What Size Solar System for Off-Grid? Honest Guide (2026)

📅 Sep 7, 2026 · Lucas Ballek · 11 min read · every number below comes from this site's deterministic simulator, not guesswork

The short answer: for a home using around 10 kWh per day, most temperate sites land around 4–6 kW of PV with 10–16 kWh of usable battery for high coverage — less in the tropics, substantially more at high latitude. Pick reliability first, latitude second, hardware third. Educational estimates only — verify with a licensed professional.

Off-grid size is a reliability choice

Grid-tied sizing asks "how much of my bill do I erase?" Off-grid asks: "how many dull days in a row must I ride through?" Two homes with identical 10 kWh/day averages can need systems differing by 2x if one accepts generator hours and the other does not. That is why this guide gives ranges, not single numbers, and why the estimator simulates five years of hourly weather instead of dividing one average day by one sun-hour figure.

Tier A, B, C: pick your outage tolerance first

• Tier A — never-generator: ride the worst week in five years on solar plus battery alone. Expect 30–60% more PV and battery than Tier B.
• Tier B — about 1 day/year shortfall: covers 98–99% of hours; a few hours per year of load-shedding or small backup. The sweet spot for most full-time homes.
• Tier C — occasional backup accepted: deliberately undersize 20–40% vs Tier B and cover 5–20 dull days with generator or load shifting.

Moving Tier C → B typically adds 20–40% more battery. B → A adds another 30–60%, almost all to survive rare multi-day dull spells.

Latitude yield bands

• Tropical (0–15°): 1500–1900 kWh/kWp/yr — Quito, Lagos, Jakarta. Strong sun, clouds matter more than season.
• Subtropical (15–30°): 1400–1800 kWh/kWp/yr — Honolulu, Delhi, Cairo. Mild winter dip.
• Temperate (30–50°): 1100–1500 kWh/kWp/yr — Madrid, Sydney, Los Angeles. Real winter dip.
• High-latitude (50°+): 850–1200 kWh/kWp/yr — Berlin, London, Oslo. December weeks decide the system.

Worked example: 10 kWh/day at 60, 80, 95% coverage

For Tier A never-generator on the same load in a temperate zone, plan roughly 7–10 kW PV with 25–40 kWh usable as a starting range. For Tier C with backup accepted, 2–4 kW with 6–10 kWh is often enough to test first.

Why the last 10% costs the most

Going 60% → 80% is cheap; 90% → 98% is expensive — you buy hardware idle for months to cover one bad February week. Many households build Tier B now on a 48 V modular bank and extend later.

Dark-week margin: why x1.5

Three overcast days at 15–25% of clear-sky output is normal. After computing one day of autonomy, multiply usable capacity by about 1.5x to ride 2–3 day clusters. Example: 10 kWh/day × 1.0 day = 10 kWh baseline → 15 kWh planning figure Tier B. Tier A often tests 2.0–2.5x; Tier C 1.0–1.2x.

Same load, three latitudes

• Honolulu (~21°N): test 3–5 kW PV, 10–15 kWh usable first.
• Lagos (~6°N): test 3–5 kW PV, 12–18 kWh usable first — battery matters more than extra panel past 5 kW.
• Berlin (~52°N): test 5–8 kW PV, 18–28 kWh usable first for the same Tier B promise.

What the hardware ranges mean

Component ranges only — exclude mounting, wiring, protection, permits, labor. Educational estimates only; verify with a licensed professional. Batteries and mains wiring can cause fire, injury, and death.

Related guides

• Off-grid battery bank sizing
• Off-grid vs grid-tied payback
• Nairobi sizing · Berlin sizing · all 66 cities

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