Yes, i did think about this in the shower.
Just to put things into proportion:
This is vienna. Vienna has an area of around 400 km².
And the blue area is the area that would have to be covered by solar panels to produce enough energy for the whole city:
Source: I did the maths myself. I assumed that per person around 30 MWh of energy/year are needed. Data for this: our world in data, energy usage per person. It’s well known that 1 m² of solar panel produces around 200 Wp and that’s 200 kWh/year. So you need about 150 m² of solar cells per person. Vienna has about a million inhabitants, so that makes 150 km² of solar panels approximately.
Does it need to be in the city, though?
Also for reference from Google ai: For global electricity needs: An area of approximately 40,000 to 55,000 square kilometers (about 15,000 to 21,000 square miles) could theoretically generate the world’s total electricity consumption. This is less than 1% of the total land area of the United States. For total global energy needs: The estimated area is around 497,000 square kilometers (about 192,000 square miles), roughly the size of Spain. This covers the total projected energy demands, including converting non-electric needs (like transport fuel) to solar-generated power.