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The 39th IEEE photovoltaic specialist conference was held between June 16th and 21st at the Tampa bay convention center in Tampa, Florida. It was a congregation of industry experts, and research giants. Researchers from NREL, Sandia National Laboratories and Universities across the globe graced the occasion to present their latest studies on photovoltaic system design, implementation and reliability of on-sun PV modules.. The program was significantly all encompassing. Besides the presentations, social activities and mixer programs were held to allow attendees to interact, network and share knowledge. Of notable interest was the presentation of the cherry award to Keith Emery. Previously unknown to me, I found that he is renowned for his contribution to photovoltaic research for his design, development and implementation of IV characterization methods. He pioneered the first generation of hardware, software and procedures to measure current-vs.-voltage characteristics as a function of temperature, spectrum and intensity for single and multi-junction cells and modules.

Oral and poster presentations at the conference were grouped into eleven categories which ran in parallel beside keynote or plenary sessions. Personally, I attended sessions in the categories of advanced PV module concepts and designs and PV modules and terrestrial systems. From the presentations, I deduced that there is a significant amount of attention being given to system performance evaluation and energy yield assessments of photovoltaic systems. As such, there is a growing interest in research on concepts for data collection which is a necessary input for energy assessments. There were also presentations on the design of experiments for photovoltaic system assessments. Particularly, I found some modeling techniques used to evaluate PV system performance to be of interest. A few of them include:

Validation of the PVLife Model Using 3 Million Module-Years of Live Site Data [1]

In this article, SunPower corporation (the manufacturers of SunPower PV modules) presented their experiments and results on long term system degradation analysis. An interesting fact is that they performed their analysis using a relatively new approach. Rather than using high fidelity diagnosis methods, they settled for noisy large statistical samples that represent records from a large number of installed systems to estimate the median system degradation rate of PV modules. As a key player in the PV module industry, the company aimed to consolidate their understanding and confidence in system degradation trends and hence they’ve developed a model called the “PVLife model” which is used to simulate module degradation characteristics. Their PVLife model operates with inputs of weather data and cell characteristics to determine degradation factors such as UV induced cell degradation, encapsulant browning, bypass diode and solder joint failures.

For comparison, degradation analysis was carried out on a total of 445 systems.  226 systems were comprised of SunPower modules which had an installed capacity of 86MW. These systems had been operating for up to 5.5 years.  There were also included 149 systems of non SunPower modules which were as old as 11.5 years with an installed capacity of 42MW. Altogether, the total fleet-wide modules representing 3.2 million module-years of monitored data were used to determine degradation rates. Following a plethora of statistical analytics, they found the PVLife model to be in very good agreement with the compared module degradation rates. It was further claimed that the model results were used to develop better modules with lower degradation rates. Attention was focused on the relationship between degradation rates and the placement of the module contacts. According to their studies, it was found that front contact modules for a variety of reasons had a higher degradation rate when compared to back contact modules.

Overall, the work by SunPower suggests that they have successfully developed a working system to model the degradation mechanisms due to several factors in PV system operation. Validation of its results against a large dataset of on-sun measurements was shown to be in very good agreement

Simulations of Energy Yield Improvement in Utility-Scale PV Plants Using Distributed Power Point Trackers [2]

Researchers from First Solar Inc. presented their research on the use of distributed maximum power point trackers (MPPT). It was identified that any energy losses in utility scale PV installations decrease the financial value of the system. They aimed to analyze methods that might reduce the losses in utility scale PV installation such as partial cloud cover induced mismatch loss in the system. Since similar loss mechanisms due to building shading has been analyzed in detail, their focus was directed at non-uniform irradiance patterns created by cloud edges on utility-scale PV installations.  A model was developed to simulate the mismatch loss. The model simulates a PV array with a variable number of strings on a mounting structure. It simulates the movement of a cloud edge over the PV array whilst outputting the array IV characteristics based on voltage and current relationships. A study was then conducted on varying string lengths in the arrays for 10 and 15 modules in a string. Results from the analysis using their model showed a decrease in net energy loss when multiple maximum power point trackers were used. The key energy losses were found to be dependent on the length of the cloud edge. Measurement of the cloud edge in correlation the utility –scale system performance was prescribed to be conducted to further assess the impact of distributed MPPT in decreasing net energy losses.

Overall, the conference was a great learning experience. Its success encourages me to look forward to the next annual conference, which is scheduled to be held in Denver, Colorado

Jafaru Mohammed's picture.

-Jafaru Mohammed

M.A.Sc Electrical and Computer Engineering

Department of Electrical Engineering and Computer Science

SUNLAB Research Group

University of Ottawa, Canada.

References

[1]         E. Hasselbrink, M. Anderson, Z. Defreitas, M. Mikofski, Y. Shen, S. Caldwell, D. Kavulak, Z. Campeau, D. Degraaff, S. Corporation, R. Robles, and S. Jose, “Validation of the PVLife Model Using 3 Million Module-Years of Live Site Data,” in Photovoltaic Specialists Conference, 2013. PVSC’13. 39th IEEE, 2013.

