Is This Legit?

[Hashim]

Hey everyone,

 

I found this image off of Facebook, and it seemed too insane to be true, so I wanted to find out just how legitimate it is... hence my being on here - the first result that came up when I typed "science forum" into Google - in an attempt to get the answer from the horse's mouth. Is it true - is the amount of energy that hits the Earth in an hour enough to meet the world's energy demands for a whole year? Is it maybe a half-truth, one that's been oversimplified, or is it just plain wrong? Would really appreciate an answer, thanks.

 

[iNow]

Yes, it's legit.

http://www.nature.com/nature/journal/v443/n7107/full/443019a.html

[swansont]

And we can just run the numbers to confirm that. The area presented to the sun is around pi*(6.4 x 10^6 m)^2 = 1.25 x 10^14 m^2, and we get about 1.3 kW/m^2 at the top of the atmosphere, so that's around 1.6 x 10^14 kWh.

 

In 2008, the world used 132,000 TWh, which is 1.32 x 10^14 kWh

http://en.wikipedia.org/wiki/World_energy_consumption

[MigL]

Remember though, that the Sun also heats and powers all natural processes of this world.

Capturing all of it for our own use would leave none for natural processes.

[iNow]

Er, huh? We don't need to capture it all, nor could we. That's beside the core point that solar is more than enough to power all of civilization if we can do a better job of capturing and storing it.

[MigL]

Err, huh ? Just clearing your throat ?

That's not the point I was making either.

 

One could cover the world with solar collectors and have several hundred times more energy than we currently need.

But the world would die.

 

Solar collectors could be built in space to collect the 'wasted' energy which goes off to deep space, as our world subtends only a small angle of the Sun's circumference.

 

Sorry if I didn't make myself more clear.

[ajb]

MigL has a good point, and one that is not usually discussed in the context of renewable energy.

 

I have no idea of the numbers here, but for sure at some point wave/tide, wind and solar energy production will effect the global weather of the planet. Just energy conservation considerations tell us this.

[michel123456]

And we can just run the numbers to confirm that. The area presented to the sun is around pi*(6.4 x 10^6 m)^2 = 1.25 x 10^14 m^2, and we get about 1.3 kW/m^2 at the top of the atmosphere, so that's around 1.6 x 10^14 kWh.

 

In 2008, the world used 132,000 TWh, which is 1.32 x 10^14 kWh

http://en.wikipedia.org/wiki/World_energy_consumption

Is that the whole Earth surface or half of it (the half that faces the sun)?

-------------------

And I suppose a lot of this energy is re-emitted at night.

[overtone]

So if we are about 40% efficient in capture (about the limit of a thermal solar setup), and make no advances in efficiency of use, we would need to cover something like 58k square miles of the earth's surface to run everything on captured solar.

 

That's a square area about 240 miles on a side. Of course that would not do - we'd need probably four times the area spread around so it's always in the sun. But even that's less than we've covered with parking lots and the like.

 

As far as affecting the weather - that train left the station long ago.

 

Oops - just realized they were measuring at the top of the atmosphere. So multiply the area by ten, the square sides by the the square root of ten - it's still feasible. It's still in the range of area we've already roofed, paved, etc.

Edited May 24, 2015 by overtone

[swansont]

Is that the whole Earth surface or half of it (the half that faces the sun)?

-------------------

And I suppose a lot of this energy is re-emitted at night.

 

I used pi*r^2. The projection of the surface facing the sun.

 

Some re-emitted at night. Some during the day. A fair fraction never makes it to the surface.

MigL has a good point, and one that is not usually discussed in the context of renewable energy.

 

I have no idea of the numbers here, but for sure at some point wave/tide, wind and solar energy production will effect the global weather of the planet. Just energy conservation considerations tell us this.

 

overtone has a point ; as discussed in another thread, a fair fraction of solar PV can go on rooftops, so that disruption has already happened, or would happen anyway just by putting up the building.

[ajb]

Of course manufacturing and installing such devices has some environmental impact. What I mean is that eventually if one removes enough energy from the atmosphere and oceans then there will be great effects on the weather. We already see this due to fossil fuels where the composition of the atmosphere is changing, but this was not my point. I am not saying that today wind farms are changing global wind patters, maybe locally one can measure some effects, but if we remove enough of the energy from the atmosphere the weather must be effected. Right now that effect is tiny and swamped by the other troubles we have created.

