Design and Testing of Solar Dish-Stirling System with Solar Tracking System

Alınma: 14.11.2017 Kabul: 13.03.2018 Enerji, hayatımızda kullandığımız evrenin önemli unsurlarından birisidir. Yaptığımız herhangi bir işte mutlaka enerji kavramı ile karşılaşırız. Enerjiyi hem üretip hem de tüketiriz ve bunun için hem fiziksel hem de kimyasal reaksiyonlar gerçekleşir. Hayatımızın en küçük noktasından itibaren sürekli enerji üretmeye ve bu enerjiyi en verimli şekilde kullanmaya çalışırız. Dünyamızda da enerji üretimi ve enerjiyi kullanmak adına çok çeşitli alanlarda çok farklı metotlar kullanılıyor. Birincil enerji kaynağı olan “Güneş” dünyanın temel enerji kaynağıdır. Güneş dünyayı aydınlatmayı, ısıtmayı, canlıların yaşamasını ve ikincil enerji kaynaklarının ortaya çıkmasını sağlar. Günümüzde enerji ihtiyacının büyük kısmını fosil kaynaklar karşılanmaktadır. Teknolojinin Yenilenebilir enerji kaynaklarının kullanılması yavaş gelişimile den fosil yakıtlar ön plana çıkarmıştır. Ancak fosil kaynakların çevreyi kirletmesi, enerji üreten tesislerin işletilmesinin pahalı olması ve kaynakların sınırlı olması daha farklı enerji üretim yollarına başvurmayı zorunlu kılmıştır. Bunlardan birisi de güneş enerjisi sistemleridir. Güneş enerjisi sistemleri doğa dostu özellikleriyle enerji üretiminde ön plana çıkmıştır. Gün geçtikçe güneş enerjisi Ar-Ge çalışmalarına artan ilgi, üretimde artmaya ve işletim maliyetlerinde azalmaya olanak sağlamıştır. Yapılan tez çalışmasında amaç yenilenebilir enerji kaynağı olan güneş enerjisinden faydalanmaktır. Bu çalışmanın hedefi, güneş enerjisi orta sıcaklık uygulamalarında kullanılan, teknolojisi hızla gelişen ve yoğunlaştırıcı kolektör tiplerinden biri olan “güneş takip sistemi ile kontrol edilen stirling motorlu jeneratör” sistemini incelemek, tasarımını yapmak, kolektör üretiminde kullanılan malzemelerin özelliklerini araştırmak ve temin etmek, deney düzeneği kurmak, kolektör performansını incelemek ve bilgisayar ortamında simülasyonunu gerçekleştirmektir. Son olarak çıkan deney, teorik ve simülasyon sonuçları karşılaştırılarak sistemin doğruluğu hakkında bilgiler elde etmektir.


Introduction
Solar energy is one of the famous renewable energy sources that can be used as an input energy source for Stirling engine.Solar Stirling systems convert the thermal energy in solar radiation to mechanical energy and then to electrical energy.Solar Stirling systems have demonstrated the highest efficiency of any solar power generation system by converting nearly 30% of direct-normal incident solar radiation into electricity after accounting for parasitic power losses [1].Solar Stirling system produces electricity by using parabolic collector and Stirling engine.Dish/Stirling concentrating solar power (CSP) converts solar heat into electricity by focusing solar radiation onto a receiver containing a heat-engine known as a Stirling engine.

Solar Stirling System Components
The main components of a solar Stirling engine Systems are the solar collector (dish-satellite) with the sun-tracking system, the solar receiver and the Stirling motor with the electric generator.The designed system is shown in figure 1.

Collector Calculation 2.1.1 Geometrical considerations
The concentration ratio is defined as the ratio of the radiant flux density in the focal spot   to the direct irradiance on the aperture of the collector  , .As the direct irradiance at the collector aperture is just the direct normal irradiance, is the ratio of the radiant flux density at the focal spot to the direct normal irradiance.The concentration ratio C can be determined as follows [2]: In present study the concentration ratio is 96 time.Because of the collector area C ap is 4.9 m 2 and the receiver area C im is 0.05 m 2 .The concentration ratio C is shown in figure 2.

