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High-efficiency perovskite crystals produced at Los Alamos that approach silicon in conversion efficiency. Photo: Los Alamos National Laboratory via Flickr (CC BY-NC-ND).
High-efficiency perovskite crystals produced at Los Alamos that approach silicon in conversion efficiency. Photo: Los Alamos National Laboratory via Flickr (CC BY-NC-ND).
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New solar tech slashes energy payback time to a few months

The Ecologist

5th August 2015

Solar panels made using perovskite technology pay back the energy used to make them ten times faster than those using silicon. In time, this could lead to similar falls in price.

Perovskite technology is still pre-commercial, but the very low energy cost indicates that major price falls relative to the current generation silcon panels are to be expected as the new technology matures.

A new study shows that perovskite solar technology slashes the energy used in making solar panels.

The crystalline silicon panels that dominate the market may take 30 months to four years to 'pay back' the energy used in their manufacture. Amorphous silicon comes out better at under two years.

But according to the new study by scientists at Northwestern University and the US Department of Energy's Argonne National Laboratory, perovskite solar modules have an 'energy pay back time' (EPBT) of just two to three months.

The EPBT of solar panels is based on the time it takes for panels to produce electricity equivalent to sum of all the energy needed to mine, process and purify raw materials, and to manufacture and install the final product.

Perovskites lag behind silicon in conversion efficiency, but they require much less energy to be made into a solar module. So perovskite modules pull ahead with a substantially shorter energy payback time - the shortest, in fact, among existing options for solar power.

"People see 11% efficiency and assume it's a better product than something that's 9% efficient", said corresponding author Fengqi You of Northwestern's McCormick School of Engineering and Applied Science. "But that's not necessarily true. One needs to take a broad perspective when evaluating solar technology."

In fact, some perovskite cells have achieved 19% efficiency using an inexpensive and versatile 'spray-on' technology developed at the University of Sheffield - still lower than the 25% achieved by the highest-performing silicon cells, but getting close. Los Alamos National Laboratory achieved 18% efficiency in January this year using cystalline perovskite cells.

Life cycle assessment

In what's called a cradle-to-grave life cycle assessment, You and his colleagues traced a product from the mining of its raw materials until its retirement in a landfill. They determined the ecological impacts of making a solar panel and calculated how long it would take to recover the energy invested.

"Soon, we're going to need to produce an extremely high number of solar panels", said You. "We don't have time for trial-and-error in finding the ideal design. We need a more rigorous approach, a method that systematically considers all variables."

This study looked at the energy inputs and outputs of two perovskite modules - the crucial panel components that convert sunlight into electricity. To get a complete picture of the environmental impacts of a perovskite the researchers also analyzed metals used for electrodes and other parts of the device.

One of the modules tested includes lead and gold, among other metals. Many perovskite models have lead in their active layer, which absorbs sunlight and plays a leading role in conversion efficiency. The module used gold as its cathode in order to prevent corrosion.

"People in the research community have expressed concern because everyone knows lead can be toxic", said Seth Darling, an Argonne scientist and co-author on the paper. "However the team's assessment showed that gold was much more problematic."

Gold isn't typically perceived as hazardous, but mining the precious metal is extremely damaging to the environment. So before putting a perovskite panel on the market, the gold will need to be replaced by more sustainable - and less expensive - materials, for both environmental and economic reasons.

Commercial production within two years

In 2013 Science magazine listed perovskite solar cells as one of the year's ten  biggest breakthroughs. "A new breed of materials for solar cells burst into the limelight this year", the citation stated.

"Known as perovskites, they are cheap, easy to make, and already capable of converting 15% of the energy in sunlight to electricity. While that remains below the efficiency of commercial silicon solar cells, perovskites are improving fast. One particularly promising feature is that they can be layered on top of silicon solar-cell material to harness a range of wavelengths that neither could capture alone."

Perovskite technology is still pre-commercial, but the very low energy cost indicates that major price falls relative to the current generation silcon panels are to be expected as the new technology matures.

A further challenge will be to extend the lifetime of perovskite modules to make sure they are stable enough for long-term commercial use enduring for decades on end, said You, who believes the panels could soon be on the market:

"Despite a few necessary improvements, perovskite technology could be commercialized within two years if researchers use comprehensive analysis to optimize the selection of raw materials and manufacturing."

One of the motivations for this study, according to the authors, was the need to improve technology so that solar energy can be scaled up in a big way to meet the projected doubling of global energy demand by 2050 in an environmentally friendly way.

"How quickly do we have to get a technology to market to save the planet?" asks Darling. "And how can we make that happen?"

 


 

The paper: 'Perovskite Photovoltaics: Life-Cycle Assessment of Energy and Environmental Impacts' is published in the journal Energy & Environmental Science.

Also on The Ecologist: 'Seven breakthrough solar technologies - but will they work?' by Zachary Davies Boren.

This research was conducted in part at the Center for Nanoscale Materials, a DOE Office of Science User Facility supported by the DOE's Office of Basic Energy Sciences, and was funded by Northwestern's Institute for Sustainability and Energy.

Principal source: Megan Fellman, science and engineering editor at Northwestern, and Payal Marathe, Argonne National Laboratory.

 

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