A New View to Solar Power: Windows That Can Multitask as Solar Generators

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 into the 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 not ready yet, even though one company called New Energy is developing its trademark Solar Window and making considerable progress with it.

This week the brains at the Massachusetts Institute of Technology (MIT) made an 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 in question is a photovoltaic cell based on organic modules, which harnesses the energy of infrared light while allowing visible light to pass through. Coated onto a pane of standard window glass, it could provide power for lights and other devices, and would lower installation costs by taking advantage of existing window structures.

The concept  is explained in detail in the journal Applied Physics Letters and will appear in the next print edition that's due out soon. The authors of the paper are Vladimir Bulovi?, professor of electrical engineering in the Department of Electrical Engineering and Computer Science and Richard Lunt, a postdoctoral researcher in the Research Laboratory of Electronics.

They say one of the key advantages of the technology is that it reduces cost. That is because between half and two thirds of the cost of traditional thin-film solar power systems is down to installation and up to half of the cost of the panels themselves is for the glass and structural parts, which in this case are not necessary.

Improvement

The selling point of Bulovi? and Lunt's research is that is also acts on a long-standing efficiency problem that transparent 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 with partially infrared-reflective coatings, is more transparent and efficient and compares to non-transparent organic photovoltaic cells.

In the case of new buildings and replacements that would have to be carried out anyway, adding the transparent solar cell material to the glass would add little to the cost, they say. Besides, with modern double-pane windows the photovoltaic material could be applied to the inner surfaces where it would be protected from weather and window washing. The only real extra work to complete the system in a building would be installing the wiring connections to the window and a voltage controller.

There are some environmental savings during manufacturing as well as the process of fabricating solar cells keeps the glass panes at ordinary room temperature, Bulovi? said. Installations of the new system would also block much of the heating effect of sunlight streaming through the windows, potentially cutting down on air conditioning needs within a building. In addition to being suitable for coating directly on glass in the manufacture of new windows, the material might also be coated onto flexible material that could then be rolled onto existing windows, Lunt said.

The research is in its infancy but it holds promise as an interesting addition to a clean energy mix of solutions. So far, the researchers have achieved an efficiency of 1.7 percent in the prototype solar cells, but they expect that with further development they should be able to reach 12%, making it comparable to existing commercial solar panels. "It will be a challenge to get there," Lunt said, adding that what the next steps are optimization of the composition and configuration of photovoltaic materials, according to the principles of excitonic engineering.

Image credit: MIT