Nanowire Photovoltaics at the Materials Research Society’s 2013 Spring Meeting

I recently attended the 2013 Materials Research Society’s (MRS) Spring Meeting from April 1^st  to 5^th in San Francisco, California. The MRS brings together members of industry, academia, and government to discuss the latest in materials research across a wide variety of disciplines. There were 56 parallel technical sessions, an exhibit, and a wide variety of tutorial sessions taught by leading scientists and engineers.  I presented a poster entitled, “Flux engineering for height dependent morphological control of branched nanowires” in a section focused on nanostructured semiconductors and nanotechnology. I attended talks primarily focused on nanowire growth and applications. Numerous talks focused on the use of nanowires in photovoltaic devices that I believe are of interest to the Canadian Photovoltaic Innovation Network.  Here I will briefly discuss a couple of highlights.

Results from a paper recently published in Science detailing high performance solar cells consisting of nanowire arrays were presented by a member of The Nanostructure Consortium at Lund University in Sweden.¹  P-i-n junction indium phosphide nanowire arrays were employed in the devices, resulting in a maximal efficiency of 13.8% at one sun. InP nanowires have extremely low surface recombination velocities, removing the need for surface passivation as required by nanowire composed of alternative materials (such as Si). Interestingly, the devices exhibited short circuit current densities at 83% of the highest performance planar InP cells, while only covering 12% of the surface (as compared to 100% surface coverage in planar devices). The authors concluded that ray optics is not suitable to model the interaction of light with subwavelength nanostructures due to resonant light trapping. As a result, the authors suggested that nanowire PV devices could potentially reduce the amount of material required to fabricate cells by producing photocurrents comparable to planar devices.

An interesting talk entitled, “Band-gap and structural engineering of semiconductor metal oxides for solar energy conversion,” described the use of 1-D nanostructures (nanowires) to serve as direct pathways for charge extraction in dye-sensitized solar cells (DSSCs).² In this work, zinc oxide (ZnO) nanowires were used due to their high electron mobility. In a typical nanoparticle film, electrons undergo “zig-zag” transport, increasing transport time and the probability for recombination or trapping. As a result, much of the generated charge carriers are not collected, leading to low performance. Direct “straight-line” conductive pathways are provided for electrons by implanting ZnO nanowires into the nanoparticle film. As a result, charge collection efficiency is significantly improved.  The implementation of ZnO nanowires improved efficiency in DSSC devices by 26.9% in the best performing device.

References

1. Wallentin, J. et al. Science 339, 1057, (2013).

2. Bai, Y. et al. Advanced Materials 24, 5850, (2012).

-Allan Beaudry

Ph.D Candidate, Year 2

Electrical and Computer Engineering Department, University of Alberta

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

How Have We Measured Up?

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 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

Ph.D Candidate, Year 4

Department of Electrical Engineering, University of Alberta

 

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-Solar PV Technologies and Innovations: Building an Export Market

Chair
Ian MacLellan, President and CEO, Ubiquity Solar Inc.
Panelists
Nic Morgan, Co-founder and VP Business Development, Morgan Solar
Jan Dressel, President & Managing Director, SPARQ Systems Inc
Ray Morgan, Director Outreach, PV/Solar & Semiconductor, SEMI Americas
Rafael Kleiman, Professor, Director, McMaster University
Clemens van Zeyl, CEO & Co-Founder, ARDA Power Inc.

 

An interesting panel discussion took place on innovation. The panel discussed the meaning of innovation from different points of view. Everyone agreed that Solar is happening faster than everyone expected. In 2001, it was predicted that the world market for new installations in 2010 would be 2.8GW. In 2006, the prediction was increased to 5.5GW. The actual result for new installations in 2010 was 16.8GW. According to PV experience curve, PV module price is estimated to be as low as $0.15/W by 2050. For more information, check out the white paper issued by CanSIA here.

Innovation trends for PV:

• Silicon is and will continue to be the main PV technology, giving a hard time to thin film technology.
• Organic PV might be a player in 20-30 years for specific applications
• Improving reliability in manufacturing yield and PV life time
• Integration of solar systems in commercial buildings by removing the inverter, ie: DC power lines as most instruments work on DC.

Finally, to go the last mile in innovation, it has to be on the system level!

