While this may look promising, and seem the perfect way to increase renewable penetration, paving the way to a decarbonized energy sector, please stop. …and reconsider if it is the best solution.
Why decarbonize the power sector alone… if we can decarbonize the transportation and the power sector at the same time?
How? Investment in electric vehicles (EVs) must be economically efficient in itself (cheaper than the CO2 emmitting vehicles) so every € invested has already a return via mobility (for the owner/user). This means using the available storage is relatively “free” to the power sector. In my opinion, subsidizing battery storage (gathering dust inside a building) is a stupid idea compared to incentivizing the “transport-sector-decarbonizing-storage” or, to say it other way, batteries-with-wheels. EVs should be incentivized not only by governments trying to reduce the energy sector trade unbalances and reducing CO2 emissions, but also by utilities willing to increase the customer’s bill (an EV customer is billed aprox. a 30% more)
For centralized storage it is clear that pumped hydro is the most efficient and competitive solution, and for example in Spain, the power balance in the grid is mainly done with hydro (just check any day on the generation mix on www.ree.es). International grid connections could improve this, but as you may know Spain is still not so well interconnected with France.
For seasonal distributed energy storage, new solutions are being offered with hydrogen (that can also be used for transportation), such as the product offered already by Fronius. For energy storage during months, batteries are not as efficient.
Consider the same spanish grid mentioned above, and imagine 1 million EVs (just 3% of actual number of vehicles in Spain) when charging “slow” (3 kW) this distributed storage is valley-filling 3 GW (aprox 15 % of a typical valley load) storing 20 GWh of (probably wind) energy. When using two-way charging posts (what is called V2G-Vehicle to Grid or V2H-Vehicle to Home- see this post) this could reduce the peak load up to 3 GW (up to 10 %)
With “only” a 5% of vehicles as electric, the spanish demand curve could be teorethically flattened to 30-35 GW – 24/7. And if one of every 3 vehicles where electric, also theoretically the complete actual electric demand could be covered from EV batteries during 6 hours, with slow bidirectional charging points (fast bidirectional 50 kW could allow the same with 625000 connected vehicles).
In summary, EV smart battery storage can help build a CO2 free transport sector at the same time it helps build a CO2 free power sector.
So, if you think we have to invest in home and distributed batteries, please think again.