[juloo]

What does low tech means in this context ? It's still a computer, with complication on top: solar panels, battery.

All the hardware they use requires some energy to be built, the network consumes a lot of energy too.

How does this compare to a VPS server at a cloud provider or using the grid electricity (no solar panel) ?

I'd expect individual VMs to use less energy compared to a decicated computer.

Is it really greener to stop using the grid electricity but instead buy a small solar panel ? Surely that'll be less green than the grid 20 years in the future.

The article contains many sources but doesn't compare other solutions. 2.5 watts is impressive, though.