Patent Description:
Solar power is accelerating as a mainstream power generation source in global markets. In order to further broaden its economic value, greater productivity of solar power system is desired by customers. Crystalline solar photovoltaic systems predominantly capture light on the front side of solar panels, on the front "face", which can be considered "monofacial" solar panels. One method to increase power production is to harvest reflected light from the ground on the back side of the solar panels, on to special solar cells, that are designed to harvest "bifacial" energy. Bifacial solar panels have been used in the solar industry for over <NUM> years.

In this context, <CIT> discloses a solar panel having a panel front and a panel back, comprising an array of solar cells and an element comprising a visually distinguishable feature. Each of the solar cells has a front and a back, wherein at least the front is capable of converting at least a portion of solar light incident thereon into electrical energy. There are spacings between at least some of the solar cells. The element comprising the visually distinguishable feature is located at at least one position selected from the group consisting of between the panel back and the panel front, on the panel front, on the panel back, at the panel front, and at the panel back, such that the visually distinguishable feature is at least partially distinguishable on viewing the panel front. The nature of the visually distinguishable feature and/or the location of the element relative to the solar cells does not completely prevent solar light incident on the panel front from being incident on at least a portion of the array.

Furthermore, <CIT> discloses a solar collector assembly, which includes a frame supporting a solar collector and a frame member defining a tilted pivot axis. Support struts may be used to elevate one end of the frame and may be pivoted between an orientation generally parallel to the frame member and to an orientation generally away from the frame. Anchorless, ballast type bases may be used to support the solar collector assembly. Several assemblies may be stacked on top of one another in a storage or transportation configuration using spacers extending between the frames.

There are several key limitations on the design of bifacial solar panels that limit their utility. Initially, there is light loss through the solar panel, around the crystalline solar cells, impacted front side power. Typical crystalline modules have significant areas between the cells, that are not covered by active solar cell material. Light entering these zones on a monofacial modules is largely reflected, and scattered, by standard white backsheets, and partially recovered through total internal refection (TIR) onto the front sides of solar cells. On bifacial modules however, this light energy is lost because the backside of the solar panel is transparent, per design, to allow the back of the cells to receive light. While this is necessary for rear side bifaciality, front side power suffers, approximately <NUM>-<NUM>%. This is significant loss of power.

A bifacial solar panel array provides an opportunity for enhanced collection from these dead spaces through the use of more specific reflecting surfaces. The present disclosure addresses all of these shortcomings of the known systems.

The present disclosure is directed to systems and methods for increasing power output from a solar module containing bifacial solar cells by increasing the gap between solar cells arranged along the centerline of the module such that light can pass there through. The light impacts a torque located on a backside of the solar module and is reflected back in the direction of the solar module to be absorbed and converted to electrical energy by the solar cells on the backside of the solar module. The location of the torque tube a specified distance from the solar module improves the yield of the recovered solar energy by the back side of the bifacial solar module.

One general aspect (not an embodiment of the invention) includes a solar module including: a frame, a plurality of bifacial solar cells supported by the frame. The solar module also includes a gap formed between two or more of the solar cells, the gap being formed proximate a centerline of the solar module and configured to a allow passage of light from a first side of the solar module to a second side of a solar module, where the light passing through the gap is reflected back onto the plurality of bifacial solar cells and converted to electrical energy.

Implementations may include one or more of the following features. The solar module where the gap is between <NUM> and <NUM>. The solar module where the gap is between <NUM> and <NUM>. The solar module where the gap is between <NUM> and <NUM>. The solar module where the gap is <NUM>. The solar module where absorption of the reflected light passing through the gap increases backside irradiance by between <NUM> and <NUM> percent. The solar module where absorption of the reflected light passing through the gap increases backside irradiance by between <NUM> and <NUM> percent. The solar module where absorption of the reflected light passing through the gap increases backside irradiance by about <NUM> percent.

One general aspect according to the invention as recited in claim <NUM>, includes a solar tracker including: a torque tube. The solar tracker also includes a plurality of solar modules mounted on the torque tube, each solar module including a plurality of solar cells. The solar tracker also includes a gap formed between at least two solar cells, the gap configured to allow light to impact the torque tube and be reflected onto a backside of the plurality of solar modules, wherein the gap is formed between adjacent solar cells within a single module.

Implementations may include one or more of the following features. The solar tracker where the gap is formed between adjacent solar modules is not part of the present invention. The solar tracker where the plurality of solar modules are mounted about <NUM> above the torque tube. The solar tracker where the gap is between <NUM> and <NUM>. The solar tracker where the gap is between <NUM> and <NUM>. The solar tracker where the gap is between <NUM> and <NUM>. The solar tracker where the gap is <NUM>. The solar tracker where absorption of the reflected light passing through the gap increases backside irradiance by between <NUM> and <NUM> percent. The solar tracker where absorption of the reflected light passing through the gap increases backside irradiance by between <NUM> and <NUM> percent. The solar tracker where absorption of the reflected light passing through the gap increases backside irradiance by about <NUM> percent.

