Future of Crystalline Silicon Photovoltaics

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

Ph.D Candidate, Year 4

University of Toronto, Toronto, Ontario

CanSIA 2012-Solar Energy within a National Energy Strategy

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

CanSIA 2012-Integrating Solar Thermal with Geothermal

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 20^th 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].

 

    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).

 

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

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.

CanSIA 2012-Community Power and Partnerships

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

CanSIA 2012-Smart Grid Breakout Session

At CanSIA Solar Canada in Toronto I attended a breakout session that focused on developing grid technologies for the integration of solar PV and other renewables. The speakers covered a broad range of topics, including weather forecasting for solar load balancing (Rhonda Wright-Hilbig, IESO), economic modelling of renewable penetration (Justin Malecki, Clearsky Advisors), and PV-pilot projects in isolated communities (PJ Fernandex, ABB and Scott Henneberry, Schneider Electric).

Rhonda Wright-Hilbig started off by discussing how the Independent Electricity System Operator (IESO) sees the Ontario grid evolving over the next few years and how they will meet the challenges created by these changes. Of note, they expect the complete retirement of coal powered electricity by 2015, with the Ontario Power Generation shutting down three coal fired plants last year alone. To compensate for the loss in generation capacity nuclear, hydro, natural gas and solar are seeing increased deployment, with the expectation that Ontario will hit 3 GW of solar PV generation, out of 20-24 GW for the entire grid, by 2018.

Solar PV generation has some unique characteristics, such as variability in output from weather and seasonal cycles, which must be characterized to ensure the smooth operation of the grid. During the talk Ms. Wright-Hilbig emphasized that each generation technology has a particular set of characteristics that must be accounted for, for successful grid integration. In this sense, solar PV is no different than any other generation technology. However, solar and wind generation are unique in their sensitivity to meteorological conditions. In response IESO has developed a Centralized Forecasting Service (www.ieso.ca/centralized.forecasting) that all renewable projects with greater than 5 MW generation are required to participate in. This services allows IESO to anticipate changes in renewable generation and respond accordingly.

Grid storage is another method to smooth out variability in renewables. As such, storage technologies are expected to play an increasing role in Ontario’s and Canada’s grid. However, at this early stage, making accurate predictions about the rate of deployment is difficult. Justin Malecki from Clearsky Advisors sees 100-1000 MW of grid storage deployed across Canada over the next decade. In part, these numbers will depend on the rate of renewable generation deployment across the nation, which leads to the wide-margin of error in these forecasts.

Both forecasting services and storage allow for active and passive management of the renewable energy supply. Few specifics were offered for demand-side management, as these technologies have yet to be made widely available. However, several of the speakers emphasized the important of demand-side management technologies. Scott Hanneberry firmly stated this point by claiming that the most efficient storage is a flexible load. IESO expects to start seeing smart-appliances like hot water heaters, electric vehicles, and other home automation technologies across Ontario in the future. All of these technologies will help them manage peak demand more effectively and shift loads to low-demand time during the night.

Overall, it was clear that the global industry is climbing the learning curve for a high-penetration of renewables on the grid. In Canada and Ontario the investments are being made today to facilitate significant renewable deployment in the coming years.

Joshua LaForge

PhD Candidate in Electrical and Computer Engineering Department

University of Alberta

 

CanSIA 2012-State of the Solar Industry in Canada

Hello everyone! I was recently in Toronto attending Solar Canada 2012, a conference on the Canadian solar industry. The conference was put on by CanSIA “a national trade association that represents approximately 650 solar energy companies throughout Canada”. The conference featured panels of industry leaders discussing issues such as policy, market trends, and the future of the solar energy in Canada. I will be giving a brief summary of one of the talks I attended, which highlighted the current state of the solar industry. Panelists included Mike Crawley, President of International Power Canada, Doug Urban, Managing Director of Hanwha Solar Canada Inc. ,Mike Dilworth, Vice President and Country Manager of SunEdison Canada, Kerry Adler, Director, President and Chief Executive Officer, of SkyPower Global and Terry Olynyk, Director of Renewable Energy, PCL Constructors. Their discussion covered what the solar industry looks like in Ontario today, the issues that it is currently facing, both financially and politically, as well as what the future holds.

