# Biaxial-Type Concentrated Solar Tracking System with a Fresnel Lens for Solar-Thermal Applications
## 1 Introduction  
The growth of technology and the economy is heavily dependent on energy consumption and the demand for energy is increasing steadily every year. Environmental issues such as global warming and eco-friendliness have begun to attract attention in mainstream society. In addition, the consumption of fossil fuels also seriously affects our global environment; therefore, seeking other, environmentally friendly energy resources has become a worldwide priority. Solar energy, due to its green nature, and its easy acquisition at low cost, has demonstrated great potential as one of the top clean energy sources. According to a marketing report from the US marketing research and analysis company, BCC Research, the global markets for industrial and utility solar thermal technologies amounted to $929 million in 2008, which increased further to $3.7 billion in 2009 [1]. Therefore, the market for solar energy has great future potential. To date, many countries have devoted efforts and resources to Stirling engine research for varying applications such as national defense, power generation, and aerospace [2]. Waste-heat [3; 4], solar [5; 6; 7], biomass [8], low-temperature [9], and small Stirling engine systems [10; 11] are examples of new power generation applications. Among these power systems, the solar Stirling engine is the most promising technology. The solar Stirling engine uses a parabolic reflector as the main heating element. The engine is installed at the base of the optical tracker with a rotational mechanism where the parabolic reflector is connected. This rotation/reflector subassembly is then assembled with engine, heating head, and power generation system to form the complete solar power system. The parabolic reflector focusesand projects the sunlight onto the surface of the heating head to drive the Stirling engine to generate electricity. In 2008, U.S. SES, Inc. and Sandia National Laboratories co-developed a Stirling solar dish collector power system, the Suncatcher [12]. The power generated from this system is 5-25 kW and the system operation temperature is 750 \({}^{\circ}\)C with energy efficiency of 29.4%. Infinia, Inc. [13] built a small dish Stirling generator, the Infinia Solar System, which was the size of a television satellite receiver. The system can generate 3 kW of power with 30% efficiency. These improvements in power generation techniques heavily depend on the sunlight tracking technology. Therefore, this study explored the effect of the focal point position of the focused sunlight to the heating surface area on the heating head. In addition, we are hoping it can also be applied to the development of future heating head modules. The tracking approach and the system structure for the solar tracking system need to be compatible. Different tracking structure requires different tracking approaches. Generally, the two major solar tracking systems [14] are altitude-azimuth with biaxial rotation and west eastern-south northern with individual axis rotation. The advantages of the altitude-azimuth system are its wide rotation angle for the azimuth and less interference during tracking. This mechanism can also be used at broader regions on earth. However, it is more challenging to prepare the control algorithm for tracing the trajectory of the sun. For the solar tracking mechanism, passive and active tracing are the two major control approaches. The difference between them is mainly due to the use of electrical energy and the control program. The passive system uses passive components or physical/mechanical changes of the materials to change the structure of the tracking mechanism for sunlight tracking. However, the active control mechanism needs motor, control IC, tracking program, and sensing elements for tracking the position of the sun [15; 16; 17; 18; 19]. [PERSON] _et al._[20] designed an active single axis solar tracker with two light-dependent resistor (LDR) sensors that are located on the surface of the photovoltaic (PV) panel.