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A typical solar tracking system adjusts the face of the solar panel or reflective surfaces to align with the sun as it moves across the sky. The system moves though one rotation per day. It is this relatively slow motion that enables the time-compression approach for ALT. The time-compression ALT approach entails using the system more often than under normal conditions. For a solar tracker, we may be able to increase the speed of the tracking to experience an entire day of movement in an hour, for example. If we run the test though 24 cycles per day, the system experiences 24 days of use in 1 day. The calculation of the acceleration factor is then (11.9) AF = use cycle duration test cycle duration = 24 h 1 h = 24 Time compression in this fashion is easy to use and understand. In the above simple example, the acceleration factor is 24, or each day of testing represents 24 days of use. One consideration is in verifying whether the failure mechanisms of interest have the same chance of occurring as when the system is in actual use. One can imagine a test that cycles the solar tracking system so fast that the heat buildup and associated failures that occur have little to do with the failures during actual use. In the design of the test, one must be careful not to introduce conditions that would alter the causes of failure, thus inducing failures that are irrelevant. Another consideration is that the use of a system in the field experiences a wide range of environmental conditions that are difficult to reproduce in the laboratory. If dust buildup is an important element causing tracker motor failures, then including some replica of dust buildup during ALT may be necessary. The closer the testing conditions mimic the use conditions, the better. In most cases, understanding the failure mechanisms and the primary stresses that cause the failure to occur enables the design of a meaningful accelerated life test..
Single-axis solar tracking systems follow the solar by moving in a single axis (vertical or horizontal). Generally, the inclination angle is adjusted manually at certain intervals during the year and automatic movement is provided in the east–west direction. Single-axis systems are more cost-effective than two-axis systems but have lower yields in terms of efficiency. Single-axis solar tracking systems are moved on the vertical or horizontal axis depending on the solar trajectory and the weather condition
While single-axis utility-scale solar tracker installations have widely proliferated in the heady solar market, the more commercial and industrial-oriented dual-axis tracker has not enjoyed such rapid growth, despite the economic advantages the second axis offers by following the sun much more closely. Part of the reason that the market for dual-axis trackers has not boomed is that most U.S. manufacturers are smaller companies, compared with the large corporate manufacturers of single-axis trackers. Another reason is that single-axis trackers are most economic in regions with large flat sites, like the U.S. Southeast and Southwest, where utility-scale projects are largely centered, although this is changing. Another key reason is that many developers focus primarily on up-front project cost rather than lifetime yield and low ROI.
