You have a terrace or a metal roof and wonder how many solar panels can you fit in there and how much savings in electricity bill will you get from those solar panels, then you have come the right place.
In this article we will see how much roof area is needed to install solar panels and learn to calculate rooftop area for solar system.
As a rule of thumb we can install 1 kW of solar panels in 100 sq.ft of shadow free area on a RCC roof.
On a metal shed 1 kW of solar panels can be installed in 85 sq.ft of shadow free area.
Calculate rooftop area needed to install solar system:
Before we calculate area needed to install solar system we need to know the number of solar panels needed for your house. Here is a short explanation to calculate solar panels requirement of any house.
How many solar panels does my house need:
Your house solar requirement depends on your average monthly consumption of electricity (kWh).
To calculate this have a look into your latest electricity bill there you will find a table that shows your unit consumption in the last one year.
Once you find your annual power consumption data then follow the steps below.
- Take average of your monthly consumption that will be your monthly average consumption.(Average = Sum of values / No of Values).
- Then divide this average unit consumption by monthly solar generation from 1 kW system, this should give you your house solar requirement in kW. (I live in India here average power generation from 1 kW solar panels is 115 kWh, If you don’t know solar generation in your area then take 100 kWh for calculation purpose).
- Then divide this kW of solar with wattage of one solar panel, you will get the total number of solar panels your house needs.
Let’s see an example, Jason’s house last 12 month electricity consumption is 400,300,512,415,300,125,588,452,300,700,500,547 so how many solar panels will Jason need for his house?
- First let’s take an average of all the values to get the average monthly consumption, this turns out to be 428 KWH.
- Second step is to divide this monthly consumption by our 1 kW solar panels monthly generation (115 kWh), this will give us 3.72 kW of solar.
- Third step is to divide this 3.72 kW with wattage of one solar panel (lets use 330 Wp solar panel). On calculation we get 11.27 ~ 11 or 12 Solar Panels.
There it is Jason’s house needs 3.72 kW of solar or 12 solar panels each of 330 Wp to offset 90 % of their electricity bill.
Now that you know your solar panels requirement, let us see what is the dimension of one solar panel and area needed to install one solar panel.
The size of a solar panel depends on its wattage and cell configuration. A 100 watt solar panels will be smaller in size when compared to a 350 watt solar panel because it has more solar cells.
Most solar panels used in 2020 for residential, commercial and industrial solar projects have rated power of above 300 watt peak (Wp).
The standard size of a solar panel is:
- The size of a 250 watt solar panel with 60 cell configuration is 39 inch X 66 inch (3.25 ft X 5.5 ft).
- The size of a 330 watt solar panel with 72 cell configuration is 39 inch X 77 inch (3.25 ft X 6.42 ft).
- The thickness of both 6 cell and 72 cell solar panel is around 40 mm..
So if we do the math, the surface area of one 330 watt solar panel is equal to 2 sq.meter or 21.51 sq.ft (Area of a rectangle = Length X Breadth).
The below table shows size and weight of a 330 watt solar panel.
Size And Weight of 72 Cell 330 Watt Solar Panel:
| Solar Panels | Size | Weight |
| Canadian solar Dymond Series | 1968 X 992 X 58 mm | 27.5 kg |
| Vikram Solar Eldora Grand Series | 1955 X 991 X 40 mm | 22 kg |
| Waaree Solar Aditya Series | 1960 X 990 X 40 mm | 22.5 kg |
| Trina Tall Max Series | 1956 X 992 X 40 mm | 22.5 kg |
| Jinko Solar Panels | 1956 X 992 X 40 mm | 26.5 kg |
Rooftop area needed to install solar system:
Once you know the number of solar panels you need to install then use the below formula to calculate the area needed to install it.
Area required for solar panels = Total number of solar panel x area of one panel.
For example for a 7.5 kW system has 23 solar panels each of 320 watts which means area needed to install 7.5 kW of solar panels is,
Area for 7.5 kW of solar panels = 23 x 21.50 = 495 sq.ft
This is just the area required to mount all the solar panels back to back and side by side to each other.
In real life we have to leave space between rows and columns of solar panels so that we can easily clean the solar panels every now and then, and also have safe access to perform maintenance if and when needed.