Edited May 24, 2015 by ajb

[swansont]

Of course manufacturing and installing such devices has some environmental impact. What I mean is that eventually if one removes enough energy from the atmosphere and oceans then there will be great effects on the weather. We already see this due to fossil fuels where the composition of the atmosphere is changing, but this was not my point. I am not saying that today wind farms are changing global wind patters, maybe locally one can measure some effects, but if we remove enough of the energy from the atmosphere the weather must be effected. Right now that effect is tiny and swamped by the other troubles we have created.

 

True, but the point of the exercise is that we only need 1/24 of 1/365 (~0.01%) of the energy we already get.

[Danijel Gorupec]

Working further from swansont's 0.01%...

 

If we only cover 10% of Earth area (supposing that more would make deep scars over natural world), then our current consumption is more like 0.1% of what we can obtain from solar in a "green" way.

 

In 100 years, it will be 1% (no change in consumption increase rate)

in 200 years, it will be 10%

in 300 years, it will be 100%

 

Now, 300 years is a looong time, but not that long that one would not be interested to ask - and what then? My guess is that it is simply not possible to continue our current growth rate for more than few hundred years. If we want to stay green, we will either have to stop advancing (either by loosing interest or by war) or we will have to miniaturize ourselves.

[ajb]

True, but the point of the exercise is that we only need 1/24 of 1/365 (~0.01%) of the energy we already get.

True, and I can't imagine that we will need to harness a large proportion of the energy that reaches us.

[swansont]

Working further from swansont's 0.01%...

 

If we only cover 10% of Earth area (supposing that more would make deep scars over natural world), then our current consumption is more like 0.1% of what we can obtain from solar in a "green" way.

 

In 100 years, it will be 1% (no change in consumption increase rate)

in 200 years, it will be 10%

in 300 years, it will be 100%

 

On what do you base these numbers?

[Danijel Gorupec]

I was looking for long-term energy consumption trends. The first graph I found here http://oilprice.com/Energy/Energy-General/A-Look-at-World-Energy-Consumption-Over-the-Last-200-Years.html

 

Of course, I am not sure if this page is correct, but 10 times energy consumption increase over 100 years sounds quite real to me. Of course, the same trend does not have to continue.

[swansont]

I was looking for long-term energy consumption trends. The first graph I found here http://oilprice.com/Energy/Energy-General/A-Look-at-World-Energy-Consumption-Over-the-Last-200-Years.html

 

Of course, I am not sure if this page is correct, but 10 times energy consumption increase over 100 years sounds quite real to me. Of course, the same trend does not have to continue.

 

Yes, that's part of my objection: the trend does not have to continue. This being a science discussion board we look for mechanisms, rather than blindly extrapolating. How does energy consumption track with population, for instance?

Per capita energy consumption over the last ~40 years has ticked up (first graph in your link); how much of that is (primarily) China and India adopting a more industrial economy? If we subtract them, maybe it's flat?

 

Looking over the mast 200 years is and naively extrapolating is probably the worst thing you can do, since it covers a large part of the industrial revolution, where we went from essentially zero energy production to what we have now. Once that's in place, though, industry isn't solely driven by new ways to use energy, but also by making existing processes better, and part of that is improved efficiency. e.g. more people have cars over time, but once you hot one car per person, that con't increase (much), so improved gas mileage, or a transition to a more efficient electric car, reduces the load. So it's not unreasonable to expect per capita energy use to flatten and perhaps even decline once you reach a certain stage of development.

 

That's the trend in "mature" industrial economies, e.g. the US and Europe. Flat or declining per capita energy use. We also generally have declining "native" population (i.e excluding immigration)

[Danijel Gorupec]

I hope you are right... my point was not to make a prophecy what will happen after 300 years, but to demonstrate that geometric progression of energy consumption (as it was in the last 100 years) is incompatible with any 'green' future - no matter what energy source one chooses. It is this progression that needs to be controlled to make 'green' world at all possible.

 

(Off topic: I have fear that such geometric progression is part of human nature and cannot be stopped. That is, if ever forcefully stopped by lack of resources, I am afraid it might lead to economic instabilities of the 'fall-of-Rome' type... I am only saying this to explain why it is not easy to me to accept future without some 'plan B' on hand.)

