Most Texans already know that the state’s fortunes were and are fueled by oil and natural gas. What many don’t realize, however, is just how much the future of the Lone Star State will be powered by renewable energy. With the Green Energy in Texas series, we will explore various aspects of the green energy industry and keep you informed on how those changes and innovations might affect your Texas electricity bill.
Solar Panels — The Shocking Inside Story
In our first installment, we looked at the status of solar power in Texas. Because solar panels seem to make electricity in an almost magical way, we’re going to first look at how a basic solar panel makes electricity. No, you won’t need your chemistry text books. It’s so simple that it’s…well…illuminating.
And while there’s been lots of buzz over solar panel prices going down in recent years, it’s helpful to understand how that story comes from the cost of the silicon that makes solar cells.
How Do Solar Panels Work?
A solar panel is composed individual solar cells. Each cell is a sandwich made from a polycrystalline silicon wafer that has been treated with a thin N-type coating (called “doping”) that changes the polarity to negative and wire contact is installed there. The top of the waffer is then coated with anti-reflective coating. the back of the wafer then gets a coating of aluminized conducting material which gives that side a positive polarity and the positive wire contact is put on there.
When a photon of light enters the cell, transfers its energy to one of the polycrystalline silicon’s electrons. Now at a higher energy state, the electron breaks loose from its orbit and heads out of the cell through the negative contact with all the other electrons hat have been hit by photons. This movement of all these electrons is an electric current.
An individual solar cell can make .5 volts DC — not even enough to light a single LED. However, when wired in a series, 36 cells can put out between 12 and 17 volts. The more cells, the higher the panel’s wattage output. Some panels with 96 cells can reach up to 400 watts.
What is Polycrystalline Silicon?
Polycrystalline silicon, commonly called “Polysilicon”, is becoming the most common type of silicon that goes into solar cells. It contributes about 20 to 30 percent to the cost of a solar panel, or 6 to 15 percent of PV system costs. It starts off as silicon dioxide (SiO2), or silica, and occurs in sand, clay, and rock. Quartz rock generally has the highest amounts of pure silica with low amounts of other metals such as iron, aluminum, etc. To use it, the silica must be purified by refining it into metallurgical silicon. To get metallurgical grade silicon, the quartz silica and carbon (coal) are heated together in an electrode arc furnace to over 3600°F. At this temperature, the carbon robs oxygen from the silicon to form CO2, leaving silicon that is 98% pure. Producing cheap pure silicon requires lots of cheap quartz and cheap electricity. Making metallurgical silicon uses 11–13 MWh per ton.
Polysilicon comes refining metallurgical grade silicon to an even purer form of silicon, 99.9999999% pure. The standard method is the Siemens process which was developed for the semiconductor industry because silicon chips required higher quality silicon to work. The process begins by dissolving metallurgical silicon in hydrochloric acid at 572°F. Trichlorosilane (HSiCl3) is then distilled out from the acid solution. This compound is put into a Siemens deposition reactor. Inside the reactor are two silicon electrode rods that act as seed rods. The reactor is heated to 2012°F and the silicon from the trichlorosilane leaves to form rod that bridges the two silicon seed rods. Rods of polysilicon crystals are then sliced into wafers for cells and this is what gives them a shattered glass look.
Obviously, silicon refining is an energy intensive process that adds to its cost. Until 2000, most of this highly pure polysilicon went to making semiconductors. This made solar cells expensive. Since then, a wide variety of other semiconducting materials have taken polysilicon’s place. Since solar cells don’t require polysilicon to be quite as high a purity as semiconductors, other processes have been developed that deliver solar cell quality polysilicon at a lower price.
Both the changes in the international supply and demand for polysilicon as well as the competition to reduce the cost in manufacturing led to a rapid decline in the polysilicon spot price from $400/kg in 2008 to as low as $20/kg by 2012. The current price is around $16/kg.
How do solar panel prices affect your Texas electricity bill?
The cheaper solar panels get, the more likely that your neighbors and other homeowners and businesses in your community will install them. Five or six might not make a difference to the local TDU, but 100 or 200 will. Like many other states, Texas is looking into harnessing the power generated by all these solar installations that are distributed through out a local area. We’ll get into all in the next installment of our Green Energy in Texas series.