What size solar panel kit do I need?

Residential solar power kits are generally available up to 4kW (4000W) systems. As an example, the Plug-In Solar panel DIY kits available from Insulation Superstore start at 250W and rise in 250W increments up to the largest 4kW system. With 16 sizes to choose from in just this range alone, you may find yourself asking; ‘What size solar panel kit do I need?’.

With this in mind there are 3 key areas to consider when choosing the correct size Plug-In Solar Power kit.

  • How much electricity do you / will you use?
  • How big is the area where the panels will be installed?
  • Your budget?

How much electricity do you / will you use?

The most reliable point of reference for a retrofit solar kit will be the existing electricity bills for a property. Each home has a ‘base load’ which is the amount of energy used in an average day/week/month to power all the appliances in the property. You can work this out for your property by looking at your own electricity bills, or keeping records using your
electricity meter.

According to Ofgem, an average household with medium energy consumption uses between 3200 and 4200 kWh per annum. Taking the higher end of this scale (4200) and dividing by 12, the result is an average 350kWh per month. Calculate the daily average by dividing this number by 30, i.e. 350 ÷ 30 = 11.66kWh (rounded up to 12kWh). So, for example, if you want to cover half (50%) of your electricity costs using Solar Power, you simply multiply your daily average electricity usage by this percentage.

In the above case, 12kWh per day, therefore 12 x 50% = 6kWh. You will then need to know the average kWh per day each Plug-In Solar Kit generates. Make sure you refer to the manufacturers guidelines (when comparing, don’t forget that this can vary based on assumptions made in those calculations). A 250W Plug-In Solar Kit generates approximately 245kWh per year, that’s 0.67kWh per day (Please refer to this link http://www.pluginsolar.co.uk/plugin/downloads/Plug-In-Solar-Calculator.pdf for details of what this figure is based on).

This would mean that 9 x 250W solar panels, making up a 2.25kW (2250W) Solar Kit, are needed to cover an estimated 50% of the total average electricity costs for the example household. (9 x 0.67kWh = 6.03kWh). However, even if you have worked out that a 2.25kW Plug-In Solar kit is what’s required to meet your energy needs, the number of solar panels may need to be adjusted if there is not enough space to locate them. This is when we come on to stage 3:

How big is the area where the solar panels will be installed?

Plug-In Solar kits can be installed on tiled/slate pitched roofs, on a flat roof, or on the ground. The number of panels you can install may be limited by this available area, but please ask us for help with designing your system, so we can help you achieve the biggest possible system for your needs.

What size solar power kit will fit the available budget?

Your budget will ultimately dictate the size of the solar panel kit that can be purchased. A lower budget will require a compromise on the number of panels you can install. This means that the percentage of the energy costs covered by the panels will also be lower, but you will still make savings. As Plug-In Solar kits are modular in nature, it is possible to buy the kits incrementally, starting off small and building up a to bigger kit. This also helps to spread the cost across a few months/years. However, if the budget is higher and space allows, it is worth considering increasing the number of solar panels. This will maximise the levels of energy that the solar panels will generate for the property, resulting in bigger savings.

Extra Savings

In addition to installing solar panels, there are also a number of other ways in which you can save energy, or use energy more efficiently in your property, which will help you save even
more money on your bills. Such items include:

  • LED Lighting – You could save up to £240 per year: http://www.telegraph.co.uk/finance/personalfinance/householdbills/10756999/How-to-save-240-a-year-with-LED-lightbulbs.html
  • Energy Recovery Device – Energy Recovery Devices, such as Immersion Diverters allow you to divert any excess electricity from the solar panels to your immersion. This allows you to heat up your water with free electricity.
  • Batteries – Domestic battery systems allow you to capture energy from the solar panels that can be stored. The energy can then be used during darkness hours or periods of no sun.
  • Timer Switches – Modern timer switches allow the user to turn on appliances remotely. This enables you to run appliances more efficiently during times when the solar panels are producing the most energy.

Please note: The performance of solar PV systems is impossible to predict with certainty due to the variability in the amount of solar radiation (sunlight) from location to location & from year to year. The calculations above are estimates containing assumptions. Therefore they are for the purpose of illustration only, and do not constitute financial advice. If you are looking to power something bespoke, need a system that is larger than 4kW, or can run off grid, we can help. However, we recommend contacting our helpline to assist with these customised calculations.

For more information on any of the above, please contact our helpline on 01752 692 206. Alternatively, use the live chat in the bottom right hand corner.

Would you like to empty your basket?

Yes No


It seems you are running an older version of Internet Explorer. Our site does not support these old browsers as they do not house the technology that allows our site to be safe and secure.

If you wish to access our site please either upgrade your browser or download an alternative.