Free planning tool

Solar battery sizing calculator

Pick the critical loads you must keep running, set backup hours, and we'll size the battery — lithium or lead-acid.

  • PRD §10 formula: battery kWh = backup ÷ usable DoD ÷ inverter efficiency
  • Compares lithium (85% DoD) vs lead-acid (50%) capacity
  • Quotes installed cost for both chemistries side-by-side
  • Backed by the same engine as the full solar calculator

Results are planning estimates. A licensed installer site survey is required before purchase.

Deterministic engine

Same PRD §10 formulas every run. No black-box AI in the sizing path.

Transparent confidence score

See exactly which inputs lifted or capped your score (PRD §11).

Verified installer marketplace

Optional: request quotes from installers vetted in your country.