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Solar panels that cost up to £16,000 will knock just £70 a year off household bills, which is almost half the original estimate, energy experts have admitted. Undercover investigation by consumer champion Which? has found many firms selling solar panels are overestimating how much energy the panels produce

Environmental advisers the Energy Saving Trust (EST) has cut its estimate on how much households could save on their electricity bill using solar panels from the previous £120 a year.

The EST had estimated that about 50 per cent of the energy produced by solar panels is used in the home. It now says the figure is more like 25 per cent.

This is because solar panels work only during the day, when most people are out. The admission comes as solar panel salesmen have been criticised for misleading many households over the benefits of these panels, which can cost as much as £16,000.

The Government has also come under criticism for its controversial green taxes, which are levied on all households via their energy bills to pay people with solar panels to generate their energy.

Every home in Britain could be paying £300 a year through gas and electricity bills by the end of this decade to fund climate change schemes. These schemes have resulted in 300 million energy-efficient lightbulbs being sent in the post to households.

Now an undercover investigation by consumer champion Which? has found many firms selling solar panels were overestimating how much energy the panels would produce.

Jenny Driscoll, energy campaigner with Which?, says: ‘Consumers must really be on their guard when it comes to solar panels. There is a massive amount of exaggeration about the benefits from salesmen.

‘Remember the households that will benefit the most from solar Photovoltaic (PV) panels are those with sunny, south-facing gardens who are in all day.’

PV panels convert sunlight into electricity. They are being advertised by many big names, including Sainsbury’s and British Gas.

Which? found that homeowners can pay between £7,000 to £15,600 for them to be installed on their roof. Around 45,000 homes in the UK have had solar panels installed.

Many of these were convinced to make the investment by a salesman who boasted of huge savings.

A big attraction is that householders are actually paid for the energy they generate, regardless of whether or not it is used.

But the actual savings homeowners can make are vague, as much depends on where their property is, which direction the roof faces, and the weather. Working out the benefits is also a complicated sum.

For example, the EST says a typical household pays £560 a year for their electricity.

They might pay £12,000 to install solar panels.

If only 25 pc of the energy generated by the panels is used in their own home, they would save £70 a year on electricity bills — reducing their bill to £490.

The homeowners are also paid about 35p per kWh for the energy they use.

The remaining 75 pc of unused energy that has been generated will be sold back to the grid for about 41p per kWh. A typical family makes about £800 a year from doing this. However, most solar panels do not store energy — to do this homeowners must install expensive batteries.

So at night, in the evening and on cloudy days — when the solar panels cannot produce any energy —the homeowner must buy electricity from their supplier at a rate of about 20p per kWh. Although this is still a saving, it is not nearly as much as the saving they would make if they simply used their own energy.

These green, so-called ‘feed-in’ tariffs, are paid for by other homeowners by a levy on their energy bills.

By 2020 every household will be paying about £11 a year to fund the scheme. Rosalyn Foreman, of the EST, says: ‘While these are typical estimates, it’s quite possible that someone could save more than £70 if they were at home in the day or set all their appliances to run in daylight hours.’ Which? says there is still a lot of confusion regarding how much energy is produced by solar panels and how much money people can make.

This is partly because some salesmen are giving people misleading information.

Solar panels need to be installed on a building with a roof or wall that faces within 90 degrees of South, without being overshadowed by other buildings or trees.

Yet seven out of the 12 salespeople in the Which? investigation recommended installing solar PV panels on a shaded part of the roof.

Also, under Government rules installers are not obliged to take into account where people live when calculating how much energy can be produced.

In fact, this will depend on your home’s location and the weather.

Virginia Graham, chief executive of solar panel trade body the REAL Assurance Scheme, says: ‘We have always been clear that the people who will benefit most from panels are those who are in during the day.

‘We are also working with charities to ensure that vulnerable consumers are protected from mis-selling. We would like to see doorstep mis-selling banned because it is a unsuitable way to promote this technology.’

The Daily Mail, 6 July 2011