Patent Publication Number: US-2023151686-A1

Title: Smart window with solar powered diffusion

Description:
BACKGROUND 
     Technical Field 
     The present disclosure is directed to smart windows with automated window coverings and powered by solar panels. 
     Description of the Related Art 
     Growth in population and the enhancement in building services and comfort levels have increased energy consumption in buildings. Buildings and construction together account for 36% of global energy use. In a typical office building, artificial lighting consumes the bulk of the energy followed by cooling and heating operations. See,  International Energy Agency, Global Status Report  2017, and  Key World Energy Statistics  2014. Office buildings have a relatively high proportion of lighting energy consumption per unit area due to their functional and operational requirements as described in H. Hens, “Thermal comfort in office buildings: two case studies commented,”  Build. Environ.  44 (2009) 1399-1408. 
     Daylight received through windows can significantly reduce lighting energy consumption in office buildings. See M. T. Ke, C.-H. Yeh, J.-T. Jian, “Analysis of building energy consumption parameter and energy savings measurement and verification by applying Quest software,”  Energy Build.  61 (2013) 100-107, the entire contents of which are incorporated herein by reference. Daylighting provides a pleasant and attractive indoor environment that can foster higher productivity and performance as described in P. Plympton, S. Conway, K. Epstein, “Daylighting in Schools: Improving Student Performance and Health at a Price Schools Can Afford,”  National Renewable Energy Laboratory Report,  CP-550-28059, Golden, Colo., 2000. 
     Realizing an indoor environment with visual comfort by admitting daylight through windows requires both a) control of interior brightness and b) suppression of glare. The former can be realized by adjusting interior electric lighting depending on the amount of daylight admitted thorough windows. The latter requires blocking direct solar radiation which is known to be the primary cause of glare. See U.S. Pat. No. 5,663,621 to Popat, the entire contents of which are incorporated herein by reference. Popat analyzed then known approaches for automatic window coverings or “smart windows,” and pointed out their disadvantages: the brightness regulating systems merely regulate brightness but do not block direct solar radiation; glare blocking systems require modifications of conventional louvers and prevent independent adjustment of transmitted daylight; integrated systems either do not address preventing glare caused by the direct solar radiation, or require complicate systems including sensors and interconnection to lighting system. Based on such analysis Popat disclosed a controlling method of an electronically controlled window covering which can block direct solar radiation while admitting substantial diffuse illumination, utilizing a controller which pre-stored data defining a desired setting of louver angle as a function of the time of the day and the day of the year, for the prevailing latitude, longitude, and window azimuth orientation, and based on measured results on the exterior brightness. 
     On the other hand, renewable energy deployment and policies to modernize electricity production and consumption are propelling numerous advances in energy efficient buildings. Renewable energy includes solar and wind power, biomass and so on. Inherent loss due to transmitting power over long distances makes onsite power generation attractive, especially solar power. Solar panels may be placed on the roof of a residential home, or commercial building, and connected to the building&#39;s or the municipal power grid, thereby providing electricity for onsite consumption. 
     Several U.S. patents disclose apparatus which integrate solar cells into window coverings. For example, U.S. Pat. Pub. No. 2014/0116497A1 discloses an onsite solar power generation apparatus configured as an interior window covering. The electric power generated by the solar cells is converted to AC power and provided to the building power grid. U.S. Pat. No. 7,617,857 discloses venetian blinds with solar cells mounted on top surfaces of the controller and an adjustment mechanism of the slat position and orientation to control the amount of light the venetian blinds permits to pass inside. The solar cells are configured to output power to a battery which then is configured to drive LEDs attached to the slats for providing indoor lighting. 
     Chinese Pat. Pub. CN102865030B disclosed a solar driven shutter with solar cells mounted on the louver, a drive mechanism for turning and lifting movement of the louvers using the collected solar energy, and a control device configured to operate based on a light sensor output and a pre-installed light intensity. 
