Patent Application
20100313933
It is known that mirrors can be used to boost the performance of solar panels by directing to the solar panels sunlight that would otherwise not be received by the solar panels. However, as sunlight varies in its incidence angle, mirrors may lose their effectiveness in reflecting the sunlight to the solar panels. In addition, hot spots may be generated when a certain area of the solar panels receives much more than normal sunlight. Consequentially, mirror boosters have not been widely used in photovoltaic (PV) power generation systems.
There is a need for an improved reflector-solar receiver that increases the performance of solar panels during a majority of the clear days of a year while avoiding the hot spot problem. The present invention meets such need.
In one general aspect, the present invention relates to a reflector-solar receiver assembly, which comprises a reflector and a solar receiver. The reflector has a substantially planar light reflecting face, the solar receiver has a substantially planar light receiving face. The normal direction of the substantially planar light reflecting face and the normal direction of the substantially planar light receiving face are at an angle of about 90°.
In a preferred embodiment, the present invention relates to a solar panel-reflector module (SPRM). The SPRM comprises at least two of the reflectors and two of the solar receivers. The solar receivers are photovoltaic cells, photovoltaic panels, or combinations thereof.
In another general aspect, the present invention relates to a method of installing a reflector-solar receiver assembly that comprises a reflector having a substantially planar reflecting face and a solar receiver having a substantially planar light receiving face at an installation site on Earth. The method comprises placing the substantially planar light reflecting face at an angle of about γ−23.5° or about γ+23.5° from the gravitation line of the installation site, where γ is the latitude of the installation site, so that the substantially planar light reflecting face reflects at least a portion of sunlight to the substantially planar light receiving face during a majority of the clear days of a year.
In another general aspect, the present invention relates to a method of installing a reflector-solar receiver assembly according to embodiments of the invention at an installation site on Earth. The method comprises placing the normal line of the substantially planar light receiving face at an angle of about γ−23.5° or about γ+23.5° from the gravitation line of the installation site, where γ is the latitude of the installation site, so that the substantially planar light reflecting face reflects at least a portion of sunlight to the substantially planar light receiving face during a majority of the clear days of a year.
Other aspects, features and advantages of the invention will be apparent from the following disclosure, including the detailed description of the invention and its preferred embodiments and the appended claims.
The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
In the drawings:
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention pertains. Otherwise, certain terms used herein have the meanings as set in the specification. All patents, published patent applications and publications cited herein are incorporated by reference as if set forth fully herein. It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise.
As used herein, a “reflector” refers to an optical device that has a reflecting surface that reflects light. Examples of a reflector include mirrors of various shape and form, including, but not limited to, flat mirrors, mirrors formed of spherical surfaces, or cylindrical surfaces, and reflective surfaces that have somewhat less reflective efficiency than the conventional mirrors, such as a thin aluminum sheet with a protection layer on its top, as well as reflectors due to internal reflection, such as those comprise one or more clear materials. In the context of the present patent, a reflector is considered to be “one” reflector if the geometric form of its light reflecting face can be described by a simple mathematical equation. If the geometric form of the light reflecting face of a reflector body can only be described by two or more simple mathematical equations, the reflector body is considered to comprise two or more reflectors. For example, if a segment of the light reflecting face of a reflector body can be expressed by a linear function while the other segment of the light reflecting face of the reflector body can be expressed by that of a cylindrical trough, this reflector body is considered to comprise two reflectors, even if the light reflecting surface of the reflector body is a smooth compound surface. Ideally, a perfect reflector has no losses of light, and a perfect reflecting surface precisely follows a desired mathematical description or an ideal design.
As used herein, a “clear material” is a material that is substantially transparent to solar radiation.
As used herein, “normal direction” of a surface refers to the normal line of the surface, i.e., the line that is at a right angle with the surface, that has a direction pointing away from the surface.
As used herein, the direction of the gravitational line points to the gravitational center of the Earth.
As used herein, a “solar receiver” or “solar panel” refers to a light receiving device that comprises at least a solar cell. The solar receiver can receive and convert light via photovoltaic energy conversion process. The light receiving face of a solar receiver is capable of receiving light from all sources, including that directly from the sun or that indirectly from a reflector, and facilitating the use of the light received for an intended purpose.
