"AWS's continued lack of transparency is a problem that will likely become a bigger concern to its customers. AWS has recently stated that it is currently 25 per cent renewably powered, but with no additional detail provided,"
Which could mean "we get out power from the national grid in the country where our datacentre is located, and the statistics provided by our power suppliers suggest that 25% of the power that they supply to us comes from renewable sources".
Electricity can't be stored to any grid-scale meaningful extent, and it can't be labelled or assayed. For any company foolishly paying a premium for renewably sourced electricity, there's another one being subsidized to take the electricity generated by dirty power stations at a (slightly) lower price! Any claim for a grid-connected facility that it's "100% renewably powered" is greenwash, pure and simple.
Which isn't to say that renewable generation is pointless, but that targeting particular consumers is pointless (except if they have a facility that might be running with solar power off its roof, or might be using its "waste" heat constructively, and aren't.)
The greenest thing that server farm operators could do is to invest in cooling systems that dump "waste" heat into water, that could then be sold to surrounding communities for indoor heating during eight or more months of the year. Sadly, there seem to be no economic incentives being provided to encourage the recycling of "waste" heat so it ceases to be wasted. Solar or wind generation, yes. Running indoor heating with energy that's already been used once, no.