How to turn your electricity bill into the size of a solar system? Step by step

Last updated: October 18, 2026

To convert your electricity bill to the size of a solar system: Add up your 12-month consumption in kilowatt-hours (kWh), divide by the expected annual output per kilowatt-hour (approximately 1,500 to 1,800 kWh in most regions of the Kingdom), then multiply the result by the percentage you want to cover. The result is the panels' capacity in kilowatts, from which you can calculate the number of panels and the size of the inverter.

Where can I find the consumption details on my electricity bill?

Your electricity bill contains a lot of information, but what matters to you when designing your solar system is:

• Consumption in kilowatt-hours: The difference between the current and previous meter readings is usually shown as a clear number in the readings table.
• Invoice period: Some invoices cover more or less than 30 days, so pay attention to the number of days when calculating the average.
• Subscription type and breaker capacity: It helps you to know whether the meter is single-phase or three-phase, and this determines the type of inverter.
• Consumption log: Many bills and the electricity company's app display a charge for consumption in previous months, which is the fastest way to collect data for the year.

The amount on the bill should not be used as the basis for calculations, as it varies depending on the tariff bracket on your bill, fixed fees, and VAT. The panels produce kilowatt-hours, so the comparison should be made using the same unit.

First step: Collect 12 months' worth of bills

Consumption in the Kingdom almost doubles between winter and summer due to air conditioning. If the system were designed based on the January bill, it would be very small, but if designed based on the August bill, it would be large and costly, resulting in a significant surplus in winter. Therefore, we calculate the total for the entire year.

Illustrative example: Villa consumption during a year

The numbers in the table are hypothetical for illustrative purposes and represent a typical pattern for a house with multiple air conditioners:

The daily average is 31,150 ÷ 365 ≈ 85 kWh. The monthly average is around 2,600 kWh, although August alone is more than three times that of February.

Step two: How much does one kilowatt of power from the panels produce per year?

This is the divisor in the equation. It is roughly calculated as follows:

Annual kW production = Daily peak solar hours × 365 × Performance factor

• Peak hours in most cities of the Kingdom are approximately 5 to 6 hours per day as an annual average.
• The coefficient of performance (COP) reflects losses due to: panel heat, dust, cables, and inverter efficiency (typically 95 to 98%). The total losses are typically 15 to 25%, resulting in a COP of 0.75 to 0.85.

In our example, we use 5.5 hours and a factor of 0.8: 5.5 × 365 × 0.8 ≈ 1,600 kWh per kilowatt-hour per year. This figure varies depending on the city, orientation, tilt angle, and shadows; therefore, the final study results may differ slightly from the initial calculation.

Step three: Determine the coverage percentage and calculate the capacity.

100% does not necessarily cover the consumption. The percentage depends on the surface area, budget, and system type. Based on the previous figures:

The calculation method for a 70% line, for example: 31,150 × 0.7 ≈ 21,800, then 21,800 ÷ 1,600 ≈ 13.6 kW, then 13,600 ÷ 550 ≈ 24.7, so we round it up to 25 panels.

When should you choose partial coverage?

• When the surface does not accommodate the full number of panels.
• When most of your consumption is at night and there is no mechanism to export the surplus, it is best to design the system for daytime consumption.
• When you want to start with a first phase and then expand, provided you choose an inverter that allows adding panels later.

What does the coverage look like month by month?

The 70% figure represents the annual average, but it's not evenly distributed. Let's consider a 13.6 kW system over two separate months, using approximate figures for clarity:

• January: Assuming approximately 4.8 peak hours and a performance factor of 0.8, production ≈ 13.6 × 4.8 × 31 × 0.8 ≈ 1,620 kWh, and consumption 1,400. That is, production exceeds consumption this month.
• August: Assuming approximately 6.2 peak hours and a slightly lower coefficient of performance (0.78) due to heat, production is ≈ 2,040 kWh, and consumption is 4,300. That is, coverage of approximately 47% only.

Therefore, it is important to know how the winter surplus is calculated in grid-connected systems according to the requirements approved by the competent authorities (such as the Saudi Electricity Company and the Electricity Regulatory Authority), because this affects the feasibility of choosing full or partial coverage.

Step four: From panel capacity to inverter and surface

After determining the capacity of the panels, three decisions remained:

1. Inverter capacity: In grid-tied systems, the inverter's power rating is typically close to or slightly lower than that of the solar panels, with a panel-to-inverter ratio of around 1.0 to 1.3, because the panels rarely produce their full power output in hot conditions. For a 13.6 kW solar panel system, a 12 kW or 15 kW inverter is generally suitable.
2. Single-phase or three-phase: The meter determines this. Bills help you understand your subscription type; details are in the article. Single-phase or three-phase inverter.
3. Surface area: A 550-watt panel covers approximately 2.6 square meters, but with row spacing on a concrete surface, it requires roughly double that. 25 panels would require approximately 110 to 130 square meters of clear surface area.

If you have a list of appliances instead of bills (such as a new, unoccupied house), the alternative method is to calculate the loads one appliance at a time, as described in the article. Calculating the size of your home's solar system.

Errors that disrupt the transfer from the invoice to the system

• Divide the amount by the approximate price per kilowatt-hour: The figure is inaccurate due to tiers and fees. Take your consumption directly from the bill.
• Forgetting about upcoming changes: A new addition, a swimming pool, an electric car, or replacing old air conditioners with inverter air conditioners will change the consumption.
• Expect the bill to become zero every month: Summer production is higher, but it does not keep pace with the surge in air conditioning consumption, as coverage is higher in winter and lower in summer.
• Neglecting shadows: A tank or wall that shades part of the panels reduces the production of the entire chain if it is not accounted for in the design.

After installing the system, you can compare the actual production with the calculations using the inverter application, as explained in the article. Monitoring system production from mobile. To find out when the system cost will be refunded based on the same invoice numbers, read How to calculate the payback period.

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