[2]         A. Pope, J. E. Schaar, M. Schenck, F. Solar, and S. Francisco, “Simulations of Energy Yield Improvement in Utility – Scale PV Plants Using Distributed Maximum Power Point Trackers,” in Photovoltaic Specialists Conference, 2013. PVSC’13. 39th IEEE, 2013.

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Last year I had the opportunity to attend two big international Photovoltaics (PV) conferences.  The keynote speeches at both conferences discussed the future of crystalline silicon (c-Si) and ideas for high efficiency low cost c-Si PV technology. With less expensive organic PVs in the market and efficiency mark of thick crystalline silicon cells jammed at ~ 26% , these issues have been the hottest break-time discussion topics among people working in c-Si PV.

Recently, a very interesting article on “exotic silicon” by researchers at University of California, Davis on January 25, 2013 in Physical Review letters stirred up excitement in c-Si PV world. This exotic silicon, also called BC8 silicon, is a type of silicon that can be formed under extremely high pressure and is still capable of maintaining its stability at normal pressures. So what’s exotic about this silicon?? It can produce multiple electron hole pairs per incident photon in contrast with one e-h pair/photon generation in normal c-Si! The simulations run through the National Energy Research Scientific Supercomputing Center at the Lawrence Berkeley Laboratory predicted ~ 42 % efficiency in BC8 silicon solar cells under one sun that can be increased to ~ 70% by concentrating sunlight on the cell.

Wondering if you can actually make this exotic silicon? The answer is yes! Joint research between MIT and Harvard University shows that one can convert ordinary c-Si into high efficiency exotic silicon merely by shining it with laser light or by applying chemical pressure.

Conclusion: Silicon is an exotic element.  I think c-si will keep holding its share in future PV market with its surprising properties and contribution from researchers.

Check out the links and papers below for more information on this exciting research

  1. Lin, Yu-Ting,  Sher, Meng-Ju, Winkler, Mark T., Mazur, Eric,  Gradecak, Silvija Pressure-induced phase transformations during femtosecond-laser doping of silicon, Journal of Applied Phyics 5-110 (2011)
  2. Sher, Meng-Ju, Franta, Benjamin, Lin, Yu-Ting, Mazur, Eric, Gradecak, Silvija The origins of pressure-induced phase transformations during the surface texturing of silicon using femtosecond laser irradiation, Journal of Applied Phyics 8-112 (2012)
  3. http://www.energymatters.com.au/index.php?main_page=news_article&article_id=3572

Kitty Kumar

-Kitty Kumar

Ph.D Candidate, Year 4

University of Toronto, Toronto, Ontario

We are constantly inundated with projections, estimates, and forecasts of our future global and photovoltaic (PV) energy requirements. How much energy will we need by 2050? How much of our energy should come from PV? How much PV capacity can we install by 2020? Will that be enough?

I thought it would be interesting to see how we’ve done on our last decade of projections for global PV installations. The European Photovoltaic Industry Association (EPIA) is among various organizations that project and report the status of the PV market. From a series of EPIA’s Solar Generation (SG) reports ranging from SG1 (2001) to SG6 (2011) I looked at year-over-year projections for total global installed PV capacity, and plotted them alongside the actual installed values (see Figure 1).

Figure 1 for Ryan Tucker's blog

Figure 1 Cumulative installed photovoltaic capacity values and estimates from several EPIA reports.

It turns out that we’ve consistently beat the projections by large margins. In fact, the 2010 installed value (>39 GW) is more than a factor of three higher than the 2001 projections for that year (~13 GW). We can see from the plot in logarithmic scale that the installed capacity keeps jumping off of the exponential prediction curves.

The industry has made well on its promises. We must realize that the solar industry is in an enormous state of growth, but only because we are so far behind. This exponential growth is not sustainable for the industry. Certainly there has been amazing growth in the past decade, and we hope that this trend will continue for the following decade or two. Beyond that, let’s just hope that the total capacity is a significant portion of the global energy supply, and the industry can happily transition into a more steady growth state. In the meantime, I’m happy to take every megawatt of PV that we can get!

 

Ryan Tucker

-Ryan Tucker

Ph.D Candidate, Year 4

Department of Electrical Engineering, University of Alberta

 

Panelists:

David Brochu – Vice President Development, North America, Recurrent Energy

F. Michael Cleland – Nexen Executive in Residence, Canada West Fountation

Senator Grant Mitchell – Vice Char, Standing Committee on Energy, the Environment and Natural Resources, Liberal Senator, Alberta, Senate of Canada

Jon Kieran – Director, Development, EDF, EN Canada Inc.

