Solar energy calculator explained: From your device list to panel size, inverter, and battery size

Last updated: October 20, 2026

The solar energy calculator on the MITS website transforms your list of devices and their operating hours into a suggested system: the panel capacity in kilowatts peak and their number, inverter capacity, battery capacity if needed, and the expected annual production in your city. You start by selecting the system type, then the city, then add the devices, and the result appears instantly with an explanation of how the calculation was made.

What exactly does the solar energy calculator calculate?

The calculator answers four questions that anyone thinking about solar energy would ask:

• How many kilowatt-hours do I consume per day? From the total power of the devices × operating hours, taking into account the actual operation of devices whose compressors operate intermittently, such as refrigerators and air conditioners.
• How many boards do I need? Daily consumption divided by peak solar hours in your city, with a margin for losses.
• What is the transformer's capacity? From continuous load and the highest load at the moment of device startup, with a reduction in temperature.
• What is the battery capacity? From nighttime consumption, permissible discharge depth, and transformer efficiency.

First step: Choose the system type

If you're unsure about the differences between the systems, read the article The difference between On-Grid, Off-Grid and hybrid systems Before we begin.

Step two: City, subscription type, and installation method

Select the city from the list, and the calculator will display the city's peak solar hours and annual kilowatt-hour peak (kWh) production. For example, in Riyadh, the calculator displays 6.1 peak hours per day and an approximate annual production of 1,840 kWh per kWh.

• Subscription type (Residential, Commercial, Agricultural, Government): Affects the financial savings account.
• Installation method: Inclined at the ideal angle towards the south, or almost flat with a slight slope. The ideal angle yields higher production; details are in the article. Best orientation and tilt angle for panels.
• Available space (Optional): If you enter them, the calculator will alert you if they are not sufficient for the suggested panels.

Step three: Add your devices and their operating times

For each device, you can enter its power in watts, the number of devices, daily operating hours, and operating time: night, day, or both. The list includes pre-installed devices (LED lighting, refrigerator, split and window air conditioners, television, washing machine, water heater, pumps), and you can add any other device.

Why is runtime important? Because what operates during the day is powered directly by the panels, while what operates at night requires energy stored in batteries. A single device operating for extended periods at night can double the size of the batteries.

In the technical settings, you can adjust the actual operating ratio for compressor-equipped devices, and the starting current for devices that draw higher power at the moment of operation.

Illustrative example: A small house with a hybrid system in Riyadh

This is the default example that appears when you open the calculator; the numbers are approximate:

The total is approximately 11.1 kilowatt-hours per day. Note that the refrigerator and air conditioner are not calculated at full capacity all the time, because the compressor switches on and off.

How did the computer arrive at the proposed system?

1. Panels: It proposed 3.23 kW peak, i.e., 5 panels with a power of 645 watts, requiring approximately 24 m² and producing about 5,933 kWh per year.
2. Converter: The continuous load was 1.57 kW, and the peak load at startup was 5.17 kW. After reducing the heat and fluctuation margin, the required power was at least 4.31 kW, so a 5 kW transformer was chosen. The transformer can typically handle 1.5 times its rated power for a few seconds during startup.
3. Batteries: Nighttime consumption requires 6.3 kWh of storage, and after dividing by the depth of discharge of the 90% and the efficiency of the 95% transformer, the suggested capacity of lithium phosphate batteries is 7.4 kWh.

In the storage option, you can increase the reserve from «night only» to one or two days without sunlight, and the battery capacity increases accordingly.

How do you read the results and graphs?

• Monthly production versus consumption: It explains that production increases in the summer and decreases in the winter, so you know the months when you might need the grid or generator.
• System components: Panels, converter, and batteries, with a line explaining the battery calculation.
• Financial analysis: Estimated cost, savings, and payback period based on subscription type; these are hypothetical figures that change according to market prices and your tariff.
• Complete your project: Links transfer the number of panels directly to Solar Mounting Structure Calculator, and the project cables to the cable tray calculator.

Common mistakes when using a calculator

• Enter the air conditioner's capacity as shown on the label, in thermal units: Enter the electrical power in watts, not the cooling capacity.
• Forgetting about night vision devices: Such as cameras, routers, and outdoor lighting; they are small but operate for long hours.
• Choose one or two days as a backup if needed: This significantly increases battery size and cost. Only choose it if a prolonged power outage is a real possibility.
• Ignore the space: Make sure the surface or ground is sufficient, and pay attention to shadows from tanks and walls.

For those who prefer manual calculations, the method is explained in detail in an article. How do I calculate the size of my solar system?Battery calculations are discussed in the article. Calculating battery capacity for nighttime operation.

Frequently Asked Questions