Reflecting on Applications and Efficiency
Understanding Conservation of Energy
Figure 1: Conservation of Energy Credit: Lesics [1]
The First Law of Thermodynamics for a closed system is known as ΔU = ΔQ + ΔW. However, open systems are more widely used since the system can exchange mass and energy with its surroundings. Through an open system, a control volume has a boundary where energy balancing occurs. The mass is changing from entering and leaving this control volume as the mass flow rate. Here a substance like a gas or liquid is flowing. Each system has an inlet and outlet where pressure, temperature, and velocity may change. We can then apply the equation seen in Figure 1 to find Heat Transfer, Work, Power Output, and even Thermal Efficiency. [1]
Technological Applications with the Conservation of Energy Equation and Efficiency
Geothermal
Figure 1: Geothermal Process
Credit: GreenFire Energy Inc.
Geothermal power plants utilize steam to create energy. The heat exists naturally from the ground in the form of pockets or water and is used to power the turbines. It works similarly to a Rankine cycle. In [2]. it states that "steam rotates a turbine that activates a generator, which produces electricity." Rankine cycles are used by producing superheated vapors and using them to rotate a turbine and produce energy.
The efficiency of Geothermal power plants can range from 10 to 17% [3]. However, it is mentioned that the efficiency depends on certain conditions of the plants and multiple different factors such as single flash plants, double flash, etc. It also is reliant on the location to reintroduce this water back into the reservoirs for continuous use. Moraine Valley would have an efficiency of 12%, falling in the range of normal geothermal power plants.
Since the Geothermal power plant can be analyzed like a Rankine cycle, the equations used in class would be a good basis to start off to figure out different values. Of course, the geothermal plant would have to be constantly working at an ideal state to use the Rankine cycle equation continuously. There will be changes to the equation depending on if it would be a single or double flash or dry steam plant. A similar thermal efficiency equation that can be used for a geothermal plant would be 1 - (Wapc/Wgross) [3]. Wapc is the total power consumption while Wgross is the gross electrical power. By using this equation the efficiency would be in the same range mentioned before, 10 to 17%. The Analysis section has a similar thermal efficiency that is found.
Solar Power
Figure 2: Solar Power Process Credit: MDPI
Generally, solar panels are used in a gas or steam power turbine systems. Gas turbines are normally picked over steam for their higher efficiencies and are more cost efficient to run. The photovoltaic solar cells capture sunlight which is used to pass along energy either to the storage or along loops to the turbine for power generation. The shape, positioning, and connections with each panel collect the most sunlight during periods of time throughout a day. The turbine uses fossil fuels to combust and expend the energy given to power lines which will power homes and buildings.
When you take into account efficiency, the system needs to be assessed at a perfect performance state to get a good grasp of the system's quality. "The efficiency analysis method’s essence is to comprehensively consider the utilization degree of energy in two aspects: quantity and quality [1]." [3] The quantity of each subsystem can be used in our Conservation of energy equation for a Brayton cycle by calculating for each W and Q at the inlet and outlet. For example using Qin = h3-h2=Cp(T3-T2) to fin heat into the system. This can help us solve each process to find the differences in states to find end results.
"Concentrating and collecting subsystems include optical loss and thermal energy loss to convert solar energy into heat." [3] This includes heat transferring with exergy, lost energy at the inlet and outlet, and the characteristics of each subsystem. The loss is used to calculate the thermal efficiency of a system as well as factors like work supplied. When pairing the power generation of gas and steam, you will see increased "High conversion efficiency systems: SHGT systems can achieve thermal cycle efficiencies up to 50%, depending on system configuration and power level. These cycle efficiencies are significantly higher than efficiencies of state-of-the-art solar steam cycles." [4] For a normal solar power system, you can get a value of around 20% after taking Wout/Qin. This coincides with our calculations from our Analysis section.
Wind Turbines
Figure 3: Wind Turbine Process
Credit: EIA
Wind turbines are operated with the wind causing rotors to move which supplies energy. The blades spinning are always at a constant momentum converting energy based on the rotors which are usually made up of coils. The coils transfer the energy made via a cable down to a generator for storage.
When putting wind turbines into use, the KE taken from the wind is primarily our extractor. "The torque control of the generator allows varying the speed of the turbine rotor by applying MPPT strategies to achieve as much as possible maximal extraction of wind power." [5] Wind turbines are made usually with carbon fiber as it is able to take forces more easily. This has an impact on the control of the blades with the wind's velocities and the rotor's potential to generate power. An example is "wake" where you reduce wind speeds. "With specific combinations of these parameters, simulation results show that the efficiency of a 7×7 floating offshore wind farm may be raised by 42.7% when implementing YITuR in comparison to greedy operation." [6]. YITuR is experimentation with a unique yaw angle (between wind and blade) and a different induction rate for energy transformation. Parameters like the amount of wind controlled in a flow pattern, rotor heat, and energy dissipation can all affect the efficiency of the system in the way it performs. This efficiency lines up well with our Analysis page.
