If using Google Sheets, you are giving Google a lot of information about you. Google can and will read all of the contents of every file you upload and use the information for advertisement targeting.
As a software developer, I'd say the majority of the processing power needed at the server side is the advertisement targeting information collection. The software itself, if you could use it without ad targeting, would require relatively little resources.
The server side of a web application can vary tremendously depending on which language they use: compiled or interpreted. So, there can be at least 10x differences in the needed server resources. I don't know what language Google Sheets is programmed in (the client side is obviously JavaScript and strictly speaking you should take into account the client-side energy consumption as well, but the server side language is unknown).
The storage part also needs some resources, but that depends on how much storage space you need. You can calculate it by figuring out the energy usage of various storage technologies.