As used herein “Solstice” means the day when the site of installation of the solar energy generating system is oriented closest towards or furthest away from the Sun. For Northern Hemisphere, “Winter Solstice” refers to the solstice in December, when the sun is directly over the Tropic of Capricorn in the Southern Hemisphere. “Summer Solstice” refers to the solstice in June, when the sun is directly over the Tropic of Capricorn in the Northern Hemisphere. For Southern Hemisphere, the order is reversed in the context of the present application.
As used herein a “bifacial solar receiver” or “bifacial solar panel” refers to a class of photovoltaic cell or solar panel that has two substantially planar light receiving faces and the normal directions of the two substantially planar light receiving faces of a bifacial solar panel are about 180° from each other. Bifacial solar receivers can be made using methods known in the art or are commercially available from companies, such as Sanyo, Hitachi, etc.
As used herein, the phrase “substantially at an angle of α,” “at an angle of about α” or an expression similar thereto includes any angle of the value α or the value α−α1 to α+α1, wherein α1 is less than about 20% of α, for example, less than about 15%, about 10%, or about 5% of α. Depending on the context of the phrase, the maximum value of α1 to be allowed in an embodiment of the present can be determined using methods known in the art in view of the present disclosure.
As used herein, “in contact” or “contact” when used to describe the relative locations of two objects means that the two objects are adjacent to each other in close proximity. In one embodiment of the present invention, when two objects are in contact or contact with each other, they touch or connect with each other without having any physical gap between the two objects. The gap-less contact is used when seamless connection or junction is preferred, for example, when more than one reflectors are in contact with each other to form a compound reflective surface. In another embodiment of the present invention, when two objects are “in contact” or “contact with each other”, there is a physical gap between the two objects. The gap-existing “contact” is preferred when there is a need to prevent the accumulation of debris, such as rain, snow, leaves, dirt and dust, etc., at the junction or contacting point between the two objects, for example, between a reflector and a solar-receiver in a solar module.
In one general aspect, the present invention relates to a reflector-solar receiver assembly, that comprises a reflector and a solar panel, wherein the reflector has a substantially planar light reflecting face, the solar receiver has a substantially planar light receiving face, and the normal direction of the substantially planar light reflecting face and the normal direction of the substantially planar light receiving face are at an angle of about 90°.
Referring to
Referring to
Referring to
In a preferred embodiment, a substantially planar light reflecting surface of the reflector 1 is substantially at an angle α of 47° with the top protection layer 3. The normal direction of SPRM 20 refers to the normal direction of the top plane formed by the top edges of the reflectors and the top edges of the solar panels in the SPRM 20, which is shown as arrow 4 in
In another embodiment, as illustrated in
In a preferred embodiment, the at least two solar receivers, 2a and 2b, are adjacent to each other and their normal directions are substantially at an angle (α) of 47°. In another preferred embodiment, the at least two reflectors, 1a and 1b, are adjacent to each other and their normal directions are substantially at an angle of 133°.
In an embodiment, the present invention also relates to a reflector-solar receiver assembly comprising a solar receiver that is a bifacial solar cell having two substantially planar light receiving faces. The assembly also comprises two reflectors, each of which having a substantially planar light reflecting face. The normal directions of the substantially planar light reflecting faces of the two reflectors are substantially 133° from each other.
In a preferred embodiment, the top edge 4a of the bifacial solar panel 4 is on the centerline of the cylindrical trough reflector 3b, and the lower edge 4b of the bifacial solar panel 4 is in contact with the cylindrical trough reflector 3b. The edge 4b can be in contact with the cylindrical trough reflector 3b of any angle on the arc.
In another general aspect, the present invention relates to a method of installing a reflector-solar receiver assembly, which has a reflector having a substantially planar reflecting face and a solar receiver having a substantially planar light receiving face. The method comprises, at an installation site on Earth, placing the substantially planar light reflecting face of the reflector at an angle of about γ−23.5° or γ+23.5° from the gravitation line of the installation site, where γ is the latitude of the installation site and 23.5° is the tilt of the polar axis of the Earth, so that the substantially planar light reflecting face reflects at least a portion of sunlight to the substantially planar light receiving face during a majority of the clear days of a year.
