Green Fest will use the portable solar sound system created by Crow Weaver and the Native Earthling Band.
The Band's solar sound system collects sunlight via three photovoltaic panels. Each SunWize SW115 panel outputs 115 watts of power, for a total of 345 watts. The panels provide direct current at 16.7 volts. The SunWize panels have a "rated" working life of about 50 years, at which point the cells will still put out 85% of their design power.
The solar panels are wired into a charge controller that regulates the current supplied to the battery. This is the heart of the Solar Stage. The charge controller keeps the battery topped up while protecting it from being damaged by overcharging. The life of the battery is directly impacted by the quality of the charge controller, so this is not a place to skimp. The Solar Boost 2000E from Blue Sky Energy is a pretty good one.
The inverter takes 12 volt direct current from the battery and converts it into standard 120V alternating current to run our gear. The band has considered running directly off 12V DC, but has found it difficult to find gear that can do that without major modifications to the power supplies. Their inexpensive Whistler PP300AC inverter does a pretty good job. It will shut down automatically if the battery voltage drops too low, preventing the batteries from being discharged completely.
The two batteries are sealed lead-acid gel cell batteries (Type 8G8D) with a capacity of 265 Amp-hours at a nominal 12 volts. These batteries are designed for deep discharge cycles, unlike the battery in a car, which are optimized for the big surge of power needed to start it.
Even on an overcast day, diffuse sunlight is enough to charge the system's battery.