Choosing reflection material
One of below mentioned reflectors can be chose and it is important to choose the ideal one taking all factors into consideration as it will define the light intensity and system output power.This study, AL Foil Band 45 mm * 0.06 mm * 40 M has been used.As it has 88% high reflection ratio beside of its low cost [3].Reflecting surfaces and reflection ratios are shown is table 1. Table 1.Reflecting surfaces and reflection ratios [3] Reflector Surface Material Reflection Ratio Silver 0,94 ± 0,02 Silver Rear Coated Mirror 0,88 AL Foil Band 0,88 Acrylics Coated AL 0,86 AL 0,82 ± 0,05

Calculation of Collector dimension
The dimension of the collector depends basically on the desired electrical output of system, the available radiation and the total efficiency of the conversion of radiation to electrical energy.The respective collector diameter can be determined as follows [4]: Where:   is the desired electrical system power,   the solar-to-electric system efficiency and DNI the direct normal irradiance at the design point.In present study the desired electrical output is 250 w.System efficiency between (17-20) %, where the different came from different working times and other factors like weather, pollution..etc.The direct normal irradiance in Kilis City is more than 1360 kWh/m2 a year, this area also receives nearly 1400 hours of solar irradiation in a year [5].

Double Axis Mechanism Design
In this project we designed double axis mechanism to get max thermal energy from sun radiation.The mechanism with solar tracking control are always direct the collector toward the sun.Z-Y axis mechanism (Horizontal, Vertical) and X-Y axis's mechanism (Left-Right) movement is being carried out with 2 DC motors and their gears [5].The designed double Axis's mechanism shown in the figure 2.

Solar Tracking System Proteus Simulate
In this project, we used Arduino as processor which received the sun location information from four LDER fixed on the collector axis.After processing received information the Arduino send the control signal to double axis mechanism which moves toward the sun.The system simulation in Proteus was done before purchasing any control items.The Proteus simulations help us to be sure if our program will work correctly or not.The Proteus simulation is shown in Figure 4.The other Statuses: LDRX > LDR: If LDRL > the others, so LDRL output has (0.1-3.91)V, our aim is to reach status 1 with mechanism motors which is move according to received control signal from Arduino.(X: LT, LD, RT or RD).The bile of material (BOM) which used in solar tracking system control panel in this project is shown in Table 2

Stirling Engine and Generator 2.4.1 Thermodynamics analysis of the Stirling cycle using MATLAB
The engine is divided into 5 control volumes for this analysis, and it is assumed that the expansion and compression processes follow the adiabatic law.

Assumptions:
1.The expansion and compression process is adiabatic 2. The temperature of hot end heat exchanger, cold end heat exchanger and regenerator is constant.3. The working fluid obeys ideal gas law.4. The specific heats for the working fluid (Helium) are constant.5.The pressure is uniform throughout the engine at all instants.6.The volume inside the engine varies in a sinusoidal manner.7.There is no leakage of working fluid from the engine.8. Perfect regeneration occurs in the regenerator volume.9.The heat transfer in the hot end heat exchanger and cold end heat exchanger occurs at constant temperature.10.The initial pressure is known 11. 0-degree crank angle corresponds to topmost position of displacer [6].

