The Limits of Solar Power

The Limits of Solar Power

There are two types of solar power, Photo Voltaic (PV) Solar, and Concentrating Solar. Additionally, there are three types of concentrating solar: Tower; Trough; and Parabolic.

Solar is fundamentally not suitable for use in the United States, partly because it is unreliable. Actually, solar is not needed in the United States. 

The United States is blessed to have abundant supplies of natural gas, where natural gas power plants (NGCC) are the least costly to build, provide the least expensive electricity, and are reliable.

PV Solar

PV Solar is probably best known because it can be put on roof tops in addition to open fields. As a result, PV installations have been seen by millions of people.

Map of insolation levels in the United States.

PV Solar installations are only marginally viable in areas where there are high insulation levels, which only occur in the Southwestern United States. Even in Florida, it takes eleven years for a homeowner to recover an investment in PV rooftop solar. In the northern states, insolation levels are too low to allow PV Solar to make any economic sense … especially since snow and ice-cover suppress the output of electricity.

Concentrating Solar

There are 90 (76 trough and 14 tower plants) in 14 countries. Of these, 31 have some sort of thermal storage, typically salt, that allow the plants to operate for 2 to 10 hours after sunset.

These thermal storage installations have had major problems.

In fact, there have been so many problems with concentrating solar that the National Renewable Energy Laboratory (NREL) has issued a report, called Best Practices, identifying many of the problems associated with concentrating solar.

Only 9 of the 90 were built in the United States, with the remainder built around the world. The 9 are: Three Ivanpah towers, two Genesis towers, a single Nevada tower, and two Mojave trough installations.

The 9th, the Crescent Dunes tower, was shut down due to equipment failure, primarily with the salt thermal storage system.

Concentrating solar is not even economically viable in the Southwestern United States where insolation levels are the highest.

According to the NREL report, the levelized cost of electricity (LCOE) for concentrating solar is around 20 cents per kWh, which compares with an LCOE for NGCC power plants of 6 cents per kWh. 

In addition, the NGCC power plant is reliable and operates 24/7, year round.

Ivanpah, is probably the most dramatic installation in the United States, as it uses three towers where a veritable sea of mirrors focuses sunlight onto receivers at the top of each tower.

Ivanpah power towers, from NREL report


Photo showing mirrors surrounding a single power tower. The mirrors are on motorized pivots so they can follow the sun across the sky.

Birds flying through the concentrated sunlight are killed by the intense, hot beams of light.

Trough systems rely on long rows of troughs where the troughs’ parabolic shape focuses sunlight onto a tube that carries a fluid that drives a turbine generator.

Photo of solar troughs from NREL

The separation of hydrogen from the fluid has been a major problem at these installations.

The third type of concentrating solar is the Parabolic system as shown in the accompanying picture, where the sunlight is captured by the parabolic reflector and then focuses it onto a receptor.

Parabolic concentrating solar.

The sunlight heats a fluid that drives a sterling engine that generates electricity.

Few, if any, of these parabolic systems have been used commercially.

While solar power is not economically viable in the United States, it can make sense elsewhere in the world. Countries such as Spain and Morocco, that lack cheap natural gas or oil, can find solar power to be economic.

Oil producers, such as Saudi Arabia, can use solar to avoid using valuable oil or natural gas for generating electricity, which allows the country to sell the oil and natural gas on the world market for a large profit.


PV Solar has marginal usefulness in the southern and Southwestern United States, but little value elsewhere in the lower 48 states. If batteries are included in an installation, the costs can far outweigh any benefits.

All types of concentrating solar should be abandoned in the United States.

Concentrating solar is expensive to build, generates expensive electricity, and is unreliable.

. . .

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