One of the most pressing issues that was brought up was the high level of uncertainty in Ontario’s solar energy market. Uncertainty scares away investors, and as a result less green-energy jobs are created, and the development of solar power slows.  Canadian solar manufacturers are currently on the lookout for the recent ruling from the World Trade Organization (WTO), which claims that Ontario’s Feed-in-Tariff (FIT) program, part of the Green Energy Act, violates international trade law “by unfairly pressuring producers of clean energy to buy hardware and services from companies located in the province.” [1]. To give a bit of an overview, the Green Energy Act stipulates that in order for a solar power producer to qualify for Ontario’s FIT program, 60% of the installation must be produced by Canadian manufacturers (this is the domestic content clause of the Act)[2]. This promotes the development of a solar manufacturing industry in Ontario.  The WTO ruling challenges this part of the Act. Ontario solar manufacturers fear that if Ontario complies with the WTO and removes the domestic content requirements from the FIT program, then they will not be able to compete with foreign manufacturers. Without the FIT program, and without the requirement for Canadian produced content, manufacturers would go out of business. This leads into another point of uncertainty, and that is the government’s stance on green energy. There is possibility of an election coming up next year, and in the previous election opposition leader Tim Hudak said that he would abolish the Green Energy Act entirely. Even without a change in government, the Liberal leader Dalton McGuinty is leaving office soon, and there is a strong possibility that his successor will have a different approach to green energy.  All in all, the level of uncertainty in the Ontario market makes investment quite risky.

The issue of uncertainty and the potential threat to Ontario solar manufacturers brings up a dilemma that was touched upon in the previous paragraph. Ontario solar manufacturers cannot compete with foreign competition (particularly China, who manufactures very cheap solar panels) without the domestic content clause of the FIT program.  In the opinion of some panelists, we are wasting our efforts propping up an industry that is not meant to be. By forcing solar installations to be manufactured in Ontario where it is more expensive to do so, the final cost of the installation becomes artificially high, which can discourage investment. By getting rid of the domestic-content clause, overall prices will be driven down and more people will be willing to install solar panels. As well, with increased installations there will be more jobs available to people. What we have here is a fundamental difference in vision for the future of the solar industry in Ontario. Do we want to prop up manufacturing in Ontario and further develop our green-energy sector, even if prices are driven up? Or do we want to scrap manufacturing, and instead focus on the cheap installation of solar energy? It is tough to choose a side. We want Canada to play an active role in solar energy on an international level, and having a strong manufacturing sector is a way to do that. However, the ultimate goal of solar energy is to provide clean power on a large scale, and the way to do that is by making is cheap enough that more people will buy it. In any case, the panel highlighted that one of the biggest questions in the next few years will be whether or not Ontario has a future in solar manufacturing.

Another point that was stressed by the panel was the need to communicate with the public. Solar energy creates jobs through manufacturing and installation, and there are financial benefits to those who own installed systems through the FIT program. These aspects need to be stressed to the public to help drum up support for the industry. Public support will ultimately lead to political support, which will strengthen the industry, and make it immune to changes in government. Looking at the energy sector as a whole, solar is at an advantage when it comes to public relations. Coal is polluting and dangerous to the environment and health.  Hydroelectric power is clean, but does irreversible damage to ecosystems. Nuclear power, while also clean and safe, still has a potential for catastrophic failure and its relationship with the public has always been strained; the accident at Fukushima is still fresh in people’s minds. Wind power is safe and clean, but often faces opposition from people who don’t necessarily have any grudge against it, but don’t want turbines built near their homes. This is where solar power stands apart from other power sources. It is safe, clean, renewable, and is more favourable to wind when installed near communities. Not to mention that it creates jobs, and through the FIT program average homeowners can make money from it. Considering all these aspects, acceptance of solar power is easy to sell to the public. With more money invested in advertising campaigns, we can rally more support behind solar power in Canada.

The use of renewables is growing across the world. Germany is leading the way, with over 24 GW of installed solar capacity in 2011 [3]. This accounts for almost 15% of their total power capacity. In Canada for 2011, solar accounted for only 0.01% of energy production [4].  Solar power is still in its infancy in Canada, and there is a lot of work to be done if we plan on becoming a world leader in renewable energy. Despite the uncertainty in Ontario’s solar industry, and in what the future may hold, one thing is for certain: solar power here to stay.

-Kevin Boyd, MASc Candidate, Year 1, McMaster University, Ontario

[1].
http://www.theglobeandmail.com/report-on-business/industry-news/energy-and-resources/wto-rules-against-ontario-in-green-energy-dispute/article5461941/

[2].
http://m.gowlings.com/knowledgecentre/publicationPDFs/20120615_Gowlings-Ontarios-FIT-Domestic-Content-Requirements_EN.pdf

[3].
http://www.energici.com/energy-profiles/top-10-reports/item/5075-solar-installed-capacity-2011

[4].
http://www.electricity.ca/media/Electricity101/Electricity%20101.pdf

Towards low-cost and sustainable dye-sensitized solar cells

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.

The Thinner the Greener

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.

 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.

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].

Zahidur R Chowdhury

Electrical and Computer Engineering, University of Toronto.