Calculations for work and efficiency:
We will perform the analysis in the following steps.These steps will also help in coding the analysis in MATLAB.
8. Now repeat all above steps by incrementing crank angle for every iteration and take cumulative sum of work dW after every iteration [7].9. Once the crank angle reaches 360, stop the iterations.We now have our work output W from the cycle in J/cycle.
The formula to calculate the terms involved in above steps, are given as follows, Regenerator temperature Moles of working gas inside engine Maximum hot end live volume Maximum cold end live volume associated with displacer: Maximum cold end volume associated with power piston: Regenerator volume: We now define 3 arrays to store 3 volumes, namely H(N) to store instantaneous hot end volume, C(N) to store instantaneous cold end volume and V(N) to store total instantaneous engine volume.The hot end live volume is given by: The cold end live volume at any instant N is given by: The total volume at any instant N is then given by: Now the pressure at any instant can be given by: The change in volume will simply be: And total work will be: The instantaneous work will now be; Nomenclature and symbols are shown in table 3.
To get the work output per cycle we just repeat above calculations by differentially incrementing F from 0 to 360.The following engine parameters are chosen to get the work output for the test case presented.These are not randomly chosen parameters, but have been decided after running the analysis numerous times and then optimizing them for the targeted power output [8].Choosing Stirling engine parameters are as below:   The hot end heat exchanger and hot end working volume are constant and equal as we are assuming the process to be isothermal.Similarly the cold end heat exchanger and cold end working volume are assumed to be at the same constant temperature [9].Work per cycle in J by numerical integration: 2.5

The Used Stirling Engine:
Alfa type double cylinder Stirling motorgenerator is used in this application.This engine achieves all simulation result parameters and has also below properties, Cylinders covers are made from Stainless steel.Cylinders are made from Copper.Flywheel and piston are made from Aluminum Double cylinder system provides stable performance and output power.The generator is connected to the motor with two belts.The technical specifications are dimension: L * W * H (205X150X111) mm, flywheel diameter is 64mm and wheels diameter is 29 mm.

Testing
The designed project was designed and set up in Kilis, Turkey, based on previous initial evaluations.The Experimental setup and testing were carried out on the roof of electrical and electronic engineering faculty of Kilis 7 December University, as shown is figure 7.In this situation, there is no ability to take any measurements, because the system is not ready for testing due to the previous problems.After solving the problems which face us in first test day, the testing repeated.The measurement results have a good agreement with simulation result.Regarding experimental result the motor speed and out power increase radically with the temperature differential.Same result was achieved in MATLAB program.Comparison the test result and MATLAB analysis is shown in Figure 8 and Figure 9.

Test Conclusions
Results from this experimental testing indicates that the engine power, and speed all increase with increasing temperature differential.While the system was initially sized for 150 W, there are several factors that made this power output unattainable: 1.The engine manufacturing quality is not perfect.2. The friction present in the engine (Friction is a large decrease factor in the performance of a Stirling engine).3. The engine design hot and cold cylinder close to each other which cause overheat.

Results and Recommendations
1.The high efficiency of solar Stirling engines makes them an attractive replacement for traditional stations.With their inherent high maintainability and reliability would be perfectly suited for supplementary or whole system power providers.2. Most usual energy generation methods have harmful effects on the environment.Which cause risk for all beings.Power Plant like Thermal, Nuclear and Hydro electrical Power Plants, have high generation capacity but they destroy the nature very bad as it may not recover again.To protect our world from alike situations and to get high quality energy with less efforts, less risk and higher productivity.3. Using this method decrease using other methods which may cause risk and help us to protect our environment which gives this method high rank rating.4. If we compare this method with other power generation systems we will find it is the best one because of its low cost and high reliability.5. Making use of the solar energy as cheapest renewable energy and highest efficiency clear is the aim in this project.For our future finding clean new methods to generate power and support related researches had better be a goal.

2 .
Cold end working volume in cm 3 = 18 cm3  3. Working piston working volume in cm 3 = 18 cm 3 4. Hot end heat exchanger volume in cm 3 = 3 cm 3 5.Cold end heat exchanger volume in cm 3 = 3 cm 3 6.Regenerator volume in cm 3 = 1.75 cm 3 7. Hot end heat exchanger temperature in K = 800 K 8. Cold end heat exchanger temperature in K = 300 K 9. Effective regenerator temperature in K = 450 K 10.Phase angle between displacer and working piston = 90 11.Working gas is Helium 12. Mass of gas filled in engine = 0.1 moles 13.Specific heat ratio for Helium = 1.6667 14.Alfa type components are shown in figure6.

Figure 6 .
Figure 6.The Alpha configuration Stirling engine

Table 3 .
Nomenclature and symbols 1. Hot end working volume in cm 3 = 18 cm3