After a very fruitful and useful discussion with Dennis Pottratz, a local solar energy expert, I have a much better idea of how to maximize resources. After determining that our load is 2.5 W + 4 W = 6.5 W for each R-PI and speaker pair, I wondered about simply doubling the number of speakers per R-PI, thus halving the number of total units. My thinking is that each R-PI can produce a stereo audio signal, and each side of the stereo field could feed 2 speakers. This new model allows us to have fewer but more robust units. The new load, therefore, could be 2.5 + 4 + 4 = 10.5W. If each unit were to operate for 12 hours per day, that would mean a total load of 126 watt hours. At 12 volts, this amounts to 10.5 amp hours. According to Dennis, it’s good to have 3-5 days of backup power. In May, we can assume an average of 4 “sun hours.” Given these factors, he recommends a simple flooded lead acid battery (of the RV/deep cycle variety), and a 50W solar panel. As it turns out, he can get a panel for around $150, and a battery can be procured in town for around $75 (12V, 100 amp hours). It makes more sense, to me, to have our power supplies be fewer in number and go a little farther rather than building many power supplies that are used minimally. Form follows function.