Innovations in solar technology belong to today’s students

Students at Lind-Ritzville High School (LRHS) resumed their pursuit of knowledge on Monday.

Their purpose: to exceed expectations and, one day, use their educations to make a positive impact on society.

While students’ contributions to the betterment of the world may not be immediate, their opportunities to build off of current research expand every day.

Solutions to the growing demands for efficient energy sources are a prime example. The Institute for Energy Research reports that solar energy accounts for only 0.5 percent of energy consumed in the United States.

Currently, this statistic is limited by consistent availability of the Sun and the cost of active solar technology.

The photovoltaic cell, an active solar energy technology that transforms solar energy to electrical energy, was developed in 1954 by Calvin Fuller, Gerald Pearson, and Daryl Chapmin.

Christiana Honsberg and Stuart Bowden, contributors for PVenergy.org, explain the basics of the cell’s technology, “[The] process requires firstly, a material in which the absorption of light raises an electron to a higher energy state, and secondly, the movement of this higher energy electron from the solar cell into an external circuit.”

After transferring its energy into the circuit, the ground-state electron returns to the cell.

The passing of sunlight through the materials or the conversion of solar energy to heat reduces the efficiency of the photovoltaic cell.

In fact, only six years after the innovation of the photovoltaic cell came the announcement of its limitations.

William Shockley and Hans Queisser calculated the Shockley-Queisser Efficiency Limit, a theoretical projection of the maximum amount of solar energy each material can convert to electrical energy.

The upper limit is 32 percent efficiency.

Today, many efforts are being made towards defeating the Shockley-Queisser Limit to produce more efficient photovoltaic cells.

In May, researchers at the Massachusetts Institute of Technology (MIT) devised a breakthrough.

The Shockley-Queisser Limit is based on several assumptions, including among others, the presence of only one semi-conductor in a cell, the inability of the Sun to be concentrated, or the loss of usable energy to heat.

By circumnavigating these assumptions, efficiency can be increased.

David Chandler, contributor for MIT News Office explained, “There are some possible avenues to increase that overall efficiency, such as by using multiple layers of cells, a method that is being widely studied, or by converting the sunlight first to heat before generating electrical power. It is the latter method, using devices known as solar thermophotovoltaics, or STPVs, that the team has now demonstrated.”

“Instead of dissipating unusable solar energy as heat in the solar cell, all of the energy and heat is first absorbed by an intermediate component, to temperatures that would allow that component to emit thermal radiation,” Chandler explained of the new technology.

He continued, “By tuning the materials and configuration of these added layers, it’s possible to emit that radiation in the form of just the right wavelengths of light for the solar cell to capture.”

Because specific materials absorb only a specific wavelength most efficiently, “this improves the efficiency and reduces the heat generated in the solar cell.”

MIT professor Evelyn Wang, who collaborated with Ph.D student David Bierman and five others explained, “We believe that this new work is an exciting advancement in the field.”

Also in May, the University of New South Wales (UNSW) in Sydney, Australia, made their own contribution to the efficiency of photovoltaic cells.

Researchers set a new world record of 34.5 percent efficiency for a photovoltaic cell without concentration (via mirrors or lenses) of the Sun.

Instead of heating a material that emits a specific wavelength of light, the UNSW researchers filter the light. This allows different wavelengths to be absorbed by their respective efficient material.

Fiona Macdonald, journalist for Science Alert, reported, “The sunlight passes through each of these layers… and energy is extracted by each at its most efficient wavelength. Any unused light passes on to the next layer, and so on, to squeeze the most out of every single beam.”

Mark Keevers, one of the UNSW researchers explains, “This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient.”

Progress still needs to be made, however. Macdonald said that UNSW’s “solar cells aren’t likely to end up on the rooftop of your home or office anytime soon – they’re harder to maintain and more expensive than the standard single-[layer] solar cells we’re used to seeing.”

“The next steps,” Chandler said of the MIT research with applications to all photovoltaic innovations, “include finding ways to make larger versions of the small, laboratory-scale experimental unit, and developing ways of manufacturing such systems economically.”

As LRHS students return to school, they have long-term goals in mind; perhaps the next innovations in solar energy will be ones they make themselves.