You can use the table below to get a rough idea on how much rooftop area is needed to install solar panels.
| Solar System Size | No Of PV Panels (330 W Each) | Area Required |
|---|---|---|
| 1 kW Solar System | 3 | 65 sq.ft – 90 sq.ft |
| 2 kW Solar System | 6 | 145 sq.ft – 180 sq.ft |
| 3 kW Solar System | 9 | 205 sq.ft – 270 sq.ft |
| 5 kW Solar System | 12 | 285 sq.ft – 450 sq.ft |
| 8 kW Solar System | 25 | 580 sq.ft – 720 sq.ft |
| 10 kW Solar System | 30 | 750 sq.ft – 900 sq.ft |
In the area column the values on the left indicates the minimum area you will need to install those many solar panels and the values on the right indicates ideal area you will need to install those many solar panels keeping in mind the cleaning and maintenance space.
The area should be shadow free area, meaning this area should receive direct sunlight for at least 5 hours in a day ideally between 10:00 am to 04:00 pm.
How Much Power Does 1 kW Of Solar System Produce:
The generation from solar panels totally depends on the number of hours your region receives sunlight in a day and the number of such sunny days in a year.
I live in Mumbai, India we are blessed with over 5 sun hours in a day and around 300 such days in a year, hence going solar makes sense and power generation is good hence low ROI.
In India, on an average 1 kW of solar panels produces 4 kWh of electricity in a day, 115 kWh of electricity in a month, 1,380 kWh in a year .
This value goes up by 15 – 20% in the summer season, and goes down by 30 – 40% in rainy season and 10 % during winter season.
So taking an average of all the seasons we can take monthly solar panels generation as 115 kWh.
You can check out this article by EAI to know more – Factors affecting rooftop solar output
You can refer the below table to get an idea on monthly generation from solar system. This data is only for India, here we have almost 300 sunny days, if you live in a place where you get around 300 sunny days then use it or else data will vary.
| Solar System Size | Monthly Generation |
|---|---|
| 1 kW Solar System | 110 kWh |
| 2 kW Solar System | 220 kWh |
| 3 kW Solar System | 330 kWh |
| 5 kW Solar System | 550 kWh |
| 8 kW Solar System | 880 kWh |
| 10 kW Solar System | 1110 kWh |
Monthly Savings In Electricity Bill from 1 kW Solar System:
Now lets talk out money, how much electricity bill can you expect to save from 1 kW of solar. Will it save all your bill or just 10 % of it lets find out.
If we calculate the savings in electricity bill by installing 1 kW of solar then you the following equation.
Monthly savings from 1 kW solar = kWh generated by solar in a month X Electricity tariff (Rs/kWh).
(Tariff is the amount your electricity provider charges you for one unit (kWh) of electricity. I live in Mumbai here tariff is Rs 11/kWh. If you don’t know then just divide your monthly electricity amount by your monthly electricity consumption both can be found on electricity bill.)
Monthly Savings from 1 kW solar = 115 X 11 = Rs 1,265.
So there it is 1 kW of solar panels can save upto Rs 1,265 in a month if you live in places which receives 5 sun hours in a day and 320 such days in a year.
If the electricity tariff in your area is less then savings will be less and can be easily calculated the same way.
You can refer the below table to get an idea about solar system generation and savings in electricity bill from it. I have assumed tariff of Rs 10 for this calculation which is average in India
| Solar System Size | Monthly Generation | Monthly Savings |
|---|---|---|
| 1 kW Solar System | 110 kWh | Rs 1,110 |
| 2 kW Solar System | 220 kWh | Rs 2,220 |
| 3 kW Solar System | 330 kWh | Rs 3,330 |
| 5 kW Solar System | 550 kWh | Rs 5,550 |
| 8 kW Solar System | 880 kWh | Rs 8,880 |
| 10 kW Solar System | 1110 kWh | Rs 11,000 |
Conclusion on area needed for solar system:
We can install 1 kW of solar panels in 100 sq.ft of shadow free area, that is 3 solar panels each of over 300 watt in 100 sq.ft of shadow free area.
1 kW of solar panel will produce an average of 115 kWh of electricity in a month, if the solar panels installation is done correctly and your region receives 5 sun hours in a day and 320 such days in a year.
Remember the generation from solar panels is heavily sacrificed if the solar panels are installed under shadow.
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Reference:
- To know more about sun hours –http://wgbis.ces.iisc.ernet.in/energy/paper/hotspots_solar_potential/results.htm
- To calculate sun hours – https://www.solarpowerauthority.com/how-to-calculate-your-peak-sun-hours/
- To calculate ideal angle of inclination for solar panels – http://www.solarpaneltilt.com/
- https://mnre.gov.in/sites/default/files/schemes/Benchmark%20Order%20FY%202019-20.pdf
