The garden office has got one entirely unused feature — a large roof! What better place to mount solar panels for an off-grid power supply …
These Sharp PV modules (ND-R245-A6) [PDF datasheet] are manufactured in Wrexham and (although pricing is very opaque) appear to cost around £250 per module. I would need three or four. Each module produces a peak of 30V, 8A (= 240W) although in reality I’d guess the voltage would vary wildly from 0-30V.
Inverters, the part which normally converts the DC and highly variable power from the modules to mains AC voltage, are expensive, costing likely as much or more than the panels themselves. As this is an “off-grid” installation, this is useless. It would seem to be better to use the power to charge car batteries.
The car batteries provide the smoothed 12 V supply which would be used to run servers and lighting.
So there seem to be two problems in the way: (1) How to charge the batteries. I think I need something like this? (2) How to power servers directly off 12V …
As always, it becomes much clearer once you have the key search term, and the word in this case is caravan. Apparently people who own caravans, static caravans, narrow boats and so on are in precisely this situation, and there are special purpose charge controllers used for this (made by Steca, amongst others).
Here and here [both PDF] are two excellent starter guides for the self-builder.
Now all I need to do is to size my requirements and work out how to power a server off a 12 or 24V supply.