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.

  • squaresinger@lemmy.world
    51·
    3 days ago

    Vienna has around 68km² of roof surface.

    But there are two nice facts that make the whole calculation easier:

    • Resources used in a city don’t need to be produced inside the city. Imagine we had to grow all the crops and lifestock consumed in a city also inside of the city borders. Or gas, oil, coal, water or any other resource. Cities can only exist by importing resources from the outside. And luckily power cables are a thing, so it’s quite easy to import electricity from outside of the city.
    • Solar isn’t the only kind of renewable energy. The area north east of Vienna is dotted with wind turbines. There’s a huge amount of hydropower all over Austria. In fact, 87.5% of the electricity generated in Austria is generated by renewable energy, and the remaining 12.5% are pretty much only to cover the times when renewables don’t output enough power.

    So the whole point is kinda moot. If we would put solar on all rooftops in Vienna, it would be enough to cover for the entire remaining fossil-based electricity generation in Austria if we had the means to store that excess energy.