How Many Solar Panels Do I Need?

1. Calculate your daily electricity needs

To understand how many solar panels you need to power your home, you first need to calculate your daily electricity consumption.

Check past energy bills to find out how much electricity your home uses. These will tell you how much electricity you have used over a certain period of time in kilowatt hours (kWh), depending on how often you are billed (for example, monthly or quarterly).

If you are billed monthly, you will have to divide your electricity consumption by 30 kWh; if you are billed quarterly, you will have to divide the figure by 90, and so on. A house in the UK with a monthly electricity consumption of 320 kWh, will use about 11 kWh of electricity per day (320 / 30).

2. Calculate the average number of hours of sunshine per day in your area.

This information is quite difficult to get, but fortunately, the Met Office has calculated the average number of hours of sunshine per day in the UK for each month, so you won’t have to sit outside and count them yourself!

Obviously the number of hours of sunshine per day varies each month, so it is best to take an average for the year.

Based on the available data, in the UK, the house used in the previous example receives about 4.5 hours of sunshine per day throughout the year.

3. Calculate the average power of a solar panel using the hours of sunshine

Once you have calculated the average number of hours of sunlight your home receives per day, you can determine how many solar panels you will need.

This will depend on how much power you get from the solar panels. Power determines the amount of electricity a solar panel can produce. Solar panels range in size from about 240 watts per panel to 370 watts.

To calculate the amount of electricity produced by a solar panel, you need to use the following multiplication: hours of sunlight per day x the output of the solar panel.

Normally, an average solar panel is about 300 watts, so in our example we will use this figure. A 300 watt solar panel will produce 1,350 watt hours, or 1.35 kWh of electricity per day (4.5 x 300). This is based on a house in the UK that receives about 4.5 hours of sunlight per day.

4. Divide the electricity output of a solar panel by the daily electricity consumption

To calculate the number of solar panels your home needs to cover 100% of its electricity consumption, simply divide the daily electricity consumption by the daily electricity production of one solar panel in kWh.

For example, according to our example, if a house consumed 11 kWh of electricity per day, it would need to install 300-watt solar panels to produce enough energy (11/1.35).

Final Thoughts Working with these measures will give you an idea of how many solar panels you will need to install to power your home.

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