Use a garden tractor 12V battery or 2, 6V rechargeable lantern batteries. Mount a 12V solar panel somewhere on your panel.....to collect indoor ambient light. I have many solar powered products in my home that only receive ambient indoor light. Clocks, nite lights and environment indicators.....temp, pressure, humidity. I have several solar powered atomic clocks and nite lights, have worked for years on ambient light. Those garden stick in solar lights, work just fine inside.