WO2023031655A1

WO2023031655A1 - Sunlight steering apparatus and solar energy harvesting system comprising the same

Info

Publication number: WO2023031655A1
Application number: PCT/IB2021/058107
Authority: WO
Inventors: Mathieu Rubi; Sebastián Alagón Carrillo; Chin Lee ONG
Original assignee: Freshape Sa
Priority date: 2021-09-06
Filing date: 2021-09-06
Publication date: 2023-03-09

Abstract

There is described a sunlight steering apparatus (10) comprising upper and lower rotatable disk-shaped prism arrays (100, 200) that are positioned one above the other for rotation about a common rotation axis (RA). Each of said upper and lower rotatable disk-shaped prism arrays (100, 200) is supported such that incident sunlight is allowed to pass successively through the upper rotatable disk-shaped prism array (100) and then through the lower rotatable disk-shaped prism array (200). An optical path of incident sunlight passing through the upper and lower rotatable disk-shaped prism arrays (100, 200) is selectively adjustable by rotation of the upper rotatable disk-shaped prism array (100) and/or the lower rotatable disk-shaped prism array (200). The sunlight steering apparatus (10) further comprises first and second drive units (D1, D2) that are configured to respectively drive the upper and lower rotatable disk-shaped prism arrays (100, 200) into rotation about the common rotation axis (RA) to cause adjustment of the optical path of incident sunlight passing through the upper and lower rotatable disk-shaped prism arrays (100, 200).

Description

SUNLIGHT STEERING APPARATUS AND

SOLAR ENERGY HARVESTING SYSTEM COMPRISING THE SAME

TECHNICAL FIELD

The present invention generally relates to a sunlight steering apparatus and a solar energy harvesting system comprising the same.

BACKGROUND OF THE INVENTION

Standard photovoltaic (PV) panels, as commonly found on rooftops, are typically mounted in a fixed position. Orientation of such standard PV panels is accordingly chosen in such a way to maximize exposure to sunlight, albeit in suboptimal manner as a compromise is made with regard to exposure to incident sunlight over the course of a day and, moreover, a year. Standard PV panels are therefore reasonably low priced, but yield comparatively low energy conversion. Ideally, in order to maximize energy conversion, incident sunlight should hit the relevant PV panel perpendicularly to the panel. The farther the incident light is from the perpendicular axis, the lower is the projected area of the incident light, and the lower the energy conversion.

First solar tracking systems were introduced on the Nimbus 1 meteorological satellite that was launched during the year 1964. Sun tracking systems found major interest in concentrated photovoltaic (CPV) technology in the late 80’s. High accuracy tracking allows higher energy concentration ratios, therefore greater PV efficiency. Essentially three sunlight tracking concepts are found on the market, namely:

1 . concepts relying on the use of fixed collectors and one or more moving mirrors (or other optical components) to reorientate and concentrate sunlight onto fixed PV cells;

2. concepts relying on the use of moving collectors that are capable of moving along one, two or more axes to track the sun; and

3. concepts relying on the use of optical systems to redirect and steer the incident sunlight onto PV cells. Sunlight tracking is typically relatively costly to implement as such systems require high-precision motorization and mechanical components. Maintenance and cleaning of such sunlight tracking systems is furthermore critical in order to maintain tracking accuracy, which also comes with a price. The space required to implement sunlight tracking systems might furthermore be rather significant, which may also lead to issues in that the sunlight tracking system will generate shading or otherwise compromise exposure of the PV cells to incident sunlight. Moreover, typical sunlight tracking systems are not suitable for installation on rooftops and/or for smaller private installations.

Motion free optical tracking (MFOT) has been proposed in the art, notably by company Renkube (www.renkube.com), as for instance discussed in the paper titled “Performance Analysis of BDRF based Reflectors, MFOT and Fixed Tilt PV”, L. Santhanam, B. L. Bangolae and D. Gopal, 2020 47^th IEEE Photovoltaic Specialists Conference (PVSC), 2020, pp. 2374-2379 (DOI: https://doi.Org/10.1109/PVSC45281 .2020.9300912). The MFOT technology developed by Renkube basically relies on the use of fixed prisms that are attached along the PV panel to increase redirection of light at times the PV panel is not performing at its peak, thereby increasing energy conversion efficiency during the early morning and late evening times. An efficiency increase of up to 20% is said to be achievable over the course of a year using MFOT technology.

This being said MFOT technology also has limitations. In particular, although some improvements are made in terms of efficiency, sunlight steering is in effect entirely passive and cannot therefore be monitored or adjusted throughout the day or the year. A compromise is therefore still being made with regard to exposure to incident sunlight over the course of the day and of the year. MFOT technology is not therefore suitable for use in association with mid to high CPV technology which requires high-accuracy all day long.

Motion free optical tracking solutions relying on the use of “electro-optic” prism arrays made from a material whose refractive index can be varied by applying an electrical field have also been disclosed, for instance in U.S. Patent No. US 6,958,868 B1 and International (PCT) Publication No. WO 2007/114871 A2. Company Insolight (www. nsolight.ch) has come up with a hybrid solution called “planar optical micro-tracking” that in essence relies on the combined use of a protective glass cover with embedded lenses and a mobile back plane. An underside of the protective glass cover is provided with an optical layer having embedded hexagonal lenses to concentrate incident sunlight into a plurality of light beams and the mobile back plane is configured to perform horizontal movements of a few millimetres during the day to keep the PV cells aligned with the light beams. Solutions based on or deriving from this principle are disclosed in European Patents Nos. EP 3 378 103 B1 , EP 3 549 257 B1 and European Patent Publication No. EP 3 745 469 A1 .

