White Gold !

Electricity generation and water desalinisation - powered by heat collected in highly saline lakes

How many people in rural Australia realise that the ongoing scourge of salinity has a gold lining. White gold - perhaps?. Salt lakes can be used to produce ENERGY - surely one of the most valuable commodities in our community. There are many parts of Australia being used to produce wheat at a margin of $150 /ha/year when they could be producing energy worth $15,000/ha /year !

Solar Ponds
Our aim is to revive the technology of solar ponds and make it a serious player in the alternative energy stakes.
Links to related information
on solar ponds
Site Index Kyoto agreement
Contacts
Who are we?
Heat from salt lakes
What is a solar pond ?
Electricity from salt lakes
(The organic Rankine cycle engine)
Generating fresh water using the sun
(Using solar ponds to power reverse osmosis desalination)
Economic analysis
Economics of solar ponds and solar powered fresh water supplies)
Do we know how to do it?
(History of solar ponds in South Australia)
Opportunities for
new development in rural areas
Where is the saline water in South Australia Comparison with other green power alternatives The reverse osmosis method of making fresh water from salt water

Solar ponds - what are they ?

Energy from salt lakes<

Any lake absorbs heat from the sun. Normally, heat is lost as warm water rises and loses heat to the air. However, a salt lake, about 3m deep, managed so that the water on top is of (relatively) low salinity and the water on the bottom is of very high salinity, will not circulate to release heat because the water on the bottom is so heavy with salt it cannot rise. The deeper water gets very hot - to over 100 degrees in the right circumstances - 80 degrees is common. The main management problem is to extract heat at the right rate so the lake does not boil or 'turn over' and lose its heat.

Run like this, such ponds are called 'Salt Gradient Solar Ponds' or just 'Solar Ponds'. Effectively, the pond acts as a very large, low cost, collector of solar heat. (There are also other types of solar ponds)

As a form of solar energy, the solar pond collector has major advantages.

  • The heat storage is massive, so energy can be extracted day and night.
  • Solar ponds can have very large area at low cost.
  • The major production potential is during peak electrical power demand (and price) in mid summer
  • The technology for extraction of heat and conversion to electricity is well understood. (Basically an industrial air conditioner run in reverse)

The scientific principles on which solar ponds operate is well understood and documented.

(SOLAR POND DIAGRAM}
Solar ponds in action
Solar ponds are currently used in Europe, USA, the Middle East and Australia. The heat they produce is used to warm swimming pools and glasshouses and for a range of industrial processes.
(as well as power production)
{pyramid Hill pic}

Getting the energy out of the pond

Energy, in the form of hot water, is extracted by circulating fresh water in pipes laid on the bottom of the pond.


This picture of the Solar pond at Pyramid Hill (near Kerang in Victoria) shows the mesh of pipes running down the wall of the pond. These circulate fresh water through the bottom of the pond which is heated by the saline pond water

The plastic rings on the surface are used to reduce the circulation effects caused by wind


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Electricity from solar ponds !

Taking the process one step further, to create electricity from the solar pond hot water is also a well understood technology. The convertor is called an 'Organic Rankine Cycle Engine' an ORC engine for short - named after a 19th century engineer.

If the hot water from a solar pond (or any other source - such as industrial waste heat) is used to evaporate a low boiling point chemical (such as a hydrocarbon liquid) then that vapour becomes a high pressure gas which can be used to drive a turbine and produce electricity. Once used, the gas is recirculated, cooled, condensed and recycled - same as in a refrigerator.

In fact, an ORC engine is actually an industrial scale air conditioner - but run in reverse.

Solar pond built at Alice Springs in 1972 with close up of the Organic Rankine Cycle power generator.


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Pure, fresh, water from solar ponds

In the 'driest state', water is at a premium. Water is overused and lack of fresh water is limiting development in many areas. Groundwater based supplies for both town water and irrigation are becoming salinised, and in many places there is often limited supplies at any quality.

In many places - such as the Eyre Peninsula, development has come to a standstill because of limited supplies of adequate quality water.

Up until now, remote area water supplies have been solved by piping water from places where there are supplies to the drier regions of the state. With the whole state running out of water, we need to look at new ways to obtain fresh water.

Where a town has a ready supply of saline water (either from the sea or from groundwater bores), the most likely way for remote towns to get fresh water is by the reverse osmosis method of extracting the salt from salt water. This is done by forcing water at very high pressure through a 'filter' which is fine enough to stop the salt from passing through. Unfortunately this requires very large amounts of energy to drive the pressure pumps. About 1kW of electricity is needed to produce 10 klitre /day in larger units.

Unfortunately, remote towns often do not have plentiful power supplies, and what there is, is scarce and sometimes unreliable.

Another problem with this method is that the last bit of salt cannot be extracted and a reverse osmosis plant bypasses about 20% of its output as VERY saline water which has to be 'disposed of' in an environmentally friendly manner.

15kLitre / day reverse osmosis water purification plant made by Pall Rochem.

The combination of solar pond (or wind) produced electricity being used to power a reverse osmosis water purification plant has become an attractive option in the last few years because of technolgy improvements, 'green energy' subsidies, and substantial price decreases.

The use of a solar pond to power a reverse osmosis plant is particularly suited to much of South Australia because the next best alternative - wind power, is unreliable or there is just no wind. Many towns which are short of fresh water supplies are near the coast or on areas where there is large saline groundwater supplies. In areas like the Murray Darling Basin where there are ongoing programs to pump saline water into saline disposal basins, the use of solar ponds to power the pumps (and local towns) is an obvious option.

