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Analysis Sees Many Promising Pathways for Solar Photovoltaic Power

solar pv power

Illustration shows the MIT team’s proposed scheme for comparing different photovoltaic materials, based on the complexity of their basic molecular structure. The complexity increases from the simplest material, pure silicon (single atom, lower left), to the most complex material currently being studied for potential solar cells, quantum dots (molecular structure at top right). Materials shown in between include gallium aresenide, perovskite and dye-sensitized solar cells. Courtesy of the researchers.

New study identifies the promise and challenges facing large-scale deployment of solar photovoltaics.

David L. Chandler | MIT News Office

In a broad new assessment of the status and prospects of solar photovoltaic technology, MIT researchers say that it is “one of the few renewable, low-carbon resources with both the scalability and the technological maturity to meet ever-growing global demand for electricity.”

Use of solar photovoltaics has been growing at a phenomenal rate: Worldwide installed capacity has seen sustained growth averaging 43 percent per year since 2000. To evaluate the prospects for sustaining such growth, the MIT researchers look at possible constraints on materials availability, and propose a system for evaluating the many competing approaches to improved solar-cell performance.

pv capacity

Chart from the MIT report shows the extremely rapid worldwide growth of photovoltaic installations over the last 15 years. Courtesy of the researchers.

The analysis is presented in the journal Energy & Environmental Science; a broader analysis of solar technology, economics, and policy will be incorporated in a forthcoming assessment of the future of solar energy by the MIT Energy Initiative.

The team comprised MIT professors Vladimir Bulović, Tonio Buonassisi, and Robert Jaffe, and graduate students Joel Jean and Patrick Brown. One useful factor in making meaningful comparisons among new photovoltaic technologies, they conclude, is the complexity of the light-absorbing material.

The report divides the many technologies under development into three broad classes: wafer-based cells, which include traditional crystalline silicon, as well as alternatives such as gallium arsenide; commercial thin-film cells, including cadmium telluride and amorphous silicon; and emerging thin-film technologies, which include perovskites, organic materials, dye-sensitized solar cells, and quantum dots.

With the recent evolution of solar technology, says Jean, the paper’s lead author, it’s important to have a uniform framework for assessment. It may be time, he says, to re-examine the traditional classification of these technologies, generally into three areas: silicon wafer-based cells, thin-film cells, and “exotic” technologies with high theoretical efficiencies.

“We’d like to build on the conventional framework,” says Jean, a doctoral student in MIT’s Department of Electrical Engineering and Computer Science. “We’re seeking a more consistent way to think about the wide range of current photovoltaic technologies and to evaluate them for potential applications. In this study, we chose to evaluate all relevant technologies based on their material complexity.”

Under this scheme, traditional silicon — a single-element crystalline material — is the simplest material. While crystalline silicon is a mature technology with advantages including high efficiency, proven reliability, and no material scarcity constraints, it also has inherent limitations: Silicon is not especially efficient at absorbing light, and solar panels based on silicon cells tend to be rigid and heavy. At the other end of the spectrum are perovskites, organics, and colloidal quantum dots, which are “highly complex materials, but can be much simpler to process,” Jean says.

The authors make clear that their definition of material complexity as a key parameter for comparison does not imply any equivalency with complexity of manufacturing. On the contrary, while silicon is the simplest solar-cell material, silicon wafer and cell production is complex and expensive, requiring extraordinary purity and high temperatures.

By contrast, while some complex nanomaterials involve intricate molecular structures, such materials can be deposited quickly and at low temperatures onto flexible substrates. Nanomaterial-based cells could even be transparent to visible light, which could open up new applications and enable seamless integration into windows and other surfaces. The authors caution, however, that the conversion efficiency and long-term stability of these complex emerging technologies is still relatively low. As they write in the paper: “The road to broad acceptance of these new technologies in conventional solar markets is inevitably long, although the unique qualities of these evolving solar technologies — lightweight, paper-thin, transparent — could open entirely new markets, accelerating their adoption.”

The study does caution that the large-scale deployment of some of today’s thin-film technologies, such as cadmium telluride and copper indium gallium diselenide, may be severely constrained by the amount of rare materials that they require. The study highlights the need for novel thin-film technologies that are based on Earth-abundant materials.

The study identifies three themes for future research and development. The first is increasing the power-conversion efficiency of emerging photovoltaic technologies and commercial modules.

A second research theme is reducing the amount of material needed per cell. Thinner, more flexible films and substrates could reduce cell weight and cost, potentially opening the door to new approaches to photovoltaic module design.

A third important research theme is reducing the complexity and cost of manufacturing. Here the researchers emphasize the importance of eliminating expensive, high-temperature processing, and encouraging the adoption of roll-to-roll coating processes for rapid, large-scale manufacturing of emerging thin-film technologies.

“We’ve looked at a number of key metrics for different applications,” Jean says. “We don’t want to rule out any of the technologies,” he says — but by providing a unified framework for comparison, he says, the researchers hope to make it easier for people to make decisions about the best technologies for a given application.

Martin Green, a professor at the Australian Centre for Advanced Photovoltaics at the University of New South Wales who was not involved in this work, says the MIT team has produced “some interesting new insights and observations.” He says the paper’s main significance “lies in the attempt to take a unifying look at the issues involved in choosing between PV technologies.”

