Solar basics 2 min read
How Many Solar Panels Do You Need? A Step-by-Step Calculation
Work out the number of panels and system size yourself from your electricity bill, with examples for a home, factory and farm, and the factors that change the result.
GPS Engineering Team
Before asking for a quotation it helps to know the rough size of your plant. The method is simpler than you think: all you need is your electricity bill.
Key takeaways
- Step one: find your average monthly consumption in kWh.
- Each installed kW produces roughly 150 kWh per month on average in Egypt.
- Number of panels = system size in watts ÷ panel wattage.
- Available space may cap the size before consumption does.
Step 1: Find your consumption
Add up the last 12 months in kWh and divide by 12. If you only have amounts in pounds, divide by the approximate price per kWh of your tier.
Step 2: Calculate the required size
Size (kW) = annual consumption ÷ annual yield per kW
In Egypt we use an average of 1,800 kWh per kW per year (higher in Upper Egypt and on the Red Sea, slightly lower in the Delta and on the north coast).
Step 3: Count the panels
Panels = (size × 1,000) ÷ panel wattage
Worked examples
| Case | Monthly use | Required size | Panels (620 W) |
|---|---|---|---|
| Home | 600 kWh | 4 kW | 7 |
| School | 6,000 kWh | 40 kW | 65 |
| Factory | 60,000 kWh | 400 kW | 646 |
Step 4: Check the space
Each kW needs roughly 6.5–8 m² depending on roof type and mounting. If space is short, the plant size is set by area and covers part of your consumption. See space requirements for solar.
Factors that change the result
- Shading: stacks, tanks, neighbouring buildings.
- Orientation and tilt: south-facing is best in Egypt.
- Heat and dust: losses are modelled in the design.
- Load profile: daytime or night-time consumption.
An engineer visits to measure the space, review consumption and give a final quote.
How much would your plant save?
Get system size, cost and expected savings in under a minute.
GPS engineers have designed and built solar plants across Egypt for 15+ years. Here they share what they learn in the field.
Frequently asked questions
Should I cover 100% of my consumption?
For grid-tied systems we usually design to cover annual consumption or slightly less, since annual surplus isn't normally paid out.
Can I add panels later?
Yes, if there is space and inverter headroom, or by adding a new inverter. We plan for it from the start if growth is expected.
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