How many watts of panels do you actually need? Start with the watt-hours your loads consume each day, then divide by realistic sun hours and efficiency—this guide shows the estimate before you buy hardware.
Benefits
- Works backward from load: daily Wh → required harvest → minimum array watts at your site.
- Accounts for peak sun hours by season and latitude instead of assuming 8 h of full sun.
- Highlights when to add 20–30% headroom for clouds, batteries, and inverter losses.
How it works
- Total daily watt-hours from appliances, pumps, lighting, and standby draws.
- Look up or estimate peak sun hours for your location and worst-case month.
- Divide Wh by (sun hours × efficiency); the result is baseline panel wattage before safety margin.
FAQ
How do I estimate solar panel wattage needed for my home or cabin?
Add up daily Wh (watts × hours for each load). Divide by peak sun hours and system efficiency. Example: 3,000 Wh/day ÷ (4.5 h × 0.85) ≈ 784 W of panels minimum—then add margin for weather.
How many watts of solar per 1,000 Wh of daily use?
It depends on sun hours and efficiency. At 5 peak hours and 80% efficiency, 1,000 Wh/day needs about 250 W of array rating. At 3 peak hours the same load needs roughly 417 W.
Is estimated wattage the same as what I will produce each day?
No. The estimate is nameplate STC watts sized to meet your Wh budget on average. Actual harvest varies with tilt, temperature, shading, and season—use solar daily yield tools to sanity-check output.
Technical specifications
- Estimate: panel_W ≈ daily_Wh ÷ (peak_sun_h × efficiency).
- Sun hours: use monthly or winter values for conservative off-grid sizing.
- Efficiency: 75–85% typical for small PWM systems; MPPT often higher.
- Margin: +20–30% on result unless a multi-day storage model is applied.
Load audit before panel count
Wattage estimates fail when daily Wh is wrong. List each device with runtime—fridge duty cycles, pump hours, inverter idle draw. A 10% error in Wh propagates directly into undersized or oversized array quotes.
From watts needed to module count
Once you have minimum array watts, divide by your chosen module rating (e.g., 400 W) and round up. Roof layout, string voltage limits, and MPPT window may force a slightly larger physical array than the Wh math alone.