Christian Vachon – President, Enerconcept Technologies

CanSIA concluded with a panel discussion on the development of a national energy strategy. The panelists consisted of David Brochu of Recurrent Energy, F. Michael Cleland of Nexen, Senator Grant Mitchell, Jon Kieran of EDF EN and Christian Vachon of Enerconcept. All members of the panel had the opportunity to express their opinions on how we need to proceed as a nation towards developing our energy strategy.

Four years ago Canada entered the Kyoto protocol in an effort to curb human-generated green house gas (GHG) emissions. Entering Kyoto was a move in the right direction for Canada, but ultimately we developed an unrealistic plan that we could not uphold. After failing to meet target reductions of GHG’s, Canada withdrew from the Kyoto protocol at the end of 2011. Canada needs to learn from its mistakes and work on developing a national energy strategy that will benefit Canadians.

What would a national energy strategy look like, and how would we get there? We could start by increasing engagement and advocation for development of an energy strategy for Canada. Promotion of open discussion to define what is important to Canadians in a energy strategy needs to occur. Why do we need a national energy strategy?  How much do we focus on making renewables a central part of our energy policy? Should we be putting a price on carbon, and would a carbon tax hurt Canada? How can we focus on the longevity and long term views of an energy strategy for Canada? There are many questions to be answered with no readily apparent solutions.

Where do solar energy and other alternative energy sources fit within Canada’s national energy strategy? Following the success of the feed in tariff (FIT) and micro-FIT programs, Canada has developed FIT 2.0  which will put another 160MW of solar energy online. The arrival of FIT 2.0 was not a surprise, but we will likely be seeing less government subsidy of solar projects. We cannot be reliant on a technology that requires subsidy to be sustainable. Fortunately, we have already seen instances where solar energy can be produced at grid parity. With the dropping prices of solar energy and the ever escalating price of non-renewable energies, it is essential for solar to be a large part of Canada’s energy strategy. With the help of the FIT programs, Canada aims to be recognized as a leader in the installation and manufacturing of solar modules.

Canada needs to sculpt an energy strategy that can drive our economy, promoting growth in an underdeveloped sector. An energy strategy that will advance job growth within Canada, and ultimately will lead to a more sustainable country.

 

-Matthew Schuster

M.ASc

Queens University

Thanks to the Photovoltaic Innovation Network, I participated in Solar Canada 2012 in Toronto, Ontario. This conference/exhibition is the largest national solar event in Canada, and is hosted by the Canadian Solar Industry Association (CanSIA). This year the event was quite large, in part due to the fact that it was CanSIA’s 20th anniversary.

In this conference, I participated in some talks and visited some booths; one of the talks that was really interesting to me was about Solar thermal, Geo-thermal and the opportunity to integrate these two technologies together. Solar thermal installations consist of a solar thermal collector on the roof, a control unit with a pump and a potable water storage tank. The collector absorbs the light from the sun and converts it into heat. This heat is transferred to a liquid which circulates through the collector and down into the solar storage tank (fig-1). There are a lot of solar thermal projects within Canada (as they can easily deployed, even in residential areas), but one of the biggest is at Oxford Gardens retirement home in Woodstock, Ontario. This solar thermal project is saving on air conditioning costs by up to 40%, or approximately $20,000 per year; for heat savings, up to 60% or approximately $40,000 per year, according to Suni Ball from Proterra Solar[1].

 

dummypic1

    A geothermal heat pump, ground source heat pump (GSHP), or ground heat pump is a central heating and/or cooling system that pumps heat to or from the ground. It uses the earth as a heat source (in the winter) or a heat sink (in the summer). Heat pumps provide winter heating by extracting heat from a source and transferring it into a building. In the summer, the process can be reversed so the heat pump extracts heat from the building and transfers it to the ground. Transferring heat to a cooler space takes less energy, so the cooling efficiency of the heat pump gains benefits from the lower ground temperature (fig-2).

 

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The combination of these two systems has many benefits [2]:

-Both systems don’t use fossil fuels at the point of use

-Geothermal is the backup for the solar thermal while the Geo-thermal can also provide cooling.

-Large flexibility in the heating appliances that can be used with both systems.

-Using the geothermal loop field as a storage tank to absorb the excess solar energy in the summer.  This advantage allows you to oversize the solar thermal system and increase the solar thermal contribution to the winter heating.

A study has been done [3] for the viability of a combined system in Milton, Ontario. This study shows that a combined system is feasible for space conditioning. For the house in this study, the seasonal solar thermal energy storage in the ground was sufficient to offset the large amount of Geo-thermal pump system length that would have been required in conventional systems. They showed that the economic benefit of such system depends on climate, as well as borehole drilling cost.

To conclude, a hybrid Solar-Geo-thermal system could be an outstanding solution to the high demand of energy in today’s world. It has a lot of benefits like sustainability, being clean (non-polluting) and having the ability to work all year round. Another important benefit is the possibility of using this system for all kinds of applications such as residential, commercial and industrial.

