A Geothermal Energy Essay On Electricity Generation.

Selection link will be available soon in the course home page to choose your topic of interest from the list below.  One topic can only be selected by maximum of nine students. Only few references are suggested below just to start with. Please also use other references to complete the task.

Explain the technology of generating electricity using geothermal energy and discuss the advantages, problems and future prospects.

See for example:

MW3.4 and 3.5 from the Course Introduction

http://www.agea.org.au/

http://www.geodynamics.com.au/IRM/content/home.html

http://www.petratherm.com.au/

http://www.geo-energy.org/

2. Nuclear Reactors.

Discuss the technology, current status and prospects of 4^th Generation, integral fast nuclear reactors. See the Barry Brook web site below.

http://bravenewclimate.com/integral-fast-reactor-ifr-nuclear-power/

http://www.sciencedirect.com/science/article/pii/S0301421513006083 (may require UniSA username and password via the library)

3. Discuss the technology, current status and prospects of solar thermal electricity generationwith particular reference to the possible replacement of the Port Augusta power station with solar thermal power. Jemalong pilot solar thermal plant in New South wales can be taken as a case study for Australian condition.

http://www.repowerportaugusta.org/

http://www.vastsolar.com/portfolio-items/jemalong-solar-station-pilot-1-1mwe/

4. Discuss the technology, current status and prospects of carbon capture and storage from coal fired power stations. See info below re projects in Australia, the Netherlands and Poland.

See: http://www.newgencoal.com.au/

http://www.csiro.au/en/Research/EF/Areas/Coal-mining/Carbon-capture-and-storage

http://www.zeroco2.no/projects/countries/poland

http://www.carboncapturejournal.com/ViewNews.aspx?NewsID=3482

Discuss the objectives of the Australian Solar Cities project and discuss progress, activities and targets in Adelaide and one other city and the lesson learned from the projects.

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0ahUKEwiKmqCHwo3MAhVGppQKHUnlCQMQFghKMAU&url=http%3A%2F%2Fwww.industry.gov.au%2FEnergy%2FEnergyEfficiency%2FDocuments%2Fsolar-cities-journey.pdf&usg=AFQjCNE2Yu8gWibzI-5weoa91n_XZmmdHg

Discuss the problem of peak load in South Australia and how it might be reduced, the mixture of generators i.e. coal, gas, wind, diesel etc. and their greenhouse gas emissions, the impact of the current electricity generation mix on the grid due to the high penetration of renewable energy and proposed policy and technology solutions.:

https://www.aemo.com.au/-/media/Files/Electricity/NEM/Planning_and_Forecasting/SA_Advisory/2016/2016_SARER.pdf.

Discuss the technology, current status and prospects of energy storage technologies (Mechanical, Electrical, Chemical, and Thermal energy storages). Discuss the role of energy storage in allowing high penetration of Renewable Energy generation in Australia.

Electricity Generation

A Technical Report on Electricty Generation from Geothermal Energy Source

Geothermal energy is perhaps a classical manifestation of the exciting fields of Thermodynamics, Electricity and Geoscience being merged to design and develop a system that is very critical to the existence of humanity. Notably, without energy, societal progress of any form may almost be impossible. Traditionally, the fossil fuel sources have been used vehemently for electricity generation. However, due to the increased environmental concern, experts have warned of an impending grand menace to the existence of humanity thanks to the fossil fuel sources. However, the focus has now shifted to the alternatives. Therefore, it is on this premise that Engineers have been in the search for clean, efficient and sustainable energy sources. Admittedly, geothermal energy source has proven beyond reasonable doubt that it can serve humanity in a relatively safe and efficient fashion. Now, basically, what does geothermal energy mean? From the etymological definition, it can be described as energy in the form of heat that originates beneath the earth’s surface; as geo means the earth surface while thermal describes heat energy. In a more elaborate fashion, however, the geothermal energy originates from the heating of the natural underground water that is entrapped between rocks next to the magma. The magma is a very hot material. Scientists assert that the heat normally originates from the radioactive decay of the materials such as uranium and in the process producing heat; which is then passed to the rocks entrapping the natural water (UCSUSA, 2017). Next, this heat would normally find its way via the rock crevices, fissures and cracks to directly heat the entrapped natural water to boiling point. Due to the pressure build up, it finally finds its way out to the external earth’s surface; thereafter the pressure and kinetic energy of the boiling stream can be harnessed to produce electricity. But how is that done? Now, this technical report is aimed at providing information in a succinct manner so as to help readers comprehend the technologies involved in the harnessing of geothermal energy to generate electricity. In the same breadth, fundamental issue of concern during design and development of the entire system will also be elucidated. Furthermore, there will be a deliberate attempt to uncover the latest harnessing technologies. Therefore, certainly, this report will provide a substantive material to the design engineers in the mentioned sector. But firstly, let us understand, in the next section, how production of electricity from geothermal energy is done.

