To find out how many solar panels your household needs, you need to calculate your electricity costs - we've created a step-by-step guide to help you do just that.
Step 1: How much electricity do you use?
For this to work, you'll need your electricity bill, whether it's a paper version or your online account. It will tell you how much electricity you use per month or per year. Use the annual figure or multiply your monthly expenses by 12 to determine how much you use. The energy used is measured in kWh. Now divide this number by 365 to get your daily dose.
Example: annual consumption = 3500 kWh.
3500 ÷ 365 = 9.6 kWh of usage per day (or 9600 Wh)
Step 2: How much electricity do you want your solar system to generate?
Determine how much annual cost of electricity you want your solar system to generate. As a general rule, the more energy a system produces, the higher its initial cost.
For this example, we've based our numbers on households wanting to get their energy entirely from solar.
Household electricity consumption per day = 9.6 kWh (9600 Wh)
Solar generated electricity demand = 100 percent
Step 3: How Much Sunlight Gets into Your Room?
You need to calculate how many hours of sunlight your home receives each day. Solar hours vary from day to day, month to month and region to region. The Met Office reports that the average number of hours of sunshine in the UK in 2021 will be 4.1.
3500 ÷ 365 = 9.6 kWh of usage per day (or 9600 Wh)
Solar generated electricity demand = 100 percent
Sunshine hours = 4.1 per day
Step 4: Power source the solar panel
Now estimate the output of each solar panel in the system. UK household panels range from 200W to 450W. In this example we will use a 350W panel.
Our daily energy consumption = 9.6 kWh (9600 Wh)
Solar generated electricity demand = 100 percent
Sunshine hours = 4.1 per day
Nominal power of the panel = 350 W
Step 5: How much will you earn?
Using these numbers, we can calculate our potential energy production per day. We will use this formula:
Solar panel power x average hours of sunlight x 0.75* = Wh per day
* We use a modifier of 0.75 to account for any variables such as the solar panel not facing exactly due south or being in the shade most days.
350 W × 4.1 hours of sunlight × 0.75 = 1076.25 Wh per day
Step 6: How Many Panels You Will Need
Now we need to determine how many panels we need for daily use. To do this, divide the amount of energy you use per day (calculated at the beginning of this process) by the amount of energy your system was able to produce in the previous step.
9600 Wh ÷ 1076.25 Wh = 8.92 panels
So in our 350W panel example, we need nine solar panels to produce enough power to meet our electricity needs. Keep in mind that you can sell unused electricity back to the grid, so we will consider installing 10 panels so that we can quickly recoup our investment.
