Solar system size estimator
Estimate the kWp, panel count and roof area needed to offset a chosen share of your annual electricity use.
Your situation
Defaults are starting points from typical published ranges — never facts. Change any value that does not match your situation.
Estimate only. Based on the assumptions you entered. Get a site-specific survey before spending money.
System size needed
3.20 kWp
Panel count
8
at 420 W each
Approx. roof area
17.6 m²
Expected annual generation
3,200 kWh
Offsetting 100% of annual consumption does not mean independence from the grid. Generation and demand rarely coincide hour by hour.
Formula with your numbers
kWp_needed = 4000 × 80/100 / 1000 = 3.200 kWp
panel_count = ceil(3.200 × 1000 / 420) = 8
roof_area = 3.200 × 5.5 = 17.60 m²
Frequently asked questions
Does 100% offset mean I am off-grid?+
No. Annual offset means yearly generation roughly matches yearly consumption. You still import at night and on dull days, and export surplus at other times, unless you have a very large battery and accept limited autonomy.
How much roof area do panels need?+
A rough planning factor is ~5–6 m² per kWp for typical crystalline modules including gaps. The factor is editable because module wattage and layout vary.