Consider the changing
arc of the sun at different times of the year in the planning process
“Peak irradiation is 1,000 watts per square meter. If
we have a 740 watt solar array and our motor requires 600 watts to achieve the desired fl ow rate, we can double the array size to 1,480 watts and maximum fl ow rate will occur from the pump on days with irradiation of 500 watts per square meter. “Consider the changing arc of the sun at different
times of the year in the planning process. To maxi- mize the capture of sunlight modules, PV panels must be mounted tilting toward the sun, which means that solar modules must be installed facing south in the northern hemisphere and facing north in the southern hemisphere. The optimum tilt angle is determined by the location’s latitude. In the summer, the tilt should be the latitude minus 15 degrees and in the winter, it should be the latitude plus 15 degrees. As a year- round compromise for pumping applications, the tilt can equal the latitude.” “Plan for shading when designing a solar-powered
water system,” Macias continues. “Shading caused by distant objects doesn’t have a signifi cant effect because diffused light, or light bouncing off of other surfaces, will contribute to module outputs. Shading from near objects will cause more severe drops in power and can easily stop the complete output from a module. Any modules connected in series to a shaded module will be brought down to the shaded modules level. Shad- ing can reduce the output from a module or series of modules to zero.” When choosing a location for the solar power instal-
lation, make sure that nearby trees will not provide a shading effect on the PV panels. Even though trees may not be a current problem, they will continue to grow and may become a shading problem in the future. Trees have leaves in the spring and summer which increases the amount of shade. Tools and computer apps are available for viewing
the solar path. Sunseeker, for example, provides a fl at view compass and an augmented reality 3-D camera
tscra.org
showing the solar path, its hour intervals, its winter and summer solstice paths, rise and set times and a map view showing solar direction for each daylight hour.
Safety “PV panels generate DC electricity which should be
respected,” said Macias. “Develop and follow a safety program based on local safety rules and codes of practice. Consider three 185-watt modules in a series; they generate 150 volts whereas less than 42 volts of either DC or AC electricity is considered safe. Handle PV modules with care and respect.” A switch for disconnecting solar panels from the
pump is an important safety measure and is part of every professional installation. The disconnect switch is placed between the solar generator and controller. It must be a DC type for high amperage and connected as per the manufacturer’s instructions. A disconnect switch is a national electrical code requirement in most countries. The system controller allows the pump to start and
run at reduced output in low sunlight hours. Through maximum power point tracking (MPPT), a system can be optimized to produce 10 to 15 percent more water in a day. The controller also protects the pump from running dry, stores system performance data, and shuts off the pump when the tank is full. “Although a disconnect switch is used to cut off
power to the pump, PV modules produce power when they are in daylight and cannot be switched off,” Ma- cias says. “Before working on the equipment, cover PV modules with a sheet or cover of opaque material to stop power generation. “Effi ciency in water engineering is taking a creative
approach to meet needs,” Macias concludes. “Use the most reliable water source, which is often a deep well. Design a system to deliver the required water at the right time with the power available. Size the system so it is independent of any other power source in meeting water requirements. “It is important to look at the maintenance costs as-
sociated with any solar pumping system. Some systems contain non-serviceable components, which means that the entire pump, motor, and controller have to be replaced when they quit functioning properly. This leads to higher maintenance costs than are incurred by replacing individual parts. Compare systems by gallon per day performance, maintenance costs, life span and warranty coverage. Evaluate suppliers by their reputations and service.
May 2015 The Cattleman 63
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