[MichaelApproved]

Thats an empty tree hugger comment. The amount of energy required to grow a plant over several weeks/months is much less than what's required to move a truck around.

I also don't like the argument that the amount of sunlight that hits the Earth in one hour can power the world for who cares how long. I don't like It because it assumes its actually possible to capture all the sunlight that hits the Earth, nevermind that we're actually already using a large part of that energy to grow our food and warm the planet.

The Sun should play an important part in replacing fossil fuels, which I believe we must do, but make good arguments for it, not empty ones.

[hugh3]

Yes and no. I don't think it's an empty tree hugger comment, but I do think we need actual numbers in order to discuss these things.

World energy usage: 474 exajoules per year

Incident solar flux: 1000W per square metre

Let's suppose (optimistically but not unrealistically) we can get 10% efficiency (over day and night, so more like 20% during the day).

How much land (or indeed, water) do we need to cover with solar cells? About 150,000 square km.

So, while the cost of building all these solar cells is significant, the proportion of the Earth's surface they take up isn't.

[jerf]

When people propose the "cover 150,000 km^2 with solar cells solution", I like to see them go on the record as saying that if we actually tried, they would not immediately turn around and start screaming about the 150,000 km^2 of Mother Earth we just converted to industrial land.

Solar of any form has a major power density problem. At least, it does in the biosphere, which it should be observed is only a rather small percentage of the universe....

[hugh3]

I like to see them go on the record as saying that if we actually tried, they would not immediately turn around and start screaming about the 150,000 km^2 of Mother Earth we just converted to industrial land.

Oh, don't get me confused with a tree-hugger. I'm about as anti-greenie as you can get. I'm just here to do the mathematics.

I'm for whatever source of energy is cheapest.

[MichaelApproved]

Transporting electricity is expensive and inefficient. If you take 150,000 sq km of the most efficient solar land, you still have the problem of transporting the electricity created from that to the places that need it.

[pxtreme75]

You should not forget that, in-some point, ALL types of energy were sun energy. This was transformed to everything else including fossil fuels. Sun energy that arrives to earth is enormous. Even the planet itself uses only a tiny small portion of it to sustain life on all forms. My comment wanted to make this clear.

However, since you mention maths... here are the maths (taken from http://www.ecoworld.com/energy-fuels/how-much-solar-energy-h...)

In full sun, you can safely assume about 100 watts of solar energy per square foot. If you assume 12 hours of sun per day, this equates to 438,000 watt-hours per square foot per year. Based on 27,878,400 square feet per square mile, sunlight bestows a whopping 12.2 trillion watt-hours per square mile per year. With these assumptions, figuring out how much solar energy hits the entire planet is relatively simple. 12.2 trillion watt-hours converts to 12,211 gigawatt-hours, and based on 8,760 hours per year, and 197 million square miles of earth’s surface (including the oceans), the earth receives about 274 million gigawatt-years of solar energy, which translates to an astonishing 8.2 million “quads” of Btu energy per year.

In case you haven’t heard, a “quad Btu” refers to one quadrillion British Thermal Units of energy, a common term used by energy economists. The entire human race currently uses about 400 quads of energy (in all forms) per year. Put another way, the solar energy hitting the earth exceeds the total energy consumed by humanity by a factor of over 20,000 times.

Clearly there is enough solar energy available to fulfill all the human race’s energy requirements now, and for all practical purposes, forever. The key is developing technologies that efficiently convert solar power into usable energy in a cost-effective manner.

[MichaelApproved]

Your numbers are meaningless because you're not taking into account the energy that's needed to sustain the climate.

[pxtreme75]

And what is this number? Without hard facts do you count this as a counter argument? My main point is that all energy on our planet was originated from the Sun.