1. List critical loads and hours → daily kWh (W×h÷1000).
2. Choose backup days → usable kWh = daily × days; adjust for DoD & efficiency.
3. Inverter: cover biggest continuous load + 2–3× surge.
4. Costs: ~$350–$600/kWh batteries; $900–$2,500 hybrid inverter; BOS $500–$2,000.
5. DC vs AC coupling; warranty cycles; ambient temp limits.
6. TOU arbitrage + solar self‑consumption can offset costs.
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