- The sun, estimated to be between 4.5 and 5 billion years old, is about halfway through its lifetime, meaning it will exist for another 5 billion years. From a practical point of view, the sun then is an infinite, renewable resource.
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Solar electric panels do not feed a current directly into a building, because the amount of current they produce is directly tied to the amount of sunlight they receive. Since sunlight varies through the day and disappears altogether at night, solar power systems must be designed to provide a stable power supply. This is done by using the panels to charge batteries; the batteries then feed steady electrical current into a building. There are therefore two major components in a solar power system, both with finite lifespans: the solar panels and the battery.
- Good photovoltaic cells come with a 20- to 25-year warranty. The cells will continue to operate for several years after their warranty expires, but their efficiency and electrical output will begin to decline. Unless damaged, photovoltaic cells rarely simply cease to operate. Instead, they gradually break down.
- Photovoltaic cells typically transfer energy to batteries, which usually do not last as long as the solar panels. A typical battery lasts five to 10 years. A solar energy-system owner can expect to replace the batteries at least once during the lifetime of the system.
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A solar ovenMost other solar energy products are simple, have few or no electronics or moving parts, and will keep operating for decades so long as they are adequately maintained and not damaged. Solar water heaters, for example, work on a simple principle of concentrating heat. Even the hot water is often moved using nothing more than gravity and convection. If such a heater is made using all heavy-duty plastic parts, it will only need to have its seals replaced once every five to 10 years. Solar cookers are even more durable, being essentially insulated boxes with solar reflectors. Also, solar light tubes have taken the skylight a step further by using reflectors to concentrate sunlight. Some can do this even to the extent of providing illumination with moonlight. When combined with convention electric lights in a hybrid system, light tubes provide significant energy savings.
