ANU recently completed development of an enhanced solar air heater in conjunction with our commercial partner T3 Energy (www.t3e.com.au). This project is supported by the Australian Greenhouse office through its Renewable Energy Commercialisation (RECP) program.

The system is designed to produce solar heated air, solar hot water and photovoltaic electricity all from the one array. Furthermore, it uses phase change material (PCM) to store heat for later use.

The solar collectors integrate with the roof forming a weatherproof skin. The panels are modular in design and a typical house may use 40-50 of them in an array. Our research regards the modelling, design and operation of the array.

The phase change material used is paraffin wax. The wax is encapsulated in custom designed containers and stored in a heat bank which looks like a hall cupboard. The system uses a controller to determine which of six modes of operation should be used to maintain a comfortable indoor temperature.

This project is funded by a grant of $600,000 from the Australian Greenhouse Office (AGO). It is to develop and commercialise a solar air heating system that is suitable for space heating as well as for commercial applications such as drying. A solar air heating system consists of a number of individual solar air heating modules that can be arranged end-to-end or side by side to provide any desired heat or temperature output under the design conditions.

Solar energy that is intercepted by the unit is converted into hot air which can be either used directly, or stored in phase change material (PCM) thermal storage for later use. PCMs store energy by changing phase from solid to liquid (ie melting) and releasing heat by changing phase from liquid to solid (ie freezing). A range of PCMs are being evaluated, all with a melt/freeze temperature of about 40oC. The choice of the most appropriate PCM is based on a number of factors, including cost, latent and sensible heat, and thermal conductivity in both the liquid and solid phases and its effect on the overall thermal performance of the complete system. A number of installations have been completed by our commercialization partner, T3Energy.

Project Extension

As an extension to the above project, we were granted a further $1,000,000 to carry out a number of extra tasks to improve the energy efficiency and cost effectiveness of the existing solar air heating system. A number of technologies are being evaluated for their effectiveness:

1. Low reflectivity glass. Conventional glass is highly reflective to incoming solar radiation when the solar beam arrives at an oblique angle. With low reflectivity glass, a high percentage of the incoming solar radiation is transmitted into the unit, even at oblique angles of incidence, thus increasing the amount of energy available for conversion to heat.

2. Selective surface on absorber plate. Currently the absorber plate, which intercepts the solar radiation and converts it into heat, consists of matt black “Colorbond” steel sheet. This is highly absorbing to solar radiation, but is also highly emitting to long wave or “thermal” radiation that is emitted by the absorber surface. This thermal radiation loss can be greatly reduced with the application of a selective surface that remains highly absorbing to solar radiation, but emits thermal radiation only weakly, thereby reducing thermal radiation losses and retaining most of the incoming energy within the unit.

3. Alternative materials for the body of the unit. Currently the case of the solar heater unit is made of sheet metal. We are currently experimenting with lighter and more highly insulating materials. The most promising is polyurethane, the casing made from this material is produced as a single moulding, using a die that was constructed at the Department of Engineering’s workshop. Such a casing is lighter and easier to handle, cheaper and more highly insulating than the current sheet metal unit.