Volume 44, Issue 1 - January 2009

Solar Insights

Solar Basics
How Glass Fits into the Solar Market
by Dr. Alex Marker 

In just one hour’s time, the amount of energy from the sun that shines upon the earth’s surface exceeds the energy consumption of all of mankind in an entire year. The solar market has been growing at approximately 30 percent year-over-year for the past decade in an attempt to capture this renewable energy resource. As businesses look to recession-proof their operations, many are examining what role they can play in the solar boom. Understanding solar energy is perhaps the most difficult initial hurdle for any company trying to find its place in the market.

To understand the business behind solar energy, it helps to first understand the different technologies involved. The phrase “solar energy” is a catch-all for several different types of technology that harness the sun’s radiation and convert it to energy. At a first-level, energy producing1 solar can be broken down into two categories, photovoltaics (PV) and concentrating solar power (CSP). 

Photovoltaics
PV power describes the process of converting sunlight into electricity utilizing solar cells. Solar cells are solid-state devices in which photons (or packets of light) are absorbed by atoms. This process results in the production of electrons, which flow into wires connected to the cell, thus providing electric current to lighting systems or other electrical loads. All of the electricity produced by the cell comes directly from the sun. Solar modules (solar panels) are series of solar cells wired together and enclosed in self-contained glass units that protect the cells from the environment. These solar modules generally exist in three forms: monocrystalline, polycrystalline and thin-film. 

Concentrating Solar Power
CSP plants are utility-scale power plants that generally produce more than 50 MW of electricity, enough to supply the energy needs of thousands of homes. In one variation of CSP, called parabolic trough, hundreds of trough-shaped parabolic mirror-arrays continuously track the sun. These parabolic mirrors concentrate the sun’s thermal energy onto receivers, located along the mirrors’ focal line. The concentrated solar radiation heats thermo-oil heat transfer fluid flowing through the receivers. This hot fluid is then used to produce steam, which drives a turbine, generating electricity. These parabolic trough facilities represent a proven technology that has been successfully deployed in California for close to three decades. 

There are other variations all of which create energy through a conversion of heat. 

The Role of Glass in the Solar Market
The glass in PV must offer high optical transmission, low reflection and durability. Anti-reflective coatings are commonly used to increase the transmission properties of the glass. 

For parabolic trough CSP, glass tubing forms the outer layer of the receiver, which sits at the focal point of the parabolic mirror. Similar to PV, the requirements for glass in CSP are mainly optical clarity, high transparency and durability. Because CSP is a thermal-based technology, retaining the heat in the tube is essential for an efficient system. A key challenge exists in compensating for the different coefficients of expansion between steel and glass, as the systems are heated up to 750 degrees Fahrenheit during the day, and then at night cool down to lows near freezing. 

Glass is a critical component in all types of solar energy, and its unique material properties ensure that it will remain a critical part of the technology for many years. However, the glass industry must consistently deliver technological improvements that will enable solar technologies to operate with higher efficiencies and at lower costs. 

1 Solar technology can also be used to generate heat for water systems. This is accomplished through capturing the thermal energy from the sun. 

Dr. Alex Marker is a research fellow with SCHOTT North America Inc. in Elmsford, N.Y. Dr. Marker's opinions are solely his own and not necessarily those of this magazine.

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