Interested in knowing more about the thin film solar panel?
SolarPowerBeginner had a chat with Joshua Pearce to find out the current state of thin film solar cell technology and where it's headed.
Dr. Pearce is an assistant professor in the Department of Mechanical and Materials Engineering in Kingston, Canada.
His primary research concentration is in photovoltaic materials and he routinely consults for industry on energy, solar and environmental related issues.
Without further ado, the solar power expertise of Mr. Pearce:
SolarPowerBeginner:One of the main thrusts of your research involves making solar cells more efficient and
less expensive. What areas of current photovoltaic study do you see as most promising in accomplishing this?
Joshua Pearce: There are two main strategies you can use to accomplish these twin goals and our group works on both of them.
The first is to use whatever technology is available to make very high efficiency solar cells and then work on reducing their costs. At Queen's University we are working with indium gallium nitride (InGaN) materials. Being that we can engineer the material to absorb any color of light, InGaN has the potential to make very high efficiency solar cells.
(Sunlight has a very broad spectrum of colors ranging from uv that gives you sunburns, all the visible colors, and into the infrared. Traditional solar cells can only collect solar energy from a few colors efficiently).
If an InGaN solar cell is stacked with many layers each absorbing a different color, it could have efficiencies over 50%. Although the starting materials for this type of cell are relatively expensive, the performance would be so much better than traditional cells that they could cost less because you would need less balance of systems (e.g. wiring, racking, etc.).
In addition, the cells would also be designed to use relatively small amounts of these materials in very thin layers so they would not really cost that much more to manufacture than traditional cells.
The other way to attack the problem of inexpensive solar energy is to use a very abundant cheap material and try to do the best you can with it. In our case we have been working with amorphous silicon. This is a relatively crummy semiconductor material, which you can literally make from beach sand. These cells work, but commercially only have efficiencies from 6-10%.
Our group is working to improve these efficiencies while gaining a better understanding how such materials with numerous broken atomic bonds, defects, and voids actually function.
Our goal is to use a method of engineering the microstructure of the material and improving the light trapping (catching all the sunlight that hits the cell) to improve the amorphous silicon solar cell efficiency.
SolarPowerBeginner:Thin film solar panel technology is a rapidly expanding segment of the solar market. What
are the pros and cons of the current thin-film technologies like amorphous silicon, copper
indium gallium (di)selenide, and cadmium telluride?
Joshua Pearce: All three thin film PV materials families offer promise because they can be manufactured on large inexpensive substrates such as glass or plastic, while using much less material than conventional crystalline silicon (c-Si) cells. Although thin film cells have slightly lower efficiencies than c-Si, which does result in slightly higher balance of system (BOS) cost, thin film PV costs significantly less to manufacture.
The overall result is thin film PV has the lowest cost of PV generated electricity and can rival fossil fuel generated power in cost. This cost advantage and continued robotic automation in production has allowed thin films to be the fastest growing PV market segment. Last year growth was at a staggering 123%!
I can speak the best to amorphous silicon. Amorphous silicon (a-Si) was the first thin-film material to yield a commercial product, being initially used in consumer items such as calculators. A-Si is the most advanced thin film technology as it shares technical lineage to the a-Si-based transistors that run millions of flat panel displays.
Now a-Si is expanding its markets with its increasing efficiencies, proven manufacturability, and innovative products such as building-integrated systems.
A-Si based solar cells can be considered the 'greenest' solar cell as they contain no toxic substances and posses an excellent ecological balance sheet. They need very little energy to manufacture and thus when put in the sun are net energy producers with the fastest energy payback times.1 The energy payback times are less than 2 years for a-Si frameless panels located in Ontario.
A-Si PV also uses hardly any material. The silicon present in a sandwich bag of sand, if turned into the active layer in an a-Si panel could cover half of the roof of the average home and provide all of the home's energy needs aggregated over a year.2
The advantages of the copper indium gallium (di)selenide (CIGS) and cadmium telluride (CdTe) is they can be manufactured with capital equipment that costs very little money and overall they have higher efficiencies than a-Si based cells. The primary disadvantage is that they both use the toxic heavy metal of cadmium. (CIGS cells also contain a cadmium sulfide layer).
A lot of work has been done to try to guarantee that the Cd will be recycled and not put into a landfills. In normal working conditions the Cd bound up in solar cells is completely safe although some green design specialists advocate never using toxic substances.
SolarPowerBeginner:Which emerging thin film solar panel technologies do you see as having the potential to increase efficiency and decrease costs?
Joshua Pearce: I think all three materials (a-Si, CdTe and CIGS) will continue to improve efficiencies and decrease costs. I can say with some authority3 that a-Si based solar cells if manufactured above the GigaWatt level will result in solar energy directly competitive with conventional (polluting) grid electricity.
It is the same economy of scale process that drove down costs in the computer industry. My first 'real' computer going to university had 1 GB of memory and cost several thousand dollars – now that the industry has scaled up you can buy a 1 GB memory stick for under $20.
The same is happening with the PV industry – as it scales up, the prices have been dropping. For a-Si if you are making even more than 100MW your manufacturing costs are under $1/W, which is where things start to get really interesting for literally turning off fossil fuel plants. As you get even larger and shoot up by another 10X to a GigaWatt the costs come down even further to where you can think about your installed costs being that low.
