Solar power may be the single most important power source in our future. Certainly other technologies, such as wind power, will also be prevalent, but no other technology (I am excepting the possible cold fusion technology, since it has not been fully developed and may never be) has the potential to generate as large of an amount of power.
The reason for this is that sunlight is constantly hitting earth somewhere, and it generates many petawatts of energy, more energy than the entire earth consumes. In fact, in 2002 more energy was striking earth in an hour than all of humanity uses in an entire year. Plenty of that energy is used by plants, but there is plenty that is just wasted.
We already have solar cells, so why aren't we taking advantage of all of this available energy? The answer, of course, has to do with the cost of solar cells and, along with that, the efficiency of solar cells. Up until recently, solar cells were only capable of converting about 20 percent of the light they received into electricity. So-called third-generation photovoltaic cells have been able to push that mark up above 40 percent efficiency, which is an incredible feat.
The reason that solar cells are so inefficient has to do with the fact that they are not sensitive to all the forms of light hitting earth. In the diagram, I show that, inside the solar cell during the conversion of light energy (photons) into electrical energy, some of the energy can be lost. In my example, 0.3 eV of energy is lost.
This can become important, especially if the solar cell is sensitive to lower energies. In that case, a lot of energy can be lost if higher energy light is striking the cell. You get the reverse problem if you try to use solar cells that are sensitive at higher energies. In that case, you actually lose all of the lower energy light since it is not energetic enough to make the electrons jump to the next energy level.
To get around this problem, scientists have come up with solar cells that are capable of absorbing different colors (which signify different energy levels) of light. To do this, layers of material are stacked on top of each other, and each layer is sensitive to a different color of light, which increases the solar absorption. This has allowed researchers to push the efficiency of solar cells beyond the 40 percent mark, and in theory, they can go even further (to over 60 percent efficiency).
Of course, for solar power to become a viable option for consumers, it will also have to come down in price. To that end, researchers have been able to come up with a less toxic and less expensive way to produce solar cells. In order to increase the efficiency of solar cells, they are coated with cadmium telluride, which is both expensive and toxic. Magnesium chloride was recently discovered to be just as effective as cadmium telluride, and it is nontoxic as well as roughly 300 times cheaper, so the cost of solar may come down quickly in the near future.
Looking to the future, the price of solar should only drop, especially as researchers improve silicon photovoltaics (since silicon is cheaper than other materials used in solar cells). Already this year, several records have been set and broken for the efficiency of solar cells made from silicon (now in the high 20s, percentage wise, still nowhere near the 40 percent mark, though). So in another few years, who knows? There may be a few solar panels on your house!