     On the other hand, a diffuser (also called a light diffuser or optical diffuser) is known in optics field as a material that diffuses or scatters light to transmit soft light. A diffractive diffuser that exploits the principles of diffraction and refraction with micro surface structures has been developed for engineering a specific spatial-configuration and intensity profile of light sources. The diffractive diffusers are commonly used in commercially available LED illumination systems. Usually, the diffuser material is GaN or fused silica with processed rough surfaces. Even a laser beam is reported to be converted to a divergent diffused light. See for example, https://en.wikipedia.org/wiki/Diffuser_(optics) and http://www.agc.com/en/products/electoric/detail/doe_and_diffuser.html, the entire contents of which are incorporated herein by reference. 
     Conventional systems such as those described above still do not adequately address the needs and demands of modern energy efficient buildings which are ideally energy neutral with respect to energy consumption/generation for lighting and/or heating/cooling. Accordingly it is one object of the present disclosure to provide a system and method for controlling lightning using a smart window that receives electrical power from solar cells integrated thereon. 
     SUMMARY 
     In an exemplary implementation, a solar powered smart window for a window of a building includes a light diffuser configured to convert an incident direct solar radiation to a diffusive light toward interior direction and situated at a predetermined opened position, a light diffuser positioner, a driving mechanism including a motor and a transmission mechanism, a solar panel placed at a proximity of the window, a control unit configured to receive and monitor an output power of the solar panel and to compare with a predetermined threshold output power of the solar panel. The controller is further configured to move the light diffuser to a closed position via the light diffuser positioner and the driving mechanism, and to hold the light diffuser at the closed position with a latch mechanism, when the output power of the solar panel is not smaller than the predetermined output power for longer than a predetermined duration time while the light diffuser is at the predetermined opened position. The controller is further configured to release the latch mechanism and to cause the light diffuser to return to the predetermined opened position when the output power of the solar panel lowers to a value smaller than the predetermined output power for longer than the predetermined duration time while the light diffuser is at the closed position. 
     In another exemplary embodiment, a method includes storing a predetermined condition to cause a positional transition of the light diffuser and a positional information of a predetermined opened position as an initial condition; monitoring the output power of the solar panel; comparing the output power of the solar panel with a predetermined value; making decision whether a positional transition is necessary for the light diffuser; and either a) causing a transition of the light diffuser from the predetermined opened position to a closed position via the driving mechanism, when the output power of the solar panel is not smaller than the predetermined value for longer than a predetermined time duration while the light diffuser is at the predetermined opened position; b) causing a return of the light diffuser from the closed position to the predetermined opened position when the output power of the solar panel is smaller than the predetermined value for longer than the predetermined time duration, or c) maintaining a current position when either of conditions for above a) or b) is not satisfied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG.  1 A  illustrates schematically a structure of a smart window covering shown in a front view according to a certain embodiment of the present disclosure; 
         FIG.  1 B  illustrates schematically a structure of a smart window covering shown in a side view according to a certain embodiment of the present disclosure; 
         FIG.  2    illustrates schematically an exemplified block diagram of a driving mechanism (A) and a latch mechanism (B) of the smart window covering according to the embodiment of the present disclosure; 
         FIG.  3    illustrates an exemplified block diagram of the control unit  160  of the smart window covering of the embodiment of the present disclosure; 
         FIG.  4 A  illustrates schematically the predetermined opened position (A) of the light diffuser in the embodiment of  FIG.  1   ; 
         FIG.  4 B  illustrates schematically the predetermined closed position (B) of the light diffuser in the embodiment of  FIG.  1   ; 
         FIG.  5 A  illustrates schematically a structure and operation principle of the light diffuser for a certain embodiment of the present disclosure; 
         FIG.  5 B  illustrates schematically a structure and operation principle of the light diffuser for a certain embodiment of the present disclosure; 
         FIG.  6 A  illustrates schematically a structure of the smart window covering according to a certain embodiment of the present disclosure as (A) a front view from interior at a closed position; 
         FIG.  6 B  illustrates schematically a structure of the smart window covering according to a certain embodiment of the present disclosure as (B) a side view at the closed position; 
         FIG.  6 C  illustrates schematically a structure of the smart window covering according to a certain embodiment of the present disclosure as (C) a side view at the predetermined opened position; 
         FIG.  7 A  illustrates schematically a smart window covering according to a certain embodiment the present disclosure as (A) a front view from interior; 
         FIG.  7 B  illustrates schematically a smart window covering according to a certain embodiment the present disclosure as (B) a side view; and 
         FIG.  8    is an exemplary flow chart of a controlling method for a solar powered window covering according to a certain embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a,” “an” and the like generally carry a meaning of “one or more,” unless stated otherwise. The drawings are generally drawn to scale unless specified otherwise or illustrating schematic structures or flowcharts. 
