Converting heat into electricity

Following the growing interest in geothermal energy, a new invention has been designed to convert heat from this sustainable source into electricity. But what does this man for plumbers?

Since its debut in 1970, the very best of Australia’s home-built gadgets have made their mark on ABC TV’s The New Inventors program. In the black tie grand final last year, the University of Newcastle’s invention, Granex, was crowned the winner of the series as well as the people’s choice.

Granex was developed initially for geothermal power generation. Geothermal energy is derived from volcanic activity that heats water contained in porous rock deep underground, called aquifers.

The opportunities for plumbers in the use of geothermal energy are growing, which is why industry representatives ought to spend more time learning about how this invention works.

Currently, geothermal energy is being used for residential hot water systems. It is an area plumbers would do well to be involved with. Geothermal heat pumps can be used to provide domestic hot water when the system is operating. In America, many residential systems are now equipped with desuperheaters that transfer excess heat from the geothermal heat pump’s compressor to the house’s hot water tank. A desuperheater provides no hot water during Spring and Autumn when the geothermal heat pump system is not operating; however, because the geothermal heat pump is more efficient than other means of water heating, overseas manufacturers are beginning to offer ‘full demand’ systems that use a separate heat exchanger to meet all of a household’s hot water needs. These units cost-effectively provide hot water as quickly as any competing system.

The use of geothermal technology means plumbers and electricians need to work very closely together. This has been reflected in the recent amendments to AS3500.

This brings us to new geothermal technologies being created on our own shores.

Granex technology delivers a higher thermal efficiency than conventional power plants and increases the amount of electricity that can be generated from low-grade heat sources such as geothermal and industrial waste heat. Overall it demonstrates an effective and economically viable technology platform for power generation from such sources.

The team of researchers working on this new invention were led by Professor Behdad Moghtaderi and Dr Elham Doroodchi, a husband and wife team who are both chemical engineers at the University of Newcastle’s Priority Research Centre for Energy.
For five years, they worked with Granite Power Limited (a Sydney-based company focused on low-to-medium temperature, low cost, green energy) to develop the technology that is Granex. According to Behdad, the inspiration for this product came from a problem that industry had when dealing with low-grade heat sources.

“The increasing concern regarding the consumption of fossil fuels and reduction of greenhouse gases led to our research and development with regard to maximising the efficiency in power generation and renewable energy resources,” he says.

“Conventional systems that are used to generate electricity are usually based on coal-fired power plant technologies, a high-grade heat source. We specifically designed our system to tailor to a low-grade heat source, such as geothermal. As the temperature of the heat is low, you can expect a relatively low output.”

After countless trials and tests, the team developed a 1kW proof-of-concept power plant, which was found to demonstrate a 40% improvement in terms of thermal energy efficiency and power generation.

“Granex is essentially a ‘heat engine’ that you can compare to the engine in a car. Rather than burning petrol to get mechanical work out of the car, Granex converts heat into electricity.”

While this heat-exchange technology achieves extra efficiency from using steam and specialised fluids, it does not convert steam back to water. Rather, Granex is a development of the conventional Organic Rankine Cycle (ORC) technology, which is used to convert low to moderate (130-450°C) temperature heat into electrical energy.

By incorporating the concept of a Regenerative Supercritical Rankine Cycle (a thermodynamic cycle that converts heat into work), Granex improves the thermal efficiency of the cycle and increases the net electrical output that can be recovered from a low-grade heat source. This forms the heart of the system.

“People ask me what a Regenerative Supercritical Rankine Cycle is, and it’s basically a very dense gas that is compressible. That’s the key to our technology,” he says.

“Essentially the working fluid within the Granex system is heated up by the heat source, be it geothermal, solar, etc. It is heated up to a maximum temperature and expanded through a turbine, which runs to generate electricity. The amount of electricity that is generated depends on the scale of the system.”

Behdad says the easiest way for plumbers to visualise Granex in action is to imagine the technology as an engine that sits on the surface above your chosen geothermal source. When the heat is extracted from the ground, it passes through Granex where it is converted into electricity.

“You would be surprised as how much heat it can store – it’s much higher than ambient temperature. Granex can tap into any low-grade heat source and convert that heat into electricity.”

Behdad advises plumbers to watch this space as they become more familiar with geothermal technology.

“There is a whole range of industries that could benefit from Granex. At the moment we are negotiating with many different industries, ranging from tile and brick manufacturers to chemical plants to mining companies,” he says.

“We are currently developing relatively small units and in the future we will look at expanding the Granex technology. There are no technical barriers; it more about gaining interest from industry at this stage.”

The plumbing industry should be very interested. There is no doubt that geothermal technologies are a major resource. An alignment with the electrical industry and with such products as Granex will in future create myriad design and installation opportunities.

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