Solar Pond Project
Innovative technology to collect solar energy for heating purposes and reduce greenhouse gas emissions
The project is supported by the Australian Greenhouse Office Renewable Energy Commercialisation Program.
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What is a solar pond?
A solar pond is a shallow body of saline water several metres deep, set up so that there is increasing salinity with depth. Solar radiation entering the pond is stored as heat in the lower layer. This heat (up to 80 °C) is then available on a 24 hour basis.
A solar pond can store solar heat much more efficiently than a body of water of the same size because the salinity gradient prevents convection currents. Solar radiation entering the pond penetrates through to the lower layer, which contains concentrated salt solution. The temperature in this layer rises since the heat it absorbs from the sunlight is unable to move upwards to the surface by convection. Solar heat is thus stored in the lower layer of the pond.
In the summer it is expected that the Pyramid Hill solar pond will reach temperatures of above 80 °C. This heat will be available through the night as well as the day. In winter, the pond will still be able to supply useful heat because the temperature of the lower layer will remain some 30 °C above that at the surface. This temperature difference can be utilised to produce useful heat. See solar ponds for heating for more information.
Solar ponds are technically proven, with some 60 systems having been constructed around the world, mostly to provide process heat to industry. The RMIT University Energy Conservation and Renewable Energy Group has an experimental 55 metre square solar pond on the RMIT Bundoora East campus.
The aim of the current project is to make solar pond technology commercially available for prospective users in Australia and overseas as an economically attractive option for industrial process heating and other heating applications in regional and rural areas remote from the natural gas distribution system.
See under commercial applications for more information on the uses of solar ponds.
RMIT University, Geo-Eng Australia Pty Ltd and Pyramid Salt Pty Ltd have been awarded a $550,000 grant under Round 2 of the Australian Greenhouse Office - Renewable Energy to demonstrate and commercialise a novel system using a solar pond for generating heat for a range of industrial processes.
A demonstration solar pond heating system has been constructed at Pyramid Salt’s facility at Pyramid Hill in north-central Victoria, and is providing heat for use in high-grade salt production and aquaculture. The 3000 square metre solar pond has been integrated into a salinity-mitigation scheme. The performance of the solar pond and associated heating system is being monitored. An economic evaluation of this demonstration facility and of potential commercial solar pond process heating systems is being conducted.
Solar ponds have strong market prospects to provide process heat from sunlight in other rural industries too, such as dairy products, food processing, and fruit and grain drying, especially in salt-affected areas. There are many such industries in the Murray-Darling Basin and other areas with high salinity levels in Australia. Commercialised solar pond technology can therefore reduce greenhouse gas emissions and fuel costs in a wide range of rural industries.
The two-year project started in February 2000.
The project goals
- To construct, commission, monitor and evaluate the technical performance and economic viability of a solar pond for supplying process heat
- To obtain the technical, economic and marketing information and expertise required for the grantees to be in a position to begin commercialising this technology in Australia and overseas by the end of the project
- To evaluate the potential of the use of solar ponds for process heating in Australia to reduce greenhouse gas emissions
- To raise industry and public awareness about the commercial potential of solar ponds for process heating, and for consequent greenhouse gas reductions.
The planned project output
- A demonstration solar pond supplying process heat to industrial processes at Pyramid Salt’s site in Pyramid Hill, northern Victoria.
- An evaluation of the technical performance and economic viability of solar ponds for process heating.
- An assessment of the potential for solar pond process heating to reduce greenhouse gas emissions in Australia.
- Geo-Eng Australia Pty Ltd, Pyramid Salt Pty Ltd and RMIT University to be in a position to begin commercialisation of solar pond design, construction and commissioning first in Australia and subsequently overseas.
- A heightened industry and public awareness about the commercial potential of solar ponds for supplying process heat, and reducing greenhouse gas emissions.
Solar ponds for heating
The solar pond at Pyramid Hill is being used to supply heat to dry air used in the salt production process. The solar heat will substitute for heat currently supplied from electric heating elements, thus reducing electricity consumption and cutting greenhouse gas emissions.
Using the same basic arrangement, solar ponds can be used to supply heat to a range of industrial and commercial applications requiring heat in the temperature range 45 – 80 °C.
Economics of solar ponds for heating
It is estimated that solar ponds in climatic regions similar to northern Victoria can produce process heat (40 - 80 °C) for a wide range of applications at an average cost of about between $10 and $15/GJ. The results from the current project will provide actual data on cost of energy delivered, for the demonstration facility and in commercially available systems.
Heat from solar ponds is therefore expected to be competitive with the use of LPG and electricity in rural areas. Currently heat in rural areas costs over $20/GJ for LPG (at 43 c/litre). Heat from electricity (that is, direct heating rather than from heat pumps) costs over $45/GJ at peak rate, and $9/GJ off-peak. Solar pond heating would not be competitive in areas where natural gas is available, since this is priced typically at only $4-5/GJ.
In salt-affected rural areas such as the Murray-Darling Basin, certain areas of Western Australia, as well as much of inland Australia, solar pond technology could be a competitive source of heat for local industries since saline water and salt is locally available, usually along with sufficient land and high insolation.
Industries with potential applications for solar ponds
Solar ponds have the potential to provide low-grade heat in industries such as the following:
- salt production (for enhanced evaporation or purification of salt, that is production of ‘vacuum quality’ salt)
- aquaculture, using saline or fresh water (to grow, for example, fish or brine shrimp)
- dairy industry (for example, to preheat feed water to boilers)
- fruit and vegetable canning industry
- fruit and vegetable drying (for example, vine fruit drying)
- grain industry (for grain drying)
- water supply (for desalination)
The applications of the technology are certainly not limited to these industries. Basically the generic requirements for a practical solar pond application are these:
- no access to natural gas, and hence reliance on more expensive fuels such as LPG, electricity or fuel oil
- demand for heat in the 40 – 80 °C temperature range
- saline water and salt preferably available locally
- availability of relatively flat land on which to construct the solar pond
- relatively high annual average solar radiation
Solar ponds may also be considered as a source of factory and office space and water heating at suitable rural sites.
The demonstration solar pond and associated heating system at Pyramid Hill began supplying heat for commercial salt production in June 2001. The thermal performance of the solar pond and heating system are being monitored and evaluated, and to date results have been promising. An economic assessment of this demonstration facility, and of potential commercial solar pond industrial process heating systems is being conducted. Geo-Eng Australia and Pyramid Salt, in conjunction with RMIT University, are in the process of preparing the technology for commercialisation.
The Pyramid Hill demonstration solar pond facility was officially opened by The Hon Dr Sharman Stone, MP, Parliamentary Secretary to the Federal Minister for Environment and Heritage, on Tuesday 14 August 2001. Gwen Andrews, Chief Executive, Australian Greenhouse Office (now the Department of Climate Change), also spoke at the opening, which was chaired by Professor Neil Furlong, Pro-Vice Chancellor Research and Development, of RMIT University. Project Leader, Professor Aliakbar Akbarzadeh, of RMIT’s School of Aerospace, Mechanical and Manufacturing Engineering, gave an introduction to solar pond technology and the Solar Pond Project, including a demonstration of setting up a salinity gradient. Gavin Privett, a Director of Pyramid Salt, spoke about the role of solar ponds in salt production facilities and salinity mitigation, and expressed his optimism about the future prospects of solar pond technology. Peter Wood, Managing Director of Geo-Eng Australia, described his company’s role in designing and constructing the solar pond, and the monitoring system, and about the potential commercial applications of the technology.
Preparations for Stage 2 of the Solar Pond Project, which will centre on the generation of electricity from solar ponds, has begun.