In a preferred embodiment, the present invention relates to a method of installing the reflector-solar receiver assembly such that the normal direction of a substantially planar light receiving face of the solar receiver of the reflector-solar receiver assembly is substantially 180° from the sunlight at noon on either Winter Solstice or Summer Solstice day.
In another embodiment, the reflector-solar receiver assembly is a reflector-solar receiver assembly according to embodiments of the present invention.
In
While placing the reflector and the solar receiver at a right angle from each other is optimal for a new solar energy installation, using such an option in existing plants may involve altering the original supporting structure for the solar panels, which may be costly. In one embodiment of the present invention, a method is provided to retrofit an existing photovoltaic power plant installed on a substantially horizontal surface, wherein the solar panels are installed in such a way that the normal direction of the solar panels are tilted at an angle of γ (γ is equal to the latitude of the installation site) from the gravitational line. The method comprises installing a reflector to the existing solar panel installations, so that the reflector is parallel to sunlight at noon on the Winter Solstice day, with the sunlight reflected by the reflector pointing towards the polar side (north on northern hemisphere, and south on southern hemisphere), and that the lower edge of the reflector is substantially in contact with the lower edge of the solar panel. Although such a method of installing the reflector-solar panel assembly does not minimize the area of solar panel, the original supporting structure of the solar panels does not have to be altered, which may be optimal in certain places. Again, a gap can be included between the lower edges of the reflector and solar panel to prevent the collection of debris.
To cover the same horizontal area, the substantially planar light receiving face of the solar receiver 2 in the assembly 10 installed by the method of the present invention is cos 23.5°×100%=92% of the light receiving face of the prior art solar panel 50 installed by the conventional method, assuming that no shade is formed on the solar panels and all incident direct sunlight hits the solar panels directly or via a reflector in both the reflector-solar receiver assembly 10 and the conventional design 50.
A preferred reflector-solar receiver assembly according to the present invention is the assembly 15 illustrated in
The tilted angle of SPRM 150 can be calculated by the following formula:
Tilt angle=47°−(90°−latitude−23.5°)=latitude−19.5°(when the tilt angle is greater than 0°)
When the normal direction of a substantially planar light receiving face of a solar panel of the SPRM is 180° from the sunlight at noon on Winter Solstice, the power generated from the solar PV plant using the present invention is in theory equal to that with conventional design but involves less light receiving face of the solar panels on Winter Solstice. The power generated from the solar PV plant using the present invention is more than that with conventional design on the days other than Winter Solstice, even with 8% less solar panel area. For example, at noon of Summer Solstice day, the amount of light received by the solar panels using the present invention is in theory close to 50% more than that from the conventional PV power plant for most locations in industrialized nations. In practice, some of the light hitting a solar panel or reflector does not come directly from the Sun and some of this diffuse light can be from angles that do not allow the reflected light to reach the solar panel, so the practical difference at noon of Summer Solstice day is somewhat smaller than 50%.
In addition, at a higher concentration of light, the efficiency of the solar cell is generally increased when the temperature of the solar cell is held constant. In the present invention, the intensity of sunlight hitting any area of the solar panel due to the direct sunlight and the sunlight reflected from the reflector is always below two suns. In addition, the heat dissipation rate from the solar cells of the solar modules of the present invention can be increased in order to keep the temperature of the solar cells at the desirable value.
The much increased solar power output in summer is particularly desired. More sunlight is available in summers, especially at noontime. The sunshine time is longer and the sunlight is typically stronger in the summer, because the light does not have to travel through as a thick layer of atmosphere as in the other seasons, and the summer sky is typically less cloudy in many locations. In addition, the demand for electricity is stronger during summer days, especially summer afternoons due to the peak demand for electricity from air conditioning applications. The intensity of direct sunlight hitting the solar panel of the SPRM of the present invention is about 1.49 suns with a perfect reflector at noon of Summer Solstice day.
In an embodiment of the present invention, the reflector-solar receiver assembly or the SPRM according to embodiments of the present invention can be installed together with a one-dimensional tracker, preferably, the “polar” or “azimuth” type. An additional advantage of using an azimuth tracker is in that the height of the system does not change with time of the day and can be very low, thereby results in a lower peak wind load than the systems on other types of trackers. Such low profile azimuth tracker can also be supported on a bigger area, resulting in much reduced stress and/or torque at the base of the tracker. Therefore, azimuth trackers are recommended for use with the reflector-solar receiver assembly or the SPRM according to embodiments of the present invention, especially those shown in
The reflector-solar receiver assembly or the SPRM according to embodiments of the present invention can be manufactured and installed by various means.
