A new kind of solar cell could give windows the ability to generate electricity. The polymer solar cells (PSCs), developed by researchers at the University of California, Los Angeles (UCLA) absorb mostly infrared, not visible, light, making them almost 70 percent transparent to the human eye.
The cells are made from a photoactive plastic that converts infrared light into an electrical current, according to an article in ACS Nano that describes the research. Applications could include high-performance, visibly transparent photovoltaic (PV) devices, such as building-integrated PV and integrated PV chargers for portable electronics, said study leader Yang Yang, UCLA professor of materials science and engineering, and director of the Nano Renewable Energy Center at California NanoSystems Institute (CNSI).
A new kind of polymer solar cell that is almost 70 percent transparent to the human eye could give windows the ability to generate electricity by absorbing mostly infrared, not visible, light. (Source: UCLA)
PSCs aren't entirely new, but truly transparent ones are. Previous attempts to make PSCs that are partially or completely transparent to the naked eye have either resulted in devices that are transparent to visible light but not very efficient, or efficient devices that aren't really transparent. The researchers say that this is mostly because the devices were not fabricated with the best combination of polymeric PV materials and efficient transparent conductors. For example, opaque metal electrodes have typically been used.
The UCLA PSCs are lightweight, flexible, and have a maximum transparency of 66 percent at 550nm. They incorporate near-infrared (NIR) photoactive polymer and use a highly transparent silver nanowire-metal oxide composite conducting film as the top transparent electrode. The NIR light-sensitive photoactive polymer balances transparency at visible wavelengths by harvesting solar energy from NIR wavelengths while being less sensitive to visible photons.
The transparent conductor is a major breakthrough, the researchers say. It's made of a mixture of silver nanowire and titanium dioxide nanoparticles. This composite electrode makes it possible for the PSCs to be fabricated in high volume at low cost, via mild solution processes. The transparent PSCs have a power-conversion efficiency of 4 percent.
Other authors of the study are CNSI director Paul S. Weiss; CNSI postdoctoral researcher Yue Bing Zheng; materials science and engineering postdoctoral researcher Rui Zhu; doctoral candidates Chun-Chao Chen, Letian Dou, Choong-Heui Chung, Tze-Bin Song, and Steve Hawks; and Gang Li, former vice president of engineering for Solarmer Energy Inc. The study received funding supported from the Henry Samueli School of Engineering and Applied Science, the Office of Naval Research, and The Kavli Foundation.
If these solar cells can really be effective in generating electricity--and consquently saving lots on an energy bill--what a boon for consumers. I would hope that if the technology reaches the commercialization stage that the makers offer both windows with the technology baked in, but also some sort of upgrade or modification kit for those of us who own homes and don't want to go through the expense of subbing out existing windows for new models. That is a major, major project.
I wouldn't mind having those windows, either, even here in the woods. There are various types of films that can be added to windows that purport to do something similar. Here are some recent ones:
It's sources report the following efficiencies for conversion of sunlight into biomass (usable energy)
Plants 0.1% - 2 %
Crops 1% - 2%
Sugarcane 7% - 8%
At 4%, this device is on the high-side when compared to energy-harvesting bio-fuels. With even more development, this material could be quite a winner -- and we could continue to use our corn and soybeans to feed people and livestock rather than engines...
This is a really cool development. The real key (costs aside) will be integration of "power windows" into a local smart grid. In this case local would mean within the confines of the building that the windows are installed in. What a great way to harvest power for low voltage lighting, though.
I don't think a smart grid is needed. Some of the original solar power designs in the 70s were passive: the power generated is used by the building that generates it. You don't need a smart grid to do that.
I agree with you totally. This idea of adding solar cell polymer material to windows is the best one yet for generating electricity. With the amount of sunlight passing through windows daily, I would imagine sufficient amounts of electricity can be generated easily. The next item to include in the energy conversion process is an innovative way to store the energy for use on cloudy days.
All kinds of passive storage methods have been developed, many of them in the 70s and 80s, some more recently, Most of them derive from building designs that are thousands of years old. This is not new technology.
Energy harvesting technologies are well-known to produce really tiny amounts of electrical current -- at the microamp- and even nanoamp-level in some cases. Any idea how much these films could produce, Ann?
Chuck, I didn't see any data on actual energy produced, only efficiency ratings. Kevin did some rough back-of-envelope calculations in his comment, and came up with an estimate of 1.2 KWH of power per square meter of window per month (given certain reasonable assumptions).
At 4% efficiency, and a practical application on the south side of office buildings, cost is going to be the deciding factor. Let's hope that taxpayers don't get stuck funding this as the total outpput could be rather restricted.
