Researchers at Los Alamos National Laboratory have demonstrated a 6″ prototype of a quantum tuned, double paned, solar powered window. The window is special, even for a solar window, in that the outside window pane has quantum dots changing ultraviolet and blue light into more easily absorbable frequencies for off the shelf solar cells to turn into electricity. The same technology applied to a standard solar panel suggests a decrease in cost of electricity from said panel of up to 34%.
“The approach complements existing photovoltaic technology by adding high-efficiency sunlight collectors to existing solar panels or integrating them as semitransparent windows into a building’s architecture,” said lead researcher, Dr. Victor Klimov.
To transform a window into a ‘tandem luminescent sunlight collector’, the Los Alamos team deposits a layer of highly emissive manganese-doped quantum dots onto the outside surface of the outer glass pane (top layer on the left image below) and a layer of copper indium selenide quantum dots onto the inner surface of the inside (bottom) pane.
The outside pane absorbs the blue and ultraviolet portions of the solar spectrum, and re-emits in the colors that a standard solar cell can absorb. Then, the re-emitted light is guided by internal reflection (center image below) in the glass pane to the edges of the window, where solar cells are perpendicular to the glass pane.
The third image demonstrates the purple and blue wavelengths being absorbed and redirected to the edges, while the remaining light continues to the second glass pane – which also redirects to solar cells at the pane edges.
“The prototype device exhibited a high optical quantum efficiency of 6.4% for sunlight illumination and solar-to-electrical power conversion efficiency of 3.1%.”
The authors tested many materials and suggested many combinations to fine tune (and increase) efficiency. For instance, using a window size piece of glass – ~20 inches – the tandem window can more than double the volume of photons delivered to PV cells.
In addition, to a standard double pane window – the researchers also suggested using the first layer of glass to sit atop a standard solar panel.
The industry has attempted to solve the ‘wasted spectrum’ problem by using multijunction solar cells. The International Space Station uses a multijunction solar panel that reaches up to, and above 40% efficiency. Historically, these products have been very expensive. Quantum dots applied to glass are much less so:
The total cost of glass materials of $2/m2 for a 1×1 m2 tandem LSC. Approximating the cost of other constituents required to assemble a complete device by $1/m2, the total cost of the tandem LSC is ~$5.01/m2. This is approximately 20 times lower than the typical cost of the Si-PV module (~$100/m2).
A standard commercial solar panel is about two square meters in size for an approximate cost of $10 per panel ($8.33 for a 60 cell residential solar panel) – if applied to a modern 350W solar panels, the cost would add 2.9¢/W to the cost of the module.
A prior study noted that a 5% efficient solar glass product could produce the equivalent of 40% of the US’ electricity needs if widely deployed – proportionally, a 3.1% efficient product could cover 24.8% of US electricity if similarly deployed.
The author suggests application of this quantum dot layer, with further refinement, could offer a cost savings on solar electricity of 34% versus a standard, standalone solar panel. A question is out to the Dr. to determine if the % efficiency applies to an area equivalent to a window, or the area of solar cells along the edge of the glass pane. If it is the glass pane, the effective efficiency gain would be much lower, however, savings of 28-34% off of the output material (electricity) suggests the effective area is greater than the edge of the pane solar cells.
I’m of course most interested in how much efficiency this could add to a standard solar panel via altering only the outer glass layer of the panel. This seems like it’d add one extra benefit – those already absorbed blue and violent photons wouldn’t be hitting the main panel and bouncing around uselessly, heating the place up and lowering efficiency. They’d be getting flipped in color and turned into electricity.
At 2.9¢/W for a new machine or two in the production line and some seemingly cheap, readily available material – I definitely would be interested in seeing cheaper solar electricity.
I thought to include the researcher’s full title on the Dr’s email to me as it seemed quite glorious:
Dr. Victor Klimov, Ph. D., D. Sc./Laboratory Fellow/Director, Center for Advanced Solar Photophysics/Los Alamos National Laboratory
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