Solar Power Calculation – Formula In-depth Explanation And Examples

Solar Power Calculation

Solar power is one of the few affordable green energy options. Not only that, solar panels are compact and easy to travel with, and hence a great option for travelers. But there are a few solar panel calculations that you need to do before you set up a solar panel system for your house, office, or RV.

In today’s article, we have compiled some of the most basic solar panel calculations. Use these solar power calculations to find out the perfect solar panel system setup for your needs.

Without any further ado, let’s begin.

Solar Panel Size Chart

One of the biggest concerns customers have is the size of solar panels. However, contrary to popular belief solar panels come in tons of different sizes. The different size variants make it easier to buy a solar panel that is perfect for your property.

The two most common configurations for solar panels are 60 cells and 72 cells. The average size for one cell is 6 inches. A 60 cells solar panel is laid out as a 6 x 10 cells grid. Meanwhile, the 72 cells solar panels are laid out in a 6 x 12 grid.

Following are the dimensions for each of these solar panel configurations choose the one which suits your needs the most.

60-cell solar panel size: 39 x 66 inches (3.25 x 5.5 feet)

72-cell solar panel size: 39 x 77 inches (3.25 x 6.42 feet)

Moreover, 60-cells and 72-cells are the most common solar panel configurations, but some manufacturers also sell 96-cells solar panels. The size of 96-cells solar panels is below:

96-cells solar panel size: 41.5 x 62.6 inches (3.41 x 5.2 feet)

Note: Even though these are the standard sizes of commercial and industrial solar panels, the size may vary from manufacturer to manufacturer.

Cell Configuration Width (in inches) Height (in inches) Depth (in inches)
60-cells 39 66 1.3 to 1.6
72-cells 39 77 1.3 to 1.6
96-cells 41.5 62.6 1.38

Solar Panel Size Chart


Solar Power Calculation
Solar Power Calculation

How Much Solar Panel Power Load Wattage Do You Need?

Choosing the right solar panel can get tedious sometimes. Would 1x 60-cell solar would be enough for your RV or do you need to get 5 solar panels? However, once you know how much solar panel power you need you can easily calculate the numbers of solar panels you need.

Following is the formula to calculate how much solar panel energy you need.


Solar panel power calculation formula = You average load wattage x Hours per day x 1.5


  • Load wattage or simply wattage means the amount of electricity an electrical appliance uses.
  • Here, “hours per day” refers to the amount of time you are planning to use solar panel power.
  • The value 1.5 is used here to cover the working bugs of household electronics. In other words, not all TVs use the same wattage, the power needed varies from brand to brand. In cases like this, the 1.5 value reduces the chances of you running out of power.

Example #1

Assume you are getting solar panels for TV and fridge with 0.5 kWh and 1.0 kWh respectively. And you are going to use both of these appliances for 2 hours, then here is how much solar panel power you would need.

Solar panel power calculation formula = Average load wattage x hours per day x 1.5

= (0.5 + 1.0) x 2 x 1.5

= 1.5 x 2 x 1.5

Solar panel power needed = 4.5 kW


Example #2

If you are getting the solar panel for TV and fridge. But you use TV for 2 hours and fridge for 3 hours, then here is how you can do it

Solar panel power calculation formula = Appliance 1 (Average load wattage x hours per day) + Appliance 2 (Average load wattage x hours per day) x 1.5

= (0.5 x 2) + (1.0 x 3) x 1.5 = 1 + 3 x 1.5

= 4 x 1.5

Solar panel power needed = 6 kW


How to calculate the average load wattage you use?

If you want to calculate the solar panel power you need then it is crucial to know the average load wattage you use. But how would you calculate the average load wattage you use? Well, it is easy, and here’s how you can do it.

  1. Firstly, make a list of all of the appliances you are planning to use. For example, if you are buying solar panels to run a hairdryer and TV then add these appliances to your list.
  2. Secondly, look up the wattage or Wh of the appliances on your list. For example, the average wattage for a TV is 0 to 0.5 kWh. And average wattage for a hairdryer is 1.5 to 2.0
  3. Lastly, you can add the wattage for both of these appliances and get your hourly wattage load. (0.5 + 2.0 = 2.5)

Here is the average wattage per hour for some of the commonly used electrical appliances.

