The National Renewable Energy Laboratory, (NREL), has demonstrated a prototype of a solar powered smart window. The smart window lowers building temperatures by shifting from clear to opaque under strong sunlight. When the shift to opaque occurs, the solar prototype begins electricity production.

The prototypes tested reached up to 11.3% efficiency. The material is based on the lab/headline favorite material perovskite.

One potential smart window feature is darkening of windows to minimize heat coming into a structure. Heating, cooling, and ventilation of commercial structures is up to 80% of their energy costs.

In the USA, up to 80% of residential units and 50% of commercial units, use some sort of ‘Low-E’ (low heat emission) glass. In this particular hardware, the smart darkening process begins the electricity producing magic when the glass becomes a solar cell via a heat driven a chemical reaction.

The chemical reaction described:

Upon illumination, photothermal heating switches the absorber layer—composed of a metal halide perovskite-methylamine complex—from a transparent state (68% visible transmittance) to an absorbing, photovoltaic colored state (less than 3% visible transmittance) due to dissociation of methylamine. After cooling, the methylamine complex is re-formed, returning the absorber layer to the transparent state in which the device acts as a window to visible light.”

An image of the structural shift in the paragraph above is noted below:

solar window displays 10% efficency

In the image d. above, the unit was able to produce at high levels for only the first cycle of clear to opaque. The unit quickly falls from 1 mA to 50% by the 3rd shift. NREL notes this, obviously, need be fixed.

The paper, in the section titled ‘Mechanism of switchable device degradation’, breaks down the observations of the chemical issues leading to the degradation. Existing smart windows work for 50,000 cycles. A standard solar panel is expected to be above 80% efficiency for 9,125 full day cycles (25 years).

The ‘champion’ prototype peaked at 11.3% efficiency – while the average of the five units was 10.3%.

Recently, a group released an analysis suggesting that 40% of US electricity could be supplied via the windows of structures. Their model projected that the 5 to 7 million square feet of  glass would need be about 5% efficiency in order to hit those numbers.