The idea of turning windows into solar cells in not exactly new. It is,in many ways, an ideal solution. It can be seamlessly integrated intothe architecture of a building and generate power at the same time,making the most of a larger solar harvesting area in the case of tall,vertical buildings. It’s a win-win situation.But the technology is notready yet, even though one company calledNew Energy is developing itstrademark Solar Window and making considerable progress with it.Thisweek the brains at the Massachusetts Institute of Technology (MIT) madean announcement of a new technology that attempts something similar,that is, to turn the entire surface of a building’s windows into a solar farm. What’s more, without making the windows opaque.The technology inquestion is a photovoltaic cell based on organic modules, whichharnesses the energy of infrared light while allowing visible light topass through. Coated onto a pane of standard window glass, it couldprovide power for lights and other devices, and would lower installation costs by taking advantage of existing window structures.The concept isexplained in detail in the journal Applied Physics Letters and willappear in the next print edition that’s due out soon. The authors of the paper are Vladimir Bulovi?, professor of electrical engineering in theDepartment of Electrical Engineering and Computer Science and RichardLunt, a postdoctoral researcher in the Research Laboratory ofElectronics.They say one of the key advantages of the technology is that it reduces cost. That is because between half and two thirds of thecost of traditional thin-film solar power systems is down toinstallation and up to half of the cost of the panels themselves is forthe glass and structural parts, which in this case are notnecessary.
The selling point of Bulovi? and Lunt’s research is that is also acts on a long-standing efficiency problem thattransparent solar cells have encountered, namely efficiency. So far,less than 1% of incoming solar radiation is converted to electricity.They say the chemical formulation for their cells, when combined withpartially infrared-reflective coatings, is more transparent andefficient and compares to non-transparent organic photovoltaic cells.Inthe case of new buildings and replacements that would have to be carried out anyway, adding the transparent solar cell material to the glasswould add little to the cost, they say. Besides, with modern double-pane windows the photovoltaic material could be applied to the innersurfaces where it would be protected from weather and window washing.The only real extra work to complete the system in a building would beinstalling the wiring connections to the window and a voltagecontroller.There are some environmental savings during manufacturing aswell as the process of fabricating solar cells keeps the glass panes atordinary room temperature, Bulovi? said. Installations of the new system would also block much of the heating effect of sunlight streamingthrough the windows, potentially cutting down on air conditioning needswithin a building. In addition to being suitable for coating directly on glass in the manufacture of new windows, the material might also becoated onto flexible material that could then be rolled onto existingwindows, Lunt said.The research is in its infancy but it holds promiseas an interesting addition to a clean energy mix of solutions. So far,the researchers have achieved an efficiency of 1.7 percent in theprototype solar cells, but they expect that with further developmentthey should be able to reach 12%, making it comparable to existingcommercial solar panels. "It will be a challenge to get there," Luntsaid, adding that what the next steps are optimization of thecomposition and configuration of photovoltaic materials, according tothe principles of excitonic engineering.