Farbod Ghods-Farbod Ghods

Ph.D Candidate, 1st Year

Department of Engineering Physics

McMaster University

References

[1]- http://oxfordgardenssolarproject.com

[2]- http://www.dma-eng.com/

[3]- Rad et al, COMBINED SOLAR THERMAL AND GROUND SOURCE HEAT PUMP SYSTEM, Eleventh International IBPSA conference, Glasgow, Scotland, July 2009.

Advantages of community ownership include:

–        better support from citizens for solar and in particular incentive programs

–        opportunity to educate citizens on renewable energy

–        citizens who are more aware of their own energy usage and often undertake energy efficiency measures.

–        51% of renewable energy in Germany is community owned (includes both direct ownership and cooperatives).  There are many RE coops in Europe, e.g. Belgian coop with 40,000 members.

Jon Worren – partnership between developers and coops for “set-aside” in FIT2.0 will involve 51+% ownership by community group, but <50% voting rights for the community group, and creation of a Special Purpose Vehicle.  OPA wants the developers to manage it.  There are some big cultural differences between developers and community groups, seeing as this is new territory and the applications need to be sorted out very quickly, these partnerships are akin to “shot-gun” marriages.

–        No further advice or decisions on how sound partnerships should be created was discussed by the expert panel – it seems a new, unknown space!

Mike Brighan – TREK now has offering statement approved.  Have 400 members, raised 500K in 5yr bonds at 5% in a few weeks, this is with a very established and forewarned member base.  Have access to 12M$ “angel debt financing” to cover gaps between payments to the project and when capital is raised.  Are paying a premium to developers to bring them projects, purchasing turn-key from them.   Advocates their “non-profit” model, where profits in excess of 5% go to education and outreach.

Joan Haysom – OREC one of first to get offering statement approved.  Model it to sell 20 yr preference shares with an intended return of 5%.  Raise $1M during 9 weeks of the summer 2012, and have now signed agreements for 5 micro-FITs on housing coops, and a joint venture part ownership of a 250kW nearly signed, All to be built in next 1-6 months, producing revenue in 2013.  Have several projects in development for FIT2.0.  Preferred approach is 100% ownership, but have considered alternatives.  In future we will look at non-Fit opportunities and other renewable energy technologies.

Kris Stevens – He advocates for the window to be open long enough (2 months) to give community groups enough time to collect affidavits related to proof of community ownership and undertake sufficient due diligence on these projects and partnerships.

-Joan Haysom, Solar Energy Project Manager at Centre for Research in Photonics, University of Ottawa

Joan Haysom

Among various solar cell technologies, dye sensitized solar cells (DSSCs) have attracted widespread commercial and academic interest due to their relatively high efficiency and low production cost [1-5].

In DSSCs, dye molecules undergo optical excitation, followed by rapid electron transfer to TiO2.  The ionized dye molecules are then reduced by iodide ions (I) in the electrolyte, which form triiodide ions (I3). The counter electrode uses electrons that flow from the photoelectrode, through the external circuit, to reduce triiodide ions back to iodide, completing the cycle [6, 7].

The dye sensitizer plays a critical role in the light harvesting. Recently, the highest power conversion efficiency of DSSCs based on the Zn-complex dye has achieved 12.3% [8]. But typically ruthenium based complexes are well known to get higher efficiencies. Ruthenium is a rare and potentially toxic heavy metal and ruthenium complexes are expensive. So, there is a need to develop new precious metal-free dye sensitizers that can replace the traditional ruthenium sensitizer. In recent years, organic dyes have attracted lot of researchers because of their variety of molecular structures, high molar extinction coefficient, low cost and simple and environmentally friendly preparation process. In the last decade, many investigations on p-conjugated molecules with donor–acceptor moieties, such as oligothiophene [9], indoline [10], triphenylamine [11] and coumarin [12] have been conducted.

To catalyze the triiodide reduction reaction, platinum is typically used [13, 14].  The high cost and limited availability of platinum is not compatible with a low-cost sustainable technology.  Therefore, researches have been investigating various alternative catalysts, including cobalt sulfide [15-18], carbon black [19-21], graphite [22, 23], graphene [24, 25], and carbon nanotubes [26].

Researchers are also investigating the possibility of fabricating DSSCs on low-cost substrates, instead of transparent conducting oxide (TCO). Typically the TCO is a fluorine-doped tin oxide (FTO), which accounts for approximately 50% of the total cost of DSSCs [27]. Also, these substrates have several advantages over TCO, i.e., low weight, bendability, portability, and high strength. Conductive substrates such as indium tin oxide (ITO)-coated polyethylene terephthalate (PET) film [28], ITO-coated polyethylene naphthalate (ITO-PEN) film [29], composite structure consisting of electrospun polyvinylidene fluoride (PVDF) polymer nanofibers and TiO2 nanoparticles [30] have been reported.

