Size solar from your bill
Short answer
Divide your monthly bill by your rate per kWh to get monthly kWh. Divide by 30 for daily kWh, then by 3.6 (4.5 sun hours × 80% efficiency) to get kWp. A ₱5,000 bill at ₱12/kWh needs about 3.9 kWp, or seven 630 W panels.
| Monthly bill | Energy used | System size | Panels | Roof space |
|---|---|---|---|---|
| ₱3,000 | 250 kWh | 2.5 kWp | 4 | ≈ 11 m² |
| ₱5,000 | 417 kWh | 4.4 kWp | 7 | ≈ 20 m² |
| ₱8,000 | 667 kWh | 6.3 kWp | 10 | ≈ 28 m² |
| ₱10,000 | 833 kWh | 8.2 kWp | 13 | ≈ 36 m² |
| ₱15,000 | 1,250 kWh | 12.0 kWp | 19 | ≈ 53 m² |
| ₱20,000 | 1,667 kWh | 15.8 kWp | 25 | ≈ 70 m² |
Step 1: Find your monthly kWh
Your bill shows the kWh you used. If you only have the peso amount, divide it by your rate per kWh. Example: ₱5,000 ÷ ₱12 = 417 kWh a month.
Step 2: Turn it into daily kWh
417 kWh ÷ 30 days = 13.9 kWh a day.
Step 3: Divide by sun hours and efficiency
Central and Northern Luzon get roughly 4.5 peak sun hours a day on average. Real systems lose about 20% to heat, wiring and the inverter. So each kWp of panels makes about 4.5 × 0.8 = 3.6 kWh a day.
13.9 ÷ 3.6 = 3.86 kWp.
Step 4: Count panels and roof space
With 630 W panels: 3,860 W ÷ 630 W = 6.1, so round up to 7 panels (4.41 kWp). Allow about 2.8 m² of roof per panel including spacing: about 20 m².
Try your own numbers with the solar panel calculator.
Why the real design may differ
- Most homes use more power at night, so a battery or a smaller system may give better value.
- Shading, roof direction and roof shape change how many panels fit and how much they make.
- Exports under net metering earn less than your retail rate, so oversizing rarely pays.
A site visit turns the estimate into a design.
Common questions
- How many solar panels do I need for a ₱10,000 bill?
- About thirteen 630 W panels (8.2 kWp) on roughly 36 m² of roof, assuming ₱12 per kWh, 4.5 sun hours a day and 80% system efficiency.
- How much roof space do I need?
- Roughly 2.8 m² per 630 W panel including spacing, so about 20 m² for a 4.4 kWp system.
- Does a bigger system always save more?
- No. Power you export is credited at the lower blended generation cost, so the best value usually comes from a system matched to your daytime use.