JB is one of eight sailboarders who plan to enjoy seven consecutive days on a smoking hot beach in the Sonoran Desert, State of Sonora, MX, where there are no electrical outlets. It would be nice to have a supply of icy cold drinks, but there is no way to power up the 4 small portable refrigeration units. The nearest small town is 60 kilometers away. It was JBs’ appointed duty to find a solution to the serious problem of no cold drinks. JB approached Powerenz for a portable solar charger.
During the afternoon in August, the ambient temperature on the desert beach can reach 105F or higher, and one adult male can easily drink 1-2 gallons of liquids per day. After sundown and during the night, the ambient temperature is much cooler. The sailboarders use portable coolers that are rated highly energy-efficient. The model of cooler that the sailboarders use holds 47 quarts, weighs 48 pounds, can be powered using 12- or 24-volt DC or 100- or 240-volt AC, draws around 6 amps/72 watts during the initial rapid cool down period, then under 1 amp/12 watts once the interior of the cooler compartment reaches the goal temperature. Each cooler will maintain a stock of drinks icy cold all day as long as there is a source of electricity. According to JB, the coolers are turned off at night, and then turned back on in the morning. In addition to powering up the coolers, JB mentioned that it would be nice to use the system as a solar cell phone charger for their eight iPhones.
Over a 24-hour cycle, the average power draw of each cooler is approximately 12 watts. The estimated total power requirement per day is 12 watts/cooler x 4 coolers x 14 hours of operation per day = 672 watt-hours. The peak momentary power draw when all 4 coolers are turned on is estimated to be 72 watts x 4 = 288 watts. During August in the Sonoran Desert, there are clear blue skies all day, every day, and one can expect to receive 6 or more hours of strong peak sunshine every day plus another 2 hours of less-than-peak sunshine. Taking into account electrical inefficiencies, overestimating power needs, and underestimating power generation and storage, we calculated that the portable solar charger would need to produce at least 800 watt-hours in 6 hours of peak sunshine = 133 watts.
To generate at least 133 watts, a pair of lightweight, high-efficiency, folding, 88-watt solar panels would be satisfactory (total power production = 176 watts). To provide the peak power requirement of 288 watts, the system would be assembled to include four separate 12.8-volt DC plug-ins directly from the main battery, one for each cooler power cable, and each one of which could supply up to 120 watts simultaneously. To store the energy that would be harvested from the sun every day, a 100 amp-hour, 1280 watt-hour, 12.8-volt, lightweight, lithium chemistry battery would easily get the job done. To charge the battery from the solar panels, a 15-amp, efficient, MPPT solar charge controller would be perfect. All of the wiring, circuit breaker protection, connectors, extension cables, and individual plug-ins for the coolers would be included. All of the components, except the two solar panels, would be enclosed inside a durable hard carrying case that would protect the electronics from the sun, sand, insects, and saltwater spray.
Since the sailboarders would drive their two SUV’s directly onto the beach, the weight of the portable solar charger was not critical since they would not need to be carried by hand. Completely assembled, the portable solar charger was very similar to our system called Desert Heat, and weighed 70 pounds.
Once the details of the system were agreed upon, for example, the colors of the hard case and portable solar panels, and the lengths of the extension cables, the complete system was assembled, tested outdoors, and delivered to the shipper 5 days later. The system was shipped from our shop in Kennesaw, GA to Tucson, AZ, and then driven to the desert beach 4 hours away. We have been informed that the system is functioning well, and is producing enough excess power to be used as a solar cell phone charger, to recharge multiple small batteries for their digital cameras and flashlights, and power up one laptop computer.