SOLAR ENERGY: SIMPLIFIED, SUMMARIZED AND CONCENTRATED

McClatchy Tribune writer Marshall Brain: “You might be wondering if there is anything that we can do, as a society, to solve [the problems of rising gas prices and global climate change]. One possible answer is solar energy…”

For Pittsburgh, Brain summarized the ways solar energy can be put to work.

First, and most easily, it can be used in solar hot water systems.

Second, it can be used in solar photovoltaic rooftop or building integrated thin film materials systems.

Third, it can be used in solar power plant systems, often called “concentrating” solar systems.

Solar power plant systems come in four basic forms: (1) parabolic trough collectors, (2) parabolic dish collectors focused on a Stirling engine, (3) parabolic dish collectors focused on a high efficiency solar panel, and (4) solar power towers.

Power plant systems may use water or hot salts to drive turbines and also may have compressed air or pressurized steam storage systems or not. There is also a design concept which uses solar energy to move water up hill for storage as potential hydro energy.

Last year the hot investment was thin film. This year it looks to be concentrating solar power plants. (click to enlarge)

Concentrating solar collectors can gather a lot of energy
Marshall Brain, April 12, 2008 (McClatchy-Tribune via Pittsburgh Tribune-Review)

WHO
Marshall Brain, McClatchy-Tribune writer.

Solar power tower. (click to enlarge)

WHAT
Brain discusses the uses of solar energy, focusing on the huge new solar power plant projects in the processes of development and planning.

WHEN
Every sunny day the earth's surface gets ~1,000 watts of solar energy/square yard.

Schematic of solar hot water heater. (click to enlarge)

WHERE
- From the sun, earth gets thousands of times the energy humans will ever use.
- China is said rooftop solar hot water systems generating the equivalent energy of 40 power plants.
- Rooftop PV systems are most common in sunny locations like California and Arizona.

Solar power plant parabolic mirror heating system. (click to enlarge)

WHY
- Parabolic trough collectors use a field of parabolic mirrors that track the sun with tubes running through them. The tubes carry glycerin-water or treated salts. Whatever the substance, it is heated (to 500 degrees F. or higher) by the sunlight focused by the mirrors on the tubes. It is carried to a central station where the heat is used to boil water. The steam drives a standard turbine that generates electricity for the grid.
- A Parabolic dish system has a field of mirrored dish structures similar to satellite dishes that track the sun. Each focuses heat either onto a small Stirling engine or a small, high efficiency solar panel. The Stirling engine translates the heat to mechanical energy that becomes electrical energy. The solar panel generates electrical energy. The electricity is carried to the grid.
- The solar power tower uses a field of flat plate mirrors that track the sun and focus its heat onto a central source of water or salts. Like the trough system, the heat is carried to a boiler where it generates steam to drive a turbine.
- Any of the systems can be combined with a Compressed Air Energy System (CAES) or a pressurized steam storage system which holds the energy for when there is inadequate sun.
- An alternative storage system of driving water uphill is conceptually logical but likely inadequately efficient.

The Stirling Energy System, possibly the most efficient of all. (click to enlarge)

QUOTES
- Brain: “…Why solar? Because the sun's energy is free and abundant…”
- Brain: “As petroleum gets more and more expensive, solar energy looks better and better from the financial and the environmental angles. We should be seeing many more large solar projects getting under way in the near future.”