The Obama administration has announced that they plan on investing a huge amount of money into renewable energy. Solar energy and other forms of renewable energy get a lot of good publicity, however solar energy is not nearly abundant enough to be a suitable alternative to fossil fuels.

The radius of the earth is 6371 kilometers.¹ The outer atmosphere is defined as 100 kilometers above the earth's surface, so the radius of the outer atmosphere is 6471 kilometers. If you square this and multiply it by 4π you the surface of the outer atmosphere, which is 526,202,205 square kilometers.

Now according to NASA solar energy hits the earth's outer atmosphere at a rate of 342 watts per square meter on average.² Therefore solar energy hits the earth at the rate of approximately 180 petawatts.³ We could alternatively use wikipedia's current figure of 174 petawatts⁴, but lets be generous.

Now humans consumed energy at a rate of 15.79 terawatts in 2006.^5&6 Now if you divide 180 petawatts by 15.79 terawatts you get 11400.

However not all that energy reaches the earth. 6% is reflected by the atmosphere, and 20% is reflected by clouds.
11400*(74/100) = 8436
Now the current record for solar to grid energy conversion for a solar power plant is 31.25%.⁸
8436*(31.25/100) = 2637
Finally, if we assume that it's too costly to build solar power plants in the middle of the ocean, only 29.1 of the surface of the earth is covered with land.⁹
2637*(29.1/100) = 768

This means that 1/768th of the earth's landmass would have to be taken up by solar power plants, or 32% efficient photovoltaics, for solar energy to account for 100% of human energy consumption. This is not at all feasible by any stretch of the imagination.

Factoring in wind power and other forms of renewable energy into this equation doesn't change it much (if at all). The truth is that there simply isn't enough renewable energy available per square kilometer, especially with human energy consumption rising.

Therefore with the purpose of avoiding catastrophic global climate change that greenhouse gases may cause, I propose an aggressive nuclear energy program. We theoretically have an unlimited supply of nuclear energy. Mankind needs to urgently convert its fossil fuel power plants to conventional light water nuclear reactors to make use of our limited supply of uranium 235, which will buy us the time to perfect the technology behind alternative types of reactors, such as breeder reactors, that utilize our unlimited supply of uranium 238.

¹ http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
² http://earthobservatory.nasa.gov/Features/DelicateBalance/balance2.php
³ http://www.google.com/search?q=(342+watts+per+square+meter+*+526202205+square+kilometers)+in+petawatts
⁴ http://en.wikipedia.org/w/index.php?title=Solar_energy&oldid=261138251#Energy_from_the_Sun
⁵ http://www.eia.doe.gov/pub/international/iealf/table18.xls
⁶ http://www.google.com/search?q=472.27379313571+*+10^15+btu+per+year+in+terawatts
⁷ http://www.nasa.gov/images/content/57911main_Earth_Energy_Budget.jpg
⁸ http://www.sandia.gov/news/resources/releases/2008/solargrid.html
⁹ https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html

http://www.popsci.com/scitech/article/2008-12/machine-might-save-world

All we need is one working fusion reator, and we'll never have energy as a pressing concern again.

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In this machine, energy output is dependant on the volume of plasma it contains, while energy input is dependant on the surface area.

Assuming that at the current size, let's say volume 1 of the device, for any increase in size the radius of the plasma vs. the radius of the device increases proportionally, as does the energy intake and output, he only has to scale it up so much, before any scaling results in exponential energy increases.

Post has been edited 1 time(s), last time on Dec 31 2008, 11:35 pm by Syphon.

I won't consider fusion reactors to be an alternative to anything until a 10 MW or greater fusion reactor is built.

Fusion is great, perhaps better than U-238 reactors. We should pour money into both, but in the meantime we should construct U-235 reactors, we can't afford to keep burning coal.

342 watts per what measure of time? Millisecond, second, hour, day, week, month, year? After multiplying by square meter of the Earth's surface, you compared it to the consumption of energy in one year. Yet I think more than 342 watts hits a square meter on Earth over the course of an entire year.


http://zebu.uoregon.edu/1998/ph162/l4.html


And from your #4 source:


Post has been edited 4 time(s), last time on Jan 1 2009, 1:44 am by Hercanic.

Dude, a watt is a joule per second. 342 joules per second per square meter.

As for the rest of your post I don't really see where you're disagreeing with me. You're just restating my figures except with different units of measurement.

I'm not disagreeing with this. In fact I assumed the sun hit the earth with more energy than this. 3,850,000 exajoules per year is equal to 122 petawatts, less than the figure of 180 petawatts I gave.

EDIT: sorry for the double post

I doubt we (the US) will throw our money into a nuclear program. The Sierra Club has kept nuclear energy at a standstill, as they are the driving force behind anti-reactor construction for decades. Chernobyl pretty much guaranteed environmentalist PACs like the Sierra Club will do whatever they can to keep the government from passing bills regarding any energy source even potentially dangerous.

Well that's a pity, because it's our most feasible method of stopping global climate change by far.

