Solar Power Science
A few years ago, you had to travel to sunny California to see solar energy panels soaking up the sun and converting it to electric power. Not anymore! Solar energy photovoltaic cells are popping up on rooftops across the country and I’m now considering them the top of my new home. In 2011, the Cincinnati Zoo and Botanical Gardens inspired many of us who live in the Midwest when they installed 6,400 photovoltaic solar panels atop their parking lot, providing shade for our cars and energy for the zoo. The fact that the annual sunshine for our area is only around 50%, compared to 73% in Los Angeles, is just one of the challenges we face when considering solar energy in the Midwest, but challenges are just interesting problems in science that are waiting to be solved!We can thank Edmund Bequerel for his initial discovery in 1839 that some materials when exposed to light generated a small electric current. He was just 19 at the time! Later, Albert Einstein described this photoelectric effect with mathematics and for this, he was awarded the Nobel Prize in 1921 (http://www.nobelprize.org/nobel_prizes/physics/laureates/1921/). Sixty years ago in 1954, the first photovoltaic cell was produced by researchers Daryl Chapin, Calvin Fuller, and Gerald Pearson at Bell Laboratories. They used silicon which was purified through a process that chemist Fuller had designed – the process turned silicon into an excellent conductor of electricity. The scientists added gallium and lithium metal to the silicon; the electrons in lithium are weakly held so it takes only a little light energy to get the electrons moving and an electric circuit flowing.Photon Power – The sun provides light and warmth for this world and with a bit of help from scientists and engineers, it brings us solar powered electricity. However, all this is actually the work the incredible little photon. Light, whether from our sun our light fixtures, is made up of photons. Photons are unusual because they are both particle and wave in nature, and they are a source of energy that can be converted. When photons hit the atoms in the material of Edmund Bequerel’s experiment or the Bell Lab photocell, the energy caused the atom’s electrons to move. Electrons are equally interesting. They are negatively charged particles and when they are able to move, as they do in a conductive material like a copper wire (or even a lemon for that matter!) the movement creates an electric current.
The photovoltaic cells that you see on rooftops are similar to those that Bell Lab designed. The materials at work are called semiconductors and are made from silicon combined with other atoms that are either rich with electrons (N-type), or lacking electrons (P-type). Semiconductors are not just found in solar cells – they also fill your tablets, cell phones, computers and just about every other electronic device made today. When photons hit the N-type material, the energy from the photon is enough to cause the electron to move into the P-type semiconductor where there are vacant spaces or holes. This creates the electric circuit.
Solar Electric Power – Solar fields are sprouting up along the west coast, in the deserts of the southwest, and on the rooftops of buildings and homes across the US. You can view a map of the major solar installations in the US by visiting the Solar Energy Industry Association’s website (http://www.seia.org/map/majorprojectsmap.php). California leads the country in solar powered utility companies, businesses, and homes (http://www.seia.org/research-resources/solar-market-insight-report-2014-q1) and in late November 2014 operations began at the world’s largest solar facility (550 megawatts from arrays on about 3,500 acres), Topaz Solar Farm in San Luis Obispo County. Expansion of solar power is on the rise in other states as knowledge and interest in the technology grows and the cost of the solar array decreases. In fact, the expansion might just include my new roof.Which is one of the reasons I’m interested in photovoltaic cells and not just how they work and how much they cost, but also how they are made – which is why I’ve added the video below. Once the photovoltaic array is made, how do they go on my roof, how will the system work, and how much energy will I save? I have a great number of questions and I’m just beginning to learn the answers. An of course, there are challenges, too! But at the heart I’m a scientist and love a good problem to solve.Stay tuned for the next installment to Solar Power Science on SciBlip.
Solar Energy Timeline – http://www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf
The Silicon Solar Cell Turns 50 by John Perlin – http://www.nrel.gov/education/pdfs/educational_resources/high_school/solar_cell_history.pdf
How do Photovoltaics Work – http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/