The principle: shifting your production in time

Solar panels produce mostly at midday, when a household's consumption is low; the consumption peak comes in the evening, panels off. Without storage, the midday surplus is fed back to the grid (often poorly paid), and evening electricity is bought at full price. A storage battery breaks this mismatch: it banks the daytime surplus to release it in the evening and at night. This is self-consumption with storage.

A second-life battery does exactly this job, at a fraction of the price of new — provided it is properly requalified.

Is a second-life battery suited to this use?

Yes, and stationary use is actually especially favourable to it. A cell retired from mobility is retired because it lost power and density — two critical criteria for riding, but secondary for fixed storage where discharge is slow and weight is irrelevant. A cell at 80% SOH still has 80% of its original capacity: easily enough to store several kWh every day, for years.

Reliability rests on three non-negotiable conditions:

  • Cell-by-cell sorting: only cells above an SOH threshold (70% at cirBATT) are kept, and grouped by matching performance so a weak cell doesn't drag down the pack.
  • An adapted BMS: the management system must be calibrated for reused, heterogeneous cells, not simply copied from a new battery. It handles balancing, charge/discharge protection and thermal protection.
  • A documented SOH: a serious seller shows the workshop-measured SOH on each pack. Without that figure, you're buying a black box.

Sizing your battery

The simple rule: the battery should cover evening and night consumption, generally 3 to 8 kWh for a house. No need to oversize: a battery only helps if your panels produce enough surplus to fill it most days. For a 3 kWp installation, a 5 to 8 kWh pack is a good starting point.

Two notions not to confuse: nominal capacity (theoretical kWh) and usable capacity, limited by the allowable depth of discharge (DoD). An LFP battery tolerates a high DoD (80–90%), which maximises the energy actually usable day to day.

Compatibility with your installation

A battery doesn't connect on its own: it needs a compatible hybrid inverter that manages the flows between panels, battery, home and grid. cirBATT packs are 48 V, the standard voltage of the main hybrid inverters on the market (SMA, Victron, Growatt, Deye, Sofar, Solis…). Battery/inverter communication runs through the BMS (CAN or RS485 protocol). Before any purchase, we check compatibility with your inverter together.

What you gain — and the planet too

Financially, second-life storage sharply lowers the entry cost versus new while raising your self-consumption rate. Ecologically, reusing existing cells avoids manufacturing a new battery (extraction, refining, assembly): the carbon footprint of storage is cut by around 70 to 80%. For anyone installing panels to reduce their impact, it's consistency from end to end.