The UK’s first grid connected solar system has been tested on its 20th anniversary, to find it still has a 95% generation rate from its initial installation 20 years ago.

The domestic solar system was installed and connected 20 years ago by residential renewable system installers, Wind & Sun.

The 2.16kW array is south facing on an oak frame with 36, Solarex 60Wp, polycrystalline modules, and an SMA PV WR-1800 inverter – the first SMA inverter installed in the UK.

After 20 years, Wind & Sun measured solar irradiance and back of cell temperature, while performing a full I-V curve test from open-circuit voltage to short circuit current. With the results a comparison in performance was made against the original panel flash test data when it left the factory.

The system was predicted to decline in efficiency by 20% from the panel’s original performance over 20 years.

The first panel test revealed, after 20 years, there had only been a 5% decline.

When the entire array was tested, accounting for shading of nearby overgrown trees and debris build up, the panels still performed at 80% of the systems original output.

The system has generated 33MWh with no faults for the last 20 years, although an inverter upgrade of the Sunny Boy SB-2500 was fitted in 2008.

The system was installed at ‘The Autonomous House’ in Southwell, Nottinghamshire.

The house was designed in 1975 by Brenda and Robert Vale to be self sufficient for energy and water.

The Autonomous House also has rainwater harvesting, insulation and composting to remain self sufficient – Wind & Sun suggested the grid connected PV system to complement the aim of the house, by generate the house’s annual electricity use while using the grid as virtual energy storage with an SMA grid connection inverter which was already being tested in Germany.

The solar system was grid connected 27 July 1994 after the local grid company, EMBD, approved the idea and is the first UK demonstration of harnessing solar energy to supply the national grid.

Rooftop solar installations are now common across the UK and since 1994 solar installation costs have plummeted, and payback time is now around 5 years.

In 1994 the system cost was £6,900 per kW with a module cost price of £4.40 per watt – totalling a 200 year payback time.

Steve Wade, Wind & Sun’s managing director said: “The progress we have made in the last 20 years has been exceptional and it is amazing to see more and more solar systems appearing everywhere thanks to the vision of some pioneering individuals. We expect that this system could be producing for at least another 20 years.

“Solar is now firmly established as a mainstream energy source and we can now look forward with confidence to a sustainable future.”