The present disclosure is directed to systems and methods for increasing the energy yield of bifacial solar modules. In accordance with certain aspects of the present disclosure, the bifacial solar modules are employed with single axis solar tracker devices, however, other applications are considered within the scope of the present disclosure, including fixed position installations dual axis solar trackers and others.

<FIG> shows an embodiment of the present disclosure incorporated in a solar tracker <NUM> according to the invention. The solar tracker <NUM> includes solar modules <NUM> mounted on a torque tube <NUM>. The solar modules <NUM> include a gap <NUM> formed substantially along the centerline of the solar module <NUM>. Though not depicted, gaps may also be formed along the edges of the solar module <NUM> and the light passing through those gaps may be reflected back to the solar cell of the solar module <NUM> by the frame of the solar module <NUM> and other means as described in commonly owned <CIT>. The gap <NUM> is formed on the module so that it substantially corresponds with the position of the torque tube <NUM>. The gap <NUM> is a clear space (e.g., just clear glass) formed along the centerline of the bifacial solar module. As can be seen, the light passes through the solar module <NUM> and impacts the torque tube <NUM> of the solar tracker <NUM>. Typically, the torque tube <NUM> is made of a galvanized steel that has some reflective properties. The reflectivity of the torque tube <NUM> can be enhanced by the use of reflective tapes, paints, or other materials placed on the torque tube in appropriate locations. These may be metallic, white, or any reflective color.

As show the torque tube <NUM> has a circular cross-section, this cross section is advantageous in directing the reflected light at an angle to the direction of the incoming light. The result is that the light is reflected away from the centerline of the torque tube <NUM> in fan like pattern (as shown) and can be readily absorbed by the back side solar cells of the bifacial module. Minimal light is reflected directly back towards the gap in the solar module, and thus potentially lost, however, even some of this is captured by the glass in the gap <NUM> and reflected again onto the front side solar cells of the solar module <NUM>.

The torque tube <NUM>, however, need to necessarily be round to benefit from the present disclosure. Other shapes including square, rectangular, hexagonal, etc., can also benefit from the present disclosure. Such torque tubes may include reflective materials placed on the flats to help spread the angle of reflection of the light impacting the torque tube.

<FIG> depicts schematically the operation of the backside of a bifacial solar module in the <NUM> position (approximately where the module should be at noon with the sun directly overhead). Sunlight impacts the solar module <NUM> on the front side and is absorbed to generate electrical energy. Sunlight beyond the edges of the solar module <NUM> impacts the ground and is reflected onto the underside of the solar module <NUM> to be absorbed by the back side of the bifacial solar module <NUM>. In addition, diffuse light which might be reflected from many surfaces or simply part of the ambient light levels associated with the sun being above the horizon, whether on a sun filled or cloudy day can be absorbed by either side of the solar module <NUM>. Finally, at the mid-point of the solar module <NUM> the gap <NUM> allows light to pass through the solar module <NUM> and be reflected back onto the back side of the solar module <NUM> to be absorbed and converted to electrical energy. The gap <NUM>, as noted above, may be in the form of a transparent window formed into the solar module <NUM>. In some instances, this transparent window if formed of one or both the glass plates that make up the front side and back side of the solar module <NUM>. In other instances, the gap <NUM> may be a separation between two solar modules <NUM>. This may be particularly useful when a two-portrait orientation of the solar modules is employed. The gap between the two solar modules allows light to impact the torque tube <NUM> and reflect onto the back sides of the solar modules <NUM>.

Further, as can be seen in <FIG>, some portion of the light that reflects off the ground may be blocked by the torque tube <NUM>. This blocking creates shading on the back sides of certain cells in the solar module <NUM>. Shading is one of the greatest factors in overall performance of a solar module, with a shaded cell causing at minimum that cell to have its bypass diode activated resulting in no energy production from that cell. In other instances, where a single by-pass diode is used of a series of solar cells, shading can result in even greater impacts to the power production and efficiency of the solar module <NUM>. The effects of back-side shading caused by the torque tube <NUM> can be greatly reduced by use of the gap <NUM>. While the shading still occurs, in that the reflected light impacts the torque tube <NUM> and not the solar module <NUM>, the light that passes through the gap <NUM> is reflected onto the very same surfaces that would otherwise experience shading. This results in an overall improvement in the electrical energy production from the solar module <NUM> by reducing this shading experienced by the solar module <NUM>.

A variety of gap widths have been investigated from <NUM>-<NUM>. In one such test, the gap <NUM> in the solar module <NUM> was simulated at various distances. Testing was performed at around the noon-hour, when the sun is directly overhead. Irradiance was measured on six occasions each with a different gap size as shown in Table <NUM>.

