Solar cell manufacturers have branded the Royal Institute of Chartered Surveyors (RICS) "irresponsible" after the organisation published "unresearched" claims that it would take more than 100 years to pay back the cost of installing a solar panel.

The RICS said its Greener Homes Price Guide, released earlier this week, offers "impartial expert advice on the cost, energy saving, payback period, and disruptiveness of green improvements to your property," and recommends insulation and boilers as a more cost effective investment than solar panels.

However, Solar manufacturers disagreed vehemently with the study's findings, arguing that the claim that it could take an entire century for a solar panel to produce enough energy to cover the initial cost of installation was completely wrong.

"We have asked them for a withdrawal of these patently false figures," said Andrew Lee, head of Solar at Sharp Electronics. "We need to try and find out how they came to these numbers. We can only presume they were using old data."

Jeremy Leggett, executive chairman of panel manufacturer Solarcentury said RICS claims were based on serious miscalculations.

"RICS calculations completely omit to consider return on investment, when technically solar on your roof gives you better returns than leaving your money in a bank account," he said. "Furthermore, their figures do not assume any rise in energy prices, when a conservative estimate of 10 per cent a year would transform the calculations."

The solar manufacturers say RICS calculations fail to include grants from the Department of Business, Enterprise and Regulatory Reform (BERR) that allow householders to apply for funding of up to £2,500 to install microgeneration technologies.

The potential for those using microgeneration to sell power back to the grid is also omitted, according to the manufacturers. This week Scottish and Southern Energy told customers providing energy generated through microgeneration technologies that they will be paid 20p per unit for their exported electricity, meaning the average Solar Century customer would pay back their initial investment in 13 years.

The manufacturers expect return on investment periods to shorten further as rising energy costs rise and the cost of solar panels falls.

Solar firms also contested the RICS claim that the average photovoltaic panel only had a shelf life of 30 years. "Just because a solar panel has a warranty of 25 years, doesn't mean that should be taken as an indication of its lifetime," said a spokesman for Solarcentury. "Some of the first solar panels manufactured by Sharp and installed in Japan more than 40 years ago are still generating electricity today. And that's using half century old technology."

A study released by Greenpeace this week found that solar energy is becoming more economically viable and should become cost-competitive with conventional energy by 2020 across most of Europe. "Solar photovoltaic electricity has the potential to supply energy to more than four billion people by 2030 if adequate policy measures are put in place today, " said Ernesto Macias, president of the European Photovoltaic Industry Association.

However, RICS stood by its report, insisting that it would allow the solar companies to examine its figures.

"We take into account maintenance and installation costs – more than a solar vendor will give you in their pricing estimate," said a spokeswoman. "We haven't included the grants in our calculations because you can't presume everyone is going to get one."