Methods of evaluating energy technical systems efficiency

Question

Literature review: classification of energy technical systems: - As per thermodynamics first law, energy can neither be created nor can be destroyed. It can be converted into one form into the form. The energy of the universe is constant. But, the conversion of the energy from one form into another form does incur loss of energy. The 100% conversion is not possible. So, it is prime important to have efficient energy system. Similar, the storage of energy without any losses have been a challenge for engineers. It is imperative to use energy wisely. The different methods to evaluate the energy technical systems efficiency is discussed here in detail.

In our daily life, there are so many ways, energy is available to us. In day to day life, these terms such as potential energy, kinetic energy, electrical energy, mechanical energy, chemical energy, solar energy, thermal energy etc. are heard frequently. These are just different forms of the energy. If energy received from sun, then it can be said solar energy. If energy is due to height/elevation, then it can be said potential energy. Energy release due to chemical process, then it is called as chemical energy and so on.

Efficiency of   any system can be defined as output over input.

Efficiency  = Outpout / Input

High Efficiency of   any system is desirable. Receiving more output for the minimum input will result into higher efficiency. The efficiency of energy technical systems depends on various factors, which will be discussed in detail here.

Literature review: classification of energy technical systems

There are number of ways, energies are transformed into one into another.  Energy system can be classified in various ways. Energy system can be classified base on their conversion. For example:

1. Thermal Power Plant

2. Hydro Power Plant

3. Nuclear Power Plant

4. Solar Power Plant

Energy system can be classified base on way they are stored.

Answer 1

Literature review: classification of energy technical systems

1.      Mechanical storage systems

2.      Electrochemical storage systems

3.      Chemical energy storage

4.      Electrical storage systems

5.      Gravitational storage system

 Among these, the most important energy systems are:         

1.      Thermo power plant:

It is mainly concerned with generation of steam at a very high pressure. This highly pressurized steam is used to drive the blades of the turbine and thus, it generates electricity. Thus, it performs the conversion of thermal energy into electrical energy. In overseas countries, there is an upper trend in the demand for electrical power both in public and private sectors of the BRICs (Brazil, Russia, India and China) and in many Southeast Asian countries of Indonesia and Vietnam. In these countries, the generation of electric power is lagging behind the economic growth and rate of industrialization.    

Coal forms the main source of energy in these plants. Due to high heating value of coal, it can produce energy ranging from 10,500 kJ/ kg to 27,000 kJ/ kg, depending on its quality. But effective conversion of heating energy of coal into electricity is quite theoretical.

Effective conversion is limited by

• The practical inefficiency in transferring heat from combustion of coal to water, for the purpose of producing steam.
• Secondly, quality of coal matters a lot. Moisture and hydrogen content causes loss of a sufficient amount of heat energy.
• Discharge of hot ash and radiations are other forms of loss of energy
• From thermodynamic point of view, the whole process in the thermal power plant relies on the efficiency of Rankine cycle is expected to have a maximum efficiency of around 43% with steam at subcritical pressures below 221 bars and temperature of around 570 ° C.

Thus, overall efficiency of the thermal power plant is typically around 33 - 48%. However, a lot of heat energy goes waste; hence technologies have been developed for parallel utilization of this energy for various purposes (termed as cogeneration of energy).

Working of a thermal power plant is shown below:.

2.      Hydro Power Plant:

It mainly deals with conversion of hydro energy into electricity. Hydro power plant uses kinetic energy of flowing water to rotate the blades of turbine (converting it into rotational kinetic energy), whereas the generator does the rest of the work (conversion into electrical energy).The amount of electricity being generated depends on several factors. Two of those factors include the volume of water flow and the hydraulic head, the distance between the water surface and the turbines.

Its working efficiency is quite high compared to other conventional sources of energy, converting around 90% of the available energy into electricity. On the other hand, most of the plants with convention fossil fuels can maximize their efficiency only up to 60%.  Hydro-electrical power comprises of around 7.8% of energy produced all over the world.

