How Many Solar Panels Do Actually I Need?

solar-cells Going green can be somewhat of a challenging task, especially if you are trying to figure out just how many solar panels you need to meet your electric requirements.

Although you can hire a professional to work this out for you, it’s completely possible to do it yourself following these few easy steps.

How to Calculate the Number of Solar Panels

Electrical usage is measured in kilowatts per hour (kWh). Armed with this knowledge, your average daily electricity usage can be used to calculate roughly how many solar panels you actually need to cover your exact needs.

So, for example, if you use 1 kWh of electricity per day, your solar panels must be able to collect 1 kilowatt of solar energy per day in order to address 100% of your energy needs. Makes sense, right?

Here’s how you do it: 

kWh per day

1. Collect all your electric bills from the last so that you can add them all up.
2. Take this total and divide it by 12 to get your average kWh used per month.
3. Then, take your average monthly kWh and divide it by 30, the average days in a month. The total you get will give you a number for your average daily electrical usage in kWh…
4. With the average daily usage in hand, divide it by the average amount of sunlight hours your roof receives per day. This number should roughly be the number of kilowatts your system needs to produce enough power to cover your specific requirements.
5. Finally, take this number and divide it by the wattage of the solar panels you intend to purchase.

The answer you get will be the number of solar panels you require to meet your energy needs.

Now let’s try this calculation with some real numbers so it makes a little more sense.

For example, if your usage over 12 months equates to 9600kWh– this gives you a monthly average of 800kWh. Now divide it, the average days per month, and you’re left with a number of around 26.67kWh per day.

You now need to divide this number again by the average amount of sunlight hours your panels receive per day. Let’s make it 5 hours per day, just to be conservative.

So, assuming you have used 9600kWh over the last 12 months, the calculations will look as follows:

  1. 9600 kWh  ÷ 12 = 800 kWh per month
  2. 800 kWh ÷ 30 = 26.7 kWh per day
  3. 26.7 kWh  ÷ 5 (hours of sunlight per day) = 5.34 kWh

You have now established how much electricity your solar panels need to generate every hour to cover 100% of your needs.

To finally work out how many panels you require, you need to decide what wattage of solar panels you are going to use.


Assuming you are installing 200-watt (0.2 kW) panels, your calculation looks as follows:

5.34 kW ÷ 0.2 = 26.7 panels ( rounded up to 27 )

If you are opting for 250-watt (0.25 kW) panels, your calculation looks as follows:

5.34 kW ÷ 0.25 = 21.6 panels ( rounds up to 22 panels )

It makes more sense now, right?

What If I Don’t Want To Cover 100% Of My Needs?

You may not want your solar panels to cover 100% of your electrical consumption in a day, and that’s just fine. All this means is that you have a little more math to do…

solar-panel-sunlightTaking the numbers from the above calculation into consideration, decide just how much you actually want to settle for.

Let’s say you only want solar power to account for 70% of your requirements, you now take that 26.7 kWh and multiply it by 70%.

With 250-watt panels, the actual calculations will look like this:

  • 26.7 kWh per day x 0.70 = 18.69 kWh
  • 18.69 kWh ÷ 5 (hours of sunlight per day) = 3.74 kWh
  • 3.74 kWh ÷ 0.25 ( 250-watt panels) = 14.96 panels ( rounds up to 15 panels )

Again, this is a really simple calculation you can use to give you an approximate number of solar panels, but keep in mind that the solar panel’s efficiency rating and size have not been included in this scenario, and it may affect this number slightly. 

Why Should You Calculate Solar Panel Count?

Yes, it’s no secret that a contractor will also be able to tell you the exact number of solar panels that you may need. Why should you then even try to get this number when the professional can do it for you?

The answer is quite simple, really. Understanding.

solar-power-save-moneyCalculating the approximate number of panels makes the entire process easier. With this number, you will gain a better understanding of the solar project as a whole, and you will be able to create a budget and an approximate timetable around it too.

This will make the entire process easier once you start dealing with contractors. So, once the number of solar panels has been calculated, the next step is one of the most important of the whole project. You will start to vet potential contractors online. It’s extremely important to compare at least 3 estimates in order for you to establish which deal will suit your budget best.