A solar park produces most of its power in the middle of the day, whether or not anyone needs it then. Without storage, that power either goes onto the grid at whatever price is on offer, or it doesn't get used at all. The question we get asked most often, by people running or planning a park, is simple: how do you keep the power you generate long enough to use it when it actually matters.
Our answer is the Battery-Shelter, a 10-foot container built around certified second-life EV batteries. Each unit delivers 40-200 kW of power and 120-1,000 kWh of storage, takes solar input up to 300 kWp, and runs on SOFAR inverters. It sits next to the array, takes what the panels produce, and holds it until the site is ready to use it or sell it.
The modelled comparison
To show what that's worth, we built a comparison for a single site: solar paired with the grid, against solar paired with storage through a Battery-Shelter. The solar-plus-grid case needs 1.2M€ of investment and saves 120,000€ a year, for a 10-year payback. The solar-plus-storage case needs 2M€ and saves 300,000€ a year, for a 6-year payback, and avoids 400 tonnes of CO2. This is a model of one site, not a delivered project, but the gap between the two columns is the reason storage gets built.
The extra investment in the storage case buys two things. First, the ability to use power when it's needed rather than when it's produced, which is most of where the 300,000€ figure comes from. Second, a smaller draw on the grid overall, which is where the CO2 figure comes from. Neither number depends on the weather being unusually good; they come from shifting power in time, which a battery does regardless of the season.
Because the Battery-Shelter is modular, the same unit that fits a 40 kW installation scales to several units on a larger park, without redesigning the site around a single large piece of equipment. Cells go into it only after they've been tested, certified and optimised, which is what we mean when we say second-life EV batteries: not used, not recycled, not refurbished, but requalified for exactly this kind of duty.
Anyone planning a park, or already running one without storage, can write to us at contact@marnyenergy.fr and we'll work through what the numbers look like for that site specifically.