Components of Geothermal Energy

Now, before one can dwell on the production process, it is imperative to understand the different components of the system that makes this possible.

Normally, there are three main types of power plants depending on the capacity requirements. They include: flash stream, binary cycle and dry steam power plants (TEEIC, no year). The flash stream involves a back-pressure turbine converting the stream into electricity and then the low-pressure stream exiting from the system is condensed in a binary system. In dry steam plant, the steam is directly fed to the turbine since gases are rarely found in a natural system like geysers. Lastly, in the flash steam plant, hot water is allowed to flow out under its own pressure and as it does so, there is a drop-in pressure which causes it to ‘flash’ into steam and then it is directed to the turbine. The residual hot water can be recycled back to the system. Normally, the system is combined with a cooling system. Although it is the common type, it produces relatively small amounts of steam.

Typically, the power plant is composed of: the generator, turbine, piping system, cooling system, water reservoirs and source of heating (normally naturally occurring). To ensure large amounts of steam are produced, the system functions as follows: water from the reservoir is pumped to the natural ‘boiler’ to be heated to boiling point. Then, the steam generated is allowed to rise up via sunk pipes and directed to the turbines. During rising up, the steam undergoes pressure reduction and partly its quality improves. Normally, the steam is bypassed into a separating chamber where degassing is done before it can be fed. The steam is pressure laden and flows under ferocious force hence possesses sufficient kinetic energy to impinge on the blades of the steam turbine such that the whole turbine turns about its own shaft axis. It should be noted that there are many configurations of the turbine and the design normally depends on the capacity of the geothermal source. Bigger turbines could be used where there is a greater harnessing potential. There are normally multiple wells dug to boost the power capacity requirements and make the venture more gainful in terms of capital investment. The power cycle below illustrates the fundamental stages of power generation:

                                                                                     

Normally the quality of steam is a determining factor of power conversion efficiency. Both the quality of steam that enters the power cycle and the one that leaves the system are considered such that the one entering must be treated to maximize its quality especially during conversion to electricity. Maximum harnessing is often desired so that what comes out as residual hot water will be of less quality. The following thermodynamic treatments are often carried in the system:

This is normally aimed at increasing the power plant efficiency. It serves to increase the vapor temperature at the inlet to the system so that the amount of heat to be extracted from the steam will significantly be increased although pressure drops are often encountered in the process and there is a limitation to the extent of regeneration. Should the limit be surpassed then dangerous scaling can occur and destroy some system components (Valdimarsson, 2011). The recoverable heat energy due to this process should therefore cover and surpass the cost of purchase, installation, operation and maintenance of the regeneration unit for an economical power generation.

Due to systemic pressure drops, the fluid would start boiling before it reaches the separator hence throttling would first be done to increase its pressure. This is done so as to reduce the destructive impact of the steam. Thereafter, it is directed to a low-pressure separator before being fed to the turbine for heat extraction. In the low-pressure separator, it boils again and steam returns. Normally, the turbines would be arranged in stages such that extraction occurs intermittently until it is rendered low quality. The system is designed such that the pressure difference between the low and high separators is the same as that between the turbine stages (Valdimarsson, 2011)

It should be noted that the thermodynamics of such a system is so complex that it would require a separate paper to analyze. This section has only provided a sneak preview of what actually happens thermodynamically.

• Reservoir capacity

This is will often define the size, capacity and ultimately the amount of direct capital investment to the prospective power plant. This data is normally derived during the feasibility studies. Sophisticated geospatial and geo-sensing systems are often used to explore the natural ‘heat sources’ and establish their capacity potential using simulation modelling tools. Additionally, it should be established at the onset whether the reservoir is steam dominated or liquid dominated. Notably, steam dominated reservoirs are often more efficient than the liquid dominated due to higher quality of steam.