With these advancements, it is possible that DSSCs will be good competitors to their rivals in the future.

-Hafeez Anwar

 

References

1. Brian, O.; Graetzel, M., A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature (London) 1991, 353, 737-740.

2. Asbury, J. B.; Ellingson, R. J.; Ghosh, H. N.; Ferrere, S.; Nozik, A. J.; Lian, T. Q., Femtosecond IR study of excited-state relaxation and electron-injection dynamics of Ru(dcbpy)(2)(NCS)(2) in solution and on nanocrystalline TiO2 and Al2O3 thin films. J Phys Chem B 1999, 103 (16), 3110-3119.

3. Peter, L.M.;Wijayantha K.G.U., Electron transport and back reaction in dye sensitised nanocrystalline photovoltaic cells. Electrochimica Acta 2000, 45 4543–4551.

4. Heimer, T. A.; Heilweil, E. J.; Bignozzi, C. A.; Meyer, G. J., Electron injection, recombination, and halide oxidation dynamics at dye-sensitized metal oxide interfaces. J. Phys. Chem. A 2000, 104 (18), 4256-4262.

5. Gratzel, M., Photoelectrochemical cells. Nature (London) 2001, 414, 338-344.

6. Park, N. G.; Kang, M. G.; Kim, K. M.; Ryu, K. S.; Chang, S. H.; Kim, D. K.; van de Lagemaat, J.; Benkstein, K. D.; Frank, A. J., Morphological and photoelectrochemical characterization of core-shell nanoparticle films for dye-sensitized solar cells: Zn-O type shell on SnO2 and TiO2 cores. Langmuir 2004, 20 (10), 4246-4253.

7. Lee, J. J.; Coia, G. M.; Lewis, N. S., Current density versus potential characteristics of dye-sensitized nanostructured semiconductor photoelectrodes. 1. Analytical expressions. J Phys Chem B 2004, 108 (17), 5269-5281.

8. A. Yella, H. W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. Nazeeruddin, E. W. Diau, C. Y. Yeh, S. M. Zakeeruddin and M. Gratzel, Science, 2011, 334, 629.

9. Liao, Kung-Ching; Anwar, Hafeez; Hill, Ian; Vertelov, Grigory; Schwartz, Jeffrey. Comparative Interface Metrics for Metal-Free Monolayer-Based Dye-Sensitized Solar Cells. Applied Materials & Interfaces. Accepted for publication (November 9, 2012).

10. S. Ito, H. Miura, S. Uchida, M. Takata, K. Sumioka, P. Liska, P. Comte, P. Pechy and M. Gr€atzel, Chem. Commun., 2008, 5194.

11. S. Hwang, J. H. Lee, C. Park, H. Lee, C. Kim, C. Park, M. H. Lee,W. Lee, J. Park, K. Kim, N. G. Park and C. Kim, Chem. Commun., 2007, 4887.

12. Z. S. Wang, Y. Cui, K. Hara, Y. Dan-oh, C. Kasada and A. Shinpo, Adv. Mater., 2007, 19, 1138.

13. Papageorgiou, N., Counter-electrode function in nanocrystalline photoelectrochemical cell configurations. Coordin Chem Rev 2004, 248 (13-14), 1421-1446.

14. Yoo, B.; Lim, M. K.; Kim, K.-J., Application of Pt sputter-deposited counter electrodes based on micro-patterned ITO glass to quasi-solid state dye-sensitized solar cells. Current Applied Physics 2012, 12 (5), 1302-1306.

15. Wang, M.; Anghel, A. M.; Marsan, B. t.; Cevey Ha, N.-L.; Pootrakulchote, N.; Zakeeruddin, S. M.; Grätzel, M., CoS Supersedes Pt as Efficient Electrocatalyst for Triiodide Reduction in Dye-Sensitized Solar Cells. Journal of the American Chemical Society 2009, 131 (44), 15976-15977.

16. Lin, J.-Y.; Liao, J.-H.; Chou, S.-W., Cathodic electrodeposition of highly porous cobalt sulfide counter electrodes for dye-sensitized solar cells. Electrochimica Acta 2011, 56 (24), 8818-8826.

17. Lin, J.-Y.; Liao, J.-H.; Wei, T.-C., Honeycomb-like CoS Counter Electrodes for Transparent Dye-Sensitized Solar Cells. Electrochemical and Solid-State Letters 2011, 14 (4), D41-D44.

18. Lin, J.-Y., Mesoporous Electrodeposited-CoS Film as a Counter Electrode Catalyst in Dye-Sensitized Solar Cells. Journal of The Electrochemical Society 2012, 159 (2), D65.