Ahmed Gabr

PhD Candidate, 2nd Year

SUNLAB – University of Ottawa

 

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-Utilities and PV Grid Connection

In Ontario, solar power makes the most economic sense when it is close to the source of consumption.  However, since the burden of transmission costs are directly on the consumer, companies have exploited government subsidies and the low cost of uninhabited land.  Despite this situation, the microFIT program has been enormously successful.

The response of local distribution companies to the FIT program has been mixed, but it seems to be for reasons unrelated to the company’s desire or lack thereof to implement renewable energy technology.  For example, Toronto Hydro has connected 97% of all FIT applications demonstrating that the program is very achievable.  However, other LDCs (local distribution companies) have not done the same.  One reason for this is that he entire infrastructure of Ontario’s power network is very large, old and heavily regulated.  Just recently, transmission lines installed in 1926 have been replaced.  It’s not that old lines such as these don’t fulfill their intended function; it’s that in the past, the entire system was designed to transmit very large amounts of power from stations like Darlington and Niagara Falls over long distances to into the GTA.  The systems were also designed to last and so it often doesn’t make sense to immediately replace them whenever slightly better technology becomes available.  Of course, newer LDCs will be able to accommodate more FIT applications.  But this shouldn’t reflect badly on older LDCs which can’t immediately accommodate applications.  These newer systems are designed with newer technology and the application of intermittent renewable energy technology in mind whereas older systems are not.

As an aside, energy investments are typically amortized over 20+ years.  So this has not historically been a fast paced industry like the electronics industry where your computer will become obsolete within a year.  Module costs are in fact falling at a rate beyond expectations.  However, adoption of solar power into existing infrastructure can be slow for economic and technical reasons.  This effect is compounded by the domination of current power generation incumbents like oil, natural gas, nuclear, and hydro.

It seems like solar power will inevitably play a significant role in the world’s energy mix.  However, unlike the latest smart phone which is sold by the millions within days, adoption of solar power will, by the nature of energy investments, be slower in comparison.

-Nathaniel Tanti, M.ASc

CanSIA 2012-Aboriginal-led Solar Projects

During the Solar Canada 2012 conference held in Toronto, I went to several talks and panel discussions on issues facing the solar industry in Canada.  Given the current energy policies in Ontario, most of the discussion was related to Ontario’s feed-in tariff (FIT) program.  There were many interesting discussions on Ontario’s FIT program, including the financial breakdown of the program, the long-term future, the political and social element of the FIT, but the discussion that I found most intriguing was the panel discussion on Aboriginal-led solar projects in Ontario.

While the original FIT 1.0 program had some provisions to encourage Aboriginal communities to participate in the FIT by offering a higher off-take rate, the FIT 2.0 program has specific set asides and priority points for Aboriginal communities.   Given the limited capacity of the FIT 2.0 program, these priority points and set-asides have led many in the industry eager to partner with Aboriginal communities on solar installations. Before, I get into the potential socioeconomic issues with these partnerships, I want to give a brief overview of the FIT 2.0 provisions for Aboriginal communities.  In the FIT 2.0 program, a total of approximately 1 GW of more FIT contracts will be awarded.  Of this 1 GW, 50 MW or 5%, will be set aside for projects with greater than or equal to 50% Aboriginal equity participation [1].  In addition, in the FIT contract evaluation, 3 additional points will be awarded for projects with a minimum of 15% equity from Aboriginal communities and 2 additional points will be awarded for projects that have Aboriginal community support resolutions [1].  OK… I know that’s a lot to take in and reviewing the changing documentation for the FIT 2.0 program can lead to tunnel vision but the most important point to take from this is that the Ontario Power Authority (OPA) is prioritizing renewable energy generation in Aboriginal communities in a substantial and real way and they are requiring that the Aboriginal communities have a substantial (minimum 15%) equity in these projects.

Before I delve into the potential issues, I want to focus on the positives of developing renewable energy generation in Aboriginal communities.   Since Aboriginal communities are commonly in remote areas of the country, many are not serviced by the electrical grid.   For example, half of all communities in the Nishnawbe Aski Nation do not have access to the grid and thus are forced to rely on diesel generation [2].   This not only has impacts on the environment and quality of life in these communities, but is also a major economic strain with the electricity bill for some houses using electric baseboard heating being as high as $800 to $900 per month during the winter [2].  Establishing local renewable energy generation where the communities have a significant equity share in the project addresses all of these issues as now these communities have a form of electricity generation that has a low impact on the environment and can be a source of income for the community in the future.

