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How to Calculate the Number of Panels for a Load without Battery Backup?

How to Determine the Number of Solar Panels to Run a Specific Load without Battery Backup

If you need to calculate the number of solar panels for an appliance like an air conditioner, water pump, or fan to run during the day without battery backup, this article will help. It provides step-by-step calculations to determine how much power your solar panels will produce at different times of the day. This step-by-step guide will help you find out how many solar panels you need to run your electrical device during the day, especially without battery backup power.

Determine the Number of Solar Panels to Run an AC without Battery Backup

Good to know: This calculation is based only for running a load purely on solar panels without using a battery backup. If you need to determine the full setup, refer to the previous articles about Solar Panel Installation. Step by Step Procedure with Calculation & Diagrams.

How Many Watts Does My Solar Panel Produce Based on Sunshine During the Day?

This question is frequently asked: how many panels are needed for an AC without a battery? Let’s learn how to design it today. But first, we need to understand some facts about solar panels, which are as follows:

1. Solar panels produce their rated power (the wattage written on their nameplate) only when sunlight falls directly perpendicular on them. The output efficiency of the solar panel is highest during this time period. This happens only for a short time around noon when the sunlight is at its peak.

If is the power output in watts written on the solar panel, the actual power produced will depend on the angle at which sunlight hits the panel. Hence, if we need to determine the power a panel will produce at a specific time, the formula will be:

P = W × sin ⁡(θ)


  • P is the power produced by the panel,
  • is the power written on the panel,
  • is the angle of sunlight on the panel.

2. Another factor is atmospheric pollution, such as light clouds, which can reduce production.

3. The third factor is the panel getting heated by sunlight, reducing production when the temperature exceeds 50°C.

5. Fourth, it is impossible to keep the panel clean all the time, which reduces production.

5. Lastly, as the solar panel ages, its production decreases. On average, production decreases by 1% per year.

Due to reasons two, three, and four, in areas where sunshine for roughly 10 hours a day, even in summer, solar panels produce on average only 80% of the written power. If clouds are dense, production can drop below 80%. The given calculations assume minimal clouds, allowing visibility of the sun. You can also see this fact in the graph below, indicated by the red arrow on the curve.

This means that if we want to determine the power a solar panel will produce at different times of the day in summer, it will be 80% of the power calculated using the above formula:

PV Formula (1)

Let’s now use this formula to calculate the power a 550-watt panel will produce from 8 AM to 8 PM:

  • At 8 AM: very minimal
  • At 8:30 AM, angle 9 degrees, thus:

PV Formula (2)

  • At 9 AM, angle 18 degrees, power:

How Many Watts Does My Solar Panel Produce Based on Sunshine During the Day


Time Power Produced
8:00 AM Very minimal
8:30 AM 69 watts
9:00 AM 136 watts
9:30 AM 200 watts
10:00 AM 259 watts
10:30 AM 312 watts
11:00 AM 356 watts
11:30 AM 392 watts
12:00 PM 418 watts
12:30 PM 435 watts
1:00 PM 440 watts
1:30 PM 435 watts
2:00 PM 418 watts
2:30 PM 392 watts
3:00 PM 356 watts
3:30 PM 311 watts
4:00 PM 259 watts
4:30 PM 200 watts
5:00 PM 136 watts
5:30 PM 69 watts
6:00 PM Almost negligible

How Many Solar Panels Do I Need to Run an Electric Appliance without Battery Backup?

Suppose, we need to run an air-conditioner purely on solar panel without using battery backup power. For this reason, we need to understand two things about running an AC on PV panels:

  1. The time period during which we need to run the AC.
  2. The power consumption of the AC per hour.

Suppose we need to run a 1.5-ton (1800 BTU) inverter AC from 10 AM to 4 PM. If you refer to the chart or graph given above, a 550-watt panel produces only 259 watts at 10 AM and 4 PM. It produces more power during other times between 10 AM and 4 PM.

When the AC starts, it takes its maximum load, which is 1750 watts for a 1.5-ton AC.

Here, I want to clarify that when you check the inverter AC current with a clamp-on meter, it shows 3 to 4 amps, but this reading is incorrect because the clamp-on meter is designed for a pure sinusoidal wave of 50 Hz, while the inverter AC output is a modulated wave. The fundamental appears as a sinusoidal wave, but it is a combination of high-frequency waves. At high frequency, the clamp-on meter’s cores get saturated, showing a very low reading. Therefore, remember that the initial load of the AC is 1750 watts, taking about 8 amps of current.

Now, it is established that our load is 1750 watts, while we get 259 watts per panel. Thus, the total number of panels needed:

No. of panels = 1750 ÷ 2596.75 panels i.e., 7 panels.

If the AC needs to run from 11 AM to 3 PM, we get 356 watts per panel at 11 AM and 3 PM. Thus,

No. of panels = 1750 ÷ 356 i.e., 5 panels are required.

Similarly, you can calculate the number of panels for other loads, such as fans, water pumps, and other applications without backup power from batteries, using the chart, calculations, and formulas given above.

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