Short answer
A battery may be uneconomic if oversized, rarely cycled, the value per shifted kWh is small, or investment and degradation exceed benefit. Self-sufficiency is a different objective from return.
Important variables
- Actually shifted kWh
- Price spread after export revenue
- Usable round-trip efficiency
- Investment, ageing and replacement
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Worked example
Only 120 full cycles at 8 kWh and €0.18 benefit creates €173 yearly before losses. A high purchase price is hard to recover over a limited life.
Break-even: What changes the result?
Better sizing and higher evening demand increase cycles. Falling battery prices may improve future offers but should not be treated as certain in today’s scenario.
Common mistakes
- Equating self-sufficiency with return
- Assuming a full cycle every day
- Not subtracting export revenue
Terms in this guide
Sources & assumptions
- IEA PVPS — Photovoltaic Power Systems Programme (2026-08-17)
- RATIOXA — Methodology and formulas (2026-08-17)
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