An unqualified summary of alternative energy

Hey guys! I'm no Energician or anything, but I do have some BS degree from this one school in the south, so I'm going to just go ahead and offer my (in)expert opinion on alternative energy.

When you come right down to it, most of our energy sources are solar energy in disguise. Coal, oil, and natural gas were formed when plants stored the sun's energy in their biomass and then decomposed. Hydroelectricity is available when water is flowing downhill, and we force it to turn our turbines; but that water was transported to the top of the hill when it was evaporated by sunlight, and fell back down from the sky. Wind exists on Earth only because of local variations in temperature, caused (for the most part) by sunlight. And, of course, solar panels directly harvest the sun's energy. In fact, the only sources of power I can think of that don't originate from the sun are nuclear power and (arguably) geothermal.

One very interesting energy harvesting scheme is called "Ocean Thermal Energy Conversion". Essentially you have a huge pipe that goes down into the ocean to a depth of about 1,000 m, where the water is colder, about 5 C. At the same time you use water from the surface, which will be around 22 C. The laws of thermodynamics dictate that the heat will flow from hot to cold, but we put our devices in the way so that, like water falling down a hill, the whole process powers our machinations. And they say that the oceans provide a "limitless" supply of cold and hot water (maybe a dangerous idea).

Direct solar energy has a lot of promise. The above map shows the average intensity of sunlight. The blue dots represent the total area required, with current technology, to completely provide the current global demand for electricity. I think the map looks pretty neat.

However, as time wears on, our energy demands will tend to grow exponentially. Some guy made what's called the Kardashev Scale, which classifies how "advanced" a civilization is based on how much energy it can produce. To quote wikipedia, "a Type I civilization has achieved mastery of the resources of its home planet, Type II of its solar system, and Type III of its galaxy." We are estimated to have a rating of 0.72. Looking at the plot, which is on a logarithmic scale, our energy development over time is a straight line, which indicates exponential growth. Extrapolating from the data in just the last 110 years, it will take another 200 years or more to reach a rating of 1. Let's work on that, everybody.

EDIT: So on the Kardashev Scale, a Type 2 civilization will use roughly the energy output of an entire star. Freeman Dyson imagined what is now called a Dyson Sphere, a shell around a star that collects all the energy from that star. Dyson spheres have a few problems, though: If you build a solid shell around the star, then it wouldn't interact gravitationally with the star, and the two would slowly drift apart until they collided. If, instead, you build a swarm of space ships that orbits the star, then occasionally one would block the sun from the other. As you increase the number of spaceships, this happens more and more, until it becomes almost impossible to harvest all the star's energy.