SolarPowerBeginner:Sanyo is currently selling HIT solar panels which incorporates traditional crystalline
silicon technology with thin film solar panel technology. What are the benefits of this combination? Are
there any drawbacks?
Joshua Pearce: The HIT cell is a brilliant design. It uses the c-Si as the absorber layer and because it has such great properties the charges you create under illumination can easily make it out of the cell to be collected.
At the same time you are using a-Si, which has a higher bandgap, to create a strong junction and get rid of surface states that can prevent your electrons from making it out. What this means when you combine them is a very high efficiency solar cell.
In addition, this type of cell can be bi-facial (collect light from both sides), which has advantages for certain applications. The drawbacks are you still need to use c-Si which means expensive materials and large capital costs for the equipment to deposit the a-Si. Overall though the HIT cell is a superior technology to conventional c-Si based solar cells.
SolarPowerBeginner:Many people are excited about the thin film solar panel but also hesitant because the technology is relatively new. Do you feel that thin-film is sufficiently advanced to make sense as a choic for solar electric power at this time?
Joshua Pearce: This has more to do with how the technology is portrayed in the media. I got my PhD from Chris Wronski, who co-invented the a-Si cell the year after I was born. Thin film technology is not really new. You probably have a solar powered calculator from the 1980s-and 90s and those are generally made with thin film amorphous silicon.
There have been systematic improvements in both thin film technology itself and its manufacture for decades. It is more than advanced enough to begin large scale (>1GW) manufacturing today.
Incidentally, any a-Si plant at that scale will make solar panels so inexpensively that the electricity they produce will be directly competitive with fossil fuels with no subsidies of any kind. This truly is the beginning of the age of PV and thin film will take the lead.
There are many types of experimental thin film solar cells that will continue to improve and come online this decade that will push the entire PV industry forward even faster than it is already moving.
SolarPowerBeginner:Do you think that thin film solar panel technology will eventually make crystalline solar panels
obsolete or do both technologies have a place in the future of solar power?
Joshua Pearce: For the next several years crystal silicon will continue to hold market share, but, yes I think conventional crystalline panels will be pushed out of the market by thin films for two reasons - economic and energy related.
Despite the current (yet shrinking) efficiency advantage of conventional solar cells over thin film PV, conventional cells will never be able to physically compete with thin films in mass production. Thin films use so much less materials and have such a remarkably lower embodied energy - that they simply cost much less to make.
Many thin film manufacturers are producing cells for under $1/W, and of course selling them for much more because the market price is set by the more expensive crystalline silicon based technology. Traditional crystalline based solar cells will have a lot of trouble getting that low.
That said, our current fraudulent unstable economic system is a highly dubious method to use for decision making on issues as important as energy (and thus climate). Some scientists have been promoting the idea of using energy as a means of making these decisions.
So in this case the solar technology with the lowest embodied energy (if energy cannibalism4 is a concern) or the best lifetime energy production performance (energy payback time, energy return on investment) should be invested in first. This of course would favor thin film development because of its lower embodied energies (e.g. energy needed to manufacture).
SolarPowerBeginner:What thin film solar panel projects are you currently working on or excited about?
Joshua Pearce: Everbrite Solar has announced their intention to build a 150MW thin film PV plant in Kingston and partner with Queen's University5. Part of this forming partnership will enable researchers at the University and students in my lab to have access to a 1MW full scale pilot plant.
From the companies perspective this is an enormous benefit because they will have the assistance of teams of the top researchers in the country helping them improve their product. From a researchers perspective, like mine, it is even better. Access to a pilot line for experiments is really a researchers dream come true. It can become very frustrating when an innovation is proven in my lab, but it takes years to make its way into industry and then finally to the shelf.
In this case, because the experiments we run will be on a full scale system, any improvements we make can be immediately transferred to Everbrite's main production facilities. This will be very gratifying to see technical innovations develop faster and be deployed faster to drive the solar photovoltaic energy revolution forward.
I think that it is important to point out – that solar PV as a technology is ready now – and everyone should consider producing their own electricity with the sun, but we still have a lot of room to improve the technology for the future. This is necessary because we have a LOT of fossil fuel energy consumption now and we essentially have to eliminate all of it to protect the planet from climate destabilization.
This is something that PV and other renewable energy technology can and will do – it is just a matter now of how long it will take.
1. J. Pearce and A. Lau, "Net Energy Analysis For Sustainable Energy Production From Silicon Based Solar Cells", Proceedings of American Society of Mechanical Engineers Solar 2002: Sunrise on the Reliable Energy Economy, editor R. Cambell-Howe, 2002. http://www.cede.psu.edu/users/alau/ASES02_Net_Energy_PV.pdf
4. Energy cannibalism refers to an effect where rapid growth of an entire energy producing industry creates a need for energy that uses (or cannibalizes) the energy of existing power plants. Thus during rapid growth the industry as a whole produces no energy because new energy is used to fuel the embodied energy of future power plants. More information: http://en.wikipedia.org/wiki/Energy_cannibalism