over these time-ranges where investment in dedicated grid storage might be hard to economically justify.

There is already a significant amount of literature estimating the potential impact of V2G for short-duration, intra-day grid storage. But the use cases could go well beyond that. Assuming that car owners could "donate" 25% of their car's battery capacity into a grid storage pool as long as it is not used, how long would it take before this reserve would really be needed for driving? A few days, maybe weeks or only once or twice a year for a vacation trip?

To see the potential benefits, we are adding a V2G component to the previous system cost optimization LP model. For sizing the V2G model, we are using the assumptions given in section 2.2 of this research report.

Using again the Netherlands as an example, there are about 10 million cars in service today and we assume all of them be electrical in some near future. We assume that at any time about 60% of vehicles are participating in the V2G storage pool and are currently plugged in - 80% of which support bi-directional charging. We assume the average battery size per car to be 100kWh and the capacity made available to the grid is only 25% of each participating car. The maximum charge/discarge power is limited to 2kW per car, which is a small fraction of a typical 11 or 22kW wall-box home charger

As we have seen for the same model in this previous post, demand side flexibility can significantly reduce or eliminate the need for fast short-term storage to balance the grid at hours to day time-scales. On top of this model, we now add the essentially free of cost V2G capacity.

baseline | 40% flex demand (12h) | 40% flex + v2g | |
---|---|---|---|

Load (total / avg / peak) | 99.6TWh / 11GW / 17.7GW | 99.6TWh / 11GW / 17.7GW | 99.6TWh / 11GW / 17.7GW |

Generation (total / avg / peak) | 116.4TWh / 13.3GW / 48.9GW | 114.2TWh / 13.1GW / 47.8GW | 110.8TWh / 12.7GW / 46.2GW |

Generation PV / ONW / OFFW | 39.4% / 60.6% / 0.0% | 38.3% / 61.7% / 0.0% | 36.1% / 63.9% / 0.0% |

Annual Cost / Cost per MWh | 8.5B€ / 85.3 €/MWh | 7.9B€ / 79.8 €/MWh | 7.7B€ / 77.4 €/MWh |

System Efficiency | 85.5% | 87.1% | 89.9% |

Surplus | 1.5% | 1.3% | 0.7% |

Storage contribution | 28.2TWh (28.4%) | 17.6TWh (17.7%) | 18.6TWh (18.7%) |

SDS Power | 7.6GW | -- | -- |

SDS Capacity / Duration | 39.9GWh / 5.2h | -- | -- |

SDS contribution | 9.5TWh (9.5%) 236 cycles | -- | -- |

LDS Power (charge/ discharge) | 14.1GW / 11.0GW | 13.5GW / 10.6GW | 11.1GW / 9.0GW |

LDS Capacity / Duration | 5489.6GWh / 500h | 5431.4GWh / 513h | 5276.1GWh / 583h |

LDS contribution | 18.8TWh (18.9%) 3 cycles | 17.6TWh (17.7%) 3 cycles | 12.0TWh (12.0%) 2 cycles |

V2G Power | -- | -- | 9.6GW |

V2G Capacity | -- | -- | 120.0GWh (12h) |

V2G contribution | -- | -- | 6.6TWh (6.6%) 55 cycles |

While the available V2G storage pool is about 3 times the size of the short term battery storage needed for the inflexible baseline scenario, the impact on the capacity needs for the capital expensive and rarely used long & seasonal duration storage is barely reduced, even though the V2G pool takes up about one third of the remaining storage contribution at a fairly high round-trip efficiency (80-90% vs. less than 60%).

Another perspective would be the reduction in total annual system cost (8.5B€ for baseline configuration). By allowing 40% of demand across all sector to shift by up to 12 hours in a most globally optimal way, we could reduce annual system cost by 600M€ or 7%. By adding V2G on top of that we arrive at a saving of 900M€ or 10.5%. This gain in global welfare can be distributed any which way among stakeholders like electricity consumers, the government, power grid operators or as an incentive for those who are supposed to contribute a "free" resource (flexibility, spare battery capacity) for the greater good of the community.

baseline | v2g | |
---|---|---|

Load (total / avg / peak) | 99.6TWh / 11GW / 17.7GW | 99.6TWh / 11GW / 17.7GW |

Generation (total / avg / peak) | 116.4TWh / 13.3GW / 48.9GW | 114.4TWh / 13.1GW / 47.9GW |

Generation PV / ONW / OFFW | 39.4% / 60.6% / 0.0% | 38.3% / 61.7% / 0.0% |

Annual Cost / Cost per MWh | 8.5B€ / 85.3 €/MWh | 7.9B€ / 79.3 €/MWh |

System Efficiency | 85.5% | 87.0% |

Surplus | 1.5% | 0.9% |

Storage contribution | 28.2TWh (28.4%) | 28.2TWh (28.4%) |

SDS Power | 7.6GW | -- |

SDS Capacity / Duration | 39.9GWh / 5.2h | -- |

SDS contribution | 9.5TWh (9.5%) 236 cycles | -- |

LDS Power (charge/ discharge) | 14.1GW / 11.0GW | 12.6GW / 9.8GW |

LDS Capacity / Duration | 5489.6GWh / 500h | 5498.8GWh / 560h |

LDS contribution | 18.8TWh (18.9%) 3 cycles | 14.3TWh (14.3%) 2 cycles |

V2G Power | -- | 9.6GW |

V2G Capacity | -- | 120.0GWh (12h) |

V2G contribution | -- | 14.0TWh (14.0%) 116 cycles |

If we were to implement a full V2G pool without also taking advantage of demand flexibility first, we get a similar benefit as for demand flexibility alone, also increasing the number of average storage cycles for the V2G cluster from 55 to 116. Limiting the number of storage cycles and the charge/discharge power intensity can also help limit battery wear to not unnecessarily shorten the lifespan of the battery below the natural service lifetime of the car.

Given that demand flexibility is likely much easier to implement and operate than V2G, the conclusion from this analysis would be that policy makers and grid operators should focus on flexibility first. V2G can be a nice optional ad-on - generating about 50€ of annual value per car. Not enough to justify any significant investment, unless bi-directional charging is becoming the standard anyway because car owners enjoy the other benefits: using the car as a mobile power supply (V2L) or as an emergency backup power source for their house or to optimize the behind the meter utilization of rooftop solar power instead of selling it back at feed-in tarifs which can be much lower than retail power tarifs.