Yet another solution known in the art is disclosed in the paper titled “Innovative Solar Tracking Concept by Rotating Prism Array", Hector Garcia, Carlos Ramirez, and Noel Leon, Hindawi Publishing Corporation, International Journal of Photoenergy, Volume 2014, Article ID 807159, 10 pages (DOI: https://doi.ora/10.1155/2014/807159). This concept relies on the use of upper and lower prism arrays that are each made of individual prism elements that are configured to be rotatable about their own respective axes, namely a y-axis and an x-axis respectively. A stationary Fresnel lens is further positioned below the lower prism array to concentrate the solar radiation. The rotation mechanism used to rotate the prism elements is similar to a window shutter mechanism but, instead of blocking sunlight, each prism array redirects the solar rays by refraction.

So-called Risley prism systems are also known in the art for use as beam steering device, as for instance disclosed in U.S. Patent No. US 8,400,700 B2, or as star tracking device, as for instance disclosed in U.S. Patent No. US 10,379,195 B2. Such solutions make use of a pair of individually rotatable prisms that can be rotated one with respect to the other about a common rotation axis to change the optical path of the light beam. These solutions are not however immediately transposable for application in the field of PV technology.

There remains a need for an improved solution. SUMMARY OF THE INVENTION

A general aim of the invention is to provide a sunlight steering apparatus that obviates the limitations and drawbacks of the prior art solutions and that is in particular suitable for PV applications, including but not limited to CPV applications.

More specifically, an aim of the present invention is to provide such a solution that is cost-efficient to produce, while still achieving highly accurate steering of sunlight.

A further aim of the invention is to provide such a solution that is capable of coping with a wide range of angles of incidence of sunlight, while reliably maintaining a stable optical output, be it a collimated optical output or converging light.

Another aim of the invention is to provide such a a solution that is suitable for use as part of a solar energy harvesting system.

Yet another aim of the invention is to provide such a solution that is scalable and can accommodate a large variety of applications, configurations and/or dimensions.

These aims, and others, are achieved thanks to the solutions defined in the claims.

There is accordingly provided a sunlight steering apparatus, the features of which are recited in claim 1 , namely a sunlight steering apparatus comprising upper and lower rotatable disk-shaped prism arrays that are positioned one above the other for rotation about a common rotation axis. Each of said upper and lower rotatable disk-shaped prism arrays is supported such that incident sunlight is allowed to pass successively through the upper rotatable disk-shaped prism array and then through the lower rotatable disk-shaped prism array. An optical path of incident sunlight passing through the upper and lower rotatable disk-shaped prism arrays is selectively adjustable by rotation of the upper rotatable disk-shaped prism array and/or the lower rotatable disk-shaped prism array. The sunlight steering apparatus further comprises first and second drive units that are configured to respectively drive the upper and lower rotatable diskshaped prism arrays into rotation about the common rotation axis to cause adjustment of the optical path of incident sunlight passing through the upper and lower rotatable disk-shaped prism arrays.

Advantageously, the sunlight steering apparatus may further comprises a control unit configured to control operation of the first and second drive units to cause the upper and lower rotatable disk-shaped prism arrays to be rotated such that sunlight exiting the lower prism array is steered to remain substantially parallel to the common rotation axis. The control unit may be an integral part of the sunlight steering apparatus or a dedicated external control component in operative connection with the first and second drive units.

In accordance with a particularly preferred embodiment, the sunlight steering apparatus further comprises a housing supporting and guiding the upper and lower rotatable disk-shaped prism arrays at a peripheral portion. In this context, each of said upper and lower rotatable disk-shaped prism arrays comprises a peripheral gearing in driving engagement with the first, respectively, second drive unit. The peripheral gearing may advantageously be made integral with the upper, respectively lower, rotatable disk-shaped prism array. Furthermore, each of said first and second drive units may in particular consist of a worm drive comprising a motor, such as a stepper motor, driving a worm gear that meshes with the peripheral gearing of the upper, respectively, lower rotatable disk-shaped prism array. Each worm gear may especially consist of a gear arrangement with backlash compensation. In one embodiment variant, each worm gear includes a pair of worm gears that are coupled together by means of a spring element, such as a compression spring, to compensate for the backlash.

Advantageously, each of said upper and lower rotatable disk-shaped prism arrays may be guided by means of first and second, fixed guide rollers and a third, radially adjustable guide roller that cooperate with the peripheral portion of said upper, respectively lower, rotatable disk-shaped prism array. More specifically, each of the first, second and third guide rollers can conveniently cooperate with a peripheral guiding groove provided in the peripheral portion of each of said upper and lower rotatable disk-shaped prism arrays. By way of preference, the first, second and third guide rollers and the peripheral guiding groove exhibit conical cooperating surfaces of revolution. The aforementioned third guide roller can in particular be urged radially towards the peripheral portion of the upper, respectively lower, rotatable diskshaped prism array under the action of a spring element, such as a torsion spring.