[michel123456]

Working further from swansont's 0.01%...

 

If we only cover 10% of Earth area (supposing that more would make deep scars over natural world), then our current consumption is more like 0.1% of what we can obtain from solar in a "green" way.

 

In 100 years, it will be 1% (no change in consumption increase rate)

in 200 years, it will be 10%

in 300 years, it will be 100%

 

Now, 300 years is a looong time, but not that long that one would not be interested to ask - and what then? My guess is that it is simply not possible to continue our current growth rate for more than few hundred years. If we want to stay green, we will either have to stop advancing (either by loosing interest or by war) or we will have to miniaturize ourselves.

The world area is 510,072,000 km2

10% of the Earth area is 51 million km2.

That is roughly 1/3 of all land area. (148,940,000 km2)

more than 5 times the area of the U.S.A. (9,526,468 km2)

http://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_area

Built-up land occupied 167 million hectares of land worldwide in 2007, according to satellite imaging and research data sets (FAO 2005 and IIASA Global AgroEcological Zones 2000).

 

from http://www.footprintnetwork.org/images/uploads/Ecological_Footprint_Atlas_2010.pdfp13.

 

167 million hectares are 1.67 million km2

 

So 10% of the world area corresponds to about 30 times the world built-up land.

[Danijel Gorupec]

So 10% of the world area corresponds to about 30 times the world built-up land.

Yes, 10% of Earth is a very large area. However, I was speculating that maybe large portion of collectors could be installed over deep ocean water (among the least fertile area on Earth) in order to reduce biological footprint. Of course, the technology does not exist yet.

[MonDie]

AFAIK only visible, radio and some infrared penetrates to the surface. However, high-power gamma rays seem to pnetrate rather deep. Gamma powered air planes?

If they can get high enough (11/17)...

[swansont]

AFAIK only visible, radio and some infrared penetrates to the surface. However, high-power gamma rays seem to pnetrate rather deep. Gamma powered air planes?

If they can get high enough (11/17)...

 

Although the energy of the individual photon is high, there aren't that many of them. And in a lot of systems, it's one photon per electron.

[iNow]

One could cover the world with solar collectors and have several hundred times more energy than we currently need.

But the world would die.

Sure, but what remains unclear is why you are bothering to make this comment. It's unclear why you think it's relevant or how it adds anything to the discussion since nobody here is arguing that we should "cover the whole world with solar collectors" and since we only need to cover about 158 sq. miles / 254 sq. kms to power the entire planet.

 

This has been covered pretty well already above, but to add:

 

http://www.dailykos.com/story/2014/06/25/1309388/-Solar-Panel-Acreage-Needed-to-Power-the-Entire-Planet-158-mi-x-158-mi

The three squares on the map, below, represent how much solar panel acreage would be needed to power Germany (marked "D"), Europe (marked "EU"), and the entire planet (marked "Welt"):

 

 

http://fusion.net/story/129075/elon-musk-reminded-everyone-last-night-how-little-land-would-be-needed-to-power-the-u-s-with-solar/

A lot of people arent clear on how much surface area is needed to generate enough power to completely get the United States off fossil fuels, [Elon Musk] said. Most people have no idea. They think it must be some huge amount of area, or maybe some space solar panelsBut this is completely unnecessary. Actually very little land is needed to get rid of all fossil fuel electricity generation in the United States.

 

Heres the amount of land that would actually be needed to power the U.S. with solar and battery combinations, he said:

 

 

 

[MonDie]

 

Although the energy of the individual photon is high, there aren't that many of them. And in a lot of systems, it's one photon per electron.

 

They are very, very high energy! Do they comprise much of the energy hitting Earth? Apparently they come in flashes all over the sky, and our sun doesn't produce much if any.

A more detailed by-altitude graph of what penetrates would be great, but I found none.

Edited May 25, 2015 by MonDie

[swansont]

 

They are very, very high energy! Do they comprise much of the energy hitting Earth? Apparently they come in flashes all over the sky, and our sun doesn't produce much if any.

A more detailed by-altitude graph of what penetrates would be great, but I found none.

 

No, they are fairly rare. Good thing, too. If they were much more common we'd all be dead. Gammas are negligible in any discussion on solar power.