Daily energy usage is the anchor for every solar capacity calculation. This guide shows how to turn kWh or Wh per day into the panel watts your site must harvest—before batteries, inverters, or roof layout enter the picture.
Benefits
- Starts from measured or estimated daily kWh/Wh—not vague panel counts.
- Separates consumption from harvest: usage sets demand; sun hours set supply rate.
- Connects to array sizing formula used in the interactive solar panel size tool.
How it works
- Build a daily energy budget: fixed loads (Wh) plus variable runtime devices.
- Convert monthly kWh bills to Wh/day if grid history is your starting point (÷ ~30).
- Divide daily Wh by peak sun hours and efficiency to get minimum solar capacity in watts.
FAQ
How do I calculate solar capacity from daily energy usage?
Sum daily watt-hours, then panel_W ≈ Wh ÷ (peak_sun_h × efficiency). Example: 4.8 kWh/day (4,800 Wh) with 5 sun hours and 80% efficiency needs about 1,200 W of array rating before weather margin.
Can I use my electric bill instead of a load list?
For grid-tied planning, monthly kWh ÷ days gives average daily use—but peak days matter for backup sizing. For off-grid, a load audit is more reliable than bill averages because duty cycles and seasonal loads differ.
Is solar capacity the same as inverter size?
No. Array capacity (W) is how much energy you can harvest per day. Inverter watts are instantaneous power limits. Size the array from daily Wh; size the inverter from peak simultaneous load watts.
Technical specifications
- Capacity: panel_W ≈ daily_Wh ÷ (peak_sun_h × efficiency).
- Usage input: Wh/day or kWh/day × 1,000.
- Sun hours: site-specific; winter values size conservative off-grid arrays.
- Next step: pair with battery bank and charge-controller tools after array W is set.
From usage to harvest requirement
Daily usage tells you how many watt-hours must land in the battery or load each day. Solar capacity is the hardware rate needed to collect that energy given how many effective sun hours your roof or ground mount receives. Undersized arrays never catch up; oversized arrays waste capital unless storage can absorb surplus.
Seasonal usage swings
Heating, irrigation, and workshop loads often peak in months with fewer sun hours. Size from worst-case month Wh and sun-hour pairs—not annual averages alone—when autonomy matters. Summer surplus does not help a winter deficit without storage or load shifting.