Any explanation or good articles would be helpful.
In summary, "the assertion" is false.
1: https://www.ers.usda.gov/topics/crops/corn-and-other-feedgra...
2: https://www.nrel.gov/docs/fy13osti/56290.pdf
3: https://www.eia.gov/energyexplained/electricity/use-of-elect...
Besides that just the area already devoted to fossil fuel extraction would suffice, solar and wind coexist neatly with existing uses, so don't need to "use up" any land at all.
According to linked calculation Solar PV needs 19 sq m per MWh per annum
Per Wiki final total energy consumption is 7050 MTOE which translates to 610 TWH
Multiple this by 10, 1.5 to account for energy losses,1.5 for capacity factor issues and 3.33 for growth in developing countries. Rounding up say the world needs 6000 per annum
Area needed = 6000 * 10^6 * 20/10^6 = 120000 sq km
Even in a densely populated country like India that is roughly 3% of the total land area
The challenge off course is installing it cheaply and balancing demand, supply, transmission etc.
https://persquaremile.com/2011/01/20/800-million-spaces-and-...
So we have experience building infrastructure of a similar scale, though probably not quite at the speed currently needed to meet carbon emissions targets solely by building photovoltaics.
Of course, deserts, and not cities, are the best places to put solar power, especially since the shade generated can be useful for crops, and we have tons of desert in the US
We need about 900 TWh of energy in the country. A calculator tells me that's
$ calc 900TWh/MWh\*(15m^2)
(900 \* ((terawatt \* hour) / (megawatt \* hour))) \* (15 \* (meter^2)) =
13500 km^2
I was under the impression that roofs are not enough by far; perhaps it works when we add parking lots and cover all roads, or perhaps my knowledge is outdated (also because batteries have evolved since I first heard that). Either way, we'd have to cover gigantic amounts of land with electronics. Not saying it can't be done (I don't know enough about it), but not having any hydro to speak of, little space far enough from villages for wind, and no nuclear in the mix for the sake of argument... it sure seems daunting.
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.
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-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.
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).
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.
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.
As far as I know, indeed, we can't use electricity directly. But it's not just heavy industries like steel that need high heat: also general building heating, transportation (any mode), mining, everything needs to become zero carbon. Hydrogen allows us to transition some industries that can't use electricity directly as far as I know, but that extra step just introduces another efficiency into the system. Even at 1:1 (win some on building heating and mass transport, lose some on e.g. hydrogen conversions), it seems to me like a tough challenge to be self sufficient and climate neutral in western Europe. Gonna need every angle we can get.
To get a feeling if we could use rooftop solar to satisfy energy consumption. LA has an area of 1200 km², assuming 30% of the City are buildings and parking lots (not sure if that is a valid assumption) putting solar on those would satisfy about 3% of energy capacity requirements. Judging by that it doesn't seem outrageous (orders of magnitude off) to say we could satisfy all electricity demands with rooftop solar, especially if we add wind and hydro to the mix.
You assume that when someone just speaks of "the country" and "we need" 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).
For what it's worth, I just looked up land use in my country, it's "less than 7%" built up (buildings at least, sounds like it also includes roads and parking lots) according to the statistics bureau. 4/5ths is nature, recreation, agriculture. https://www.clo.nl/en/indicators/en0061-land-use-in-the-neth...
That the USA has it easy with gigantic slabs of unused land around and still they're not really making use of it, so that bodes well for those with more people per km² which I think is most other rich countries (aside from Sweden, Norway, Finland, Iceland, Canada where it's probably not sunny enough anyway, at least not in the places where there is plenty of unused space).
> would satisfy about 3% of energy capacity requirements
Which figure for energy consumption are you using here?