"alternative energy sources"

chatter about "alternative energy sources" has been around for a long time...I recall hearing this probably for the first time right after the original 1973 "oil crisis"...

what are these sources of energy? remember your physics: energy can neither be created nor destroyed, just converted from one form into another. That is not necessarily easy to do (atomic bomb), but it can be done.

(numbers used here: from Wikipedia: http://en.wikipedia.org/wiki/Orders_of_magnitude_(power) -- go look at this, there are some interesting numbers towards the bottom)

the sources you hear about:

1) Wind power. If you put a fan blade in the path of moving air, it will rotate. if you have the mechanical linkage from that rotation to a generator, you can draw electrical power from it. This is a conversion--you are taking kinetic energy from the air movement, and converting it into electrical energy. So what happens to the air as a result? It slows down. Or it cools down. Or both.

How much energy can you extract without causing some other problem? If you could remove 100% of the kinetic energy, the air would come to a stop. Well, what causes it to move in the first place? Energy from the sun, the daily heating and cooling cycle, rotational differences (you know, Coriolis). You'd also end up removing thermal energy, making the air colder; perhaps that would help with global warming :)

2) Ocean currents. Pretty much the same as wind--if you could put a fan of some sort in the water perpendicular to the Gulf Stream, the (albeit slow) ocean current would cause a rotation that could turn generators for electricity. What would happen to the water? The current would slow down, and it would get colder.

The bad thing here is that ocean life is super-sensitive to temperature changes. A drop of one or two degrees would be a disaster for marine life.

Fortunately, the engineering cost of doing this would be insane, so it's pretty unlikely.

3) Geothermal. Taking advantage of the thermal gradients underground. If the earth's core is pretty hot, as we've been taught, then this should work fairly well. I'd argue that the engineering cost is again way too high for large-scale use.

4) Solar. The biggest, and essentially inexhaustible, energy source within a light-year or two is the Sun. You can look this up (got my number from Wikipedia, so it's as trustworthy as that is): solar energy striking the earth is about 1300 watts/square-meter. I don't know if that's at the equator, the poles, or average over the entire surface, but let's use it anyway. ("1.366 kW - astro: power received from the sun at the earth's orbit by one square metre" -- sounds like equator to me)

Solar power conversion efficiency is about 10-15% right now (we've been doing this for >30 years, but that's all the better we are). So figuring other losses, let's say we can reliably get 100 watts/sq-yard. There are 3 million square yards per square mile. That means we can get 300 megawatts of electrical power for each square mile of solar cells we build. During daylight, mind you, which IS a problem. Let's suppose we gave approx 100 square miles of otherwise unused land per state to this (so Rhode Island probably can't do that, but Nevada could pick up the slack). That's 300 MW * 100 * 50, or 1.5 Terawatts. That's in the ballpark of total world electrical consumption (Wikipedia: 1.7 TW - geo: average electrical power consumption of the world in 2001 (presumably that's daily average)).

The current retail cost of solar panels is about $5/watt, which is kinda high. In large-scale construction quantities, let's say that drops to $2 installed. That means that our proposed qty above is $3 Trillion. We would not, of course, pay that all at once, and other costs would go down as that got phased in (oil consumption would drop quite a bit, because we could stop using it for power generation during the day (still need night-time--what to do?)).

The night-time issue is interesting...Options are to continue to burn fossil fuels (oil, coal) for this. Another alternative is have a lot of batteries underneath the solar panels; I doubt this is adequate for the entire night...A friend has suggested that excess power should be used to spin up large inertial masses that would thus be storing a lot of energy in their rotation (giant flywheels), and the night-time extraction would be far less than the daytime need, so they could hold enough for overnight every day, all year. This strikes me as having some real engineering problems: how big can these things be? how quickly do they wear out? what are they made of? can you spin them fast enough (material strength)?

Ultimately of course this leads (as it inevitably must) to the Dyson sphere, but we don't need to try to do that any time soon :)

But...imagine that we had spent $500 Billion on energy development instead of a war in Iraq, which has not made the cost of energy cheaper (the opposite, if anything). That's a relatively small fraction (15%) of the total needed, but it's a certainty that the process of having done so would change the world. I think it's engineering-feasible. and we MUST get off the oil.