• The high cost of solar energy has limited its use.Solar Panels image by alessbonaventura from Fotolia.com
  
  Though the sun provides the Earth with enough renewable energy to run civilization many times over, harnessing that energy has proven to be a challenge. The lower power density of sunlight means you must build large structures to produce practical amounts of energy. The high cost and low efficiency of solar cells restricts them to specialized applications.
  
  

Low Power Density

• Power density measures how much energy you can produce in a given size or area. Sunlight averages 1 kilowatt of energy for every square meter on which it falls. Realistically, if you want to produce 1 kilowatt of useful energy from sunlight, your collector has to be much larger than a square meter, as no collection system is perfectly efficient. A solar installation in DeSoto County, Florida has 180 acres of solar panels but produces only 25 megawatts of electricity. A typical coal-fired power plant generates 595 megawatts while occupying 345 acres.
  
  

Long Investment Payback Time

• While the cost of solar cells has fallen and continues to decline, it remains high relative to other power sources. Even with no fuel costs to cover, the investment payback times for solar installations run over 20 years. A solar cell's useful lifetime runs 20 to 30 years, so you don't realize much net economic benefit using solar power.
  
  

Solar Cell Efficiency

• Depending on the material from which it's made, a solar cell typically converts between 10 and 30 percent of the energy in sunlight into electricity. This effectively reduces solar energy's already low power density. To produce one kilowatt of electricity from sunlight, you need a solar panel covering 3 to 10 square meters.
  
  

Storage Costs

• The solar energy the Earth receives varies by weather and time of day. Engineers have developed battery storage systems to make solar power available on a more constant basis. These storage systems have their own costs, including those of the batteries and electronic charging systems, boosting a solar installation's price tag further.