Electrical Appliance Watt per Hour (in kWh)
Fan 0 – 0.5
TV 0 – 0.5
Laptop 0 – 0.5
Game console 0 – 0.5
Microwave 0.5 – 1.0
Toaster 0.5 – 1.0
Vacuum Cleaner 0.5 – 1.0
Washing Machine 0.5 – 1.0
Electric Kettle 1.0 – 1.5
Fridge 1.0 – 1.5
Iron 1.0 – 1.5
Dishwasher 1.0 – 1.5
Hairdryer 1.5 – 2.0
TV Theater 1.5 – 2.0
Air conditioner 2.0 – 2.5


Solar Panel Wattage Calculation Formula?

Solar panel wattage is the amount of solar energy your system requires to produce to fulfill your needs. The formula for calculating the solar panel wattage needed is given below,


Solar panel wattage calculation formula= Total load wattage/5


We already explained above that total load wattage is the amount of electricity you use per day.

Moreover, the 5 represents the direct sunlight hours. As most countries get almost 5 hours of sunlight every day we are dividing the load wattage by 5.



Assume your total load wattage per day is 10kWh, this is how you would calculate your solar panel wattage needed.

Solar panel wattage = 10/5


It simply means that you need to get a 1 kW solar panel to produce enough power for your needs.


Solar panel output per day calculation

In order to know which solar panel and how many solar panels you need, it is important to know the wattage each solar panel produces. The formula to calculate the solar panel wattage is given below.


Solar panel output per day calculation formula = average output per hour x hours of direct sunlight x 75%


A 60-cells solar panel usually produces 270 to 300 watts per hour and a 72-cells solar panel produces 350 to 400 watts per hour. Furthermore, in most regions around the world, you can get at least 5 hours of direct sunlight all year round.

Considering the above data, how output does a 60-cells and 72-cells solar panel produce?

60-cells solar panel output per day = 300 x 5 x 75% = 1.125 kWh

72-cells solar panel output per day = 400 x 5 x 75% = 1.5 kWh

Usually, people get multiple solar panels at once. So, here is how you can calculate the entire solar panel system output per day.

“Solar panel system output per day = no. of solar panels x average output per hour x hours of direct sunlight x 75%”


For example,

6 x 60-cells solar panel system output per day = 6 x 300 x 5 x 75% = 6.750 kWh


Battery Amp Hours?

Battery Amp Hours, Amp-Hour, or Ah refers to the number of amps a battery can deliver in one hour. To get the battery amp-hours, use this formula,

Battery Amp Hour = (Solar Panel Wattage/Batteries voltages) x 1.2 x no. of direct sunlight hours

Solar panel wattage is the number of watts a solar panel can offer in an hour. It can be 100W, 200W, 500W, and so on.

Battery voltage is the amount of voltage a battery can provide. The most common battery voltages are 12V, 24V, and 48V.

The value 1.2 is multiplied by the amount to ensure perfect usage.

Lastly, the no. of direct sunlight hours may be different where you live. But most countries at least get 5 hours of direct sunlight in every season.



Battery Amp Hour = (200 W/12V) x 1.2 x 6

= 16.667 x 1.2 x 5

=100 Amp-hours


How to calculate solar panel battery and inverter size?

Calculating the size of the solar panel batteries and inverter is also an important task. solar panel battery size matters as during the nighttime there is no sun to power the solar panels. You do not want to get a battery that is not large enough o hold the amount of power you need during nighttime. You can calculate the solar panel battery size as shown below.

Solar panel battery size calculation formula= Avg wattage usage per night + (Avg. wattage usage per night x 30%)



You can find out the wattage usage per night by using a wattage monitor. Assume it is 5 kWh, so,

Solar panel battery size = 5 kWh + (5 x 30%)

=  5 + 1.6

= 6.6 kWh

Increasing the battery capacity by 30% is advisable as some days due to cloudy or rainy weather you might not get enough sunlight. So, this 30% extra energy comes in handy.

Calculating the solar panel inverter is one of the easiest solar power calculations. All you need to do is find out your solar array. Solar array refers to the amount of energy produced by 1 kW solar panels. Here’s the formula to calculate the solar array,

Solar array = Total solar energy produced per day/Solar panel wattage


Assume you have a 2 kW solar panel and the daily solar panel power production is 15kW, then,

Solar array = 15/2

Solar array = 7.5kWh

In general, it is advised to size the solar panel inverter at the same size as your solar array. So, in this case, the inverter would be 7.5kWh.



With that, we are at the end of our solar power calculations guide. In this article, you got to learn a few of the useful solar power calculations. So, use them when setting up a solar power system for your house, office, or RV.

For similar articles about solar power systems, batteries, portable generators, and more, check out our blog page. Peace out!

1 Comment

  1. New to solar and trying to learn. hope you can help.
    I have 21 panels of 230W and 9 panels of 300W. What is my solar array?


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