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Abstract. A compound biaxial sun tracking system is designed to improve the
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efficiency of solar panels for power generation. The difference between sensor
signals can be judged by the system and the stepper motor can be controlled to
drive solar panels to track the sun. At the same time, the system can calculate
the elevation angle and azimuth of the sun to drive solar panels to the best loca-
tion by given information in cloudy circumstances. The advantages of the two
track methods are complementary in different situations, thus the efficiency of
solar panels for power generation is increased. The battery maintenance is taken
into consideration when solar panels do not work normally. The motion charac-
teristics of the system are analyzed to verify the feasibility of the design.
Keywords: Sun tracking; compound track; control system; AVR MCU.7512
1 Introduction
Many solar energy equipments have been widely used since the solar energy is a kind
of clean energy. However, the low transfer efficiency of the equipments had not been
olved. As far as the solar cells are concerned, they can be pided into four catego-
ies, i.e., the monocrystalline silicon solar cells, the polycrystalline silicon solar cells,
he amorphous silicon solar cells and the thin-film silicon solar cells. Monocrystalline
ilicon solar cells have the highest rate of photoelectrical conversion. The theoretical
conversion efficiency is 24% to 26%. But the current conversion efficiency of indus-
rial-scale production is about 17%. However, Monocrystalline silicon solar cells have
he high cost, complex process of production, and it is not easy to promote to use.
Solar cells commonly used in commercial are thin-film solar cells and polycrystalline
ilicon solar cells. The theoretical conversion efficiency of polycrystalline silicon is
about 20% and the actual efficiency of production is 12% to 14% [1]. The market
hare of the thin-film solar cells is increasing year by year because of its low costs.
Although a thin-film solar cell with conversion efficiency of 24.2% was developed by
nstitute for Solar Energy Systems in Fraunhofer, Germany, which is the highest re-
cord in Europe [2], the conversion efficiency of commercial thin-film batteries is only
about 6% to 8% [3]. It can be seen that the actual value of conversion efficiency is
much lower than that of theoretical value. Therefore, new methods need to be devel-
oped to improve the conversion efficiency.
Most present used solar energy devices are fixed at an angle to the sky and design-
ers must calculate the best angle to maximize solar energy collection [4]. As the sun
position changes with time, it is necessary to adopt a solar tracking device to improve
he utilization of solar energy. Previous studies show that the solar energy absorbed
by the biaxial sun tracking system is 35% higher than that of the fixed system [5].
Therefore, the study of sun tracking control system is imperative.
2 System Design
Several aspects must be taken into consideration in sun tracking system design. The
first is how to determine and respond to the sunny and cloudy. The second is how the
solar panel moves to track sun in different states. The third is how to deal with the
problem of battery overused in continuous cloudy days.
The main normally used methods of sun tracking are active tracking and passive
tracking. There are controlled release tracking, clock-type tracking and elevation an-
gle-azimuth tracking in active tracking. Passive tracking includes pressure-tracking
and photoelectric tracking. Since the active tracking is not reversible, the tracking
error will accumulate and the tracking accuracy is not high. Although the elevation
angle – azimuth tracking has higher accuracy [6], it needs to keep running, this will