19. Murakami, T. N.; Ito, S.; Wang, Q.; Nazeeruddin, M. K.; Bessho, T.; Cesar, I.; Liska, P.; Humphry-Baker, R.; Comte, P.; Pechy, P.; Gratzel, M., Highly Efficient Dye-Sensitized Solar Cells Based on Carbon Black Counter Electrodes. Journal of The Electrochemical Society 2006, 153 (12), A2255-A2261.

20. Murakami, T. N.; Grätzel, M., Counter electrodes for DSC: Application of functional materials as catalysts. Inorganica Chimica Acta 2008, 361 (3), 572-580.

21. Li, P.; Wu, J.; Lin, J.; Huang, M.; Huang, Y.; Li, Q., High-performance and low platinum loading Pt/Carbon black counter electrode for dye-sensitized solar cells. Solar Energy 2009, 83 (6), 845-849.

22. Acharya, K. P.; Khatri, H.; Marsillac, S.; Ullrich, B.; Anzenbacher, P.; Zamkov, M., Pulsed laser deposition of graphite counter electrodes for dye-sensitized solar cells. Appl. Phys. Lett. 2010, 97 (20).

23. Veerappan, G.; Bojan, K.; Rhee, S.-W., Sub-micrometer-sized Graphite As a Conducting and Catalytic Counter Electrode for Dye-sensitized Solar Cells. ACS Applied Materials & Interfaces 2011, 3 (3), 857-862.

24. Wang, X.; Zhi, L.; Mullen, K., Transparent, Conductive Graphene Electrodes for Dye-Sensitized Solar Cells. Nano Letters 2007, 8 (1), 323-327.

25. Guai, G. H.; Song, Q. L.; Guo, C. X.; Lu, Z. S.; Chen, T.; Ng, C. M.; Li, C. M., Graphene- counter electrode to significantly reduce Pt loading and enhance charge transfer for high performance dye-sensitized solar cell. Solar Energy 2012, 86 (7), 2041-2048.

26. Anwar, Hafeez; George, Andrew.E.;Hill, Ian. Vertically-aligned carbon nanotube counter electrodes for dye-sensitized solar cells. Solar Energy. Accepted for publication (November 20, 2012).

27. Yen, Chuan-Yu, Shu-Hang Liao, Min-Chien Hsiao, Cheng-Chih Weng, Yu-Feng Lin, Chen-Chi M. Ma, Ming-Chi Tsai, Ay Su, Kuan-Ku Ho, and Po-Lan Liu. “A Novel Carbon-based Nanocomposite Plate as a Counter Electrode for Dye-sensitized Solar Cells.” Composites Science and Technology. 2009, 69(13), 2193–2197.

28. M.D¨ urr, A.Schmid,M.Obermaier,S.Rosselli,A.Yasuda,G.Nelles,Low- temperature fabricationofdye-sensitizedsolarcellsbytransferofcomposite porous layers,NatureMater.4(2005)607–611.

29. T. Miyasaka, M. Ikegami, Y. Kijitori, Photovoltaic performance of plastic dye- sensitized electrodes prepared by low-temperature binder-free coating of mesoscopic titania, J. Electrochem. Soc. 154 (2007) A455–A461.

30. Yuelong Li,ab Doh-Kwon Lee,a Jin Young Kim,a BongSoo Kim,a Nam-Gyu Park,c Kyungkon Kim,d

Joong-Ho Shin,e In-Suk Choi*e and Min Jae Ko*.Highly durable and flexible dye-sensitized solar cells fabricated on plasticsubstrates: PVDF-nanofiber-reinforced TiO2 photoelectrodes. Energy Environ. Sci., 2012, 5, 8950.

Industry is steadily marching the cost of current photovoltaic technology downwards and it appears likely that photovoltaics will become competitive across most markets in the coming years and decades [1]. Many of these cost reductions will come from improvements in manufacturing, installation and in smoothing the permitting process rather than improvements in basic science [2]. This is good news for those of us yearning for a renewable energy infrastructure.

While current technologies are making their way to markets, researchers in basic science already have their eye on the next generation of technologies that will make photovoltaics even more efficient and competitive.

The efficiency of a photovoltaic cell describes the ratio between energy contained in the electricity generated by the cell to the energy of sunlight on the cell. Thermodynamics limits exist for the efficiency that no amount of innovation can overcome. This maximum theoretical efficiency is known as the Shockley-Queisser limit [3] and is only 33.7%, for the simplest photovoltaic architectures, known as single-junction devices. We would like to be build cells that operate at the thermodynamic limit, but in practice even the best research grade cells under-perform. Manufactured cells generating electricity in the market today typically only operate at an efficiency of 10-20%.

One well known mechanism to improve the overall efficiency is to couple several simple devices together into what is known as a multi-junction device. Today the best research grade multi-junction cell is 43.5%, a significant improvement. A recent commentary in Nature Materials[4] outlines a set of proposals for doing even better. The authors argue that recent innovations in the control of light made possible by nanotechnology, such as nano-sized optics, should allow us to not only build better multi-junction devices but also move closer to the thermodynamic limit for single-junction devices. Combined they argue that their plan could allow us to build devices with efficiencies between 50-70%.  Such an improvement would mean that for equally sized modules, 2.7 to 7 times more electric power could be generated compared to today’s photovoltaic modules.

