Using a datacentre such as S3 will gain the benefits of an economy of scale. Per-website S3 energy costs are going to be substantially lower than the energy cos

Using a datacentre such as S3 will gain the benefits of an economy of scale. Per-website S3 energy costs are going to be substantially lower than the energy cost of a solar-server: each solar-server that is installed will have had to have been built in factories which cost energy to run, shipped in delivery vehicles which cost energy to drive, plus the humans behind the website would require energy while building the server... all of which would easily be more than the net energy consumption of a single website in S3. That being said, the point of the project is to produce a website that is 100% solar powered. They never said they were aiming for something that is feasibly sustainable.