LIKE many other households we have been looking at the benefits and costs of installing solar panels to generate electricity. During the last few weeks we have learned a lot about the whole process and would like to pass on a few “health warnings” to your readers.

There are many websites that can provide you with information, but even those such as the Energy Saving Trust should be looked at carefully. That suggested that a 3.5 kiloWatt system here would generate a benefit of £1,533 per annum, but you have to open another page to discover that this assumes optimal orientation and tilt.

In other words, if your roof is not at an angle of 30 degrees from horizontal and pointing due south, these figures could be considerably less.

Many commercial websites that enable you to estimate the income from a system will also indicate the cost of installation and offer to put you in contact with three local installers who will give you quotations.

One such site, which also allowed a search for local installers, calculated that the cost of installing a 3.43 kW system would be £19,364 with a first year benefit of £1,426. This is based on a roof angle of 30 degrees on a south-facing roof.

Although this seems expensive, the returns are much better than other investments, at 7.37 per cent tax-free in the first year. Then, when the installers come and offer you a system at around £12,000, you feel that you are getting an even greater bargain, a return of between 11 and 13 per cent. It would appear, however, that the websites inflate the costs.

This is what happened to us, with all three of the installers we obtained through a website offering systems varying in size between 2.95 and 3.5 kW at costs from £10,240 to £12,300.

What they all failed to do was to include the correct angle of the roof or its orientation towards the sun. Whether this was deliberate or incompetent we do not know, but none of them showed us the basis for their calculations which use a standard table and format.

It was only when a local firm, which was suggested to us by our plumber, came up with a lower income from the system that we began to question the figures. The local firm had used the correct angle and orientation.

A second local firm, also in business before the solar panel boom, again managed to calculate the estimated benefits using the facts rather than producing figures that helped to sell their system.

We calculated that the difference between the correct and incorrect figures was about 10 per cent. It was then that we realised that we had been misled. Needless to say, we will not be using any of those referred installers.

PETER CLARK

Tawny Crescent

Hartford