As a rule I don’t post much on renewable technology. The news is of a steady flow of small, unremarkable, incremental improvements that keep making wind and solar energy ever cheaper. It’s the prices that do it. But every so often, something bigger happens. I think it has here:
Dominion Energy Virginia has published a bullish plan to convert 50 school buses in its territory to electric buses by 2020. That’s just the start, as the company plans to add 200 more per year to hit its target of 1,050 fully electric school buses by 2025.
The company has a request for proposals in the works for electric vehicle manufacturers with plans to open the application to school districts in its Virginia territory this Friday, September 5th, 2019. […]
Dominion is excited to use the buses as vehicle to grid (V2G) batteries, and what’s even better is that the company has stepped up to pay the difference in price between traditional diesel buses and the fully electric buses in order to gain access to this new V2G resource.
V2G – vehicle-to-grid – is the idea of using electric vehicle batteries as storage for the grid. If it works, the potential is vast.
In 2018, there were 5.1 million electric cars on the roads worldwide, and 460,000 buses. (IEA Global EV Outlook 2019 ) Taking 30 kwh as a representative battery capacity for cars (Nissan Leaf) and 320 kwh for a representative electric bus (BYD K9), we have a total EV battery capacity of ~300 Gwh. The global light vehicle stock is about 1 billion, so EVs only represent 0.5% of it. But the growth rate is staggering – over 50% per year. The IEA suggests a global EV stock of 130 million in 2030 in its New Policies scenario (reflecting current policy ambitions), not much more than 10% of the stock allowing for market growth. We would then have a global vehicle battery capacity of ~7,800 Gwh, with plenty of upside.
Suppose we can tap a mere 10% of this for V2G. That’s ~780 Gwh. The Bath County pumped storage dam in Virginia, still the world’s largest (though not for long) has a storage capacity of 24 Gwh. V2G at scale would make a serious dent in the firming problem for very large-scale wind and solar. And it’s a very cheap solution compared to pumped storage or grid batteries: the owners of the vehicles will have bought the batteries anyway, and would not need to be paid much to lend them to the grid with appropriate guarantees and at minimal inconvenience.
A schematic illustration how this would work using Dominion’s school buses (my timetable guesses, not their estimates). On a working day:
- 0000h – 0630 h: charge bus batteries in garage to 100%
- 0630h – 0930h: morning school run, buses return to garage with average 33% charge
- 0930h – 1600h: charge bus batteries in depot to 100%; available for V2G but not used much
- 1600h – 1900h: afternoon school run, buses return to garage with average 33 % charge
- 1900h -2400h: interruptible charging; >33% of bus battery capacity available for V2G to meet evening demand peak.
That’s for the 200 school days a year. For the other 165 days, the buses just sit in the garage, working exactly as grid batteries.
The scheme depends on the fact that any bus operator will buy a number of identical buses, but these will follow a mixture of longer and shorter routes. On the shorter ones, the buses don’t exhaust the charge. Given that Dominion is subsidising the purchases, they will be able to insist on as much over-capacity as they want.
There are several takeaways from this news. Continue reading “Dominion backs V2G”