The reason for that is clear from this illustration, which I found at a German nanotech research firm, Hessen Nanotech.
Based on 2006 energy demand of 470 Exajoules, water and tides could satisfy that 3 times, geothermal resources 5 times, biomass 20 times and wind 200 times.
Solar energy could satisfy it 2,850 times over.
Harnessing just a tiny portion of the solar energy striking our planet would satisfy world demand completely.
The problem is the state of the art. With present technology we can only harness 1,482 EJ from solar power. Efficiency is just not there for everyone to throw solar panels on their homes. There's barely enough power there to meet present needs, and requiring an all-out effort.
Contrast that with geothermal power, where present technology could harness 390 EJ, some 20% of the resource's total potential. If you are looking for short-term investments in alternative energy, then, look under the Earth, not to the Sun.
One pathway I have been following is the use of quantum dots, molecules of cadmium-selenide that can convert sunlight directly into electricity, much more efficiently than current methods.
Rice scientists made a breakthrough in producing such dots in 2007, but commercial applications have yet to come.
Why not? One reason might be patents.
Life Technologies, which focuses on the life science use of quantum dots, nevertheless maintains what it calls "an intellectual property estate" of patents, which it has been using to drive competitors into bankruptcy. One such victim, Evident Technologies of Troy, New York, was looking into dots' use for solar cells.
While waiting for theoretical and legal roadblocks to clear, of course, we have what we have. A group of European industrial firms have organized themselves as Desertec, proposing to build a network of solar stations across the Sahara.
Ambitious and interesting. But here's a question that will face both Desertec and you, should you decide to put one of today's solar cells on your roof.
What happens when today's cells are replaced by tomorrow's?
The answer to that question, one few are yet posing, is standards. If we can settle on a standard size for a solar cell, standard connectors and interfaces, then we may save enough on upgrades to make investing in even today's technology start to make sense.
What this points to are the many smart decisions that must be made to reach a solar energy future. We need technology breakthroughs, legal breakthroughs, financing breakthroughs and standards breakthroughs.
Who will push this all forward?