How to calculate number of Solar Panels for home?

Are you planning for a solar rooftop? If yes, then you may need to know – how to calculate number of solar panels for home?

In this article, I would give you step-by-step guidance on this.

Before we move further with the calculation, it is necessary to know some basics.

• Watt and kilowatt are units of power. 1 kW = 1000 watts. If you have 750 watts of the motor then it is 0.75 kW.
• 1 unit = 1 kWh. This means if 1000 watts of heater runs for 1 hour then it will be 1 kWh i.e., 1 unit. Another example, if 85 watts of fan runs for 24 hours then 24 hrs X 85 watts = 2040 watt-hours or 2.040 kWh i.e., 2.04 units consumed in 24 hours.

How many units 1 kW of solar panel will produce?

To calculate the number of solar panels needed for your rooftop, you must know how many units 1 kW of solar panels can produce.

In India we receive, 5 sun hours per day. If you have 1 kW of a solar panel it will generate 1 kW X 5 hours = 5 kWh. Remember this is an ideal condition. There are various factors on which solar panel generation depends and can be talked about separately.

Also, not all days we get uniform sunlight. In monsoon season we have cloudy days as well. Additionally, some days panels would be free from dust, and some days they won’t. Keeping all these things in mind the majority of solar panel manufacturing companies assume 20% power loss.

So, 1 kW solar panel would generate 1 kW X 4 hours = 4 kWh.

1 kW solar panel has three photovoltaic panels, each of 330 Wp.

Each 330 Wp panel will produce 330 Wp X 4 hours = 1.32 kWh.

How to calculate number of solar panels for home?

Let’s move further with the calculation of the number of solar panels required for your rooftop.

Follow the below steps,

Method #1

Step 1: First collect the electricity bills for the whole year. Yes, the whole year I am saying – from January to December. Make sure it should be the previous year.

Taking immediate previous year covers all the seasons. Electricity consumption is not the same in all seasons. You won’t use air conditions in winter. So, taking whole year gives close behavior of your electricity consumption.

Step 2: Note down the total units i.e., kWh consumed in each month.

Step 3: Add up all the units and divide them by 12. You will get an average kWh / month.

Step 4: Now that you know 1 kW solar panel produces 4 kWh, so in a month it will generate 120 kWh. simply divide average kWh / month by 120 kWh. You will get kW of solar panels.

Step 5: Multiply the kW of solar panels with 1000. Then divide it by 330 Wp.

You will get the number of solar panels required for your house.

(Calculation example given after method #2).

Method #2

Step 1: Collect the electricity bills for the whole previous year.

Step 2: Note down the total units i.e., kWh consumed in each month.

Step 3: Add up all the units and divide them by 365 (we have 365 days in a year). You will get an average kWh per day.

Step 4: Now that you know 1 kW solar panel produces 4 kWh, simply divide average kWh / day by 4 kWh. You will get kW of solar panels.

Step 5: Multiply the kW of solar panels with 1000. Then divide it by 330 Wp. You will get the number of solar panels required for your home.

Example

Let us understand the calculation with an example for better clarity. A house consumes electricity each month as shown in the table below.

Calculation as per Method #1

Summing up all we get a total of 5438 kWh.

Dividing it by 12 we will get monthly average consumption.

Monthly average consumption = 5438 kWh / 12 = 453.16 kWh rounding off to 454 kWh.

1 kW of solar panel produces 120 kWh / month.

Total kW of Solar panel required = 454 / 120 = 3.78 kW

One solar panel is 330 Wp.

Number of Solar panel required = (3.78 kW X 1000) / 330 = 11.46 ≈ 12

The Total Number of Solar Panels required for this house is 12.

The total kW of Solar Panel required is 3.78 kW.

Calculation as per Method #2

Summing up all we get a total of 5438 kWh.

Dividing it by 365 days, we will get per day average consumption.

One day average consumption = 5438 kWh / 365 = 14.90 kWh

1 kW of solar panel produces 4 kWh / day.

Total kW of Solar panel required = 14.90 / 4 = 3.725 kW

One solar panel is 330 Wp.

Number of Solar panel required = (3.725 kW X 1000) / 330 = 11.29 ≈ 12.

The Total Number of Solar Panels required for this house is 12.

The total kW of Solar Panel required is 3.725 kW.

You can see that in both the methods there is only minor variation.

Summarizing

In addition to the previous year’s energy consumption, you must also think about future additional loads. For example, you may require to add one or two air conditions. You may need a charging station for your electric vehicle in the future. Keeping this in mind you may require to increase the required kW of the solar panel by at least 20%.

However, if you know that no additional loads are going to get added, you can go as per the calculation.

Once you have your Solar Panel installed, you are not only saving few bucks but also reducing your carbon footprint.

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Have you done calculation for number of solar panels before? Share your experience in comment section below.

Go Solar! Save the Planet!