The sun doesn't shine all the time. Besides the problem with night and day, there is also the problem with cloudy days. And if the panel is not positioned at a right angle to the sun's rays, the efficiency drops - and the angle of the sun's rays changes continuously, so for ideal results, the panel needs to be repositioned continuously. Bottom line: on average, solar panels will only deliver about 16% of their rated capacity. Therefore, it would seem unwise to depend on solar for more than one-sixth of one's power needs.

Under ideal conditions a single 8.75 sq ft Sharp Solar Panel will generate 175 watts. Each 175 watt Sharp solar panel costs $520 when purchased in bulk.


For Future Cost Comparison

How many 175 watt solar panels would be required to replace just one-sixth of the 12,900,000,000,000 watts (12.9 Terawatts), presently produced from carbon-based fuels every hour here on Earth, assuming that the solar panels are operating at 16% (0.16) efficiency? And how much would it cost for that many solar panels?

2,150,000,000,000 watts/(175 watts per panel x 0.16) = 76,800,000,000 panels

Each panel costs about $520.

$520/solar panel x 76,800,000,000 panels = $40,000,000,000,000

Excuse me? $40 TRILLION dollars???? For just one-sixth of our energy need???

It's a pretty scary number, but just for future comparison purposes, to eventually put this number into perspective, let's calculate the cost per Terawatt:

$40 Trillion/2.15 Terawatts = $18.6 Trillion/Terawatt (remember this number!)

Umm… $40 TRILLION dollars, batteries NOT included! ...and you WOULD need batteries - LOTS of batteries! Batteries (for night time and cloudy days), controllers, and tracking apparatus (to keep the panels pointed at the sun - shown right) will probably cost another $30 trillion...(There may be an answer to the battery problem - see smart grid.)

Don't forget - the sun doesn't shine at full power 24/7. Don't forget -in the real world- solar collectors only deliver their rated power about 16% of the time; and as shown by the insolation map below, there is huge variation in different parts of the world.