how many W per m2 are needed to power an average office

Please define average. E.g. does it need heating in winter, cooling in summer, is there a kitchen etc. ?

I think the answer is in watts, not watts/m2. You then have to figure out how many m2 of solar panels you need to provide that, given assumptions about panel efficiency, average insolation, etc.

This is total back of the envelope math with some serious guessing, but may give you a ballpark. Assume you have a person for every 10 m². That person is probably going to have a laptop and a display for somewhere in the ballpark of 100 watts. So there you have 10 watts per square meter. Add another watt or two for common infrastructure - screens and conference rooms, water heating for coffee and hand-washing... That stuff just isn't going to add up to much. Then you have the big one, which is space heating and cooling. And that's also where you'll have the most variance depending on climate, time of year... Also, confounding it, most offices are going to have centralized boilers and chillers so it probably won't even appear on the renter's electricity bill. I'm going to take a shot in the dark and say you're going to need about 50 watts per square meter during peak usage, so maybe a long-term average of 10 to 20 watts per square meter. So summing that up and averaging, I'd say about 25 watts per square meter for an office?

It is dependent on climate and the building envelope.

I'm intrigued by this question, I have a bit of free time at work in about an hour. I'll try a rough estimate based on my current wfh space.

https://remotefillsystems.com/how-much-power-does-an-office-building-use/