What Size Solar System Do I Need Based on My Electricity Usage?
Your annual electricity usage directly determines the recommended solar PV system size. At a typical European yield of 1,200 kWh/kWp/yr, a household using 6,000 kWh/year needs a 5.0 kWp system. At a lower yield of 900 kWh/kWp/yr, the same consumption needs 6.7 kWp — so location matters as much as usage.
Key Factors
The relationship between annual usage and system size depends on:
- Annual electricity consumption (kWh/year) — from your electricity bill or annual statement.
- Target coverage (%) — 100% means the system should produce as much energy as you consume in a year.
- Expected solar yield (kWh/kWp/yr) — varies significantly by location, roof orientation, and local climate.
- Panel-count rounding — the actual DC array is usually slightly larger than the planning target because panels come in whole units.
Worked Examples
The table below shows recommended PV system sizes at different consumption levels and solar yields, all at 100% coverage — computed live using the Home Solar Sizer engine:
| Annual energy use | 900 kWh | 1,200 kWh | 1,500 kWh |
|---|---|---|---|
| 4,000 kWh/yr | 4.5 kWp | 3.4 kWp | 2.7 kWp |
| 6,000 kWh/yr | 6.7 kWp | 5.0 kWp | 4.0 kWp |
| 8,000 kWh/yr | 8.9 kWp | 6.7 kWp | 5.4 kWp |
| 10,000 kWh/yr | 11.2 kWp | 8.4 kWp | 6.7 kWp |
Examples use the Home Solar Sizer engine: yield = 1200 kWh/kWp/yr, 450 W panels, 100% coverage, 1.2 DC/AC ratio.
How the Estimate Works
The recommended PV size is calculated as: recommendedPVSize = (annualConsumption × targetCoverage) ÷ annualSpecificYield. The result is rounded up to the nearest 0.1 kWp. This is the same formula used by the Home Solar Sizer calculator — no additional loss factors or performance ratios are applied on top of the yield.
Understanding kWh vs kWp
kWh (kilowatt-hours) measures energy — the amount of electricity you consume over a year. kWp (kilowatt-peak) measures the rated power capacity of a solar array. A 5.0 kWp system at a yield of 1,200 kWh/kWp/yr produces about 6,000 kWh/year. The same 5.0 kWp system at a yield of 900 kWh/kWp/yr produces only 4,500 kWh — so two households with the same consumption but different locations need different system sizes.
Limitations & Assumptions
- Solar yield varies by location — the 900/1200/1500 kWh/kWp/yr values are illustrative. Your actual yield depends on latitude, climate, roof pitch, azimuth, and shading.
- This is an annual energy-balance estimate — it does not account for when energy is produced vs. when it is consumed.
- Target coverage does not equal self-sufficiency. Producing 100% of your annual consumption does not mean you never import from the grid.
- Actual roof dimensions, structural capacity, and local regulations may limit achievable system size.
- Panel-count rounding means the actual installed DC array is usually slightly larger than the planning target.
- No inverter sizing, battery storage, or self-consumption calculations are included in this estimate.
Frequently Asked Questions
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Enter Your Electricity Usage
Your annual electricity usage directly determines the recommended solar PV system size. At a typical European yield of 1,200 kWh/kWp/yr, a household using 6,000 kWh/year needs a 5.0 kWp system. At a lower yield of 900 kWh/kWp/yr, the same consumption needs 6.7 kWp — so location matters as much as usage.