By Cameron Jewell
23 May 2013 — It’s a technology that to many defies logic: using the sun’s heat to cool your home or office. But solar cooling is on the brink of a boom, and Australia is the perfect place for the technology, says the CSIRO’s Stephen White.
Solar cooling works by trapping the sun’s heat and transforming it into cold through a “sorption” cooling process. In a typical system, solar collectors installed on roofs capture the heat energy of the sun. A sorption cooling machine then converts this heat into cold. This can be done by an absorption or adsorption chiller – the same technologies used to generate cooling in a trigeneration system. The cold is then delivered to the building by a heat transfer mechanism, generally dry cool air or chilled water.
CSIRO engineers are also working on a desiccant system that could provide space cooling, heating and hot water to homes.
Recently, the Australian Institute of Refrigeration, Air Conditioning and Heating launched a solar cooling special technical group, with the goal of developing skills and building capacity in the nascent market. While the technology is still in the early stages, according to Dr White it will “absolutely” replace tradition HVAC methods in the future.
The benefits of using solar cooling could be enormous for Australia, a country whose rise in peak demand for electricity during hot summer days has translated into billions of dollars of grid infrastructure costs and spikes in the wholesale price of electricity. And our electricity-guzzling airconditioners are mostly to blame.
“What could be more logical than solar airconditioning?” AIRAH chief executive officer Phil Wilkinson says.
“Solar airconditioning could be one of the HVAC industry’s answers to reducing both greenhouse gas issues and electricity infrastructure costs. By developing skills and capacity in the use of solar cooling technology, the AIRAH Solar Cooling Special Technical Group will help enable the HVAC industry to access new business opportunities in the renewable energy industry.”
Dr White says the group will try to promote a level playing field for solar cooling in the industry. Unlike solar hot water, presently solar cooling is not a named technology for the government’s renewable energy schemes.
The need for breaking down barriers to solar cooling is quite apparent, says Dr White.
“Obviously the overarching reason is that we want to reduce greenhouse gas emissions,” he says. “Airconditioning and refrigeration account for seven per cent of greenhouse gas emissions in Australia and use 22 per cent of electricity. So it’s a major chunk we’re tackling.”
Importantly, solar cooling is also a “grid-friendly technology”, he says.
“Airconditioning is the big issue in loads. It is 50 per cent plus of peak demand. If you can handle that via a solar energy source, that is going to be a friendly solution to the grid.”
Another perk is that, in general, the times when solar cooling would be most important are the times when there is the most solar energy available.
And the greater the amount of solar energy, the more effective a solar cooling system is. This “matching” is very important in reducing peak loads.
With solar photovoltaics, peak daily loads tend to be in the evening, when solar resources are diminishing. Without storage, this makes solar PV less able to help with peak load reduction. Thermal storage can easily be incorporated to extend the operational hours of solar cooling systems.
Dr White says it will take a while for solar cooling to become commercial, but that the costs are coming down “quite quickly”.
Still, solar cooling is not a cheap option. A commercial system is at least triple the cost of traditional HVAC solutions.
But Australia is “at the forefront of the industry at a world scale”, says Dr White.
There are around 10 demonstration projects at present. Echuca Hospital in Victoria, for example, installed a $2 million solar cooling system that has saved $60,000 a year in energy costs, reduced peak demand by 14 per cent and offset 1400 tons of greenhouse gas emissions.
“As we start to head towards zero emissions buildings, we need to go beyond the first fruits of energy efficiency,” say Dr White.
And, for the Australian context, solar cooling seems to be a logical way to do this – providing cooling, reducing greenhouse gas emissions and managing peak demand in a climate that on all accounts is only getting hotter.