As described above, the normal direction of a light receiving face of the solar panel of the reflector-solar receiver assembly can be 180° from the sunlight at noon on either Winter Solstice or Summer Solstice.
Because both the solar panel and the reflector in the SPRM have downward slopes that face outwards, no water would be collected in the SPRM. It is also difficult for solid debris to be collected in the SPRM even without a top plate. Therefore, the optional top plate is not necessary for the SPRMs to be installed on the wall. However, the top plate may be desirable if no protective coating is used on top of the reflective surface of the reflector, and if the surface of the solar panel is dimpled or otherwise made rougher to improve its light-trapping efficiency.
Note that the SPRM of
In practice, the optimal design can be varied to accommodate the existing environment, landscape, conditions, etc. For example, the optimal γ−19.5° tilt may not be economically feasible when the SPRM is to be installed on an existing flat roof at high latitude. There are options that allow the SPRM to collect most, although not all, of the sunlight, while still minimizing the amount of solar cells used.
As shown in
As shown in
In another embodiment, a SPRM 40 described above in reference to
In one embodiment of the present invention, the reflector used in the present invention comprises a clear material having a refractive index of greater than 1.33. The clear material does not have a typical metallic layer. The reflector further comprises a face having parallel ridges. Such a reflector can reflect light by internal reflection.
In an optimal design, the reflector 201 is placed together with the solar panel 202 in such a way that i) the (substantially planar) back side 201b of the reflector is 90° from the solar panel 202, ii) the lower edge of the reflector 201 is in contact with the lower edge of the solar panel (or module) 202, and iii) the facets 203 of the ridges facing away from the substantial planar light receiving face of the solar panel 202 are placed horizontally. The contact between the reflector 201 and the solar receiver 202 can be gap-existing contact to avoid the collection of debris.
A reflector similar to the acrylic plate 201 can be made with other clear materials, such as glass, polyvinylchloride, polycarbonate etc., and can be made at different thickness, e.g., 3 mm in thickness or thinner. It is not a reflector in the conventional sense—only the light coming from certain angles will be reflected since it relies on internal reflection to do its job. The refractive index of the material is significantly greater than 1, preferably in the range of 1.3 to 2, and more preferably in the range of 1.4 to 1.7. The angle between the neighboring facets of the ridged side can be smaller than 90 degrees, so can the normal directions of the two facets of a ridge. In addition, the 43 degree angle can also be changed. If this angle is decreased from 43 degrees, the angle between the two facets of the ridges can be somewhat greater than 90 degrees. However, such deviations are preferably not to exceed 5 degrees for a clear material with a refractive index of about 1.5.
This invention will be better understood by reference to the non-limiting examples that follow, but those skilled in the art will readily appreciate that the examples are only illustrative of the invention as described more fully in the claims which follow thereafter.
This example compares the performance of a reflector-solar receiver assembly according to an embodiment of the present invention with that of a conventional solar panel installed on the top of a gas station. The gas station is located at latitude of 40° in the northern hemisphere of the Earth. It has a plot area of 12 m×12 m covered with a canopy that is suitable for mounting solar panels. The canopy is to be designed according to the solar panel system design.
In both designs, the solar panels face the equatorial sky (which means facing south in Northern Hemisphere or facing north in Southern Hemisphere). In the design illustrated in
In the prior art design illustrated in
In order to compare the performance of the two installations in
1). Reflector efficiency=95%
2). Solar panel efficiency=20%
3). Diffuse light is not considered
4). No credit is taken for the increased solar panel efficiency at higher solar radiation concentration
Table 1 shows the parameters and performance of the PV systems based on the present invention as shown in
In practice, a minor portion of the light that hits the roofing material in the system in
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
This application is a Continuation of International Application No. PCT/US2009/001121, filed Feb. 21, 2009, which was published in English on Aug. 27, 2009, under International Publication No. WO/2009/105268, and the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61030449 | Feb 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2009/001121 | Feb 2009 | US |
| Child | 12860855 | US |
