Solar cooling utilises heat from solar thermal collectors to generate cooling for building air-conditioning. Most conventional mechanical air conditioners use high-emission electricity derived from fossil fuels to provide the energy to compress a refrigerant and cool a building. This typically accounts for 20-30 per cent of building energy consumption and greenhouse gas emissions. Solar cooling consumes less electricity when compared to a conventional mechanical air conditioner, thereby lowering greenhouse gas emissions.

“The solar cooling technology we are developing directly uses the natural heat from the sun to power a thermally-driven cooling process,” said Dr White. He explained that while using heat to cool sounds like a strange concept, the technology in development is able use that heat in conjunction with an absorbent material – or desiccant – to dehumidify and cool air. Dr White said that the new type of desiccant cooling promises to be simpler and more cost-effective than absorption chillers.

The solar cooling system consists of:

• Solar thermal collectors to provide • the necessary heat. Depending on application, the collectors can be air collectors, flat plate collectors, evacuated tube collectors or trough collectors.
• Sorption cooling machine to convert heat • to cooling. Depending on application, the sorption cooling machine can be single stage absorption chillers, two stage absorption chillers, adsorption chillers, solid desiccant coolers or liquid desiccant coolers.
• Thermal storage to help match available • solar heat with building demand for air-conditioning. Thermal storage can be on the hot side (hot water storage) or cold side (chilled water storage).
• Backup mechanical cooling systems or • a backup gas burner are also commonly provided to address solar intermittency.

There has been strong interest in the technology in Australia, with two recent installations at the Ipswich Hospital in Brisbane and Inform Energy in Sydney. Other projects in the advanced stages of planning or construction include the Araluen Centre in Alice Springs, Charlestown Square in Newcastle and a demonstration facility at CSIRO Newcastle.

The amount of roof space required varies depending on the desired fraction of cooling to be provided by solar. A typical installation may require approximately three square metres of solar collector per kilowatt of nominal cooling capacity, leading to a roof area typically less than 25 per cent of the air-conditioned floor area. A recent European study indentified hospitals and hotels as particularly attractive buildings for the technology.

Commenting on solar cooling technology and climate change policy, Dr White said “I see no technical reason why solar cooling shouldn’t be treated on a level playing field with other renewable energy technologies. As air-conditioning is the primary cause of electricity infrastructure growth requirements, solar cooling seems equally capable of addressing greenhouse gas emissions and infrastructure investment issues.

“Solar cooling technology is uniquely suited to our climate and as the technology develops, it is likely to make an important contribution to the development of future zero-emissions buildings.”