So while industry continues to push costs of today’s technology down towards mainstream adoption, scientists and engineers around the world are already planning and developing new technologies that will lead to even more efficient, more competitive photovoltaic modules in the coming years.

-Joshua LaForge, PhD Candidate in Electrical and Computer Engineering Department, University of Alberta

Josh LaForge

[1] Technology Roadmap — Solar Photovoltaic Energy (International Energy Agency, 2010); http://www.iea.org/papers/2010/pv_roadmap.pdf

[2] Alan Goodrich, Ted James, and Michael Woodhouse. Residential, Commercial, and Utility-Scale Photovoltaic (PV) System Prices in the United States: Current Drivers and Cost-Reduction Opportunities. NREL Technical Report. February 2012. NREL/TP-6A20-53347

[3] Shockley Queisser Limit. Wikipedia. http://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit

[4] Polman, A., & Atwater, H. a. (2012). Photonic design principles for ultrahigh-efficiency photovoltaics. Nature materials, 11(3), 174–7. doi:10.1038/nmat3263

Several presentations at the European Photovoltaic Conference 2012 in Frankfurt, Germany, including those of Prof. Harry Atwater, illustrate recent breakthroughs in the area of high-efficiency thin film solar cells. One of the most interesting developments is that researchers are beginning to consider materials which have not been used conventionally as a thin film.

Absorber materials of a high efficiency solar cell typically comprise a significant fraction (~50%) of the total cell cost. One simple way to reduce the cell cost is to use less material. Processing solar cells with thin layers can present handling challenges for some of the materials – breakage being one of the primary issues. Nevertheless, thin materials that are flexible can enable versatility in production, such as roll-to-roll processing, and hence can significantly reduce the processing cost.

Alta Device[1] fabricates solar cells using a few micron thick gallium arsenide absorber layer. However, gallium arsenide is extremely expensive to use in large area solar cells, and thin films of this material tend to be fragile and difficult to fabricate. This is where Alta enters with its innovation – being able to make cheap solar modules that are practical for most applications using this material. Inventions by two leading academic researchers in photonic materials, Eli Yablonovitch and Harry Atwater, have been integrated to achieve this goal. Eli Yablonovitch developed and patented a technique for creating ultrathin films of gallium arsenide in the 1980s while working at Bell Communications Research. On the other hand, Harry Atwater worked on microstructures and nanostructures to improve the material’s ability to trap light and convert it into electricity. Amalgamation of these two ideas have resulted in efficiency increases at a more reasonable cost while using this material.

Alta’s cells have converted 28.3 percent of sunlight into electricity, which is the highest single junction one sun conversion efficiency record – in contrast, the highest efficiency for a silicon solar cell is 25 percent and commonly used thin-film solar materials don’t exceed 20 percent. Yablonovitch suggests that Alta in due course has the potential of breaking the 30 percent efficiency mark and nearing the theoretical limit of 33.4 percent for cells of this type.

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 Flexible power: Alta’s solar cells can be made into bendable sheets. In this sample, a series of solar cells are encapsulated in a roofing material. Credit: Gabriela Hasbun

Unlike gallium arsenide, silicon is a relatively inexpensive material. Interestingly silicon, which is the second most abundant element in the Earth’s crust ( ~28% by mass) after oxygen[2] , is also the most commonly used material in the PV industry (85%, multi-crystalline and mono-crystalline silicon combined) – a function of its economics and established processing industry. Nonetheless, efforts are on-going to further reduce cell price of silicon. Recently companies such as Silicon Genesis, Twin Creeks and AstroWatt have developed processes to make ultra-thin silicon wafers. Silicon Genesis and Twin Creeks uses Proton Induced Exfoliation (PIE)[3] method to isolate ultra-thin (20 micron thin) silicon wafers. In PIE, high-energy protons (or hydrogen ions) are embedded into “donor” wafers, such as thick wafers of silicon, germanium or other single-crystal materials. The ions form a uniform layer beneath the surface of the donor, as shown in the figure below. The depth of the formed layer depends on the energy of the incoming ions. The physical attributes of hydrogen permit the ions to penetrate the surface of the donor wafer without changing its inherent properties and characteristics.

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When heated, the ions then lift or exfoliate a uniform ultra-thin layer, called a lamina, from the donor wafer. The lamina becomes a production wafer and can be processed into thin solar cells or semiconductor devices. To use an analogy, the ions act like a scalpel and carve away thin, identical and functional wafers from the donor. A single donor wafer can be reused repeatedly to create multiple laminae.  These ultra-thin wafers contain only a fraction of the material currently used in a standard wafer for solar cells, LEDs or other devices. Twin Creeks reported a maximum cell efficiency of 11% using their 20 micon thin wafers.