     Furthermore, the terms “approximately,” “approximate,” “about,” and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween. 
     Aspects of this disclosure are directed to a system of solar powered smart window covering for buildings and method for controlling the same. As briefed in the background, conventional approaches of integrating solar cells into automatic window coverings r utilize solar power to drive an adjusting mechanism of louver angle and position to control the amount of light admitted into the interior. However, they do not provide solutions to maximize the diffused light admitted into the interior under condition of blocking direct solar radiation. It is understood that conventional opaque metal venetian louvers aligned at an angle to block direct solar radiation and not to block any diffusive light when viewed at an interior location close to the window, for example, in fact do fully block the diffusive light when viewed from an interior location far from the window. 
     Accordingly, one embodiment of the present disclosure provides a solution for a solar powered window covering which can maximize the diffusive light admitted into the interior while simultaneously blocking direct solar radiation, and which therefore can contribute to reducing the consumption of energy for lighting in buildings. Another embodiment of the present disclosure provides a solution for a solar powered window covering which can control the amount of infra-red radiation admitted through the window that is accompanied with the solar radiation. This solution also contributes to reducing energy for cooling interior air in hot climates, seasons or areas. 
       FIG.  1    illustrates schematically a structure of a smart window covering  100  according to an embodiment of the present disclosure. Here (A) illustrates a front view from interior side and (B), a left side view at section X-X′. The smart window covering  100  according to the embodiment includes a solar panel  120 , a light diffuser  130 , a light diffuser positioner  140 , a driving mechanism  150 , and a control unit  160 . 
     The smart window covering  100  may include a frame  110  configured to be attached to a window frame and including an upper horizontal frame  111 , a bottom horizontal frame  112 , and a pair of side frames  113 . The frame  110  may be substituted by a window frame of a building. The solar panel  120  is attached to a proximity of the frame of the window, here in the embodiment, mounted on the bottom horizontal frame  112 . 
     The light diffuser  130  includes a base plate  131  transparent for visible light; and a light diffusing element  132  which is configured to convert an incident direct solar radiation to a diffusive light toward interior. The light diffuser is configured to stay at a predetermined opened position initially and to move to a closed position when predetermined conditions are satisfied. The light diffuser is configured to block direct solar radiation and converts to the diffusive light at the closed position, as detailed in  FIG.  2   . The light diffuser  130  is further configured to return to the predetermined opened position when certain conditions are satisfied: namely when there is no need of blocking the direct solar radiation. 
     The light diffuser positioner  140  is configured to move the light diffuser  130  between the predetermined opened position and the closed position, where the light diffuser positioner  140  is configured to be driven by the driving mechanism  150  under a control of the control unit  160 . The light diffuser positioner  140  includes a supporting member  141  comprising a rigid material, a pair of pin shafts  142  embedded into the pair of side frame  113 , a pair of vertical rods  143  with a plurality of side ports  144 , an upper horizontal solid rod  145  connecting the pair of vertical solid rods at upper ends thereof, and a center vertical connection member  146  made of a solid rod or a string connecting the upper horizontal solid rod  145  at a center portion of the upper horizontal sold rod  145  with the driving mechanism  150 . An end of the supporting member  141  is perpendicularly fixed to a base plate  131  of the light diffuser  130 , where the supporting member  141  is rotatably attached to one of a pair of side frames  113  with a pin shaft  142  perpendicularly embedded into the one of the pair of side frames  113  at a portion between both ends of the supporting member  141 . The other end of the supporting member  141  is connected rotatably and slidably to one of the plurality of side ports  144  of the vertical solid rod  143 . 
     Each of the pair of vertical solid rods  143  may be vertically slidably connected to each of the pair of side frames  113  at around a bottom end portion of the each of pair of the vertical solid rods  143  with one of a pair of pin shafts  147  perpendicularly embedded into each of the pair of side frames  113 . 