In accordance with a preferred embodiment, each of said upper and lower rotatable disk-shaped prism arrays consists of a Fresnel prism structure including a repetition of individual prismatic sections that are oriented along one main direction. Even more preferably, the upper and lower rotatable disk-shaped prism arrays each have a substantially flat surface opposite the side where the Fresnel prism structure is formed, and the upper and lower rotatable disk-shaped prism arrays are positioned such that the substantially flat surfaces are oriented in the same direction, preferably upwards.

The upper and lower rotatable disk-shaped prism arrays may especially be made of polymethyl methacrylate (PMMA) or allyl diglycol carbonate (ADC), also referred to as “CR-39”.

Also claimed is a solar energy harvesting system comprising a sunlight steering device in accordance with the invention and a solar energy harvesting stage including a solar energy harvesting device positioned to receive incident sunlight passing through the upper and lower rotatable disk-shaped prism arrays of the sunlight steering apparatus.

The solar energy harvesting device may in particular include a photovoltaic panel, a concentrated photovoltaic cell, a wavelength-sensitive photovoltaic stage including multiple photovoltaic sub-cells, or a thermal battery or accumulator.

In accordance with a particularly advantageous embodiment, the solar energy harvesting system further comprises an adjustment system configured to perform automatic adjustment of the sunlight steering apparatus to maximize the amount of sunlight hitting the solar energy harvesting device. This adjustment system may especially include a sensor arrangement having multiple sensors, such as photodiodes or thermal sensors, positioned to detect a boundary of a cone or cylinder of light at an output of the sunlight steering apparatus and allow adjustment of the sunlight steering apparatus such that the boundary of the cone or cylinder of light remains within defined limits. The multiple sensors can conveniently be distributed uniformly to form a circular arrangement that is centered on the common rotation axis of the upper and lower rotatable diskshaped prism arrays.

Further advantageous embodiments of the invention are discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will appear more clearly from reading the following detailed description of embodiments of the invention which are presented solely by way of non-restrictive examples and illustrated by the attached drawings in which:

Figure 1 is a perspective view of a sunlight steering apparatus in accordance with a preferred embodiment of the invention;

Figure 2 is an exploded perspective view of the sunlight steering apparatus of Figure 1 ;

Figure 3 is a perspective view of the sunlight steering apparatus of Figure 1 with an upper housing part removed to reveal part of the inner structure of the sunlight steering apparatus;

Figure 3A is an enlarged partial perspective view of Figure 3 as identified by the dotted rectangle in Figure 3;

Figure 4 is a partial cross-sectional view of the sunlight steering apparatus of Figures 1-3A as taken along a vertical sectional plane passing by fixed guide rollers used to guide the upper and lower rotatable prism arrays of the sunlight steering apparatus;

Figure 5A is a cross-sectional view of the sunlight steering apparatus of Figures 1 -4 as taken along a vertical sectional plane passing by the rotation axis of the upper and lower rotatable prism arrays and showing these upper and lower rotatable prism arrays in a first illustrative position;

Figure 5B is a cross-sectional view of the sunlight steering apparatus similar to Figure 5A showing the upper and lower rotatable prism arrays in a second illustrative position;

Figures 6A to 6G are schematic illustrations of various embodiments of solar energy harvesting systems comprising a sunlight steering apparatus in accordance with the invention; Figures 7A and 7B are schematic illustrations of embodiments of a solar energy harvesting system comprising a sunlight steering apparatus in accordance with invention as well as an adjustment system configured to perform automatic adjustment of the sunlight steering apparatus; and

Figure 7C is a schematic top view of a sensor arrangement used in the context of the solar energy harvesting systems of Figures 7A-B.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will be described in relation to various illustrative embodiments. It shall be understood that the scope of the invention encompasses all combinations and sub-combinations of the features of the embodiments disclosed herein.

As described herein, when two or more parts or components are described as being connected, attached, secured or coupled to one another, they can be so connected, attached, secured or coupled directly to each other or through one or more intermediary parts.

Embodiments of the sunlight steering apparatus of the invention will especially be described hereinafter in the particular context of a use thereof for solar energy harvesting and photovoltaics especially, but it will be appreciated that other uses could be contemplated, including e.g. for thermal energy storage.

Figure 1 is a perspective view of a sunlight steering apparatus, designated globally by reference numeral 10, in accordance with an embodiment of the invention. Sunlight steering apparatus 10 essentially comprises a housing H supporting upper and lower rotatable disk-shaped prism arrays 100, 200 (see also the exploded view of Figure 2) that are positioned one above the other for rotation about a common rotation axis RA. The housing H is here made of multiple housing components, namely an upper housing or cover member HA, a lateral housing or cover member HB, and a lower housing or cover member HC. Housing/cover members HA, HB could be formed as one integral component or as distinct components that are then coupled to one another.

Housing H (including components HA, HB, HC) encases part of the upper and lower rotatable disk-shaped prism arrays 100, 200, namely a peripheral portion 100A, resp. 200A, thereof. More specifically, each of the upper and lower rotatable disk-shaped prism arrays 100, 200 is supported by and guided in the housing H at the peripheral portion 100A, resp. 200A, such that incident sunlight is allowed to pass successively through the upper rotatable disk-shaped prism array 100 and then through the lower rotatable disk-shaped prism array 200.

