Batteries are valuable for primary adjustment on the one hand, for ambulatory use on the other hand.
We talk a lot about batteries for day-night storage: charged by photovoltaic panels during the day to serve at night.
For the batteries to charge at noon, the production of the sun must be surplus; so it can only be in summer. In order to be needed at night, the demand at night must be greater than the possibility of zero or very low marginal cost production, nuclear, hydraulic river and wind turbines. But on summer nights, consumption is at its lowest.
Looking at things hour by hour, we can see a day-night oscillation of the battery charge only if the nuclear capacity is very low, the wind capacity very low and the PV capacity very strong, which is very far from reality .
In addition, the PEPS study [french] on electricity and heat storage shows (p.97) that the marginal value of electricity storage and the flexibility of consumption decrease significantly when their capacity increases. If I read correctly, the value of the first kW (in power) of a storage with a duration of discharge of 5 h (thus of a capacity of 5 kWh) is 80 € / year; if 2 GW capacity (10 GWh capacity) has been added to the existing capacities, the additional 1kW value is divided by 4 and is only 20 € / year. This equates to an investment of € 100 for 5 kWh, or € 20 / kWh.
Interesting result: ten times less than the cost of a battery. Is this what the PEPS study says ?
PS: With this spreadsheet here [french] that simulates power generation, storage and consumption, adding 1 GWh to the 90 GWh Steps decreases production from fossil gas and, at the same time, the un-upgraded or non-upgraded quantities of 27 GWh . If we have already added 10 GWh to 90 GWh of Steps, adding another 1 GWh decreases the quantities of 8 GWh, a 3.5-fold reduction in the efficiency of this GWh.