I agree entirely. With a consumer grade cell at 15%, a 4% cell that will probably not be properly aligned is going to need to be fairly cheap. Don't get me wrong, I love solar, I even converted my lawn mower to solar. The idea of a window that still functions as a window while collecting solar energy is fantastic, but if each window only collects 1Wh for a sunny day, the window will need to be as cheap as glass.
Commercial buildings would be a great application and these mega buildings also have some sort of budget which would allow them to invest in the storage capabilities that are so critical to making this effective. Especially since many mega buildings in cities (I'm thinking NYC) have lots of self-induced shade due to their size and number--a factor that could limit the windows' ability to harvest energy even on sunny days.
I agree, Beth, the large buildings have the scale. A small savings per window would deliver significant power. In a dense area like Manhattan, there may be some limitations on direct sunlight, but around most of the country, these large buildings are pretty clear of obstruction.
I think the main question is mean life span. This currently is the largest draw back to PV in it's current form. If these units can produce power for 30 years at a constant level then they justify the investment. The average solar panel that people are rushing to put on their roofs will have a life span (90% of peak) of about 10 years. In that time they may only generate 50% of the energy used to fabricate them.
Good point, kodaiflow. Like many alternative energy technologies, especially those taking advantage of existing semiconductor infrastructure, the big push has been to make the technology a) work efficiently and b) be manufacturable. I wonder how much LCA studies have been done--that would be really interesting to know, although there may also not be enough data yet.
Not much to it, really. I took an off the shelf electric mower and added some panels to charge batteries. I've since replaced the very heavy SLA cells with a 10AH NiMh pack, and that makes the machine much easier to navigate. It takes about three good days to recharge the cells, so sometimes I mow on a particular day to make sure I get a good solar harvest.
This is an interesting concept indeed. But aside from the discussions about relative efficiency, how much useful power is a window-cell going to produce? Then, consider the logistics of transporting the power from a window that can open, because some folks do open windows for ventillation at times. Finally, consider the expense of the hardware needed to convert whatever power is produced to a voltage-current level that can actually be useful.
My whole point is that what we have here is an interesting developement that may not be "worth the effort" to implement it. At that point it becomes valid to question how much effort and resources should be expended in that direction.
William, all the natural energy conservation methods require a little bit upfront investment and we can have a fair ROI in long term. The immediate ROI is less because, we are using the generated power for domestic use and it has to be calculated according to the tariff sheet provided by the local energy distributor. I had done a similar calculation before going for solar power to my house and it found that it will take minimum 20 years for cover up the initial investment cost. But have the proud that am using natural resources and no need to worry about tariff hike or power cuts.
I agree with Mydesign about the investment in active PV solar being worth it over the long run. However, homeowners have to be able to afford the several thousands of dollars investment and not everyone can do it. Regarding solar panel thickness, yes, that's one of the whole points of this project.
Ann, in our country both federal and state governments are offering 60% (30+30) discount for domestic house hold consumers, how are willing to invest in solar energy as a part of promoting ecco friendly energy sources. So the end customers have to bear only 40% of the cost and can have green energy with minimal investment. Am not sure about other countries, but if they are also able to follow similar policies, then investmental cost may not be a big issue.
Mydesign, we have somewhat similar programs here. The programs still have an initial up-front cost that can be beyond the resources of many people. Other programs with practically zero up-front costs leave the homeowner a renter, or lessor, of the system, not its owner. At least in my state, the offers I've seen from various solar panel installation companies seem to be aimed primarily at people who use electricity for heat. Those of us in rural areas use other sources for heat, and many, like me, are under a forest canopy so there's not a lot of sun.
Ann, in the scheme which I mentioned, the upfront cost is only 40% of the total cost and the rest is a subsidy from government, which goes directly to the service provider’s account. So customer has to pay only 40% of total cost, that too in interest free installments (2-6 EMI based on various schemes from different companies).
Mydesign, that does resemble some US programs. However, because the cost of installing solar can be around $20,000 (depending on several variables), an often-quoted figure, "only" 40% would be $8,000. Not many people have that amount available for this purpose, even in installments.
Ann, that’s surprising for me. I though all US citizens are financially well settled peoples. As far as my knowledge, the per capital income of US citizens are more than 10 times of Indian citizens. Through my previous post, I mentioned about the government initiatives for promoting solar energy.
Mydesign, your impression is incorrect. The US has been experiencing a major economic downturn for several years, including many people losing their jobs and their homes. Also, per capita average income figures are highly misleading, since a given dollar amount often buys much less here than it does in India. Classic examples are the costs for surgery and prescription drugs. In any case, it's a complex picture, especially when making comparisons.
