It might be worth looking back at the conversations a few weeks ago as a few of us have been trying out other small computers (pine64/CHIP) as possible options for a solar staker as well. The CHIP could be promising as it has lipo charging, wifi and eMMC memory on board.

With my CHIP and a 3000mAh battery I was able to get almost 10 hours of running time. I'm now waiting on a 5000mAh cell to test that (I'd hope it get's over 15 hours reliably). Unfortunately I'm not in a particularly good location for testing solar.