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> The country is about 42000 km² big It's not clear which country you're talking about; land area of the USA is 9.8 million km². Melbourne (Australia) is a mo

> The country is about 42000 km² big It's not clear which country you're talking about; land area of the USA is 9.8 million km². Melbourne (Australia) is a moderately large city of just under 10,000 km² in area. I'd (very conservatively) estimate at least 10% of that is roof space, so 1000 km² of roof-mounted panels seems pretty achievable. Global electricity consumption (averaged over the year of 2019) is approx 2.7 terawatts (per statistica.com). Lets call it 100 terawatts (storage losses, switching oil heaters to electricity). It's straightforward to get 1 kilowatt per square meter from a solar panel, so you'd need about 100k km² of solar panels globally. That's the rooflines of 100 cities the size of Melbourne.

Aachen 4y ago
> It's not clear which country you're talking about; land area of the USA is... You assume that when someone just speaks of "the country" without specifying, it's the place where people think they're the whole world. I left it out to see if exactly this would happen because I was curious. I'm surprised not one but two persons felt certain enough I must mean the USA to correct my figure for the USA in a comment. Goes to show. My username is a city in Germany but apparently that wasn't enough of a hint that it is, for once, not about the USA. Also the USA uses double the energy per capita and has twenty times more people, 900 TWh should also be a giveaway for those who know any country's energy consumption, or at least it was easy to check that I didn't merely take a wrong km² value (also, I'm using metric). Anyway, I'm glad we can supply global energy consumption this way. Now we just need a global government to distribute the produced energy to countries with higher population densities than the extreme examples you took like USA and Australia. That they can use solar effectively, both from the amount of unused land and favorable latitude, shouldn't surprise anyone. Oddly (no sarcasm here), I don't see them getting around to it either. I just looked up the landuse of my country and that's about 7% built-up area. https://www.clo.nl/en/indicators/en0061-land-use-in-the-netherlands https://www.clo.nl/en/indicators/en0061-land-use-in-the-neth... Even if we cover all of that, it's not enough, we'll need to take land away from agriculture which is already only barely enough to feed everyone in a pinch despite having a huge yield per unit area. Which is not to say we shouldn't do it. I just realized I might come across as "renewables will never work". No, with wind at sea and nuclear (easy to import from any country on Earth since it's so energy dense) we can be self sufficient even though we have enough independent neighbours that we needn't be anyway. It's just that the person I initially responded to wasn't far off, depending on which country they were talking about, and it's something people aren't being realistic about in counties near me. The reason that matters is that it influences policy: rooftop solar and wind are great, go go go, but don't stop there! Don't wait for that to complete, then discover we've replaced 2000's electricity use (not used for transportation or heating) and forgotten about the rest. That's what many countries are doing currently. See people being happy about headlines like "wind and sun were >50% of the energy mix last year!" when they really mean electricity mix and don't realize that this is about 10% of the total energy need.
- cycomanic 4y ago
  Ok point taken, funny thing is I'm German, but the 900 TWh threw me off. What I've read is that Germany is projected to have 600TWh in 2030, for perspective electricity consumption in the US is 1500 TWh atm. However your size for Germany is still off by an order of magnitude. Germany has a land area of 357,000km2. With 13500km2 for producing that electricity we are still at 5% so that is below the 7% of build up area (ignoring wind and other sources).
  - Aachen 4y ago
    Sorry but the country is actually the Netherlands. See the link I shared :D. I live in Germany these days but most of this type of info I still know better from when I lived in NL. (E.g. wouldn't know what the statistics bureau here is called, whereas in NL that's just something I grew up with hearing on the news so I know what source to trust.) That Germany wants to have 600 TWh in 2030 is crazy, I hadn't heard that yet. Very curious how this will work! The only big win I can see would be in heat pumps being 3x more efficient than anything else, but building heating is only a few % of the total use. Industries would also be big wins, but moving steel production abroad is just moving the problem like a hot potato. 82 million people using less energy than their 17 million neighbours did in 2013 would be quite an achievement! In case you remember where you read about that, I'd be curious about a link.
    - cycomanic 4y ago
      > Sorry but the country is actually the Netherlands. See the link I shared :D. I live in Germany these days but most of this type of info I still know better from when I lived in NL. (E.g. wouldn't know what the statistics bureau here is called, whereas in NL that's just something I grew up with hearing on the news so I know what source to trust.) Hah, you're reference to the username threw me off (I have to admit I did not look at the link). > That Germany wants to have 600 TWh in 2030 is crazy, I hadn't heard that yet. Very curious how this will work! The only big win I can see would be in heat pumps being 3x more efficient than anything else, but building heating is only a few % of the total use. Industries would also be big wins, but moving steel production abroad is just moving the problem like a hot potato. 82 million people using less energy than their 17 million neighbours did in 2013 would be quite an achievement! In case you remember where you read about that, I'd be curious about a link. Ok I think I see where the confusion lies. I've been using numbers for electricity production/consumption while you are talking about total energy consumption (I guess?). I think the question of how to transition heavy industry to non-fossil fuels is definitely a big one, I suspect we likely will need hydrogen technology for that (I don't think anyone knows how to do metal manufacturing with electricity directly). It's actually quite current in the situation now. One of Germanies biggest gas consumers is a copper cable manufacturer. If Germany wants to move of fossil fuels/become independent of Russian gas, copper is crucial, but at the same time to make the copper the only solution at the moment is to use gas.