Astrowatt[4] on the other hand uses Semiconductor on Metal (SOM®) kerf-less exfoliation process. A metal layer is deposited on a silicon wafer and then the wafer is subjected to a series of thermal cycles, resulting in residual stresses that exfoliate a thin layer of silicon. Astrowatt recently reported a 15% efficient solar cell using their SOM method.

It is worth noting that there are other solar cell devices that use inherently thin film structures. Examples include copper indium gallium selenide (CIGS) and amorphous silicon (a-Si) solar cells, where maximum cell efficiencies of 19.6% and 10.1% have been reported for CIGS and a-Si solar cells, respectively [5].

Chow3Zahidur R Chowdhury

Electrical and Computer Engineering, University of Toronto.

PhD Candidate (5th Year)

References:

[1] http://www.technologyreview.com/featured-story/426972/alta-devices-finding-a-solar-solution/

[2] Nave, R. Abundances of the Elements in the Earth’s Crust, Georgia State University

[3] Twin Creeks (http://www.twincreekstechnologies.com/)

[4] Jawarani et al., ‘Integration and Reliability of Thin Silicon Solar Cells and Modules Fabricated using SOM® Technology’, EU PVSEC 2012, Frankfurt, Germany.

[5] Solar cell efficiency tables (version 40) http://onlinelibrary.wiley.com/doi/10.1002/pip.2267/abstract

[6] Alta Devices (www.altadevices.com)

[7] AstroWatt (http://www.astrowatt.com)

The events of the previous month have raised some serious concerns for renewable energy in Ontario and threaten the survival of the province’s flagship clean energy policies: the green energy and economy act and the feed-in tariff (FIT). First, the World Trade Organization (WTO) is set to rule against the domestic content requirements contained in the FIT. Second, the sudden resignation of Premier Dalton McGuinty over the mismanagement of the energy file has sent tremors throughout the province’s energy landscape. Additionally, delays in implementing the new FIT 2.0 framework, continued media assaults on PV and wind, as well as the growing backlash over rising electricity rates are propelling Ontario’s renewable energy strategy into dangerous waters.

On Monday, October 15th the WTO ruling backing the EU and Japanese challenge against Ontario’s domestic content requirement was leaked [i]. This ruling will have implications for the longevity of the policy framework surrounding PV in Ontario as well as the regional PV industry. If the domestic content rule is struck down (pending a likely appeal), local module and balance-of-system producers will no longer be sheltered from foreign competition originating from low-cost manufacturers in Asia. In essence, this will expose domestic firms to the same market forces that have transformed the global PV industrial landscape over the last year or so. In turn, plant closures, consolidation and job loss are likely on the horizon. With the regional industrial development impetus for policy support removed, how long will the government continue to pay premium FIT rates for foreign-sourced renewable energy developments?

Adding fire to the flame, Premier Dalton McGuinty – a champion of the current green energy strategy – resigned on the same day as the WTO leak in the face of political fallout stemming from the costly cancellation of new natural gas units during the last election[ii]. His resignation reflects the dangers of tampering with the electricity system for political reasons and highlights the lack of a genuine long-term energy plan for the province. McGuinty’s resignation also poses challenges for the future of renewable energy support. With an election likely on the horizon, will the new Premier seek to distance his or herself from increasingly unpopular support for wind and solar? After all, the last election saw rural voters reject Liberal candidates in part due to wind opposition[iii].

Other issues have also plagued renewable energy policy in the province. Delays in implementing changes to the FIT scheme following the scheduled program review have created difficulties for the domestic industry and investors[iv]. A prominent PV firm has even entered into litigation with the province over the revisions[v]. Moreover, the last several months has seen a ratepayer backlash brewing over electricity rate increases and overgenerous incentives for wind and PV[vi]. Despite the fact that nuclear refurbishments and the rollout of natural gas are primarily to blame for rate increases[vii], the media continues to hammer renewables while giving nuclear and natural gas a relatively free ride.

In many ways, this situation was avoidable. An appropriate renewable energy policy framework with reasonable and justifiable incentives for emerging energy technologies would be far more resilient. The market-based policies in California point to the success of reasonable incentive levels. Although more moderate support may lead to fewer near-term job creation opportunities, it creates a more sustainable market, allowing for a greater degree of certainty for industrial actors and investors. Another key lesson that arises from this unfortunate situation is the need for a less politically interventionist approach to energy planning. An approach that is determined through market mechanisms or an expert bureaucracy with proper authority and regulatory oversight would be far more robust. Legitimacy needs to return to renewable energy support and energy planning in the province.

Daniel Rosenbloom
Research Associate in Sustainable Energy Policy
Graduate from the MA program in Public Policy and Administration at Carleton University