I was contemplating on the same thing. A conversion of voltage to 1.5V.
The simplest thing I can come up with is a solar panel 12V dc and a power
converting, commercial unit to 120V ac, and then down convert to 1.5 ac
and a diode to make it dc, or diode bridge, or zenner bridge with capacitors.
The most elegant would be is a solar panel with 1.5V dc output and a voltage
regulator ot 1.5V
Other possibility is to get one of those single unit solar panels that have a 120 ac
converter built in, and down convert to 1.5 and make it dc.
Other power sources could be used too, like a wind generator, a diesel generator,
an under water propeller with a generator in a current.