Stewart Milne Group says micro renewables on Sigma House at BRE did not perform as it had hoped

Low-energy homes not micro renewable add-ons such as photovoltaics are the only viable way to meet the Code for Sustainable Homes on a mass scale, a housebuilder study has concluded.

Stewart Milne Group's report into how well its Code level five Sigma Home performed when occupied revealed that the energy consumption was considerably higher than predicted and nearly twice the level of Passivhaus standards.

While the building's fabric performance was significantly better than a conventional home, its as-built heat loss parameter was around 40% worse than predicted at design stage, suggesting more effort is required in reducing energy demand rather than relying on renewables to offset avoidable heat loss and energy consumption. The company is now working on a new building system to address these issues.

Stewart Milne Group's Code level five Sigma Home
Stewart Milne Group's Code level five Sigma Home

According to the firm, micro renewable technologies such as wind turbines, photovoltaic panels and solar thermal do not consistently deliver the required performance levels and the cost savings that would make them viable.

The wind turbine on the Sigma Home was found to deliver little effective electricity and while the photovoltaics produced half the electricity consumed it was felt the capital cost and long payback period outweighed the benefit.

Difficulties were also encountered matching the supply from the solar thermal installation with demand, as it required heat storage which adds complexity.

Other areas looked at included water consumption. This was within limits set by the code but occupants felt that the low water washing machine and the toilets were unacceptable and needed replacing.

Stewart Dalgarno, director of product development at Stewart Milne, said this was the first time such a home had been the subject of such in-depth research.

“The results are fascinating and challenge much current thinking and perceived wisdom. It is clear the answer lies in improving future build systems, with a focus on airtight solutions, heating and ventilation systems and taking a 'heart and lungs' approach to the installation of services at the concept stage,” he said.

Stewart Dalgarno says micro renewables did not perform as hoped