U.S. Customs and Border Protection (CBP) is one of the world’s largest law enforcement organizations and is charged with keeping terrorists and their weapons out of the U.S. while facilitating lawful travel and trade. CBP provides security and facilitates operations at 328 ports of entry throughout the USA. Private civilian companies are involved in the protection of US borders through their manufacturing of surveillance systems that are used by CBP. FWR manufactures sophisticated surveillance and communication devices that are tested in a remote location in the desert of southern Nevada. The system includes thermal and infrared imaging, sound amplification, various optic sensors, and a variety of communication applications. FWR requested a portable solar generator that would provide power for their system 24/7. In addition to the assessment of power specs that is required to design a proper portable solar power system, the study of ambient and operating temperatures and their effects on the performance of the components of the system is critical. The temperature on the surface of the desert during mid-day peak sunshine can exceed 125F. Metal parts and black surfaces that are exposed to direct sunlight in the desert heat become too hot to touch. Under such circumstances, certain electronics will overheat, shut down, and result in failure of the system.
Portable Solar Power
The latitude of Las Vegas is approximately 36 degrees north. If a solar array is tilted south at 36 degrees, it could produce power for perhaps 8 or more hours/day. For worst case scenario estimates, one could assume 5 hours/day of peak sunshine. Taking into account the effect of temperature on performance, the size of the solar array that was needed to replace power consumed was at least 600 watts. During clear sunny days, the solar array could produce excess energy that could be stored in batteries. Since the communication system required 24 volts, the battery bank was arranged in 24-volt configuration, and the radio and other devices would draw their power directly from the batteries. No additional heat-producing electronics would be needed. The batteries would be grouped in small pairs in separate hard cases in a modular fashion so that each unit could be carried by one person. At the final destination, multiple hard cases would be interconnected using cables to form the final product. The entire system could be hauled in the bed of a pick-up truck.
The potential problem of temperature during the day was reviewed. The high temperature of the solar panels would decrease their performance, but that is a constant and would be factored into equations to calculate power production. Electronics and lithium batteries were chosen for their efficiency and temperature ratings, and would be enclosed in hard cases to block direct sunlight, and with openings in each case to allow heat to escape. The installation of fans in the hard cases to assist with cooling was considered. Electric fans require power, and that would require the solar array and battery bank to be larger and heavier. When weight is critical, other options must be considered. Another option might be to shade all of the components of the system, except the solar panels, with desert camouflaged netting and/or burlap, supported above ground on posts. Shade would reduce the temperature of the components significantly. When the entire system was tested in the desert, temperatures were monitored. If temperatures were too high, the installation of fans into the hard cases would be investigated.
Once designed, the system resembled a series of cases similar to those in the system Desert Heat, and interconnected by cables. Each individual case has its own solar array that plugs into the case. All of the cases are covered and shaded by netting that is set up a few feet above the cases. According to FWR, the system has been operating well, and critical temperatures have not exceeded 130F.