From the photo (which might be photoshopped) it appears that glass has some "light blocking" properies as well. I wondering if the use of this technology would eliminate or reduct the need for tinting which will help reduce the heat and UV energy like what is currently in autos or even new residential windows.
Jack, the material is slightly less than 70% transparent, letting in less light than 100% transparent materials. That may account for what you see in the photo, and it would presumably block some heat and possibly some UV.
Ann, do you know how that compares with your standard high-efficiency home or office window? Just thinking that if this has similar optical properties, there might be a savings in the base cost of the glass that would normally by used (by reducing the amount of "doping chemicals" which would help in the implementation of soemthing like this.
Yes, Ann, that's what I was wondering. I don't know the proper percentages, but say an average high effieciency window block 65% of a certain type of energy (heat, uv, whatever). If the solar cells take out 25% by themselves, that might mean that the cost of the base window could be reduced by eliminating an amount of the doping, and thereby helping to offset some of the cost of the solar cells.
William, windows may not generate a lot of power on their own. But with conventional electricity produced by fossil fuels, we have been conditioned to think of only a single power source technology. With alternative energy sources, the idea is often to combine different power sources and with multiple energy inputs. I've become more aware of that mix living out in the forest with electricity for lights and powering the ceiling fan (for cooling and heating), a woodstove for heat, and propane for hot water. So the idea of getting energy in a single building from solar and wind, for instance, and from window films plus panels on the roof, or those plus passive solar collection methods, makes sense.
It's true - we are very "spoiled" by the concentrated energy delivery of today's electricity and natural gas. Renewable energy sources are by nature more diffuse and present a great challenge in concentrating / converting / storing it. I think that energy-efficient designs of the future will tap into multiple energy-saving and energy-production sources (passive and active), to acheive an overall energy footprint that makes a difference in our homes.
For example, in Southern California we often pay to have our south-facing windows covered in reflective solar film to keep the home cooler - why not pay a bit more and get the added benefit of a little power? The key to practicality, of course, will be low enough cost.
I ran a thumbnail "back of envelope" calculation on the economics: A 1 square meter window can get ~1Kwatt of solar flux in optimum conditions. Derate for geometry of orientation, let's say 50%. Let's optimistically use 10 hours of sun for 30 days, and the 4% efficiency of the conversion. That gives 1.2 KWH of power per square meter of window per month. At a rate of 14 cents per KWH (my local total rate), that gives a payback of 17 cents per month, or a couple bucks per year (per window)...and that is assuming all sunny days. Sadly, I don't think this is going to produce a reasonable break-even timeframe, esp. if you include the true time-value of money in the calculation.
So...my intuitive take-away is that for solar energy to become economically viable - one needs to push as hard as possible on reducing cost and increasing efficiency. Even then, it's a challenge. To give up a huge amount of efficiency for the novelty of using windows (vs. say on your roof) for solar power does not seem to make economic sense. Note that my opinion shifted over the course of writing this comment, after I ran the calculations!
Kevin, I agree that much of the potential success of deploying a new technology like these solar windows will depend on the simple economics. There is a certain portion of the population who would invest without a positive economic calculation -- those who buy EVs -- but in most cases, the technology will have to pay for itself.
Ann, the normal Solar panels are of thick in size and it cannot be used other than fix in terrace of buildings. If the thickness is less and of comfortable size, they can be fixing in outside walls and window doors. So most of the people may prefer and in turn more natural energy can be produced.
Ann, my point is that at least for me, the things that I use that use electric power need a good bit more than small amounts. Even my computer to participate in this discussion and answe all of my daily emails needs quite a few watts. And collecting the power from a dozen windows effectively is not trivial, particularly if one complies with all of the codes, which have no regard concerning the cost of implementation. Of course in a sunny cliamte and in a building designed for maximum efficiency, things could be different. But I don't live in that part of the world.
As for the smart grid, what the main benefit would be is the quick isolation and shedding, of sections that are in a failure mode. Dumping overloaded sections quickly in order to avoid massive failures is the only way to avoid repeating the massive failures of the past. Adding additional capacity will only increase the amount of power sold, since unused capacity provides no return on investment. BUt an effective smart grid, coupled with small enough sections, will be able to shed overloads quickly, avoiding the dreaded ripple effect that caused the past power outages.
Of course critics will complain that disconnecting overloads is a lot like rationing, which it may indeed be a form of rationing. But sometimes rationing does need to happen.
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