Transparent solar collectors may replace conventional windows
Researchers working at Michigan State University (MSU) have created a completely transparent solar collector which is so clear that it could replace conventional glass in windows. The new devices – dubbed transparent luminescent solar concentrators – have the potential to not only turn windows into solar electric generators, but the screens of smartphones, vehicle glazing, and almost anything else that has a see-through surface.
Experiments with transparent solar collectors have been conducted for quite some time now, but they have resulted in variable success and many poor results – particularly around the inefficient production of energy. More to the point, most of the produced materials weren't completely transparent, rather being brightly-colored or too darkly tinted.
"No one wants to sit behind colored glass," said Richard Lunt, assistant professor of chemical engineering and materials science at MSU. "It makes for a very colorful environment, like working in a disco. We take an approach where we actually make the luminescent active layer itself transparent."
Unlike standard photovoltaic solar cells that capture energy mainly from the visible part of the light spectrum, the transparent solar collectors developed by the MSU team use microscopic organic molecules designed to absorb specific wavelengths of light invisible to the human eye. To accumulate and use this solar energy, the collector channels the light to the perimeter edge of the plastic where it is transformed into electricity by thin strips of photovoltaic solar cells.
"We can tune these materials to pick up just the ultraviolet and the near infrared wavelengths that then 'glow' at another wavelength in the infrared," explained Lunt. "Because the materials do not absorb or emit light in the visible spectrum, they look exceptionally transparent to the human eye."
As previously stated, one of the proposed uses of this completely transparent material would be in its use as a solar collector in place of conventional glazing or where transparent plastics are now used. The team admits that the technology is still at an early stage in its development, but claims that it holds the prospect of being scaled-up to commercial levels for use in industrial applications and can be produced at a reasonable cost.
"It opens a lot of area to deploy solar energy in a non-intrusive way," said Lunt . "It can be used on tall buildings with lots of windows or any kind of mobile device that demands high aesthetic quality like a phone or e-reader. Ultimately we want to make solar harvesting surfaces that you do not even know are there."
The research is also at an early level of efficiency as well; despite references to the inefficiencies of colored solar collectors, the prototype MSU devices barely produce a solar conversion efficiency of 1 percent. As a result, the team aims to reach efficiencies "beyond 5 percent" at some stage, noting that the best colored solar collectors developed elsewhere have a conversion efficiency of about 7 percent.
The research recently featured in the journal Advanced Optical Materials.
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Vendors of architectural Low-e glass claim benefits of blocking non-visible (UV and Infrared) light.
Blocking infrared light significantly lessens the warming of interior spaces. So, especially in hot climatic zones, blocking of infrared light will reduce one’s air conditioning bill. In fact, low-e should be somewhat beneficial in any climate. As PPG claims, “The silver low-e coating reflects the interior temperatures back inside, keeping the room warm or cold.” See: http://educationcenter.ppg.com/glasstopics/how_lowe_works.aspx
Blocking UV light is also beneficial. UV light bleaches wood and fabrics (including carpets, curtains, and furniture). And UV light breaks down most plastics.
I’m surprised that neither this article nor the original MSU article mention the benefits of blocking non-visible light. Until these new Transparent Solar Collectors achieve efficiencies significantly better than 1%, the blockage of non-visible light might be more valuable than the energy collected.
On another energy issue: there are no discussions regarding energy harvesting and its effect on the reallocation of energy at it relates to the environment. If we harness the oceans waves and the wind, then less of that is available for what they normally do (e.g. dispersal of toxins to "freshen" the air or ocean, habitat effects, etc.). If our windows absorb specific energy bands (rather than pass them through or reflect them), is there any balance being upset?
As for efficiency: if these cells absorb that energy band with a 1% efficiency, but the majority of the sunlight's spectrum is in that band, then maybe 1% is efficient relative to something that absorbs 7% of something that constitutes a lesser percentage of the energy. So it seems that there are more questions than answers in this article.