Usually the best solution is the simplest solution. I'm using a LM386 now for the preamp in my Wind Harp. The LM386 has low power needs and has good tonal quality, plus its use as a preamp is simple and efficient. I will also use two solar garden lights wired in series to supply power. To draw power from the solar lights just simply connect a set of leads from the the battery holder terminals. Bring out the wires and connect in series. Below is the schematic and photos of the solar lights.
The schematic of the preamp using the LM386 and two garden lights.
Remove the screws that hold the two halves of the garden light together. Solder wires to the battery holders inside the garden lights and connect in series.
Closeup showing circuit board (perfboard), connectors for power, input and output. Hide all this wiring inside the bottom bowl of the garden light.
For more info about garden lights and how they work, visit "Garden Light Autopsy" at my website here. Or get the pdf here.