     The driving mechanism  150  of the light diffuser positioner includes a motor  151 , a latch mechanism  152  to latch a motion of the driving mechanism, and a transmission mechanism  153  to transmit the motion of the motor  151  to the light diffuser positioner  140 . 
     The control unit  160  is configured to move the light diffuser  130  to the closed position via the light diffuser positioner  140  and to hold the light diffuser  130  at the closed position using the latch mechanism  152 , when the output power of the solar panel  120  is not smaller than the predetermined output power for longer than the predetermined duration time while the light diffuser is at the predetermined opened position. On the other hand, the control unit  160  is also configured to release the latch mechanism and to cause the light diffuser  130  to return to the predetermined opened position when the output power of the solar panel  120  lowers to a value smaller than the predetermined output power for longer than the predetermined duration time while the light diffuser  130  is at the closed position. 
       FIG.  2    illustrates schematically an exemplified block diagram of a driving mechanism (A) and a latch mechanism (B) of the smart window covering according to an embodiment of the present disclosure. The driving mechanism  150  includes a motor  151  and a transmission mechanism  152 . The motor  151  may be a conventional axial rotation motor or a linear motor. The transmission mechanism  152  includes either one of a gear transmission or a belt transmission, and a latch mechanism  153  configured to hold a motion of the driving mechanism being electrically controlled, as illustrated in  FIG.  2 (B) . 
       FIG.  3    illustrates an exemplified block diagram of the control unit  160  of the smart window covering of the embodiment of the present disclosure. The control unit  160  includes a memory  161 , a monitor  162  of the output power from the solar panel  120 , a controller  163 , a power source  164 , and a human interface. The memory  161  is configured to store a predetermined threshold output power of the solar panel, a predetermined duration time, and a present position of the light diffuser. The monitor  162  is configured to receive an output power from the solar panel  120  and send a monitor signal to the controller  163 . The controller  163  is configured to control the driving mechanism. The power source  164  is configured to supply an electric power required for an operation of the smart window covering. The human interface  165  is configured to accept an input for the conditions to be predetermined. The controller may be further configured to manage receiving the output power from the solar panel  120  and charging the output power to the power source  164 . The power source may be constituted by a capacitor for energy storage, a rechargeable battery, or a combination of them, and may further include a constant-voltage direct -current (DC) power supply circuit. The power source  164  may also be supplemented by a DC power generated by AC to DC regulator  166  of AC power from a commercial grid, and may further be accompanied by a DC/AC inverter to supply a residual power for domestic or local equipment. 
     The human interface enables modifications of the preinstalled conditions including the preinstalled threshold output power of the solar panel by users, based on observations of timings of transitions between the predetermined opened state and the closed states and the output power of the solar panel, under circumstances including seasonal changes of solar light. Such modifications make the system more user friendly and more matched with actual circumstance of use. 
       FIG.  4    illustrates schematically the predetermined opened position (A) and the closed position (B) of the light diffuser  130  in the embodiment of  FIG.  1   . The light diffuser positioner  140  is configured to stay at a bottom position of the light diffuser positioner  140  and situate the light diffuser  130  at the predetermined opened position (A), at initial condition or when the output power of the solar panel is less than the predetermined threshold for longer than a predetermined duration time and hence there is no need of blocking the direct solar right. At the predetermined opened position (A), the light diffuser  130  is configured to pass the diffusive light from an opening of the window toward interior as much as possible. An angle between the surface of the base plate  131  of the light diffuser  130  and a horizontal surface at the predetermined opened position may be configured adjustable, for example, by adjusting a length of the center vertical connection member  146 . 
     The control unit  160  is configured to cause an upward motion of the vertical solid rod  143 , rotate the light diffuser  130  to the closed position (B) of  FIG.  4    by pulling the center vertical connection member  146  via the driving mechanism  150 , and to hold the light diffuser  130  at the closed position (B) using the latch mechanism  153 , when following two conditions are satisfied:
         1) the output power of the solar panel is not smaller than the predetermined output power for longer than the predetermined duration time; and   2) the light diffuser is at the predetermined opened position.
 
The light diffuser  130  at the closed position (B) is configured to convert a direct solar radiation incident to the light diffuser  130  to a diffusive light toward interior direction as detailed in  FIG.  5   .