The other benefit of using a solar pond to power a reverse osmosis plant is that if the saline effluent from a reverse osmosis plant is captured and concentrated by evaporation in a lake, then we have a salt water supply to maintain a solar pond which can be used to produce hot water, which can be used to drive an Organic Rankine Cycle engine to produce electricity to power a conventional reverse osmosis plant. The only catch is that there must be enough bypassed water to keep up with the evaporation rate in the area. In most of the remote areas of SA, the effluent from a reverse osmosis plant would not be sufficient to prevent a suitable pond from drying up - additional saline water would be needed.


Why is this technology not better known?

There are four fundamental needs for this technology to be attractive.

* however, solar ponds are used in northern countries to heat glass houses during freezing winters

These requirements usually only come together in desert areas which are near coasts, or in salinised agricultural areas. The requirement for low cost land usually means a very low population where there is seldom an industrial base to use the power. Most of the first world does not have these characteristics and the third world does not have the technology.

The "Catch 22' is that scientists don't bother with this technology, don't research it, and don't apply for research grants, because it is well understood, routine, and 'low tech'. So it does not get publicity !

There seems to be no technical or economic reason why solar pond produced power and water is not done more often. The reasons seem to be geographical and political.

While Israel uses the Dead Sea as a solar pond to make electricity, the Dead Sea is so saline that reverse osmosis is not an option. Many Middle Eastern countries use reverse osmosis to get fresh water from the sea, but have ready supplies of electricity powered by cheap oil - so they have no incentive to develop solar ponds. While there have been many small scale solar ponds built in the Southern USA for industrial and community heat supplies (eg town swimming pools), there seems to be a problem in those areas in getting an adequate salt supply and cost of salt is major running expense. The USA also has very cheap oil

A local history of solar ponds

This technology was used at several remote sites in Australia in the 1970's. Australian Solar Ponds P/L (now disbanded) built an experimental 0.5ha solar pond system at Alice Springs which produced electricity (net 15kW) on and off for several years. Enreco P/L built conversion units in the 1970s (Powered by hot water from the Great Artesian Basin) of up to 150kW - one of these is still functional at Birdsville For more detail on solar pond development see 'History of solar ponds'

What will it cost?

It is expected that the cost of power produced from these methods will not be as cheap as coal fired power but will be much cheaper than photovoltaic. Like most solar energy systems, the running cost is negligable but the capital investment is considerable. Solar ponds come in at about twice the cost of wind power per watt but they are much more reliable - delivering power 24 hours a day and 365 days a year. For a detailed cost analysis see 'Economics of solar ponds for power and fresh water supplies'

It is expected that the 'greenhouse gas' penalties to be applied to power generating companies as of April 2001 will provide any number of sponsors willing to subsidise the average cost of power from these systems to accumulate 'Greenhouse gas credits'. (Now called Renewable Energy Certificates).

Rises in power prices - particuarly recent peak power price in summer (when these systems are most effective) could make subsidy unnecessary.


Improving industrial efficiency

The energy conversion units will work on any form of waste heat. There are many sources of waste heat in industry, and the potential exists to convert this waste to readily saleable electrical power with a consequent increase in the efficiency of industrial processes.

Development partners required

We are seeking partners with an interest in dealing with the hydrological, biological and engineering problems of maintaining solar ponds. Some of the skills required relate to the behavior of larger bodies of water, others to dam construction and refrigeration engineering.


Opportunities

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I see this as an opportunity to develop a new technology (or to be more precise, a new application of established technologies). There are many places in the world which have all the requirements for solar pond generated electricity and the need of new supplies of fresh water. While many of these places are in the third world (where much of our aid money is already targeted at providing potable water), there is also great opportunity in Australia.

RIGHT NOW, Streaky Bay and other towns on Eyre Peninsula cannot develop because they need both a power supply and a water supply. All the requirements are there:- salt water, sun, and low cost land.

RIGHT NOW, many towns in South Western Australia and many of the towns just west of the Great Divide in NSW have rising saline water which is wrecking buildings and roads and contaminating groundwater supplies. Solar ponds have the potential to provide decentralised town power as well as to provide power to run pumps to lower saline water levels - the same saline water which would be used to generate the power.

RIGHT NOW, Padthaway in the south east of the state has begun the costing processes to measure the value of putting the entire groundwater supply of their irrigation area through a reverse osmosis plant to lower salt levels - at a cost of 800kW electricity for most of the year! A solar pond of less than 20 ha could supply this power.

RIGHT NOW, the Murray-Darling basin authorities are spending millions of dollars to pump salt water from the ground into saline evaporation lakes to lower saline water tables and protect the rivers. Those lakes could be managed as solar ponds to generate the power for the pumps.


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While solar ponds are a novelty, they would represent a tourism opportunity.

There is obvious potential to add a salt extraction operation, although at $300/ton raw salt is generally not worth harvesting if it needs to be transported great distances. Depending on the source of the saline water, impurities in the salt may be worth harvesting - magnesium and potassium salts are marketable.

The most likely add-on industry - particularly where there is an aquaculture industry nearby, is the production of brine shrimp - a valuable fish food.


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Who are we ?

The partners in this group are

Our aim is to revive the technology of solar ponds and make it a serious player in the alternative energy stakes.


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