Geothermal energy gains esteem in Perth

 By Sharon Fisher

It may seem like overkill to drill a 1-kilometer hole just to heat your pool. But that’s what’s happening in Perth, Australia. And while heating swimming pools with geothermal energy is new, the practice holds promise…

Geothermal energy isn’t a new discovery. “The deep confined aquifers of the Perth basin in Western Australia have been explored for water supply since the beginning of the 20th century”, according to Rockwater, an Australian geothermal consulting company. “The availability of warm water was an additional asset and was very popular with laundries and bathing services”. The city was named #5 of the Geothermal Cities of the World by the Geothermal Energy Association.
But where does the warm water come from? The ground under Perth is a hot sedimentary aquifer (HSA): hot because of geothermal energy; sedimentary because the rock is broken into pieces, unlike a solid piece of granite, so it’s permeable to water; and an aquifer because it contains water.

                                                            The 3 different geothermal energy types: volcanic, hot sedimentary aquifer and enhanced geothermal, or hot rocks (AGEA)

It’s easy for geothermally heated water to rise and go back down to its source without having to expend much energy pumping it; but the water found at a depth of 1 kilometer is only about 55 C – not hot enough to generate much power. It’s easy, however, to use heat exchangers to collect the heat from the water and use it to heat swimming pools, which Perth has been doing since 1997. Meanwhile, the cooled water gets injected back into the ground so it doesn’t go to waste. All told, almost a dozen geothermal wells have been drilled in Perth, and according to Rockwater, which said it had completed 70 percent of the direct-use geothermal projects in the area.

We need hotter water

A $26 million geothermal-heated pool opened up in a Perth suburb in 2018, the thirteenth geothermal pool in the city. The pool is said to save 800 tons of carbon dioxide per year and saves the city about $530,000 per year in utility costs. In addition, Rockwater has developed shallow-aquifer systems whereby groundwater-supplied heat pumps are used primarily for space heating and cooling buildings, the company said. An experimental home in Perth used a source 60 meters deep and 150 millimeters wide for geothermal heating and cooling, compared with a similar home built next door.

The geothermal-heated "Scarborough pool" in Perth (Eliza Borrello, ABC News)

If scientists continue drilling, they may find much hotter water with more potential for energy, said Klaus Regenauer-Lieb, now head of the School of Petroleum Engineering at the University of New South Wales in Sydney. In a 2010 interview, Regenauer-Lieb said that drilling to 1.5 kilometers would produce water hot enough to perform desalinization, while drilling to 10 kilometers would produce enough electricity to power an entire city.
Not every region in Australia is that lucky, though, because HSA isn’t found everywhere. In fact, a number of other geothermal projects in Australia have been abandoned. It may be 2030 before geothermal energy outside Perth becomes successful, writes Bianca Nogrady in the Guardian. Until then, it’s everybody into the pool. Perth’s geothermal pool, that is.

Cover image by: Robert Montgomery, Flickr

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Sharon Fisher