Humans currently (2010) consume about 510,000,000,000,000,000 BTU per year.
Earth receives 3,649,800,000,000,000,000,000 BTUs per year from the sun.
World-wide energy consumption doubles every 35 years. At this rate, it will take a little less than 490 years in order to exceed our external energy input.
Ok, thats great, but what about things that aren't computers which require some sun too. Sunlight is vital for humans to produce vitamin D. Its also vital for growing the things we eat. If we eat up too much sunlight for computers, we will certainly die.
Majority of the world is ocean, and majority of the ocean doesn't have very much life. This is because life springs up and eats up all available resources, then dies, floats to the bottom of the sea floor and stays there as there is little to swish it around the nutrients to be eaten by other organisms. As such, most of the life exists around the coasts and up-swells in the ocean currents bringing the nutrition from the sea floor to the surface where phytoplankton can thrive and the pyramid of life grows from that. So I think its reasonable to say we can capture a decent percentage of the suns rays and convert that into energy without hurting things too much. Lets say 10% at best although the more realistic number may be much higher. At about 10%, we will exceed this energy source in about 310 to 350 years.
In other words, we won't run out of energy for a loooong time. I read lots of periodicals which say "were increasing our energy consumption and we should be concerned, blah blah blah". Sure, thats all true if solar energy won't get drastically more efficient with more research and time, which is ridiculous. So give me a personal holo-deck please, and damn the energy costs.