“The issues involved are complex,” Green adds, “and the authors abstain from betting on any particular PV technology.”

Reprinted with permission of MIT News

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Discussions

Bob Meinetz's picture
Bob Meinetz on Apr 2, 2015 7:33 am GMT

David, the statement in the study’s abstract that

[photovoltaic solar has] the scalability and the technological maturity to meet ever-growing global demand for electricity.”,

accompanied by the imprimatur of a prestigious university, leaves me curious as to whether there’s some attempt to justify it within. It’s so divorced from current reality it comes across as salesmanship.

Which, given that details are hidden behind a $70 paywall, might be an apt description.

Joe Deely's picture
Joe Deely on Apr 2, 2015 7:39 pm GMT

Bob,

Curious – which phrase don’t you agree with – “the scalability”  or the “technological maturity” ?

I believe the solar is still relatively immature technologically – plenty of room to improve.

However, even with this immaturity it is having no problems scaling.

Your home state – CA – scaled solar as a % of total electricity from 1.9%  in 2013 to 5% in 2014.  Currently at a 7-8% run-rate for 2015. (and this does not count rooftop)

Bob Meinetz's picture
Bob Meinetz on Apr 2, 2015 8:30 pm GMT

Joe, the statement specifically addressed global demand.

California is unique to the U.S., and the U.S. unique to the world. The 10th most affluent country has yet to meet 1% of its demand with solar, and probably won’t for many years to come. Residents of other countries with a fraction of our resources want what we take for granted, and it’s something solar can’t deliver – cheap energy which doesn’t disappear when the sun goes down.

Solar will never, ever meet global energy demand, nor even enough to have an effect on global warming.

Joe Deely's picture
Joe Deely on Apr 2, 2015 9:39 pm GMT

Never ever is a long time and the US and/or CA are certainly not the best markets for solar. By the way the US will come very close to 1% from solar next year and will be at 1.3%(not including rooftop) by 2016

As for the world, the historically conservative IEA has solar at 26% by 2050  16% for PV and 10% for CSP  in its most recent reports.

 PV

 

 CSP

 

 

 

Bob Meinetz's picture
Bob Meinetz on Apr 2, 2015 10:46 pm GMT

No Joe, EIA doesn’t “have” solar at 26% in 2050 – it’s a wishlist, and it’s full of caveats.

Alex Trembath has addressed this extensively here on TEC:

The IEA “Technology Roadmap” is just that: a roadmap. It is not a prediction…the IEA report states, “The vision in this roadmap is consistent with global CO2 prices of USD 46/tCO2 in 2020, USD 115/tCO2 in 2030, and USD 152/tCO2 in 2040.” Currently, there is no global carbon price. National and regional carbon prices consistently measure well below these levels. California’s carbon price is around $12/tCO2. Europe’s is around $9/tCO2. China’s municipal carbon pricing pilot schemes vary between $3 and 13/tCO2. This summer Australia repealed its national carbon tax. As MIT’s Jesse Jenkins has noted, there are convincing political economy reasons to suspect that nations will find it hard to raise carbon prices well above these current levels. So the climate policy assumptions in the roadmap are a stretch, to say the least…

Joe Deely's picture
Joe Deely on Apr 3, 2015 2:49 am GMT

Bob,

Thanks.

Good correction. I meant to say most recent roadmaps vs. “most recent reports”.  Your point about these being roadmaps vs forecasts is also correct.

I was using the IEA forecast as illustration that “solar has the “scalability” as called out in the MIT report.  We can scale to the numbers mentioned in the IEA roadmap – in my mind pretty easily. There is obviously an argument to be made on both sides on whether we will scale to those numbers or not.

I find it interesting that IEA roadmap for 2014 has shifted from the one they published just 4 years ago.

  • This roadmap envisions PV’s share of global electricity reaching 16% by 2050, a significant increase from the 11% goal in the 2010 roadmap
  • The solar PV roadmap was one of the first roadmaps developed by the IEA, in 2009/10. Since then, the world has added more PV capacity than it had in the previous four decades, and more rapidly than expected. The 210 GW of cumulative capacity expected to be reached by 2020 is now likely to be achieved five years earlier, and the capacity now expected for 2020 will be over twice what was foreseen in the 2010 roadmap. 

With 177 GW of solar installed worldwide electricity production is now at 1%. With no growth in the current solar installations the installed capacity will hit 1,200GW by 2050. This will produce about 4-5% of total electricity.  

So the only point of contention is –

1) will solar be at 4-5% of electricity production with 0% growth in yearly installations

2) will solar be at 26% as the 2014 IEA Roadmap speculates

3) or will the IEA again up its 2050 solar estimates four years from now when it sees the market is blowing past its expectations.

 

Mark Heslep's picture
Mark Heslep on Apr 6, 2015 1:17 am GMT

Right now we use 1 cu Km of oil every 300 days. Apart from the need for oil itself, which is not substitutable by electricity.”

Eventually, why not? Replacing that global rate of oil consumption requires roughly 1 TW of electric power (roughly the capacity of the US electric system alone) if used for transportation.  I suspect the infrastructure of the current global oil industry is much larger than the electricity capacity required to replace it. 

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