In effect, an optical path of incident sunlight passing through, successively, the upper and lower rotatable disk-shaped prism arrays 100, 200 is selectively adjustable by rotation of the upper rotatable disk-shaped prism array 100 and/or the lower rotatable disk-shaped prism array 200. Rotation of each prism array 100, 200 is achieved by a pair of drive units, visible in Figure 2, namely a first drive unit D1 and a second drive unit D2 that are configured to respectively drive the upper and lower rotatable disk-shaped prism arrays 100, 200 into rotation. Such rotation causes adjustment of the optical path of incident sunlight passing through the upper and lower prism arrays 100, 200. When fully assembled, one will appreciate that the first and second drive units D1 , D2 are housed within the lateral housing/cover member HB.

By way of preference, as shown in Figures 2 to 3A, each of the upper and lower rotatable disk-shaped prism arrays 100, 200 comprises a peripheral gearing 100a, 200a in driving engagement with the first, respectively, second drive unit D1 , D2. In the illustrated example, each drive unit D1 , D2 consists of a worm drive comprising a motor M1 , resp. M2, such as a stepper motor, driving a worm gear WG1 , resp. WG2, that meshes with the peripheral gearing 100a, resp. 200a, as shown in Figures 3 and 3A which show the sunlight steering apparatus 10 with housing/cover members HA, HB removed.

While worm drives are contemplated in the illustrated example, any other suitable drive unit configuration could be contemplated. For instance, motors could potentially be arranged in a vertical configuration to drive the prism arrays 100, 200 in rotation using a simple pinion meshing with the peripheral gearing of the prism arrays 100, 200. Evidently, the shape of the teeth of the relevant gearing and gears will be adapted as a function of the driving arrangement being contemplated.

Ideally, the drive units D1 , D2 and peripheral gearings 100a, 200a are chosen and dimensioned in such a way as to ensure a high rotational position accuracy of the prism arrays 100, 200. For the sake of illustration, stepper motors M1 , M2 with a step angle of 1.8° (i.e. 200 steps per revolution) and a gear reduction of 1 :20 would yield a rotational position accuracy of ±0.09° per motor step. Lab measurements have shown that an angular rotation of 1 ° of the prism array about the rotation axis RA could deviate the output angle of light by approximately 0.4°. In other words, in the illustrative example, for each motor step, the output angle of light may be adjusted by ±0.036° per motor step, which is 7.5 times more accurate than the natural divergence of sunlight (±0.27°).

Advantageously, the peripheral gearing 100a, 200a may be made integral with the upper, respectively lower, rotatable disk-shaped prism array 100, resp. 200. In that respect, any suitable optical material could be used, including but not limited to glass and polymer materials exhibiting a suitable refractive index, high transparency, low dispersivity, UV and weather resistance, as well as ease of manufacturing/machining. Suitable materials may especially include polymethyl methacrylate (PMMA) and allyl diglycol carbonate (ADC, also referred to as “CR- 39”). A combination of materials with different refractive indices may also come into consideration, especially with view to e.g. compensate any undesired chromatic aberration.

Referring to Figures 2 and 5A-B, one will note that, in the illustrated example, each of the upper and lower rotatable disk-shaped prism arrays 100, 200 advantageously consists of a Fresnel prism structure including a repetition of individual prismatic sections 110, 210 that are oriented along one main direction DR1 , resp. DR2. In the illustrated example, twenty-four such individual prismatic sections 110, 210 are juxtaposed, one next to the other, as parallel rows of prismatic sections. It will be appreciated that the relevant number of rows of prismatic sections may vary in practice and will in essence depend on the relevant size of the sunlight steering apparatus 10 and the contemplated application.

Figures 5A and 5B are two cross-section views of the sunlight steering apparatus 10 as taken along a vertical sectional plane passing by the rotation axis RA of the upper and lower prism arrays 100, 200, which views show the upper and lower prism arrays 100, 200 in different rotational positions. Depending on the actual rotational position of each prism array 100, 200 and the angle of incidence OINC of incident sunlight SL, the optical path of incident sunlight SL will be changed as a result of passing through the prism arrays 100, 200 due to refraction. How such optical path changes will in particular depend on the actual rotational position of each prism array 100, 200.

Figure 5A schematically illustrates a first configuration in which incident sunlight SL impinging upon the upper surface 100B of the upper prism array 100, with a given angle of incidence 0INC, passes in succession through the upper prism array 100 and then the lower prism array 200, changing the optical path of incident sunlight SL as a result, to exit the lower prism array 200 with an output angle 0OUT that is substantially zero. In other words, incident sunlight SL exiting the lower prism array 200 is here steered to remain substantially parallel to the common rotation axis RA. By contrast, Figure 5B schematically illustrates another configuration in which incident sunlight SL exits the lower prism array 200 with an output angle 0OUT that is greater than zero, due to the fact that the two prism arrays 100, 200 are rotated to different rotational positions.

