Solar thermal 08: Stored solar energy for space heating and industrial process heat
Renewable energy commercialisation in Australia
This technology uses phase change materials to store solar energy for space heating and industrial process heat applications.
Under the Renewable Energy Commercialisation Program, a $600,000 grant has been provided to Origin Energy and the Australian National University for an innovative renewable energy project that will provide users with stored solar energy for the heating of buildings of all kinds. The technology can also be used to provide industrial process heat for a variety of applications, such as the drying of fruits, grains, timber and leather.
Solar energy can be readily converted to heat energy with the use of suitably designed solar collectors. The most widely used application of this technology is the domestic solar water heater. Essentially, this provides hot water that can be used at any time. This is because the water itself acts as its own thermal store for the absorbed solar energy. When hot air is required, however, a major problem exists since air has no ability to store heat.
In some parts of the world, such as Canada and the Scandinavian countries, there is a substantial requirement for space heating even when the sun is shining. However, the overwhelming requirement for heat is at night and at other times when there is little or no sunlight. The only available method of storing the heat contained in hot air has been in containers of crushed rock. Although this technology works reasonably well, very large amounts of rock are required to store relatively small amounts of heat-for example, about 60 tonnes of rock are required to satisfy the storage requirement for a solar space heating system for an area of 100 square metres. Not surprisingly, the required size and weight of rock storage systems is a severe disincentive to the successful commercialisation of solar air heating technology.
The new energy storage system uses phase change materials (PCMs) for the storage of heat derived from solar energy. PCMs work by storing energy in changing phase from solid to liquid- i.e. melting. The most common example of this phenomenon is the melting of ice to form liquid water-a great deal of energy is absorbed by ice at 0ºC to transform it to water, also at 0ºC. Conversely, an equally large amount of heat is released from water to form ice (i.e. freezing) at this same temperature.
Previous work at the Australian National University has led to the development and testing of a range of PCMs that change phase (i.e. melt and freeze) at temperatures that are useful for the storage of solar energy. Three PCMs that currently exist have phase change temperatures of 30ºC, 42ºC and 58ºC- temperatures that are eminently suitable for space heating and industrial process heat applications. Because of the very high heat storage capacity of PCMs compared with crushed rock, the size and weight requirements are greatly reduced, typically by 90 per cent or more, thereby making it possible for the thermal storage system to occupy little or no useful space. In most applications the storage system can be located in the roof space or in ducting. Suitable encapsulation systems for the PCMs have also been developed and are ready for immediate commercialisation.
Origin Energy is a company that is dedicated to the commercialisation of renewable energy technologies and will be responsible for promoting and marketing this new system. The opportunities for commercialisation and the potential for the reduction in greenhouse gas emissions are very great- for example, if just 1 per cent of the potential Australian market for space heating and drying process heat were to adopt this technology, there would be an annual reduction in greenhouse gas emissions of more than 1 million tonnes. This would go a long way towards meeting Australia's international obligations in global greenhouse gas reductions, as well as providing considerable economic benefits for consumers.
For more information please contact
Dr Keith Garzoli
Centre for Sustainable Energy Systems
Faculty of Engineering and Information Technology
Australian National University ACT 0200
Tel (02) 6241 6027
Fax (02) 6241 6027
Email keith.garzoli@anu.edu.au
Internet engn.anu.edu.au/solar
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