Solar Concentrator PV Systems

The basic idea here is to essentially take a large collecting area and focus it on a smaller area, thus concentrating the energy. This means that less PV material will be required to produce a given amount of energy and this, potentially, saves expenses.

Projected expense savings are large:

100 MW year regular PV facility is 150-300 Million dollars capital cost
Using Concentrating PV (CPV) that costs lowers to 30-50 million dollars

The issue then becomes the reliability of the CPV components over time and their resistance to heat load. Also CPV systems function best under clear sky, direct-sun condition clouds significantly compromise performance.

Most common form of CPV is the solar "trough" system:

The heat exchanger:

Large arrays can be built to leverage abandoned cooling towers:

354 MW capacity located on 7 square km of desert in California So that's about 50 MW per square km.

Some equivalencies:

1 sq km with 1.5 MW wind turbines spaced out by 50 meters 600 MW
1 500 MW closed cycle gas turbine plus cooling ponds requires about 0.25 square km so on 1 sq km could get 2000 MW.
1 sq km with 25 KW (= .025 MW) Solar Sterling Engines spaced by 25 meters would be 40 MW

Many commercial systems now use something called a parabolic trough: Here the focus point of the parabolic trough is a receiver pipe. The pipe is filled with oil (not crude oil) and is heated to about 400 C. This heat energy is then used to generate electricity in a conventional steam generator.

35 KW module

Additional considerations:

Several challenges exist to using concentrators. For example, the required concentrating optics are significantly more expensive than the simple covers needed for flat-plate solar systems.

Most concentrators must track the sun throughout the day and year to be effective. This requires expensive tracking mechanisms and precise control systems. A flat plate system is stationary.

Various Designs for concentrator systems:

Linear reflector:

Solar thermal towers use these arrays.

The centralized power tower is still being invested in:

The power tower has some advantages. The molten salts are very hot (800 to 1200 F) and therefore this is a high efficiency heat engine. Because the heat capacity of the molten salts is high, they retain this heat well after the sun has set

Solar thermal electric is then dispatchable (i.e., available on demand, 24 hours).

But this technology is limited by optics and is not scalable!

Linear Fresnel Lens:

Can be made large,

Point focus array:

Most expensive but can track the sun.

Within CPV systems, the concentration ratio can have high variance.

If light that falls on 100 sq. cm of reflector surface is focused onto a 1 sq. cm surface of PV material, then the concentration ratio is 100. Current commercial design concentration ratios are in the range 200-300 suns. Anything beyond 500 suns is likely impractical due to potential heat fatigue of the material

But let's be optimistic and return to the theme of multi-use of land per horizontal footprint and envision:

The New Shopping Mall - using solar concentrated power to make hydrogen:

Process does involve some kind of "metal" catalyst

Major point: most parking lots are useless but could easily be transformed into land that produces energy.