By way of preference, a control unit (schematically designated by reference numeral 500 in Figure 1 ) is provided, which control unit 500 is configured to control operation of the first and second drive units D1 , D2 to cause the upper and lower rotatable disk-shaped prism arrays 100, 200 to be rotated such that sunlight SL exiting the lower prism array 200 is steered to remain substantially parallel to the common rotation axis RA (as shown e.g. in Figure 5A). As the angle of incidence 0INC of incident sunlight SL changes during the day, so can the rotational positions of the prism arrays 100, 200 be adjusted to ensure that a collimated output is maintained, parallel to the common rotation axis RA.

One will appreciate that, while a collimated optical output, parallel to the rotation axis RA, is preferred, other embodiments could provide otherwise. For instance, the lower prism array 200 could alternatively consist of a Fresnel lens structure to cause convergence of sunlight exciting the lower prism array 200, in which case no collimated optical output is produced at the exit of the lower prism array 200, but rather converging light. As shown in the illustrative example of Figures 5A-B, one may note that the upper and lower rotatable disk-shaped prism arrays 100, 200 each have a substantially flat upper surface 100B, 200B opposite the side where the Fresnel prism structure is formed. These substantially flat surfaces 100B, 200B are oriented in the same direction, here upwards. This is preferred in that image distortions are reduced as a result.

Referring again to Figure 3A, a preferred structure of the worm gears WG1 , WG2 will be described. More specifically, in order to compensate for the inherent backlash existing between the peripheral gearing 100a, resp. 200a, and the associated worm gear WG1 , resp. WG2, each worm gear WG1 , WG2 preferably consists of a gear arrangement with backlash compensation. More specifically, in the illustrated example, each worm gear WG1 , WG2 includes a pair of worm gears WGA, WGB that are coupled together by means of a spring element SW, such as a compression spring, to compensate for the backlash. Spring element SW in effect pushes worm gears WGA, WGB apart to ensure that worm gear WGA is constantly pressed against first ones of the tooth flanks of the associated peripheral gearing 100a, resp. 200a, while worm gear WGB is constantly pressed in the other direction against opposite ones of the tooth flanks of the associated peripheral gearing 100a, resp. 200a, thereby compensating for the backlash.

Referring to Figures 2 to 4, one may further note that each of the upper and lower rotatable disk-shaped prism arrays 100, 200 is guided by means of a set of three guide rollers identified by reference signs GR10, GR15, resp. GR20, GR25 that are distributed at approximately 120° from one another about the peripheral portion 100A, resp. 200A, of the prism array 100, resp. 200. More specifically, first and second guide rollers GR10, resp. GR20, are provided that are fixed within the housing H (see Figure 4), namely on the upper housing/cover member HA, as regards guide rollers GR10, and on the lower housing/cover member HC, as regards guide rollers GR20. The third guide roller GR15, resp. GR25, is likewise mounted on the housing H, however in such a manner as to be radially adjustable. More precisely, guide roller GR15, GR25 is urged radially towards the peripheral portion 100A, resp. 200A, of the prism array 100, resp. 200, under the action of a spring element SG, such as a torsion spring.

Even more preferably, guide rollers GR10, GR15, resp. GR20, GR25 cooperate with a peripheral guiding groove 100b, resp. 200b, that is provided in the peripheral portion 100A, resp. 200A, of each of the upper and lower rotatable disk-shaped prism arrays 100, resp. 200. As shown, guide rollers GR10, GR15, GR20, GR25 and peripheral guiding grooves 100b, 200b are advantageously shaped to exhibit conical cooperating surfaces of revolution, which ensures a more stable and robust guiding of the prism arrays 100, 200.

Referring to Figures 6A to 6G, various embodiments of solar energy harvesting systems comprising a sunlight steering apparatus in accordance with the invention will now be described.

Figure 6A shows a first embodiment consisting of a combination of the sunlight steering apparatus 10 with a conventional photovoltaic panel PV. This is in effect the simplest configuration of a solar energy harvesting system where the solar energy harvesting stage consists solely of the photovoltaic panel PV, the sunlight steering apparatus 10 being used to ensure that incident sunlight SL is steered to remain collimated with an angle of incidence, on the photovoltaic panel PV, of substantially zero (i.e. perpendicular to the panel surface). In this illustrative example, one will understand and appreciate that a cylinder of nonconverging light is produced and projects onto the surface of the photovoltaic panel PV.

Figure 6B shows another embodiment consisting of a combination of the sunlight steering apparatus 10 with a converging lens, here shown as a Fresnel lens FL, to produce a cone of light converging onto a concentrated photovoltaic cell CPV. A somewhat similar embodiment is shown in Figure 6C. In this case, a convex mirror CM is used, instead of a converging lens as shown in Figure 6B, to likewise produce a cone of light converging onto a concentrated photovoltaic cell CPV.

Figure 6D shows a further embodiment of a solar energy harvesting system that relies on the use of an optically dispersive element OD to cause dispersion of light into multiple wavelengths or wavelength bands AA, B that are directed onto selected portions of a wavelength-sensitive photovoltaic stage including multiple photovoltaic sub-cells PVA, PVB that are each sensitive to a relevant one of the wavelengths or wavelength bands AA, B.

