Solar pond pioneers tell their story
May 25, 2020
It’s often said that Central Australia has a strong history of renewable energy innovation; a history which is perhaps a little longer than you might imagine.
Back in the 1980s, what started as a fun experiment in a backyard swimming pool in Alice Springs, turned into a commercial venture, leading to projects all over Australia.
The pool belonged to long-term Alice Springs resident and former Connellan Airways pilot David Frederiksen, usually known as Freddo. He enlisted the help of his friend — American physicist Bob Collins who worked at Pine Gap. Together they built Australia’s first solar pond.
Solar pond technology was pioneered in Israel in the 1950s. By the early ’80s it was showing signs of becoming economically viable. It seemed a practical and relatively straightforward way to generate power for outback Australia.
“The pond is made up of a salt gradient,” said Freddo.
“The bottom layer is a storage zone of saturated brine (24%), with each layer getting less saline, and fresh water on top. Gravity holds each layer in place,” he said.
“Sunshine hits the bottom, gets trapped in the storage layer, and then converts into convective energy.”
Once the salt has trapped the heat at the bottom of the pond, the hot water is piped into an evaporator and put through a process which powers a generator. The phenomenon was first discovered about a century ago.
“There’s a lake in Hungary that has a salt deposit at the bottom, and when people dived into it, they could feel a huge temperature change,” said Freddo.
“Mother Nature’s been doing it for thousands of years.”
The small prototype pool was built at Freddo’s home near the Château Hornsby vineyard.
“A government minister was dining at the restaurant and we invited him to have a look at the Territory’s new energy system,” said Freddo.
“He put his hand in, burnt himself, said the f‑word, and put his hand in again,” he said.
“The Minister returned to Darwin and in no time they were all over us like a rash!”
The partners were then encouraged to build a 40 metre by 40 metre in-ground solar pond near the vineyard, 15 kilometres south of Alice Springs; now a residential area known as Connellan. There was enough power generated to pump water to the vineyard and provide the restaurant and a home with electricity.
“We used to get lots of visitors such as politicians, scientists from all over the world, tourists, and school kids,” said Freddo.
The 40m x 40m solar pond in the Alice Springs rural area. It no longer exists, but the windmill is still there
Large-scale power production from solar ponds wasn’t viable, but it was thought it could be an effective way to provide power to remote communities, and save on diesel costs.
However, managing the technology wasn’t as easy as it might have looked.
“It was like a fussy swimming pool. It had to be looked after each day,” said Freddo.
“Rabbits and things like leaves would fall in, then we’d get an algae bloom running across the pond, creating a blind and blocking sunlight.”
There was also the issue of sourcing enough salt.
The big pond needed up to 800 tonnes of salt, which was harvested from the salt lakes near Erldunda, using a simple but clever mechanical salt-harvester invented by Freddo.
The need for daily attention and access to salt rendered solar ponds less than ideal for bush communities.
By this time, Freddo had been shown a hot bore on a friend’s property in outback Queensland which opened up new possibilities.
Bob Collins said the solar ponds had a “big impact” on him, and were the reason he stayed in Alice Springs, leading to a 50-year stint in the town. He only recently moved to northern New South Wales.
“Freddo and I made a good combination, as I learned a lot of practical skills from him and I think he gained theoretical knowledge from me,” said Bob.
“The solar ponds were not a technical success, but the heat engine we developed for it then led us to geothermal work.”
Freddo and Bob’s experience and knowhow were applied elsewhere. Most notably, they were part of the team which built the geothermal power plant at Birdsville, which ran successfully for three decades. The team included Jim Lawrence (diesel mechanic), Steve Sawyer (electrical engineer) and Tony Greatorex (electronic engineer).
“I think the team of people that helped us with all these developments generated a lot of interest in renewables, and the realisation that local people could do amazing things,” said Bob.
Bob and Freddo are still enthusiastic about renewable energy; but also pragmatic about the role of solar as a percentage of the total generation capability in Alice Springs.
“In 1974 it was overcast for a month,” said Freddo.
“So even if you have 70 or 80 per cent solar, you still need a backup system. Solar is a fuel saver but it can only be number one if you’ve got big batteries,” he said.
“Variety is the way to go.”
Bob is similarly technology-agnostic.
“A lot of the work for the future of renewables will have to be in storage and a more robust, smarter grid,” he said.
“No single technology has all the answers. You have to be open and flexible in your thinking.”