       

     On the other hand, the control unit  160  releases the latch mechanism  153  and to cause the light diffuser  130  to return to the predetermined opened position when following two conditions are satisfied:
         1) the output power of the solar panel lowers to a value smaller than the predetermined output power for longer than the predetermined duration time; and   2) the light diffuser is at the closed position.
 
Here the light diffuser  130  is configured to return to the predetermined opened position by utilizing a weight of the light diffuser positioner  140 . The light diffuser  130  may be configured to utilize a driving force of the motor via the driving mechanism  150  when the power source has charged an enough energy.
       

       FIG.  5    illustrates schematically structures and operation principle of the light diffuser  500  for a certain embodiment of the present disclosure. The light diffuser (A) includes a base plate  531  transparent for visible light and a light diffusing element  532  on interior side of the base plate. A micro surface structure  532  comprising micro concave lens structures for example, formed on a surface of the base plate  531  is configured to convert an incident direct solar radiation to diffusive lights toward interior direction by diffraction and refraction as illustrated by arrows. Such micro structures are generally known as diffractive diffusers and have applied so far for shaping a beam profile of light sources as briefed in background. The light diffuser (B) further includes a diffractive diffuser  533  made of a transparent plastic sheet and pasted on an interior side surface of the base plate in addition to the monolithic micro surface structure  532  formed on the surface facing exterior side of the base plate  531 . As illustrated by arrows, the structure (B) is expected to bring a divergent refraction effect larger than that of (A). Alternatively, a transparent layer of inorganic material or compound material including SiO 2  or GaN formed on a surface of the base plate and with a rough surface equivalent to the concave structure may also be incorporated as the light diffusing element. 
     The light diffuser  500  of the smart window coverings of the present disclosure may further be configured to reflect and/or absorb an infra-red (IR) radiation by at least one of an IR reflection coating on a surface of the base plate, doping of IR absorbing metal to the base plate, or doping of IR absorbing metal oxide to the base plate. See for example, M. A. Butt, S. A. Fomchenkov, N. L. Kazanskiy, A. Ullah, R. Z. Ali, and M. Habib “Infrared reflective coatings for building and automobile glass windows for heat protection”,  Proc. SPIE  10342,  Optical Technologies for Telecommunications  2016, 103420O (6 Apr. 2017), the entire contents of which are incorporated herein by reference. In a hot climate area or during a hot summer season, the IR reflection would be effective for protection from heat and for reducing energy consumption for air-conditioning. However, when an IR absorption approach is incorporated, the solar powered window covering may desirably be installed into an exterior side of the window, for realizing an effective heat protection simultaneously with maximizing the introduction of diffusive light into interior. Because, heat reflected or absorbed by the light diffuser would eventually warm up interior air when installed interior side. On the other hand, in a cold winter day, introducing heat of the sun light into interior would be helpful to warm up room temperature and to reduce an energy for heating. From such perspective, it would be also an option to prepare two types of window coverings designed for hot climate or for summer season use with IR reflective coating and for cold climate or winter season use without IR reflective coating, and to choose one from the two types depending on each climate or season. 
     Regular window glass is known to absorb ultra violet (UV) radiation. When a thickness of the glass is larger than 6 mm, most of UV components in the solar radiations are absorbed. In a season when the interior air conditioning is not required, fresh air from an opened window is desirable. For such a purpose, the smart window covering of the present disclosure may optionally have UV blocking in combination with a thick glass plate with thickness over 6 mm as the base plate of the light diffuser. Such a window covering would satisfy both requirement of introducing the fresh outside air and blocking the direct solar radiation including reflection or absorption of IR and UV components. 
       FIG.  6    illustrates schematically a structure of the smart window covering  600  according to an embodiment of the present disclosure, (A) is a front view from interior at a closed position, (B) is a side view at the closed position and (C) is a side view at the predetermined opened position both to left side from section line X-X. A solar panel  620  is mounted on the bottom horizontal frame  612  and at a proximity of a window glass  601 . A light diffuser  630  includes a plurality of the base plates  631  each thereof integrated with the light diffuser element  632  as detailed in  FIG.  5   , the plurality of the base plates  631  attached to a positioner string  643  of a light diffuser positioner  640 . 