Eh. I'm personally a fan of nuclear energy myself, but to fight against a PAC that has a $80+ million annual budget and has successfully halted nuclear power in the US would take a political force that I doubt would rise before the Earth starts growing Mako tentacles that physically beat the crap out of humans.

Hydrogen Fusion. A cool future.

Wow. you changed my mind.... uhm, i guess im on board! well done, well written.

Could improve the efficency of our solar cells.

510,065,600km² (1.)

(5.1*10^8)(29.1/100)(1/768) = 193242km²
That is a lot of ground to cover though, and half the earth isn't sunny all day.

1.http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=surface+area+of+earth&spell=1

The situation of things is completely dismal. On one side we have liberals who would like to see us get all our energy from the sun and the wind. They're strongly opposed to fossil fuels, but also strongly opposed to nuclear power, which they see as dirty and dangerous.

One the other side we have conservatives. They think that the long term consequences of releasing trillions of tons of buried carbon into the air will be negligible and that a feasible solution to fossil fuels shortages is to either "drill now" or to invade any countries that are being uncooperative and not exporting their supply to us. They're also afraid of nuclear power plants being attacked by terrorists.

What about all the people that don't adhere specifically to those two stereotypes which you have just described. Or, if you have some reason to believe those are the only two possible points of view that people in government hold, back it up. Personally, I think such a limited and general classification is stupid. Neither liberals or conservatives are stupid, they know you can't rely soley on one or the other right now.

Also, I think in determining if solar cells can be a major part of our energy, you need to look at how that 15.79 terawatts is used, not just how much. Another thing that can factor in is the fact that the surface of the earth and other things isn't flat. Take a house with a /\ roof. The surface area of the roof is greater than the horizontal distance it encompasses, so it can capture more energy with less space than the average flatbed piece of solar equipment. Though you do have to worry about shadows at that point.

Post has been edited 1 time(s), last time on Jan 2 2009, 9:16 pm by Vrael. Reason: to not double post

That's more than made up for by the little thing we call nighttime.

Dear Syphon:
Power demands at night are significantly less, due to most businesses being closed, and people going to sleep. Plus excess energy from the day can be stored for night.

Instead of being outright replaced, traditional power could be used to fill any possible gaps, with solar reducing the strain on traditional means and thus increasing its lifespan.

---

Dear Sciwizard:
Yes, watts are joules per second. My question is the 174,000,000,000,000,000 watts that hit the Earth, is that per second as well? So another way of saying it would be 174 petajoules per second hit the Earth? If that were true, then it should be roughly equal to the 3,850,000,000,000,000,000,000,000 total joules that hit the Earth in 2002, right?

174,000,000,000,000,000 per second
10,440,000,000,000,000,000 per minute
626,400,000,000,000,000,000 per hour
15,033,600,000,000,000,000,000 per day
5,487,264,000,000,000,000,000,000 per year

Hm, almost double.


Let's put that aside for now, and look at your equations.


174,000,000,000,000,000 watts hit the Earth. Not sure if it's per second, but the way you used it made it per year. If it's per second, it would drastically alter your numbers.

26% is reflected by atmosphere. That's about 45,240,000,000,000,000 watts lost.

128,760,000,000,000,000 watts reach the Earth's surface.

Only 29.1% of the surface of Earth is land. That leaves us with 37,469,160,000,000,000 watts that could be harvested.

Solar panels at present are at best 31.25% efficient. That gives us 11,709,112,500,000,000 watts that could be converted into usable power.

In 2006, we used 15,790,000,000,000 watts for the year.

If we divide those two numbers together, 11 quadrillion watts possible by 15.7 trillion watts needed in a year, we get 742. So we need 1/742 of the Earth's surface to meet those needs.

The Earth's surface is 510,064,041 square km.

29.1% is land.

That gives us 148,428,636 sq km of land.

We need 1/742 of that land, which is 200,159 sq km.

Converted, that's 124,373 sq miles.

The US is 3,790,000 sq miles.

That means we'd only need 3% of the land in the US to supply a year's worth of power. How much of the US is taken up by housing, businesses, and parking lots whose roofs could be converted into solar panels?

Again, this is assuming you were correct with attributing 174 petawatts as the yearly amount that the Earth gets, and not the amount per second.



___

Post has been edited 10 time(s), last time on Jan 3 2009, 1:15 am by Hercanic.

Extremely insignificant amounts of, as to say compared to the energy generated at daylight.

I'd assume 174 petawatts. I don't think the Sun would give off 174 petawatts per second. If the Sun really did, Earth would be nothing but a heap of molten rock.

Eh?


And you base this off of what?

Don't Eh me. You're the genius. You'd know that already.

You're the genius here. You'd know that these things are calculated yearly. If we received 174 petawatts per second, you'd know that it is more than a million times our current gain and that is quite obvious that we'd be vaporized. Unless you didn't know that things don't vaporize when their temperatures are raised. Please, you look stupid if you ignore common sense.

Fixed for clarity since Hercanic and BeDazed don't get it.


I didn't say anything nearly so drastic. I said ~0.13% of the land in the US would need to be covered. However that is too much.