Another somewhat similar embodiment is shown in Figure 6E, with the main difference, compared to the embodiment of Figure 6D, residing in the fact that a mirror array MA is further provided to cause the incident sunlight to pass twice through the optically dispersive element OD, causing greater dispersion of light. A suitable optically dispersive element OD usable in the context of the embodiment of Figure 6E forms the subject-matter of International (PCT) Application No. PCT/IB2021/052631 of March 30, 2021 in the name of the present Applicant, titled “DISPERSIVE OPTICAL DEVICE, DISPERSIVE OPTICAL SYSTEM COMPRISING THE SAME AND USE THEREOF ESPECIALLY FOR SOLAR ENERGY HARVESTING”, the content of which is incorporated herein by reference.

Figure 6F schematically shows yet another embodiment of a solar energy harvesting system comprising a sunlight steering apparatus 10 in accordance with the invention. In this case, however, no photovoltaic stage as such is used, but rather a thermal battery or accumulator TB. Such thermal battery/accumulator TB can be any suitable device capable of storing heat energy, such as a device comprising a material capable of undergoing a phase change (or so-called “Phase-Change Material” I PCM) and performing so-called “Latent Heat Storage” (LHS). A multitude of PCMs are available, including e.g. salts, polymers, gels, paraffin waxes and metal alloys. Other suitable solutions may rely on materials capable of performing so-called “Sensible Heat Storage” (SHS), such as molten salts or metals. “Thermo-chemical Heat Storage” (TCS) constitutes yet another possible solution to perform thermal energy storage.

Figure 6G shows a somewhat similar embodiment which relies on the use of a convex mirror CM, instead of a converging Fresnel lens FL as shown in Figure 6F, to produce a cone of light converging onto the thermal battery/accumulator TB. It will be appreciated that many further variants of solar energy harvesting systems relying on the use of the sunlight steering apparatus of the invention may be contemplated.

Figures 7A and 7B are schematic illustrations of embodiments of a solar energy harvesting system comprising a sunlight steering apparatus 10 in accordance with the invention as well as an adjustment system configured to perform automatic adjustment of the sunlight steering apparatus 10. More specifically, the systems shown in Figures 7A and 7B are essentially based on the embodiments of Figures 6B and 6C, respectively, with the addition of means designed to maximize the amount of sunlight SL hitting the solar energy harvesting device, here concentrated photovoltaic cell CPV.

In the illustrated example, the adjustment system advantageously includes a sensor arrangement SP/LS having multiple sensors LS (such as light sensors, e.g. photodiodes, or thermal sensors) positioned to detect a boundary of a cone of converging light LC (or the boundary of a cylinder of non-converging light as the case may be) at an output of the sunlight steering apparatus 10 (namely the cone of light LC produced by the Fresnel lens FL of Figure 7A or the convex mirror CM of Figure 7B) and allow adjustment of the sunlight steering apparatus 10 such that the boundary of the cone of converging light LC remains within defined limits (as schematically depicted in Figures 7A-B). More specifically, the sensor arrangement SP/LS essentially consists of a sensor plate SP carrying multiple sensors LS (such as photodiodes) that are distributed uniformly to form a circular arrangement that is centered on the common rotation axis RA of the upper and lower rotatable disk-shaped prism arrays 100, 200. Any misalignment of the cone of light LC beyond a given threshold will cause one or more of the sensors LS to be triggered and corresponding adjustments of the sunlight steering apparatus 10 may be undertaken to ensure that the boundary of the cone of light LC remains within the desired limits.

Outputs of the sensors LS might be used in any suitable feedback loop in association with a suitable positioning/adjustment algorithm that will recurrently check and ensure that the boundary of the cone (or cylinder) of light LC remains within the desired limits. A minimum of three sensors LS must be used, but the more sensors LS are used, the greater the positioning accuracy will be.

Various modifications and/or improvements may be made to the abovedescribed embodiments without departing from the scope of the invention as defined by the appended claims.

For instance, chromatic aberration, if any, generated by the superposition of the prism arrays could be cancelled by working with achromatic prisms, namely prisms composed of two complementary materials of two different refractive indices.

Furthermore, the provision of a housing supporting and guiding the upper and lower rotatable disk-shaped prism arrays at the peripheral portion is one possible solution to support the upper and lower prism arrays of the sunlight steering apparatus. Other possible solutions may for instance consist in supporting the upper and lower prism arrays by means of a common central shaft and associated bearings to allow each prism array to rotate about the common central shaft.

In addition, further components and/or functions may be implemented beyond the components and functions described above. In particular, one may contemplate the addition of dedicated cooling or heat dissipation components to ensure appropriate cooling or heat dissipation of the photovoltaic cells shown e.g. in Figure 6B-E and 7A-B

LIST OF REFERENCE NUMERALS AND SIGNS USED THEREIN

10 sunlight steering apparatus

100 upper rotatable disk-shaped prism array I upper Fresnel prism structure 100A peripheral portion of upper rotatable disk-shaped prism array 100 100B (upper) flat surface of upper rotatable disk-shaped prism array 100 100a peripheral gearing of upper rotatable disk-shaped prism array 100 in driving engagement with first drive unit D1

100b peripheral guiding groove of upper rotatable disk-shaped prism array 100 110 individual prismatic sections of upper rotatable disk-shaped prism array 100 oriented along main direction DR1

200 lower rotatable disk-shaped prism array / lower Fresnel prism structure 200A peripheral portion of lower rotatable disk-shaped prism array 200