The result of these experiments demonstrated that when the size of the gap is kept within a specified size, there is a decrease in backside shading caused by the torque tube <NUM>, and an overall increase in irradiance impacting the solar module <NUM>. Further it was recognized that because increasing the gap <NUM> size results in loss of front side solar energy collection, the gains from the backside need to be considered in combination with these potential losses. The result is that a <NUM> gap, results in sufficient increases in yield that is not offset by front side losses, to make it a desirable compromise for the tested cells and modules.

It is expected that similar results will be achieved for a dirty torque tubes <NUM> (as it might be found in the field), a cleaned torque tube, a white painted torque tube, and a torque tube with reflective aluminum tape applied there to. In general, the increase in back side irradiance with the gap is between <NUM> and <NUM> percent, preferably between <NUM> and <NUM> percent, more preferably between <NUM> and <NUM> percent, and most preferably about <NUM> percent. Total irradiance gains by use of the gap may be between <NUM> and <NUM>, preferably between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, and most preferably about <NUM>.

<FIG> depicts graphically the result of adding the gap to the solar module with respect to the increases in irradiance on the back side of the solar module. The first frame of <FIG> depicts the tracker <NUM> (not an embodiment of the invention) with the solar modules <NUM> in the noon or <NUM> position. The numbers in the first frame of <FIG> are the irradiance measurement of the backs side of the bifacial solar module across the width of the solar module <NUM>. As expected, due to shading and distance from the edges of the solar module <NUM>, the center of the solar module experiences less irradiance than the edges. Thus, in the example shown in the first frame of <FIG>, the center of the solar module <NUM> experiences about half of the irradiance of the edges. This difference in irradiance has a direct correlation to the energy produced by the solar module <NUM>. The center frame of <FIG> depicts the addition of the gap <NUM> as proposed by the instant invention, and the additional reflected light paths being reflected off the torque tube <NUM> and on to the back side of the solar module <NUM>. The third frame of <FIG> depicts a graph of the resultant irradiance measurements experienced by the backside of the solar module <NUM> when the gap <NUM> is employed. As can be seen, there is a dramatic increase in irradiance and instead of having a single trough, the graph has a middle peak and two much shallower troughs. This change in irradiance has a direct correlation to the overall output of the solar module <NUM>.

<FIG> depicts a solar module <NUM> (not an embodiment of the invention). The solar module <NUM> is made up of several cells <NUM> connected in series and parallel as is known in the art. Along the centerline of the solar module <NUM> are a series of junction boxes <NUM> which are also commonly used to electrically connect cells <NUM> and strings of cells <NUM>. On either side of these junction boxes <NUM> are the gaps <NUM> formed in the solar module <NUM> which allow light to pass through the solar module <NUM> and impact the torque tube <NUM> beneath (not shown in <FIG>).

<FIG> depicts a graph of the irradiance measurements which resulted in Table <NUM>. With the addition of a gap <NUM> the irradiance measured increased in the middle portion of the solar module <NUM>, and eventually experienced the middle peak and two-trough scenario observed in the third frame of <FIG>.

<FIG> depicts a front side of the solar module <NUM> having a gap <NUM> in accordance with the present disclosure (not an embodiment of the invention). As can be seen, the gap <NUM> is formed on either side of the junction boxes <NUM> placed along the centerline of the solar module <NUM>.

<FIG> depicts a back side of the solar module <NUM>, however, the solar cells are not expressly shown. This view primarily shows the frame of the solar module <NUM>. <FIG> depicts a close-up view of the solar module <NUM> at position B in <FIG>. This view shows smaller gaps <NUM> that may be formed between the cells <NUM>. <FIG> depicts a close-up view of the centerline of the solar module <NUM> in <FIG>. In particular this view shows the relative position of the junction boxes <NUM> and the gaps <NUM> through which light passes and impacts the torque tube <NUM>, not shown. A name plate <NUM> may also be formed proximate the centerline of the solar module <NUM>.

A further observation of the present disclosure is that there must be some distance between the torque tube <NUM> and the solar module <NUM>. This distance can be seen in <FIG> and <FIG>, and its purpose is to permit the reflection and absorption of the light by the backside solar cells of the bifacial solar module <NUM>. In accordance with one aspect of the disclosure the space is between <NUM> and <NUM>, preferably between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, still more preferably between <NUM> and <NUM> and in at least one example <NUM>. At these distances, the light impacting the torque tube is reflected at angles that allow for a broad array of reflection and absorption of the solar cells of the backside of the bifacial solar module. Moreover, this separation helps to reduce or eliminate potential shading by the torque tube of the light reflected off the ground or other sources.

Claim 1:
A solar tracker (<NUM>) comprising:
a torque tube (<NUM>);
a plurality of solar modules (<NUM>) mounted on the torque tube (<NUM>), each solar module including a plurality of solar cells (<NUM>); and
a gap (<NUM>) formed between at least two solar cells (<NUM>), the gap (<NUM>) configured to allow light to impact the torque tube (<NUM>) and be reflected onto a backside of the plurality of solar modules (<NUM>), wherein the gap (<NUM>) is formed between adjacent solar cells (<NUM>) within a single solar module (<NUM>).