Motorized window coverings are one of the fastest-growing product categories for home systems integrators. But powering the things is often a major pain.

You can go the hardwired electrical route but you’ll have to find a nearby power outlet or find some Romex behind the walls. You can carry power over low-voltage cable, but you’ll still need to fish wire to a power source.

On the other hand, you can enjoy any number of battery-operated solutions, but batteries add bulk and need replacing every year or two – a total drag for homes with multiple units and tall windows.

Since most window coverings enjoy some sunshine during the day, solar power seems a natural option. Indeed, solar-powered shades exist today but the photocells are embedded in the headrail or soffit, which might not see much or any sun. Or they require some extraneous light-gathering mechanism that ruins the aesthetic.

Wouldn’t it be great if the shades themselves could power the motor?Crestron Electronics has filed a patent application for just such a solution. Photovoltaic cells embedded in the shade material absorb the sun’s energy, powering the attached motor directly and/or juicing a battery connected to the mechanism.

But of course, you already know that from the abstract of the patent application, “Motorized Roller Shade with Photovoltaic Shade Material (#20140224434),” filed February 12, 2014 and published August 14, 2014:

Presented is a motorized roller shade that includes a flexible shade material, a rotatably supported roller tube that windingly receives the flexible shade material, one or more flexible photovoltaic cells disposed on the flexible shade material, and a motor operably engaging the roller tube to rotate the roller tube to move the flexible shade material, where the motor receives power from the one or more flexible photovoltaic cells.

The patent application describes two methods for applying flexible photovoltaic cells to the shading material – printing them directly onto the flexible shade material, or printing them onto a flexible substrate that is attached to the shade material.

An electrical connection to the motor is established to move the shades up and down.

PATENT IMAGES IN THE SLIDESHOW

The patent further describes the inclusion of batteries that can be recharged when the sun is bright and the motor is inactive.

This implementation alone doesn’t seem patentable—using photovoltaics to power a motor or batteries—but Crestron seems to has some special sauce in its scaling algorithms that smooth out voltage levels which naturally vary according to the intensity of the sun and the positioning of the shades:

In another embodiment, a scaling/weighting factor is used to account for differing output voltages due to dynamic shade position. This allows for a correct voltage output based upon the actual light intensity, and not the perceived voltage output dictated by the position of the shade and its photon striking area. More specifically, instances occur where the sun may be shinning extremely bright, but only a small area of a photovoltaic cell 116 receives incident photons. In this situation, the output voltage will be relatively low compared to when the full area of a photovoltaic cell 116 receives (is struck by) the same intensity of light. Additionally, if the shade is fully down, due to the increased photovoltaic cell surface area, even low intensity sunlight will still produce a relatively large voltage, which can be higher than the output voltage produced when high intensity sunlight is incident on a small area of the photovoltaic cell. This issue causes a problem with the sensor determining where to put the shade. In order to compensate for these differing output voltages so that the shade is moved to the correct position, a voltage scaling algorithm/factor is used, which takes into account the current position of the shade and the relative sun intensity.

Flexible PV Cells

Flexible, paper-thin photovoltaics is an emerging area of research. Crestron points to a couple of inventions in its patent application (links added). Refer to patent illustrations in the slideshow below:

The flexible photovoltaic cells 116 were developed at the Massachusetts Institute of Technology. The flexible photovoltaic cells 116 (and interconnecting wires 120) are printed directly onto a substrate-independent surface (e.g., the flexible shade material 102). This printing process is accomplished by using vapors instead of liquids at temperatures less than 120 degrees Celsius. Five subsequent layers of the PV material are printed (inside a vacuum chamber) on the substrate to create an array of flexible photovoltaic cells. This process allows printing the flexible photovoltaic cells either directly onto the shade fabric, or onto a secondary flexible material that can then be attached to the flexible shade material 102 via sewing, gluing, or by other methods known in the art.

Similar flexible photovoltaic cells have been produced by Ubiquitous Energy. These flexible photovoltaic cells are also transparent and are undetectable by the human eye. These photovoltaic cells involve efficient harvesting of infrared light without affecting the visible spectrum. They utilize the excitement characteristic of small band-gap molecules that leads to oscillator bunching in order to harvest the infrared light. The small band-gap allows for greater electrical conductivity, as seen in metals, but more flexibility. In addition, the electrons can now move more freely and become elevated into the conduction band with less energy. This provides efficiencies between 21% and 35%.

A Google search for “flexible photovoltaics” yields other promising developments such as spray-on PV cells.

Will we see the solar-powered shades at CEDIA Expo 2014? Not a chance. We may never see the product from Crestron, but the patent application does showcase some interesting possibilities in the exciting area of motorized shades.