The United States has seemed to be on the edge of a massive energy crisis my entire life. As a nation, we consume an ever growing amount of energy for both electricity and transportation. While such massive power usage is not, in itself, a travesty, we persist in generating our power in a non-sustainable pattern. The United States consumed a grand total of about 100 Quads of energy last year. Of this, approximately 86% consisted of the burning of fossil fuels .
The continually decreasing amount of fossil fuels has left many contenders vying to be the next juggernaut (hehehe ) of the energy sector. A popular candidate these days is solar power. I love the concept of this abundant power source with no fuel cost. Solar has high intensity periods at the appropriate times of day for peaking power. I truly believe solar power is the energy of the future.
That said, solar has several major issues associated with its use. The systems we use today are extremely inefficient (usually 10%-20%) . Manufacturing prices have consistency problems because of a varying silicon prices. Solar panels are also much less effective at poor visibility times, e.g., in rainy weather or at night. This means that much of the time they are installed they generate little power. Even worse, their performance has been known to degrade with time. As such, solar loses the cost effectiveness battle almost every time.
The only reason we have seen a massive influx of solar installations in the last few years is because the government began giving fairly large subsidies to solar panel installers in 2006. This investment tax credit allows consumers to recoup 30% of qualifying costs on a tax break of up to $1500 . This policy was made in an effort to help the solar panel industry mature until they could be made cost effective, but the limitation period on beginning the tax relief is getting closer and solar is still nowhere close to being a viable alternative to traditional fossil fuels.
While there is definite potential here, I find the populace, even at the university level, is very ill informed about some portions of photovoltaic systems. Sure, most people can cite a variety reasons for or against solar panels and many are conscious of the solar panel’s poor power factors. A good portion of individuals can even tell you about the newer thin-film solar technologies. However, virtually no one can tell you anything about solar cell production. In that light (pun intended), let’s take a look at the four main steps for the manufacturing of traditional solar panels.
Step 1: Casting and Wafering. This is the most energy intensive portion of the process by a large margin. Chemically pure silicon is melted at high temperature and then allowed to resolidify, producing large, single crystals. As a reference, silicon melts at 1414°C. The idea is to melt the substance before holding it at a temperature just below its melting point for a prolonged period of time. As crystals of the matter solidify, the prolonged exposure at high temperature allows the crystals to grow larger and larger. They are finally pulled from the molten metalloid when they reach around 150mm in diameter. These large silicon crystals are cut before being assembled into bars and then wafers, giving solar panels their distinctive sheen. Companies try to situate manufacturing plants near sources of abundant power due to the difficulties of keeping silicon liquid .
Step 2: Solar Cell Manufacturing. The solar wafers are taken through a semiconductor processing sequence to create working solar cells. First, the crystals are coated in a light acid to etch their surface. This provides a clean, useful surface with little flaws. Silver and aluminum are screen-printed on the crystals for conduction, increased surface reflection, and to form a layer that will protect the silicon from oxidization. The last few processing steps add solar flux, solder the flux, and intensively clean the wafers. Finally, the configured cells are tested to assure everything is in working order. If the first step was energy intensive, this is the capital intensive portion of the process. The technology and control needed for the delicate processing is quite expensive .
Step 3: Module Assembly. This part is simple, comparatively, and is usually done closer to consumers. This is the assembly of solar panels into a solar frame, usually made of aluminum, and adding the glass sheet that covers the solar panels.
Step 4: Solar System Assembly. This last portion of the solar procedure is really just the mechanical and electrical integration of the new solar panels with its surroundings. This portion is usually done onsite in minor installations with only a small capital cost and little labor. Things get trickier for large solar plants, however.
If you are really interested in this, here’s a video showing a slightly outdated production model, but at least it gives an idea about how some of the process works:
Perhaps the trick to making solar feasible is to completely scrap what we do now. The method described above is used to make classic photovoltaic panels with silicon wafers and it differs from the process used to manufacture new, thin-filmed solar panels. To make these, a thin layer of silicon is deposited on a glass sheet covered with a conducting oxide layer . This is done using Chemical Vapor Deposition (CVD). CVD entails controlling a chemical reaction in which a gaseous, volatile substance is converted into a solid film on a conveniently situated material . Since this skips the solar cell manufacturing step, the whole process gets much cheaper. I should also note that various individuals around the nation are researching new and innovative photovoltaic devices. The DOE has a pretty nice list at http://www1.eere.energy.gov/solar/new_devices_and_processes.html
Solar power is currently too inefficient to be the primary power source of the world. I have confidence that we will get there one day. There is too much energy being given to us in the form of solar radiation every day for us to not utilize it eventually. The power is not limitless, but it is more than the world will need for a long, long time. Either solar panels will be designed to be much more efficient, much cheaper to manufacture, or every other energy source will become too expensive. Perhaps we will harvest this sunlight in the form of biofuels or biomass by relying on natural photosynthesis. As Americans, this should be just fine with us. Some of the best sites in the world to harvest solar power exist in the American Southwest, where it is usually sunny with little cloud cover . I firmly believe, one day, solar power will run our homes, our vehicles, and our industry.
The Department of Energy gave out over $2.2 billion to businesses, industries, and universities in attempt to research and invent superior solar panels through grant money . This research is supposed to help solar power reach grid parity by 2015, which should expand the solar cell industry . Through these steps and the rebate to consumers mentioned earlier, the US is trying to help solar power become a fixture in American power generation. Before any of this can happen, though, solar panel devices and processes are going to have to become cheaper and more efficient before they can compete with fossil fuels. For now, they have a long way to go. Solar power only generated 6 Trillion BTUs of the 42 Quadrillion BTUs Americans used to generate electricity in 2007 .
If I were on your side of the monitor, I’d ask why, in this roundabout fashion, I chose to discuss solar panel manufacturing. It is partly because I am a mechanical engineering undergraduate who immensely enjoyed his materials processing class. Mainly, however, it is because I believe the better the world’s populace understands solar panels, the better we will be able to use them. If, as denizens of modern times, we can better understand our world, we will be that much better equipped to face the future.
- Annual Energy Review, 2007, EIA