How many solar panels do I need to run an air conditioner? A practical calculation

Last updated: October 17, 2026

Running a 18,000 BTU split air conditioner on solar power during the day requires approximately 7 to 9 panels of 550 watts each, while a 24,000 BTU unit requires approximately 9 to 11 panels. The exact number depends on the air conditioner's actual capacity, operating hours, and your city. Running the air conditioner at night requires additional batteries and panels for charging. We will calculate both scenarios step by step.

Step 1: From thermal units to kilowatts

The numbers 18000 or 24000 BTU describe the cooling capacity, not the electricity the air conditioner draws. What matters in the calculation is the electrical operating power in kilowatts, which you can find on the air conditioner's label or in its manual.

As an approximate value:

• A 18000 BTU split air conditioner draws approximately 1.6–2 kilowatts during operation.
• A 24000 BTU split air conditioner draws approximately 2–2.6 kilowatts.

Inverter air conditioners typically operate at lower power levels, reducing their output once the room reaches the desired temperature. Conventional air conditioners operate at full power, then switch off and resume operation.

Step two: Calculate your daily energy intake

Energy = Power × Number of operating hours. For example: an 18,000 BTU air conditioner with a power of 1.8 kW, operating for 10 hours a day in a house in Riyadh or Qassim.

Daily energy = 1.8 × 10 = 18 kilowatt-hours.

This is a conservative estimate, as it assumes the air conditioner operates at full capacity for ten hours. In a well-insulated room, actual consumption will be lower, especially with an inverter air conditioner. However, the design, even under the most demanding conditions, ensures the panels will be sufficient on hot summer days.

Step three: Calculate the capacity of the panels and their number.

We use the standard equation: Daily energy ÷ Daily kWh production ÷ (1 − losses). We assume an average production of 5.5 kWh per kWh per day, and losses of 20%.

1. 5.5 × 0.8 = 4.4 net kilowatt-hours per kilowatt of panels per day.
2. 18 ÷ 4.4 = 4.09 kilowatts from the panels.
3. 4.09 ÷ 0.55 = 7.4, rounded up to 8 panels of the 550W class, i.e. 8 × 0.55 = 4.4 kW.

If your location is less productive (4.5): 18 ÷ 4.5 ÷ 0.8 = 5 kW, or 5 ÷ 0.55 = 9.1 kW, you will need 10 panels. In an excellent location (6): 18 ÷ 6 ÷ 0.8 = 3.75 kW, or 7 panels.

Quick schedule for split air conditioners (daytime operation 10 hours)

The calculation is based on a production of 5.5 and a loss of 20%, i.e., a net 4.4 kWh per kWh:

Note that a high-efficiency 24,000 BTU air conditioner might require the same number of panels as a standard 18,000 BTU unit. Therefore, the air conditioner's efficiency itself is a crucial factor in the decision, not just the number of panels.

Are the panels sufficient to power the air conditioner instantly?

Daily power consumption isn't the whole story. The panels must deliver more power at any given moment than the air conditioner requires. Eight panels with a nominal capacity of 4.4 kW might lose power during the midday heat (12–18%), delivering approximately 4.4 x 0.82 = 3.6 to 4.4 x 0.88 = 3.9 kW before losses due to cables and inverter. This is clearly higher than the 1.8 kW the air conditioner needs.

However, in the early morning and before sunset, production is low and may not be enough to run the compressor. In a grid-tied system, the grid automatically compensates for the shortfall. In a stand-alone system, batteries supplement the power. For a deeper understanding of the effect of heat, read the article The effect of heat on panel production.

What if you want to run the air conditioner at night?

Nighttime operation requires batteries that store energy during the day, and additional panels to charge these batteries. Continuing with the same example: a 1.8 kW air conditioner operates for 8 hours at night.

battery capacity

• Nighttime energy = 1.8 × 8 = 14.4 kWh.
• With lithium phosphate (LiFePO4) batteries with a depth of discharge of 80–90%: 14.4 ÷ 0.9 = 16 to 14.4 ÷ 0.8 = 18 kWh.
• With the efficiency of the 95% inverter: 16 ÷ 0.95 = 16.8 to 18 ÷ 0.95 = 18.9 kWh approximately.

Gel or lead-acid batteries are recommended to have a discharge depth of only about 50%, meaning they require a much higher nominal capacity for the same application. Details are available in the article. Calculating battery capacity.

The tablets are for both day and night.

The energy drawn from the battery at night must be recharged first, with a charge loss we assume to be 5%: 14.4 ÷ 0.95 = 15.16 kWh. The daily total = 18 (daytime) + 15.16 (for battery charging) = 33.16 kWh.

The panels' power output = 33.16 ÷ 4.4 = 7.54 kW, or 7.54 ÷ 0.55 = 13.7 kW. Therefore, we need 14 panels of the 550-watt category with a total output of 7.7 kW. Compare this to just 8 panels for daytime operation: the need nearly doubles at night.

Factors that reduce the number of panels required

Before increasing the number of panels, consider reducing the load itself. Every kilowatt-hour you save on your air conditioner means fewer panels and smaller batteries.

• Isolation: Insulating the roof and walls and shading the windows facing the sun significantly reduces the compressor's operating hours.
• Temperature control: Every degree lower in the air conditioner setting means longer operation, so choose a comfortable temperature, not too cold.
• Air conditioner maintenance: Clogged filters and a dust-covered condenser increase electricity consumption for the same cooling.
• Pre-cooling: Turn on the air conditioner at peak solar production time, so that the room enters the afternoon cool.

More than one air conditioner?

Add up the daily energy consumption of all the air conditioners and then apply the same equation. For example, two 18,000 BTU air conditioners with a power of 1.8 kW each for 10 hours during the day: 2 x 18 = 36 kWh, or 36 ÷ 4.4 = 8.18 kW from the panels, which is close to 10 kW system If you add the rest of the house's load, and for more options in cooling homes and buildings, see the section... HVAC.

If you prefer a quick calculation, enter your air conditioner's capacity and operating hours in Solar Energy Calculator To get an initial estimate.

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