Solar Energy – Many Types, Many Applications

Recent announcements by the U.S. Department of Interior regarding approval of large solar energy installations have generated a number of questions and a lot of excitement.

Solar tower, solar energy

Solar Power Tower

On October 24th, U.S. Interior Secretary Ken Salazar approved the $6 billion Blythe Solar Project to be built on 7,000+ acres in California’s desert region. Another approval came through for the Ivanpah Solar Project, which will produce enough energy to power the equivalent of 140,000 average American homes each year. The Blythe project will be the largest solar generation installation in the world, and is based on large solar thermal system technology with the acronym CSP.  This is where the questions come up.

Solar energy can mean many things to many audiences. A good recap of various solar technology types can be found here.

Solar module

Solar PV Module Components

Photovoltaic (PV) solar uses semiconductors and other cell technologies to convert photon energy directly to electricity with no moving parts within the cell apparatus.  Cells are placed in series in modules of various sizes, and modules are designed into entire arrays for residential, commercial and larger utility scale systems.

Concentrating PV (CPV) uses various optical light concentration schemes and devices between the sun and the PV cell to produce more energy.  These systems typically require accurate 2-axis tracking of the sun.

Solar thermal technologies are used for a variety of applications. Solar thermal uses the sun to heat water for direct use in solar hot water systems, or heats special fluids for use in a heat exchanger.

Common small-scale solar thermal systems can be found on residential buildings to heat hot water rather than using electricity.

Solar Concentrating Dish with Sterling Engine

Concentrating solar power (CSP) usually refers to larger utility scale systems that flash water to steam at industrial scale to power turbines similar to those found in coal burning plants.  CSP comes in a variety of technology types including parabolic linear troughs, power towers and dish/sterling engine systems.

Both CPV and CSP require strong solar resources like those you’d find in the desert region of the United States or in North Africa. These technologies are not suitable to higher latitudes and intermittent cloud cover.

With the price of PV modules and installation costs plummeting over the last 2 years, PV is disrupting many long held assumptions about application suitability. High thermal heat CSP technology may not be competitive in many applications, as the installed cost and LCOE is higher in many instances than PV. A good review of the situation from Michael Kannelos at Greentech Media can found here.

CSP requires large installation sizes, frequent maintenance due to a large number of moving parts, and uses large amounts

CSP Linear Trough

of water resources in many instances. But CSP has excellent storage capability and still produces useful cycling well into the evening.

The other issue with CSP is large capital costs. In order to reach competitive kWh cost, these plants need to be large and cost in the $ billions, creating large financing heartburn.

PV has the advantage of being a direct photon to electricity generator with little complexity. Heating water and then using the heat energy to drive a turbine or sterling engine has built-in complexity in energy production, efficiency and maintenance.

Additionally, PV is modular and can be installed in stages. This reduces the financing heartburn as bulk capitalization is lower, allows the array to scale on a defined timeline, and allows for rapid installation.  In this regard, solar bankability may be more common for PV in the future.

Generally, all of these technologies have advantages and disadvantages depending on application.  And with global electricity demand 20X more than planned capacity, the time is now for large adoption strategies to be implemented.

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