3 GW measures average power. Google just buys the entire output of wind or solar farms, so supply is not matched with demand.[1] This is a known problem with renewables. Elon Musk claims that he can solve it with a relatively small area of batteries like the Powerpack, but he's sold less than 1 GW so far because batteries are expensive.

[1] https://environment.google/projects/announcement-100/

I guess that accounting is natural for marketing numbers.

I don't generally think it's a problem, it's just a feature of those generation methods and just means we need overprovisioning. Whereas fossil fuels have unsurmountable problems and cause untold human suffering, famines and damage to the environment.

I think that Google has made a fantastic step forward. However, solar and wind require some form of energy storage, such as pumped hydro or batteries (which Google hasn't addressed). Overprovisioning by itself isn't sufficient.