PhD Candidate (5^th 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
)

Dangerous times ahead for renewable energy in Ontario

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 15^th 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

---

[i] 
http://www.thestar.com/opinion/editorialopinion/article/1173543–rising-electricity-prices-have-little-to-do-with-renewable-energy

[ii]
http://www.thestar.com/news/canada/article/1271913–premier-dalton-mcguinty-resigns

[iii]
http://www.betterfarming.com/online-news/did-wind-turbines-blow-rural-liberal-seats-away-4561

[iv]
http://solarindustrymag.com/e107_plugins/content/content.php?content.11382

[v]
http://www.cbc.ca/news/canada/toronto/story/2012/07/14/toronto-solar-power-lawsuit-ontario.html

[vi]
http://www.cbj.ca/mobile/business_news/canadian_business_news/ontario_electricity_subsidies_should_be_zapped_study.html

[vii] 
http://www.thestar.com/opinion/editorialopinion/article/1173543–rising-electricity-prices-have-little-to-do-with-renewable-energy

Building Integrated Photovoltaics: The future is bright

Two years ago, the global market for solar energy saw an exponential growth. This was mainly due to national supportive policies and the increased instability of fossil fuel prices. We are approaching the end of 2012 and the price of silicon modules has dropped rapidly, leaving little to no profit margins for upstream solar companies and driving many to bankruptcy. Simultaneously, governments are reducing subsidies due to the latest financial crisis while natural gas prices are dropping¹. It seems that the solar industry is in a difficult period. Nonetheless, according to a recent report from consultants McKinsey & Co ² “…these are natural growing pains, not death throes. The industry is entering a period of maturation that is likely to set the conditions for more stable and expansive growth after 2015”. Despite the market vibrations, PV prices are expected to continue dropping (Figure 1) while sales would rise, increasing significantly the PV capacity installed (Figure 2), which is estimated to outpace the installation rates of gas, wind, hydro and possibly nuclear.

Figure 1: The global PV module price learning curve for crystalline silicon (c-Si) modules, 1979 to 2015

Figure 2: Various scenaria on global cumulative installed PV capacity

By 2020, 53% to 66% of the global PV installations are predicted to be on residential and commercial buildings, while PV farms will have only 15% to 23% of the share (Figure 3). In addition, across the PV value chain at the OECD countries, it is estimated that the downstream players will have more opportunities to succeed by delivering high quality products and services tailored at the needs of the customers. This creates the conditions for Building Integrated Photovoltaic technologies to emerge in the marketplace, after 25 years of R&D.

Figure 3: IEA scenario on cumulative installed PV capacity by end-use sector

Building Integrated Photovoltaic (BIPV) refers to photovoltaic cells or modules which are integrated into the building envelope, replacing conventional and/or premium building materials – such as roof shingles, wall cladding (e.g. polished stone), windows, overhangs – rather than being installed afterwards. BIPV is a multifunctional technology ³. Besides the generation of solar electricity, BIPV might serve the additional purposes of weather and noise barrier, heat generation (BIPV/Thermal) and daylight utilization (Semi-Transparent PV), converting up to 80% of the incident solar radiation to useful energy (electricity, heat and space illumination).

Beyond the building-scale, BIPV demonstrates advantages in the community-scale as well. BIPV is located on buildings, thereby eliminating the need for specifically devoted land. In addition, BIPV provides distributed electricity generation that could contribute to grid “peak demand shaving”, resulting in reduced need for peak-capacity power plants. Finally, on commercial buildings BIPV applications, on-site electricity generation can partly meet daily electricity consumption building profile, while eliminating grid transmission losses.

Manufacturing techniques that are common in mature industries (e.g. curtain wall industry) will result in BIPV modularity, preassembly and standardization. Module prices are expected to drop, transforming BIPV to an economically attractive technology, in addition to its aesthetic superiority, energy efficiency and added value as an energy generating element, with no moving parts and inherently a permanent part of the building envelope. However, the path to success will require the solar and building industries to partner in order to reduce product and installation cost without giving up novelty; there will still be a need for government incentive measures. As the solar industry is approaching a tipping point, the timing of viability for BIPV products is now, ensuring a bright though challenging future.

References

¹ Birol, F., Besson, C., & Gould, T. (2012). Golden rules for a golden age of gas. International Energy Agency, Paris.

² Aanesen, K., Heck, S., & Pinner, D. (2012). Solar power: Darkest before dawn. McKinsley& Co., New York.

³ Montoro, D. F., Vanbuggenhout, P., & Ciesielska, J. (2011). Building integrated photovoltaics: An overview of the existing products and their fields of application. European Photovoltaic Industry Association.

⁴ Frankl, P. (2010). Technology Roadmap: Solar photovoltaic energy. International Energy Agency, Paris.

-Costa Kapsis (PhD Student in BIPV, Year 4 at Concordia University)

Cost Kapsis is a doctoral student at Concordia University and an HQP at the NSERC Photovoltaic Innovation Network (PVIN) and the NSERC Smart Net-Zero Energy Buildings Network (SNEBRN). Recipient of the ASHRAE Grant-In-Aid award, Costa’s research topic is on Building Integrated Photovoltaic (BIPV) technologies, while he involved on the passive solar design of various commercial and institutional buildings in Canada and abroad.