After some searching for information on the amount of solar available, I worked out that they would pay for themselves in a little over 300 years. This was definitely a hobby project.
For 5 years my long suffering family put up with half of our house running off grid from a bank of batteries charged by solar panels during the day, and if we were lucky, powering the lights during the night.
The batteries were housed in the long wooden box in this photo and charged from the rooftop solar panels.
In 2010 the government introduced the Feed in Tariff. In October of that year, we swapped our home made installation (it was retired to power a narrow boat) for a system installed under the Feed in Tariff scheme. We had most of our SSE facing roof covered with panels, giving us a 3kW installation of 10 panels. In that year, I also started a small company to provide estimates on the cost and returns of solar and wind microgeneration RenSMART to installers and the public.
- 3kW peak output
- HIT Panels 20% efficiency
- Sunny Boy Inverter
- Roof Direction SSE
- Generated 23,800 Units (kWh) over 9 years
- Cost £10,500
- Pay back date - Two years ago
- System life - 25 years
The Feed in Tariff, from the outset, was intended to be an incentive to help reduce the cost of solar to a point where it no longer required an incentive to make it viable. In 2019, the Feed in Tariff ended. Any new installation after that point would not receive the Feed in Tariff. I have been asked many times recently if it still makes sense to install solar panels. This is the result of my investigation.
While the Feed in Tariff was in place, the government recorded the cost of installations, and this information is readily available and published up until 2019. Using information from 2019, you can work out the average cost of an installation for a particular size. A 3kW system like ours, would have cost £6000 in 2019, so quite a reduction, but would it be financially viable.
Financial Estimates if the same system was installed this year
Estimated Cost - £6,000
Generation Forecast 23,800 Units (kWh) over 9 years 
9 years - 50% of generation (deemed exported ) at 5.5p £650 feed in tariff 
9 years - 50% of generation (deemed used on site ) at 18p £2,140
£2790 / 8 years = about £350 / year
Pay back date just over 17 years
£8750 over 25 year system life
About 5% return per year
 Taken from our current installations performance
 Although the Feed In Tariff has ended, many electricity providers pay you for exported electricity. In this case we are basing the figure on the Octopus Energy Outgoing tariff
 As the measurement of exported electricity is rarely in place, the amount used in your house is taken to be 50% of generation
So it seems that the Feed in Tariff did achieve its target of reducing solar installation costs to make them financially viable without incentive.
What about the green house gas reduction ?
Having calculated the financial returns of installing solar, I’ve calculated the reduction in greenhouse gas emissions such an installation would achieve.
Our 3kW installation was generating an average 8 Units (kWh) per day.
Using data made available from the National Grid, we can calculate that if we had used grid electricity, 8 kWh would have caused the release of 2kg CO2 per day. That does not really mean much unless you know what reduction we as a population need to make.
The average UK household has an annual carbon footprint of 20,000 kg CO2. To keep global warming to below 1.5 deg C, we need to reduce this by 50% with further reduction to 30% within ten years.
50% reduction = 10,000 kg CO2
2kg x 365 days = 730 kg CO2 = 7% of the required reduction for the average household
A solar installation in 2020 could offer a reasonable return on investment both in financial and carbon footprint reduction. If you would like to calculate estimated returns for your property try the RenSMART Quick Solar Project tool. RenSMART is a not for profit company and the tool is free to use and not linked to any kind of sales.