As Australia settles in for another long hot summer, the demand for air-conditioning is set to surge. In fact, with the World Meteorological Organisation stating that 2016 is likely to be the hottest year on record, it’s no surprise an estimated 1.6bn new air conditioners are likely to be installed globally by 2050.
Powering all these units will be a challenge, especially on summer’s hottest days. In Australia, peak demand days can drive electricity usage to almost double and upgrading infrastructure to meet the increased demand can cost more than four times what each additional air-conditioning unit costs.
Yet an emerging sector of the solar industry is turning the searing heat of summer into cooling by using solar heat or electricity. For those developing the technology, the benefits of solar cooling are obvious: the days when cooling is needed the most are also the days when solar works best.
When combined with a building’s hot water and heating systems – which together with cooling account for around half of the global energy consumption in buildings – solar cooling can drastically reduce reliance on grid energy and improve a building’s sustainability credentials. According to the International Energy Agency, solar could cover almost 17% of global cooling needs by 2050.
Currently, such systems are still the exception. “It hasn’t got into the mainstream yet,” says Ken Guthrie, who chairs the International Energy Agency’s Solar Heating and Cooling Program.
Nevertheless, several solar cooling technologies are making their way to market. While off-the-shelf systems for most are still years away, a handful of businesses have already opted for purpose-designed solar cooling systems, which experts hope will convince others to follow their lead.
Echuca regional hospital in rural Victoria was one of the first to take the leap into solar cooling. In 2010, with support from Sustainability Victoria, the hospital designed and installed a solar heat–driven absorption chiller with engineering firm WSP consultants.
A 300 sq m roof-mounted evacuated tube solar field feeds hot water to a 500 kW chiller that was set to save the hospital $60,000 on energy bills and reduce greenhouse gas emissions by around 1,400 tonnes of carbon dioxide equivalent per year.
The system was not designed to run entirely off solar (a gas-fired boiler takes up the slack on hot days), but “we have had days where we run 100% solar” for both cooling and hot water, says Echuca regional health executive project manager Mark Hooper.
The benefits of solar were clear enough that a larger 1,500 kW chiller, connected to a field of trough-shaped solar collectors that track the sun during the day, was installed during the hospital’s recent expansion and redevelopment. This second chiller started operating in November and an analysis of the resulting energy and emissions savings will be assessed in conjunction with CSIRO.
Meanwhile, Stockland Wendouree shopping centre in Ballarat, Victoria, is trialling a CSIRO-designed solar cooling system with funding from the Australian Renewable Energy Agency (Arena). Trough-shaped metal collectors on the centre’s rooftop collect solar heat that is used to dry out a desiccant matrix (much like the silica gel sachets in your shoebox) that dehumidifies air brought in from outside. The hot, dry air is then directed to an indirect evaporative cooler, which delivers cool, dry air into the shopping centre.
The yearlong trial is still under way and hasn’t yet seen a full summer to calculate energy savings, but “it’s going very well,” says CSIRO’s Stephen White. The system is 50% more efficient than an earlier iteration of the design – an important improvement given many buildings don’t have the sprawling rooftop spaces of a shopping centre to mount large solar collector arrays.
With photovoltaic cells more affordable than ever, cooling systems that run off solar electricity are already commercially available. But solar thermal systems could still find a place in the market, according to Guthrie, especially for larger commercial buildings. “There’s no single solution,” he says.
Like any solar technology, solar cooling doesn’t work 24/7. Storing the solar energy collected during the day for use overnight is possible. Stockland’s system uses thermal oil storage, for example, and Echuca regional hospital has insulated its firewater tanks to store chilled water. But there are also efforts to store heat or cooling from one season to the next using underground storage tanks.
Whichever systems a building adopts, White says the benefits of solar cooling extend beyond electricity savings. “It’s not just about the cents per kilowatt hour avoided, but it’s also about the value of the asset itself,” he says.
For Hooper, the motivation was even simpler: “We did it to ensure that our children have a future.”
