Solar Energy Update

Many advances have been made in solar power over the past few years.

This is a brief overview of solar available today.

Photo Voltaic (PV)

  • Flat panel PV installations where semi-conductors convert sunlight to DC electricity are common on residential, commercial and government rooftops. They are almost always fixed in position and cannot track the sun.
  • For utility-sized installations, the PV panels track the sun.
  • This is the least efficient of the solar alternatives, with efficiencies ranging between 15% and 20%.

Concentrating Photo Voltaic (CPV)

  • This is a more efficient alternative for PV installations, with efficiencies of around 30%.  Some manufacturers claim higher efficiencies.
  • CPV uses reflective or refractive lenses to focus the sunlight onto semi-conductor collectors.

Pictures courtesy of SOLFocus, Inc.

Concentrating Solar Power (CSP)

These systems use mirrors to focus sunlight onto a receiver that contains a fluid that then expands to drive a turbine or sterling engine to generate electricity.


CSA Power Tower
Power Tower
  • Mirrors track the sun to maintain sunlight focused onto collector at top of tower.
CSA Trough
Trough collector
  • Mirrors focus sunlight onto tube running length of mirrors.
CSA Parabolic
Parabolic Dish

Parabolic Sterling Engine System

  • Each Parabolic system is self contained with an array of units interconnected electrically.

 Some solar installations are run in combination with Natural Gas Combined Cycle (NGCC) power plants in an effort to improve the plant’s overall efficiency, and to take advantage of the immediately available back-up power if the sun stops shining.

All solar power systems are inherently unreliable and require back-up gas turbines spinning 24/7, ready to be brought on line when the sun stops shining. CSP and CPV installations are usually in remote areas and require building expensive, dedicated transmission lines to bring the electricity to where it can be used.

Efforts are being made to improve the ability of a CSP system to generate electricity after the sun sets by storing heat in a salt reservoir.

Solar has an advantage over wind, since solar generates electricity during the day, including peak periods, when the power is needed, rather than at night when the electricity isn’t needed.

Only a part of the country has sufficient insolation to permit the use of solar with any semblance of economic efficacy. The areas in red and dark orange delineate areas within the United States where there is adequate sunlight to potentially warrant installing solar power.

USA Insolation Map
USA Insolation Map

The Southwestern United States is where nearly all the CSP and CPV installations have been made.

While there have been advances, electricity generated by solar power systems remains very expensive. Solar cannot currently compete with electricity produced from natural gas or coal-fired power plants.

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