What size battery, honestly?
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A battery's job is never just "storage" — it either keeps essentials on during an outage or shifts your evening load into cheaper sun hours. This planner sizes for the job you actually want, then tells you the honest economics. Typical-module assumptions are labeled; real quotes will beat this page.
Assumptions, all public: typical module ≈ 13.5 kWh usable; round-trip efficiency ≈ 85%; essentials ≈ 35% of daily use. Battery hardware runs ≈ $800–$1,200 per kWh installed before incentives (U.S. 2026 range, in review) — a 13.5 kWh module lands near $11k–$16k, often against an ~10-year+ simple payback in shift-only use. Outage security is a feature you can price personally; most homes decide on resilience, not ROI.
When a battery earns, when it doesn't
- Retail net metering + no outages you care about: a battery is a luxury, not an investment — shifting buys nothing because exports already pay retail.
- Weak or no export credit: every kWh the battery moves to evening is one you don't buy at retail. Self-consumption becomes the whole game, and sizing up starts to make sense.
- Time-of-use rates with a real spread: check the import/export price gap on your own tariff — a wide spread is the one case where shift-only arithmetic can approach a sane payback, and only after backup value is counted at zero.
- Never size from marketing: an installer sizing a battery to your whole annual use is selling modules, not engineering. Essentials-only sizing is where nearly every home actually lands.
The quick frame: battery vs no battery, in plain language.