     The light diffuser positioner  640  includes a horizontal rod  641  attached to the upper horizontal frame  611  rotatably around a center axis of the horizontal rod  641 ; a reel  642  fixed to the horizontal rod  641 ; and the positioner string  643  made of a flexible material, wherein the driving mechanism  650  is configured to rotate the horizontal rod  641  and the reel  642  being controlled by the control unit  660 . A first end of the positioner string  643  is configured to be fixed to the reel  642  and the second end of the positioner string  643  is configured to be fixed to a proximity of the bottom horizontal frame  612  at a point  660  vertically below the reel  642  to which the first end of the positioner string  643  is attached. The positioner string  643  is made of the flexible material for example, a nylon, and configured to endure repeated usages under a tension larger than a weight of the light diffuser. See, for example http://www.chemistryexplained.com/Ny-Pi/Nylon.html, the entire contents of which are incorporated herein by reference. 
     Referring  FIG.  6 (C) , the light diffuser  630  is configured to stay on the bottom horizontal frame  612  at the predetermined opened position or at an initial condition in a state folded at a gap area  662  between adjacent two of the plurality of the base plates  631 . The light diffuser  630  in the state folded may be configured to be installed in a casing  670  mounted on the bottom horizontal frame  612 . The base plate  631  of the light diffuser  630  is in a rectangular shape with a horizontal length almost equal to but shorter than a horizontal distance between surfaces of the pair of the side frames  613 , and with a vertical height smaller than a reminder of a subtraction of a thickness of the solar panel  620  from a horizontal depth D of the bottom horizontal frame  612 . 
     Referring now to (A) and (B), the light diffuser  630  is configured to develop from a predetermined opened position (C) to the closed position illustrated by (A) and (B), by spooling of the positioner string  643 , the spooling made by the rotation of the reel  642  driven by the driving mechanism  650 . At the closed position (A) and (B), the light diffuser  630  is configured to cover most of an opening of the frame, where the plurality of the base plates  631  are aligned in a vertical direction with each thereof being aligned in a horizontal direction. 
     The light diffuser  630  is configured to return to the predetermined opened position (C) in a state folded at a gap area  662  between adjacent two of the plurality of the base plates, utilizing a weight of the light diffuser when the control unit  610  releases the latch mechanism of the driving mechanism  650 . Additionally, the control unit  660  may drive the driving mechanism to rotate the reel  642  in a direction to help the light diffuser  630  return to the predetermined opened position (C). 
     The smart window covering of  FIG.  6    may further include a guide string  644  connecting straightly and vertically the upper horizontal frame  611  and the bottom horizontal frame  612 , wherein the guide string  644  is configured to pass through a plurality of support rings  645  each thereof attached to a side of a base plate, the side of the base plate facing a same side as the guide string when folded at the predetermined opened position. 
     The light diffuser  630  of the smart window covering of  FIG.  6    may further include a spring  646 , where the spring  646  is attached to adjacent two of the plurality of the base plates  631  and configured to help the plurality of the base plates  631  return to the predetermined position, namely the folded state. 
     The light diffuser  630  of the smart window covering of  FIG.  6    may further include a diffractive diffuser sheet  633  made of plastic material and covering the gap area between the adjacent two of the plurality of the base plates, where the diffractive diffuser sheet is configured to convert the direct solar radiation incident to diffusive lights toward interior. 
       FIG.  7    illustrates schematically a smart window covering  700  according to an embodiment the present disclosure, (A) a front view from interior and (B) a side view from a section line X-X. A solar panel  720  is mounted on a bottom horizontal frame  712 . Each of a pair of side frames  713  includes a longitudinal track  780 , where the longitudinal tracks  780  of the pair of the side frames  713  face one another and each extends continuously from a bottom end  781 of the longitudinal track configured to contact the lower horizontal frame  712  to an upper end  782  of the longitudinal track located at a proximity of the upper horizontal frame  711 . Here a frame for the smart window covering  710  is inserted into the frame of the window. However, the frame of the window may substitute for the upper horizontal frame and the bottom horizontal frame of the smart window, except for a pair of side frames  713  which includes the longitudinal tracks. 
