As for collecting solar energy heat instead of electrical energy it has its own challenges with liquid heat transferences and using a liquid that won’t freeze in winter. The collection of heat energy for use in home heating is more cost effective than electrical collection for the moment. But as time progresses technological advancements in solar cell designs verses efficiencies should prevail. We are at a time in the evolution of solar energy that is similar to what the computer age went through over about 30 years. From very basic computers that were large, bulky, and costly, to very powerful computers, compact and affordable.
Solar energy is of course reliant on the sun. This fact alone means the source is not going to disappear any time soon. It can be concluded that solar energy is very reliable as a source to choose to capture, unlike oil or other forms of depleting sources. Solar capturing systems are also fairly reliable. In particular the electrical solar cell has an indefinite life span because it is a semiconductor. Presently the solar cell of today is about 14 % efficient. This efficiency will rise over time and be the main area that will bring down the cost of putting a system together. So far the economy of scale to produce these cells is beginning to have a greater impact by bringing down the price of a solar panel from over 50 dollars per watt to 6 dollars per watt.