Wind turbines act like a rotary generator which mechanically export electricity. Wind turbines are considered variable-state since it is highly dependent on wind direction and speeds. However, we can simplify it into a steady state by taking wind at an ideal state. Using the information, we can write up an equation like Qcv=-Wcv+m(h1-h2) as we solve for variables like Heat Transfer.
Hydro Power
Figure 6: Hydro Power System Credit: EIA
Water supply is abundant on the Earth and for this reason Hydro Power is one of the leading solutions. Even though dams and reservoirs are mainly used with fresh water, this fresh water is important for the environment, animals, and can be used towards powering electricity. In a Hydro Power system, water is collected on one side of a dam, and flows through consistently to meet a turbine or a pump. This turbine or pump converts the waters flow into mechanical energy which is stored in the generator. The generator can then send out the energy as electricity to power civilians needs.
We can use a pump instead of normal turbines such as "Crossflow" or "Francis". The pump turbine has a higher efficiency because of its ability to control water pressure more effectively. "Furthermore, according to the study of Ramosetal. [14], the PAT could reach a relatively high efficiency (up to 85%). A case study in Murcia, Spain indicated that the maximum installation capacity in the main pipe of water supply with flow rate 300 m3/h and water head 30 m could reach 100 kW by using PATs [15]." [7] This flor rate and water head allows for a bigger capacity of generation. Hydro Power plants do not take a lot of maintenance, and are low cost when operating. The pump turbine specifically is able to reduce the heat reduction caused by the water, which in turn harnesses that heat energy for more generation.
Calculating for its efficiency is based on the work of the shaft power, the gravity, density, water head, flow rate, and heat acquired. We can neglect the KE and PE as this usually isn't large enough to affect enthalpy. It is slightly different from our normal Conservation of energy equation in that it takes the gravitational constant for finding states of the pump as it flows downward. Using these measurements we are able to conduct that Pme (shaft power)/ Pth (theoretical power) gives us the total efficiency of the pump. [7] The 85% is very close to what we achieved in the typical range for a Hydro Power system.
Biomass
Figure 5: Biomass Power System Credit: Eco Globe
Biomass is one of the cleanest forms of renewable technology available. The biomass system takes natural resources like wood, grains, and other waste from animals transferring this into a burner/boiler. The burner combusts, burning all this waste taking the energy given off from the waste and converting it into heat. The heat is passed along a line heating or cooling water. This step can be used for monitoring buildings and environments. Taking it a step further, the water can be used in a steam turbine that can generate electricity for other needs.
A regular steam turbine paired into a biomass system with inputs of the agricultural and forestry sectors is the most common application. However, this varies per nation, for instance, Scandinavia has a large number of forests and mountainous areas. [8] The different biomass wastes from these sectors cause different levels of efficiencies and emissions. An experimentation with Poland's wetlands lead to the discovery of a biomass system that gave "The CHP unit's electrical and thermal conversion efficiency was assumed to be 38% and 43%, respectively." [8] The system was run on feedstock and biogas which was highly dependent on temperature, burn rate, and technology at hand. CHP is perfect for biomass applications because of its ability to heat and power the engine in one cycle. It is highly efficient in this regard as it can utilize wasted heat into the application. The thermal efficiency is correctly related to what our values were in the Analysis section.
The efficiency was gathered based on fuel consumption, intake chamber, heat applied, and flow rate. Meshing these variables together we can take a Rankine cycle since CHP is perfect for superheating steam to produce power. Implementing our Conservation of Energy equation we have a steady flow rate so we can set our mass and energies states equal. Then we take our enthalpy, KE, and PE and solve for our Work. We cannot neglect KE and PE in this case because of the difference in velocities and pressures from the beginning to end state.
Selecting the Best Technology
We can use a majority of this data and analysis to pick an optimal technology system to get our value and operations achieved. All of these technological systems can be implemented into various tasks and can be substituted with unique parts/operations. There will not be a complete solution for any system as technology will keep advancing and each system will work differently in application. The coasts would be able to utilize hydropower perfectly, but landlocked states would not. it depends on what and how to implement the best renewable energy technology. Our closest best use for Illinois and its surrounding areas would be the wind turbines as "8.2% of renewable resources are used through Wind turbines". [9] This is due to the fact that wind turbines have some of the highest efficiency when operated at full capacity and Chicago, Illinois always has a high winds from the thermal heat of the lake that exchanges pressure with that of the land. Grasslands liked the one at MVCC are able to expend the length that wind travels and wind turbines are more cost effective due to the cost savings of long-term run-time. For our specified location of Moraine Valley Community College (MVCC), wind turbines would not be an ideal technology to use. As stated in the Analyze section, the small campus does not have enough room to place a turbine to operate properly and safely. In this case, Moraine Valley would ideally switch to solar power. The solar panels would not be placed in a singular area, but spread out across the campus to not take up one massive area of land. MVCC has already moved towards solar power and to continue with this plan would be beneficial for the campus in the long run.