     The light diffuser  730  includes a single base plate  731  with the light diffusing element not illustrated here but formed as described in  FIG.  3   . The single basic plate  731  of the light diffuser  730  has two vertical sides  783 , where each of the two vertical sides  783  of the single basic plate is slidably inserted into each of the longitudinal tracks  780  of the pair of the side frames  713 . 
     The light diffuser positioner  740  includes a horizontal rod  741  attached to the upper horizontal frame  711  rotatably around a center axis of the horizontal rod  741 , a pair of reels  742  each fixed to the horizontal rod  741  at proximity of each of the pair of side frames  713 ; and a pair of positioner strings  743  made of a flexible material for example, a nylon, and configured to endure repeated usages under a tension larger than a weight of the light diffuser, as described in  FIG.  6   . A driving mechanism  750  is configured to rotate the horizontal rod  751  and the reel  752  being controlled by the control unit  760 . 
     An end of the positioner string  743  is fixed to an upper end of the basic plate of the light diffuser at a location  733  close to one of the two vertical side of the basic plates, the other end of the positioner string is attached to one of the pair of reels  742  configured to be situated vertically above the location  733  where the end of the positioner string is fixed to the upper end of the basic plate. 
     The light diffuser  730  is configured to stay on the lower horizontal frame  712  at a predetermined opened position, and move to the upper end  782  of the longitudinal tracks at the closed position, where the light diffuser  730  is aligned to block the direct solar radiation incident to the light diffuser and to convert to the diffusive light when predetermined conditions are satisfied, and to return to the predetermined opened position when there is no need of blocking the direct solar radiation, with the same algorithm as detailed in  FIG.  2   . 
     The window covering illustrated in  FIG.  7    is a simplified version of the present disclosure and may fit for uses in areas with a relatively cool climate or the replacing use as a winter season version where the heating effect of the sun light is preferably introduced into interior through the window. At the closed position, the light diffuser  730  of  FIG.  7    allows the direct solar radiation entering into interior from a lower half portion of the window, which would be acceptable or even preferable for example in winter season in warming up interior air, while simultaneously blocking and converting the direct solar radiation incident at a higher portion of the window, which would prevent a glare and help keeping the window bright by introducing only the diffusive light. 
       FIG.  8    is an exemplary flow chart of a controlling method for a solar powered window covering according to a certain embodiment of the present disclosure. The method for controlling a smart window with a light diffuser configured to be driven by a driving mechanism powered by an output power of a solar panel includes providing a predetermined condition to cause a positional transition of the light diffuser and a positional information of a predetermined opened position as an initial condition, monitoring the output power of the solar panel, comparing the output power of the solar panel with a predetermined value, making a decision whether a positional transition is necessary for the light diffuser; and either a) causing the positional transition of the light diffuser from a predetermined opened position to a closed position via the driving mechanism and updating a position information after the transition, when the output power of the solar panel is not smaller than the predetermined value for longer than a predetermined time duration while the light diffuser is at the predetermined opened position, b) causing a return of the light diffuser from the closed position to the predetermined opened position, and updating a position information after the transition, when the output power of the solar panel is smaller than the predetermined value for longer than the predetermined time duration, or c) maintaining a current position when neither of condition for a) nor condition for b) is satisfied. 
     A solar powered window covering which includes the features in the foregoing description provides numerous advantages. The light diffusers described in the present disclosure can block the direct solar radiation and convert it to diffusive light toward interior at the closed position. Thus, the light diffuser of the present disclosure provides a solution that provides brighter diffusive light in comparison to conventional s that block direct solar radiation. This reduces the consumption of electric energy for interior lighting. In addition, the present disclosure has the advantage of optionally revising an IR reflective layer for summer time or hot climate use. The optional IR reflective layer reduces heat flow from the window due to diffusive light during summer time, resulting in a reduction of energy for cooling. Further, the control method of the present disclosure does not require other complicated sensors for monitoring the output power of the solar panel. This feature enables adjusting of the preinstalled threshold output power of the solar panel based on an installed circumstance and seasonal changes of output power of the solar light referring the monitored output power of the solar panel. The controlling algorithm of the present disclosure realizes a more flexible and thus user-friendly system. 
     Obviously, numerous modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting of the scope of the invention, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, define, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.