Calculate the surface area required by solar panels in 6 simple steps

All of us have space constraints and have limited shed-free roof area for one reason to another. Therefore, it is very important to know the surface area of the solar panels well in advance before installing them on the roof-top.

The surface area of the panels depends on your average monthly energy needs, and the daily sun peak hours in your region.

"The over-sized panels may not fit in your roof-top while the small-sized panels can leave your space under-utilized"

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Here are the 6 simple steps of calculating the surface area of the panels.

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Step 1: Calculate your energy requirements

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Let me tell you the simple way of estimating the your average daily energy consumption in terms of units of electricity.
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1. Take out your previous month electricity bill and find the number of units consumed in that month. Your energy consumption will be different in different months of the year. Therefore, take out the utility bills of the last 12 months and add all the units consumed in that year.
2. Then divide the results by 12 days to get average monthly units consumption.​
3. On further dividing it by 30, we get the average daily units consumed.

Let us understand with the help of an example:

Determine the feasibility of your solar roof CLICK HERE!

In the above table, you can see that the average daily consumption is 11 units or 11 kWhr of energy.

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Step 2: Know the average daily solar insolation in your region

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The solar insolation plays a very important role in determining the surface area of the panels.

A region receives good sunlight will require less panel area, to produce same number of electricity units, than that of region with less sunlight.

For example, a residential solar power system installed in Delhi/NCR (India) with 5.5 sun peak hours per day will require less panel area to produce same number of units than that a system installed in New York (USA) with average daily sun peak hours of 4.33.

Well, there are many places in USA which receives more sunlight than the places in India.
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You can check the solar radiations value from: 

https://pvwatts.nrel.gov/pvwatts.php (National Renewable Energy Laboratory of the U.S. department of energy)

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Step 3: Calculating the ideal power of the panels

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After getting the average daily solar insolation or the daily peak sun hours of your region, divide your average daily consumption by it.

Read: How to size the panels of your solar power system?

I am taking the example of Delhi/NCR, in this particular case the ideal power of the solar panels is 11 kW-hr/5.5 hours = 2 kW or 2000 watts.

This is the ideal power (when there are no losses) of the panels which is required to meet your energy needs.

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Step 4: Calculating the actual power required from the panels

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We are living in the real world and we cannot ignore the losses in the system.

The 2 kW solar panels will not produce 11 kw-hr of energy because some of their power will get lost during energy conversion,  transmission and heat loss to the surroundings.

Read: What are the significant losses in the solar power system?

In order to meet the energy demand, we need to slightly increase the power of the panels to compensate for the said losses.

I am simply multiplying the ideal power of the panels by factor 1.4 to compensate all the losses in the solar power system.

In the example, the real power of the panels become 2000 watts x 1.4 = 2800 watts.

Now, the 2800 watts panels will meet the required energy of 11 kW-hr.

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Step 5: Get the standard dimensions of the solar panels

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At this point, it is important to know the standard dimensions of the solar panels available in the market.

The dimensions of one panel will help us in calculating the total surface area of the panels required to meet the energy demand.

LG 350 watts solar panel

You can see that the size of 350 watts LG solar panel is 1700 mm (length) x 1016 mm (width) x 40 mm (height).

The height of the panel is of least concern while determining its surface area.

The size of the 350 watt solar panel in feet can be written as:

5.58 feet (length) x 3.33 feet (width)

*(1 metre = 3.3 feet)

We need 2800 watts of solar panels. Therefore, number of 350 watts solar panels to add to 2800 watts are 2800/350 = 8 numbers.

The even numbers of panels are preferred while designing the solar power system as it is easy to make series and parallel combination.

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Step 6: Find the surface of the solar panels

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Now, the total surface area of the panels is the surface area of 1 panel multiplied by the numbers of panels.

In our case, it is:

{5.58 feet (length) x 3.33 feet (width)} x 8 
= 18.58 x 8
= 148.65 square feet

​​Further, it is a practice to leave some gap between the panels, so that air can pass through and keep them cool in summers.

Therefore, increase the total surface area by 2.5% to adjust the gaps.

Now, it becomes 148.65 sq. ft x 1.025 = 152.36 sq. ft.

Finally, 152.36 sq. ft. is the total surface area of the panels and the air gap which is required on the roof-top to meet the daily energy demand of 11 kW-hr.

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A final note

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Measure the shed-free area of your roof-top in advance. 

If the shed-free area is less than the surface of the panels then it is not feasible to install them on the roof-top.

You should cover your roof-top in such a way that even after installing the panels, you are still left with sufficient free space to do cleaning and maintenance of the system.

Condition: If  the Actual number of solar panels that can be fitted completely in the given area >= Required number of solar panels, then consider that power of solar panels for installation otherwise reject it.

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