It is highly efficient due to:

• Its source of energy i.e. flowing water, which serves as a renewable resource due to hydrological cycle of earth.
• It is clean and green without any release of harmful air pollutants into the atmosphere.
• Can easily meet local demands for power loads.
• Even the reservoir turns out to be a place for recreation for the public
• Though it has high capital cost but maintenance cost is comparatively low.

            However, it brings about changes in water flow and surrounding areas, which is not desirable.

               The efficiency of a hydro power plant is limited by the maximum height of the water head due to many natural factors. Hence, the power generation unit is placed at a position as low as possible to increase the water head. On the other hand, the volume of water flow is adjusted by using the penstock.

Diadram Configuration of a typical hydropower station

 

3.      Nuclear energy system

Nuclear energy involves about one-third of the world's total energy resource. Production and control of energy in the nuclear reactor comes from splitting the atoms. This energy is used to produce steam at high pressure to generate electricity. However, it requires nuclear fission reaction to occur in a controlled manner, to produce the desired amount of electricity.

In terms of efficiency, the electricity produced by combustion of coal releases around 147 million metric tons of carbon dioxide to the atmosphere more compared to nuclear system for the production of same amount of electricity. Thus, with nuclear energy system, amount of harmful pollutants decreases, which can be easily disposed off safely.   

Schematic diagram of a nuclear power plant is given below.

 

In U.S., nuclear energy systems generate electricity at an 89 percent capacity factor, which is quite higher than other types of energy-coal-fired energy source (61 % capacity factor), combined-cycle natural gas (46 %) and wind (32 %). 

 

4.      Solar power plant :

This makes use of two technologies namely:

• Photovoltaic cell or the solar cell (made up semi conductor materials, silicon alloy) technology - Conversion of solar energy into electricity.
• Solar-Thermal Electricity (in solar thermal plant) concentrates the solar energy, so as to heat up the water for production of steam. Remaining job is done by the turbine and generator.

However, production of electricity from solar energy is not so productive. Solar energy, being a renewable source, doesn't affect the environmental conditions and it is a clean source of energy. According to Shockley-Queisser limit, solar conversion above an efficiency level of 33.7 percent cannot be obtained. However, at present, commercial solar panels can achieve a maximum efficiency of around 25%.

Ongoing further research in this field of energy is supposed to overcome the barrier with new technologies. Being renewable, it is widely adopted as a clean and green source of energy. But due to its low efficiency, its application in large scale production is quite limited   

 

References

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2.        45nuclearplants.com (2007) Nuclear Reactor Design. [online] Available at: http://www.45nuclearplants.com/nuclear_reactor_designs.asp [Accessed: 15 May 2013].

3.        ayurveda (2013) Various Plants used for Generation of Electric Power : Hydroelectric, Nuclear and Thermal Energy Plants Parts  & Working. [online] Available at: http://ayurveda.hubpages.com/hub/Different-Plants-used-for-Generation-of-Electric-Power [Accessed: 15 May 2013].

4.        Bonsor, K. (2001) HowStuffWorks "Hydropower Plant Parts". [online] Available at: http://science.howstuffworks.com/environmental/energy/hydropower-plant1.htm [Accessed: 15 May 2013].

5.        Newenergyportal.wordpress.com (2009) Solar Energy | Renewable Energy Sources. [online] Available at: http://newenergyportal.wordpress.com/category/solar-energy/ [Accessed: 15 May 2013].

6.        Nexteraenergyresources.com (1997) NextEra Energy Resources. [online] Available at: http://www.nexteraenergyresources.com/what/solar_works.shtml [Accessed: 15 May 2013].

7.        Sumitshrivastva.blogspot.in (n.d.) THERMAL POWER PLANT - INTRODUCTION, COMPONENTS, PROCESSES ETC.  ~ Mechanical Guru's. [online] Available at: http://sumitshrivastva.blogspot.in/2012/09/thermal-power-plant-introduction.html [Accessed: 15 May 2013].

8.        Vikashkumarsharma.blogspot.in (n.d.) Principle of Working of Hydroelectric Power Plants ~ Electrical Engineering Technology. [online] Available at: http://vikashkumarsharma.blogspot.in/2011/03/principle-of-working-of-hydroelectric.html [Accessed: 15 May 2013].