Aachen 4y ago

> It's not clear which country you're talking about; land area of the USA is... You assume that when someone just speaks of "the country" without specifying, it's the place where people think they're the whole world. I left it out to see if exactly this would happen because I was curious. I'm surprised not one but two persons felt certain enough I must mean the USA to correct my figure for the USA in a comment. Goes to show. My username is a city in Germany but apparently that wasn't enough of a hint that it is, for once, not about the USA. Also the USA uses double the energy per capita and has twenty times more people, 900 TWh should also be a giveaway for those who know any country's energy consumption, or at least it was easy to check that I didn't merely take a wrong km² value (also, I'm using metric). Anyway, I'm glad we can supply global energy consumption this way. Now we just need a global government to distribute the produced energy to countries with higher population densities than the extreme examples you took like USA and Australia. That they can use solar effectively, both from the amount of unused land and favorable latitude, shouldn't surprise anyone. Oddly (no sarcasm here), I don't see them getting around to it either. I just looked up the landuse of my country and that's about 7% built-up area. https://www.clo.nl/en/indicators/en0061-land-use-in-the-netherlands https://www.clo.nl/en/indicators/en0061-land-use-in-the-neth... Even if we cover all of that, it's not enough, we'll need to take land away from agriculture which is already only barely enough to feed everyone in a pinch despite having a huge yield per unit area. Which is not to say we shouldn't do it. I just realized I might come across as "renewables will never work". No, with wind at sea and nuclear (easy to import from any country on Earth since it's so energy dense) we can be self sufficient even though we have enough independent neighbours that we needn't be anyway. It's just that the person I initially responded to wasn't far off, depending on which country they were talking about, and it's something people aren't being realistic about in counties near me. The reason that matters is that it influences policy: rooftop solar and wind are great, go go go, but don't stop there! Don't wait for that to complete, then discover we've replaced 2000's electricity use (not used for transportation or heating) and forgotten about the rest. That's what many countries are doing currently. See people being happy about headlines like "wind and sun were >50% of the energy mix last year!" when they really mean electricity mix and don't realize that this is about 10% of the total energy need.

cycomanic 4y ago
Ok point taken, funny thing is I'm German, but the 900 TWh threw me off. What I've read is that Germany is projected to have 600TWh in 2030, for perspective electricity consumption in the US is 1500 TWh atm. However your size for Germany is still off by an order of magnitude. Germany has a land area of 357,000km2. With 13500km2 for producing that electricity we are still at 5% so that is below the 7% of build up area (ignoring wind and other sources).
- Aachen 4y ago
  Sorry but the country is actually the Netherlands. See the link I shared :D. I live in Germany these days but most of this type of info I still know better from when I lived in NL. (E.g. wouldn't know what the statistics bureau here is called, whereas in NL that's just something I grew up with hearing on the news so I know what source to trust.) That Germany wants to have 600 TWh in 2030 is crazy, I hadn't heard that yet. Very curious how this will work! The only big win I can see would be in heat pumps being 3x more efficient than anything else, but building heating is only a few % of the total use. Industries would also be big wins, but moving steel production abroad is just moving the problem like a hot potato. 82 million people using less energy than their 17 million neighbours did in 2013 would be quite an achievement! In case you remember where you read about that, I'd be curious about a link.
  - cycomanic 4y ago
    > Sorry but the country is actually the Netherlands. See the link I shared :D. I live in Germany these days but most of this type of info I still know better from when I lived in NL. (E.g. wouldn't know what the statistics bureau here is called, whereas in NL that's just something I grew up with hearing on the news so I know what source to trust.) Hah, you're reference to the username threw me off (I have to admit I did not look at the link). > That Germany wants to have 600 TWh in 2030 is crazy, I hadn't heard that yet. Very curious how this will work! The only big win I can see would be in heat pumps being 3x more efficient than anything else, but building heating is only a few % of the total use. Industries would also be big wins, but moving steel production abroad is just moving the problem like a hot potato. 82 million people using less energy than their 17 million neighbours did in 2013 would be quite an achievement! In case you remember where you read about that, I'd be curious about a link. Ok I think I see where the confusion lies. I've been using numbers for electricity production/consumption while you are talking about total energy consumption (I guess?). I think the question of how to transition heavy industry to non-fossil fuels is definitely a big one, I suspect we likely will need hydrogen technology for that (I don't think anyone knows how to do metal manufacturing with electricity directly). It's actually quite current in the situation now. One of Germanies biggest gas consumers is a copper cable manufacturer. If Germany wants to move of fossil fuels/become independent of Russian gas, copper is crucial, but at the same time to make the copper the only solution at the moment is to use gas.