The Triple Helix @ UChicago

Winter 2018

"A Sunny Outlook" by Marianna Karagiannis

 

Solar energy has long been a source of hope in the renewable energy industry. The sun emits a vast amount of energy--in just an hour and a half, enough sunlight strikes the Earth to satisfy the planet’s demands for an entire year. This abundant energy can be harvested without emitting the harmful greenhouse gases that are warming the planet. Why, then, does solar energy supply just 10% of the world’s energy and only 0.5% of the USA’s? The simple answer is that solar energy technology remains less cost effective than fossil fuels and that solar energy is still accompanied by its own environmental effects.

To understand these challenges, it helps to first understand how solar technology works. Traditional photovoltaic cells (PV) are made with silicon and absorb photons to create an electric field. This occurs as the energy from absorbed photons excites electrons to higher energy levels and allows the flow of electrons to create the field. PV cells come in two main forms: thin film and crystalline. There are tradeoffs for each. Thin film cells are cheaper and less likely to break, but also less efficient and harder to make in comparison to crystalline cells. Both are commonly made with silicon, and many small cells are combined in an array that can be connected to a power grid.

One of the main challenges is intuitive: a cloudy day could result in no energy production. This concern is trivial for areas like the Sahara Desert, but renders solar energy a poor choice in more temperate areas such as Chicago. Compounding this issue is the lack of an effective large-scale energy storage mechanism. Even small batteries, like the kind we use for personal devices, are costly and quickly lose efficiency. Recent focus on energy storage among companies including Tesla has resulted in batteries capable of keeping vital household appliances (for a single house) powered for up to 24 hours. Though this is useful for emergencies, cost remains a significant burden and there is limited functionality for limited time. Batteries are consistently being improved upon, lengthening their lifetimes and charge capacity, but they are inherently limited by size and the choice of material. Until large scale energy storage becomes sufficiently effective at a reasonable cost for the public, we cannot rely exclusively on solar energy without risking energy shortages on cloudy days.

In addition to these challenges, there are also several environmental concerns related to the mining and refinement of the silica used in the PV cells. While energy from the sun is infinite for our purposes, silicon is not. Nearly 30% of the Earth’s crust is silicon. However, it is generally found in the form of oxides, such as quartz. Silicon is refined by reducing silicon oxides with carbon under high temperatures, which is a process that requires lots of energy. Furthermore, the refinement process of turning the silica into useful polysilicon presents an environmental challenge, as it produces silicon tetrachloride. Silicion tetrachloride, aside from being corrosive and hazardous on its own, also produces hydrochloric acid when exposed to water, hindering plant growth and preventing mollusks from growing their shells. Some manufacturers can recycle the silicon tetrachloride by turning it back into polysilicon, but this is incredibly costly, which poses further challenges. Only very few options of disposal or use exist outside of this costly recycling, meaning that as solar energy markets continue to grow there must be serious consideration for the transformation of this dangerous waste. While the environmental effects of solar technologies seem discouraging, especially since one of the most attractive features of solar energy is being “green,” these technologies are significantly more eco-friendly than fossil fuels. The production of silicon tetrachloride is nearly inconsequential in comparison to the billions of tons of carbon dioxide, sulfur oxides, and nitric oxides released by fossil fuel combustion each year. However this does not mean that environmental impacts of solar technologies should be ignored: though they are not as detrimental as fossil fuels, they can and should be invested in to improve and create a form of energy production with minimal impact.

The future of solar technology looks bright despite challenges. Research into new energy storage and more efficient conversion of pure solar energy into electrical energy has slowly been resulting in incremental improvements that are adding up. The high demand for replacements of fossil fuels has continued to drive both scientific interest into new forms of energy and expansion of new innovations into private markets, as well as efforts by domestic and international governments to become leaders in energy through tax incentives and research funding. In terms of storage, new advances in molten salt, lithium ion, and compressed air storage have helped solar technologies become a more viable large-scale alternative to fossil fuels by providing the opportunity for energy reserve. Even solar cells themselves are improving and diversifying. Promising technologies include Dye Sensitized Solar Cells (using organic dyes rather than silicon as a medium for electron excitation), which can even be made transparent. Other groups have focused on improving specific components of traditional photovoltaics, with the net result being a drastically improved overall energy output. With continued research, solar energy may soon provide an environmentally friendly, economically viable, and efficient energy source. While we may never have a world in which human energy consumption has no environmental impact, solar energy has the potential to bring us one step closer to a sustainable society.

References

[1] "2018 Solar Energy Storage and Battery Options." PowerScout. Accessed March 06, 2018.                      https://powerscout.com/site/solar-energy-storage-battery-options-2018.

[2] Brady, Jeff, Leigh Paterson, and Lauren Sommer. "Solar And Wind Energy May Be Nice, But                  How Can We Store It?" NPR. April 05, 2016. Accessed February 22, 2018.            https://www.npr.org/sections/alltechconsidered/2016/04/05/470810118/solar-and-wind-energy-may-be-nice-but-how-can-we-store-it.

[3] Mulvaney, Dustin. "Solar Energy Isn't Always as Green as You Think." IEEE Spectrum:                         Technology, Engineering, and Science News. November 13, 2014. Accessed February 22,              2018.                                                                                                                                      https://spectrum.ieee.org/green-tech/solar/solar-energy-isnt-always-as-green-as-you-think.

[4] Pukhrem, Shivananda. "How Solar Cells Work — Components & Operation Of Solar Cells."                    Solar Love. May 13, 2013. Accessed February 22, 2018.                                                                     http://solarlove.org/how-solar-cells-work-components-operation-of-solar-cells/.

[5] "Silicon." The Environmental Literacy Council. Accessed March 06, 2018.                                     https://enviroliteracy.org/special-features/its-element-ary/silicon/.

[6] "Solar Energy Technology Basics." US Department of Energy. August 16, 2013. Accessed                       February 22, 2018. https://energy.gov/eere/solar/articles/solar-energy-technology-basics.

[7] "Solar." Institute for Energy Research. Accessed February 22, 2018.                                                           https://www.instituteforenergyresearch.org/topics/encyclopedia/solar/#_ftn1.

 

 
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