While overall I feel that these provisions in the FIT 2.0 program are positive, there are some potential socioeconomic issues that can arise.  For one, with the limited capacity in the FIT 2.0 program, there will be many companies that will be eager to partner up with Aboriginal communities to develop solar projects.  For many of these companies, their interests and methods of conducting business may not be in line with that of the Aboriginal community and there are risks of some Aboriginal communities being exploited for the purposes of establishing a FIT contract.  Furthermore, the timelines and policies established by the OPA for acquiring a FIT contract will likely be more in line with the culture and practices of the partnering company rather than the Aboriginal community.  In fact, during the panel discussion, one member of an Aboriginal community suggested that they are not too concerned about deadlines and timelines in the span of weeks or months because their perspective is to view decisions made in the span of decades and generations.  Another important concern is that while the Aboriginal communities are required to have at least 15% equity in the project, this does not mean they have control over decision making.  This means that (potentially) a partnering company could dictate how and where installations are made.  This of course could have significant negative impacts on these communities and defeat the purpose of the provisions made in the FIT 2.0 program.

Overall, I believe the provisions for Aboriginal communities in the FIT 2.0 program are a positive and necessary step in the right direction but Aboriginal communities and the OPA need to review potential partnerships carefully to ensure the practices and interests of these communities are being considered.

[1]Ontario Power Authority.  Feed-in Tariff Program. Dec 2012; Available from: http://fit.powerauthority.on.ca/what-feed-tariff-program

[2] Faye, D. First Nations want Connection to Ontario Grid. March 2012; Available from:  http://www.northernontariobusiness.com/Industry-News/aboriginal-businesses/First-Nations-want-connections-to-Ontario-grid.aspx

Pratish Mahtani

Ph.D. Candidate – 4^th Year

Department of Electrical and Computer Engineering

University of Toronto

CanSIA 2012-Impacts of Ontario’s FIT 2.0 program

This plenary session was comprised of an introductory presentation and a panel discussion. The presentation provided an overview of the Ontario FIT program version 2.0, including the current status of the program, the benefits it offers to the province, as well as some of the challenges it faces. The following heated discussion invited several high level figures to participate. Among them were the current chair of the board of directors of CanSIA, as well as CEOs and technical VPs from several Ontario-based solar companies.

Regarding the future of solar PV generation opportunities in Canada, the introductory presentation pointed out that:

1. For Canada, most provinces continue to take a cautious approach regarding PV. Part of the reason can be understood by the abundance of other natural electricity resources such as hydro.
2. In future, some provinces may be able to justify uptake in solar PV generation if solar PV costs move closer to available resource options, and if PV can meet power system needs such as peak demand requirements, operational flexibility, load displacement, etc.

The panel discussion offered some heated debate over the current PV incentive programs, largely from the standpoint view of the policy makers. Here are some highlights from the panel discussion:

1. Currently in Ontario, the demand for PV systems is falling. The industry is facing over supply problems. And cost is going up. The uncertainty of future FIT programs is high. To counter these issues, panelists suggested:

-          Decrease price by improving equipment procurement process.

-          The industry has to try to gain more public support. The message delivered to the public should be more clear and persuasive, e.g. emphasizing solar PV’s role as the “peak shaver”, or benefits from reduction of the power transmission costs (due to the fact that PV power generation is highly distributed and usually geographically close to the end users).

-          Align solar with local needs.

2. There were also debates over the role of government. Someone from the industry described the current status of the PV industry in Ontario as “punching below the weight”.  The discussion then focused on what policy makers could have done better to increase the competitive advantage of solar PV in Ontario. Some comments or suggestions from the discussion:

-          Resources should be invested in the fields where 75% of the technology is happening, instead of investing too much into obsolete technologies such as nuclear power.

-          The incentive programs should be stable and transparent to attract investors. Not much time is left. We only have few opportunities ahead to get it right.

-          The PV industry should “punch together” as a whole, rather than everybody fighting on their own.

In the following Q&A session, the audience expressed disappointment over the various aspects of the Ontario FIT program, including the mismatch between the design of the program and project needs, as well as the CanSIA board election issues. In general, the solar sector in Ontario now seems to be at a crossroad, and this makes it logical to look backward to “fix” existing programs and incentives for PV generation.

Jingfeng Yang

Post-doctoral Fellow

Department of Engineering Physics, McMaster University

References:

1. http://fit.powerauthority.on.ca/home.html?q=what-feed-tariff-program