Simply put, solar photovoltaics are the most reliable source of electricity ever invented. In applications where reliability is absolutely crucial — say, all space satellites, the Mars Rover, about 99% of all off-shore Coast Guard buoys, and any other place where repairmen don't make housecalls — solar is the technology of choice, with no competition to speak of.
Solar systems typically come with a 25 year manufacturer's warranty standard, and there is no reason why they shouldn't function much longer than that. The town of Beverly, Massachussetts installed a 100 kW solar system in 1981, and more than 20 years later, the system is still performing at 92% of its rated peak capacity.
For more information on how the technology works, check out these links:
The California Solar Center has a nice history of solar's commercial development.
The technology works. The question is — will we use it in time to make a difference in the fight against global warming? We are working to jumpstart the solar revolution. Join us.