200B (upper) flat surface of lower rotatable disk-shaped prism array 200

200a peripheral gearing of lower rotatable disk-shaped prism array 200 in driving engagement with second drive unit D2

200b peripheral guiding groove of lower rotatable disk-shaped prism array 200

210 individual prismatic sections of lower rotatable disk-shaped prism array 200 oriented along main direction DR2

500 control unit

D1 first drive unit driving rotation of upper rotatable disk-shaped prism array 1001 worm drive

M1 motor of first drive unit D1

WG1 worm gear of first drive unit D1 (gear arrangement with backlash compensation) meshing with peripheral gearing 100a of upper rotatable disk-shaped prism array 100

D2 second drive unit driving rotation of lower rotatable disk-shaped prism array 2001 worm drive

M2 motor of second drive unit D2

WG2 worm gear of second drive unit D2 (gear arrangement with backlash compensation) meshing with peripheral gearing 200a of lower rotatable disk-shaped prism array 200

WGA (first) worm gear forming part of worm gear WG1 , WG2

WGB (second) worm gear forming part of worm gear WG1 , WG2

SW spring element (compression spring) coupling worm gears WGA and WGB for backlash compensation

GR10 first and second, fixed guide rollers cooperating with peripheral guiding groove 100b of upper rotatable disk-shaped prism array 100

GR15 third, radially adjustable guide roller cooperating with peripheral guiding groove 100b of upper rotatable disk-shaped prism array 100

GR20 first and second, fixed guide rollers cooperating with peripheral guiding groove 200b of lower rotatable disk-shaped prism array 200

GR25 third, radially adjustable guide roller cooperating with peripheral guiding groove 200b of lower rotatable disk-shaped prism array 200 SG spring element (torsion spring) urging guide roller GR15, resp. GR25 radially towards the peripheral portion 100A, resp. 200A, of the upper, resp. lower, rotatable disk-shaped prism array 100, resp. 200

H housing

HA upper housing/cover member

HB lateral housing/cover element encasing drive units D1 , D2

HC lower housing/cover member

RA common rotation axis of upper and lower rotatable disk-shaped prism arrays 100, 200

DR1 main direction of individual prismatic sections 110 forming upper rotatable disk-shaped prism array 100

DR2 main direction of individual prismatic sections 210 forming lower rotatable disk-shaped prism array 200

SL incident sunlight

9INC angle of incidence of incident sunlight SL impinging on the upper rotatable disk-shaped prism array 100

9OUT output angle of incident sunlight SL exiting the lower rotatable diskshaped prism array 200

PV photovoltaic panel

CPV concentrated photovoltaic cell

FL converging Fresnel lens

CM convex mirror

OD optically dispersive element

MA mirror array

AA, B wavelength bands of dispersed light spectrum

PVA photovoltaic sub-cell sensitive to wavelength band AA

PVB photovoltaic sub-cell sensitive to wavelength band AB

TB thermal battery/accumulator

LC cone of converging light

SP sensor arrangement (e.g. sensor plate)

LS sensors (e.g. photodiodes)

Claims

1. A sunlight steering apparatus (10) comprising upper and lower rotatable disk-shaped prism arrays (100, 200) that are positioned one above the other for rotation about a common rotation axis (RA), wherein each of said upper and lower rotatable disk-shaped prism arrays (100, 200) is supported such that incident sunlight (SL) is allowed to pass successively through the upper rotatable disk-shaped prism array (100) and then through the lower rotatable disk-shaped prism array (200), wherein an optical path of incident sunlight (SL) passing through the upper and lower rotatable disk-shaped prism arrays (100, 200) is selectively adjustable by rotation of the upper rotatable disk-shaped prism array (100) and/or the lower rotatable disk-shaped prism array (200), and wherein the sunlight steering apparatus (10) further comprises first and second drive units (D1 , D2) that are configured to respectively drive the upper and lower rotatable disk-shaped prism arrays (100, 200) into rotation about the common rotation axis (RA) to cause adjustment of the optical path of incident sunlight (SL) passing through the upper and lower rotatable disk-shaped prism arrays (100, 200).

2. The sunlight steering apparatus (10) according to claim 1 , further comprising a control unit (500) configured to control operation of the first and second drive units (D1 , D2) to cause the upper and lower rotatable disk-shaped prism arrays (100, 200) to be rotated such that sunlight (SL) exiting the lower prism array (200) is steered to remain substantially parallel to the common rotation axis (RA).

3. The sunlight steering apparatus (10) according to claim 1 or 2, further comprising a housing (H) supporting and guiding the upper and lower rotatable disk-shaped prism arrays (100, 200) at a peripheral portion (100A, 200A).

4. The sunlight steering apparatus (10) according to claim 3, wherein each of said upper and lower rotatable disk-shaped prism arrays (100, 200) comprises a peripheral gearing (100a, 200a) in driving engagement with the first, respectively, second drive unit (D1 , D2).

5. The sunlight steering apparatus (10) according to claim 4, wherein the peripheral gearing (100a, 200a) is made integral with the upper, respectively lower, rotatable disk-shaped prism array (100, 200).