• Production establishments

Next, the production facilities would then be designed based on the reservoir capacity. It will include design and installation of the turbine stages, piping and pumping requirements among others.

• Environmental consideration

The immediate environment of the plant plays a big role in its design and operation. It should be noted that environmental aspects such as temperature would normally dictate the capacity of the cooling system. In winter, for example, the cooling system will have to operate on a different level than in summer hence these provisions must be incorporated in the system.  

Geothermal energy is normally very clean as it produces less amounts of emissions.

It is also relatively efficient in production compared to the fossil fuel energy generators. The fossil fuel generator efficiency is at 40 % maximum currently unlike the geothermal generator efficiency which can go up to 80% (Greenmatch, 2014).

It is also renewable as it does not deplete the sources and recycling is also possible.

The system has relatively simple components that require low maintenance.

The system also produces relatively low amounts of noise than the fossil fuel generators like diesel engines

Higher investment cost during system establishment can sometimes be very prohibitive

There are also concerns on the environment due to release of pungent gases such as hydrogen Sulphide.  

The major issue that Engineers in this sector will likely improve even further is the conversion efficiency. Some research works have been launched to look into ways of harnessing the power even further. There has been reservation on the existing harnessing technologies with some experts asserting that the wells can be dug more deeply to reach out to the hotspots. This would then increase the thermal capacity of the steam. Furthermore, it should be noted that quite a huge chunk of project funds would go into the capital investment especially the drilling operation. The experts in the field will have to double up in their endeavors to discover more cost-effective means in the drilling technology. According to INS (2006), about 60 % of investment is used in the drilling technology before plant is set up and production can then be done. As mentioned earlier, the drilling technology of the future will have to produce wells and channels that not only are safe to the users but also, they can greatly support the optimized harnessing capabilities. Currently, majority of the geothermal power plants are based on very shallow wells hence significant proportion of the geothermal potential of the area is left untapped. More studies, especially in the wake of great advancement in computerized simulation methodologies, will have to focus more on providing real-time data to facilitate effective decision making that is going to foster sustainability and continuity in geothermal power generation. Additionally, exploration works will have to be supported greatly by most modern tools in geosciences and geospatial sensing technology. It should be noted that different areas exhibit different geological structures but importantly, the natural sources are likely to be found in areas where there are active volcanic activities hence more work need to be done to explore these areas for more prospective sources. Lastly, although geothermal energy has been lauded as a relatively clean energy, there will be need to review its environmental impact in future. Notably, there has been concern over possible air pollution as the unwanted and pungent gases like hydrogen sulphide are normally given off during energy extraction process. Environmentalist will have to be more interested in understanding to what extent does the whole venture affect the immediate environment.

Conclusion

In conclusion, this report has provided fundamental issues in the production of electricity from the geothermal energy sources. The author believes that the current technologies need great uplift to ensure the harnessing potential is improved.  However, geothermal energy is gaining traction among the renewable energy sources as it combines virtually all the facets of the sustainable energy generation and use. Notably, the technical description elucidated has provided a substantive material to the renewable energy enthusiast to further explore the field.

Reference

UCSUSA. (2017). How Geothermal Energy Works. Available at: https://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-geothermal-energy-works.html#.WTU3cGiGPIU

NREL. (2017). Geothermal Electricity Production Basics. Available at: https://www.nrel.gov/workingwithus/re-geo-elec-production.html

TEEIC. (no year). Geothermal Energy System Descriptions. Available at: https://teeic.indianaffairs.gov/er/geothermal/restech/desc/index.htm

Valdimarsson, P. (2011). Geothermal Power Plant Cycles and Main Components. Available at: https://www.os.is/gogn/unu-gtp-sc/UNU-GTP-SC-12-35.pdf

Bouche, D.P. (2010). Technical Considerations for Geothermal Power Plant Designs. Available at: https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/2618.pdf

Greenmatch. (2014). Advantages and Disadvantages of Geothermal Energy. Available at: https://www.greenmatch.co.uk/blog/2014/04/advantages-and-disadvantages-of-geothermal-energy

INL. (2006). The Future of Geothermal Energy. Available at: https://energy.mit.edu/wp-content/uploads/2006/11/MITEI-The-Future-of-Geothermal-Energy.pdf