Some renewable energy firms are failing to give consumers the right advice, it has been claimed.
The Energy Saving Trust said recent research by Which? backed up its own findings that some firms were providing people with inaccurate information.
Eight out of 12 installers failed to correctly calculate possible savings and others failed to explain that solar panels would put part of the roof in shade, the report found.
The Trust raised concerns that it had become more difficult for two schemes to regulate the sector amid rapid growth.
The MCS sets industry standards for installers of small-scale renewables and the REAL Assurance Scheme covers all non-technical aspects of an installation, from pre-sale contact to post-installation services.
But the Trust said the regulators were being stretched due to the uptake of electricity-producing technologies surpassing expectations and more tradesmen moving into the green sector.