6. The sunlight steering apparatus (10) according to claim 4 or 5, wherein each of said first and second drive units (D1 , D2) consists of a worm drive comprising a motor (M1 , M2) driving a worm gear (WG1 , WG2) that meshes with the peripheral gearing (100a, 200a) of the upper, respectively, lower rotatable disk-shaped prism array (100, 200).

7. The sunlight steering apparatus (10) according to claim 6, wherein the motor (M1 , M2) is a stepper motor.

8. The sunlight steering apparatus (10) according to claim 6 or 7, wherein each worm gear (WG1 , WG2) consists of a gear arrangement (WGA, WGB, SW) with backlash compensation.

9. The sunlight steering apparatus (10) according to claim 8, wherein each worm gear (WG1 , WG2) includes a pair of worm gears (WGA, WGB) that are coupled together by means of a spring element (SW) to compensate for the backlash.

10. The sunlight steering apparatus (10) according to claim 9, wherein the spring element (SW) is a compression spring.

11 . The sunlight steering apparatus (10) according to any one of claims 3 to 10, wherein each of said upper and lower rotatable disk-shaped prism arrays (100, 200) is guided by means of first and second, fixed guide rollers (GR10, GR20) and a third, radially adjustable guide roller (GR15, GR25) that cooperate with the peripheral portion (100A, 200A) of said upper, respectively lower, rotatable disk-shaped prism array (100, 200).

12. The sunlight steering apparatus (10) according to claim 11 , wherein each of the first, second and third guide rollers (GR10, GR15, GR20, GR25) cooperate with a peripheral guiding groove (100b, 200b) provided in the peripheral portion (100A, 200A) of each of said upper and lower rotatable diskshaped prism arrays (100, 200).

13. The sunlight steering apparatus (10) according to claim 12, wherein the first, second and third guide rollers (GR10, GR15, GR20, GR25) and the peripheral guiding groove (100b, 200b) exhibit conical cooperating surfaces of revolution

14. The sunlight steering apparatus (10) according to any one of claims 11 to 13, wherein the third guide roller (GR15, GR25) is urged radially towards the peripheral portion (100A, 200A) of the upper, respectively lower, rotatable disk-shaped prism array (100, 200) under the action of a spring element (SG).

15. The sunlight steering apparatus (10) according to claim 14, wherein the spring element (SG) is a torsion spring.

16. The sunlight steering apparatus (10) according to any one of the preceding claims, wherein each of said upper and lower rotatable disk-shaped prism arrays (100, 200) consists of a Fresnel prism structure including a repetition of individual prismatic sections (110, 210) that are oriented along one main direction (DR1 , DR2). 22

17. The sunlight steering apparatus (10) according to claim 16, wherein the upper and lower rotatable disk-shaped prism arrays (100, 200) each have a substantially flat surface (100B, 200B) opposite the side where the Fresnel prism structure is formed, and wherein the upper and lower rotatable disk-shaped prism arrays (100, 200) are positioned such that the substantially flat surfaces (100B, 200B) are oriented in the same direction.

18. The sunlight steering apparatus (10) according to claim 17, wherein the substantially flat surfaces (100B, 200B) are oriented upwards.

19. The sunlight steering apparatus (10) according to any one of the preceding claims, wherein the upper and lower rotatable disk-shaped prism arrays (100, 200) are made of polymethyl methacrylate (PMMA).

20. The sunlight steering apparatus (10) according to any one of claims 1 to 18, wherein the upper and lower rotatable disk-shaped prism arrays (100, 200) are made of allyl diglycol carbonate (ADC).

21. A solar energy harvesting system comprising a sunlight steering apparatus (10) in accordance with any one the preceding claims, and a solar energy harvesting stage including a solar energy harvesting device (PV; CPV; PVA, PVB; TB) positioned to receive incident sunlight (SL) passing through the upper and lower rotatable disk-shaped prism arrays (100, 200) of the sunlight steering apparatus (10).

22. The solar energy harvesting system according to claim 21 , wherein the solar energy harvesting device includes a photovoltaic panel (PV), a concentrated photovoltaic cell (CPV), a wavelength-sensitive photovoltaic stage including multiple photovoltaic sub-cells (PVA, PVB), or a thermal battery or accumulator (TB). 23

23. The solar energy harvesting system according to claim 21 or 22, further comprising an adjustment system configured to perform automatic adjustment of the sunlight steering apparatus (10) to maximize the amount of sunlight (SL) hitting the solar energy harvesting device (PV; CPV; PVA, PVB; TB).

24. The solar energy harvesting system according to claim 23, wherein the adjustment system includes a sensor arrangement (SP/LS) having multiple sensors (LS) positioned to detect a boundary of a cone or cylinder of light (LC) at an output of the sunlight steering apparatus (10) and allow adjustment of the sunlight steering apparatus (10) such that the boundary of the cone or cylinder of light (LC) remains within defined limits.

25. The solar energy harvesting system according to claim 24, wherein the multiple sensors (LS) are distributed uniformly to form a circular arrangement that is centered on the common rotation axis (RA) of the upper and lower rotatable disk-shaped prism arrays (100, 200).

26. The solar energy harvesting system according to claim 24 or 25, wherein the multiple sensors (LS) are photodiodes.

27. The solar energy harvesting system according to claim 24 or 25, wherein the multiple sensors (LS) are thermal sensors.