A system for solar irradiance management and carbon dioxide capture in energy harvesting

Abstract

According to an example aspect of the present invention, there is provided a system comprising: at least one energy harvesting device (110) configured to harvest radiative energy from two opposite sides of the respective energy harvesting device (110); a layer of a granular slag material (210) comprising at least 70% of calcium oxide and / or silicon dioxide between the at least one energy harvesting device (210) and ground, whereby solar radiance to a side of each energy harvesting device (210) not facing direct sunlight is affected by reflection from the granular slag material (210), and whereby carbon dioxide is captured from the atmosphere by reacting with calcium oxide comprised in the granular slag material (210).

Description

IRRADIANCE MANAGEMENT FIELD

[0001] The present disclosure relates to managing solar irradiance reflection toadvance energy harvesting goals and to capture carbon dioxide from the atmosphere.BACKGROUND

[0002] Stainless steel slag includes electric arc furnace, EAF, slag and argon oxygendecarburisation, AOD, slag and ladle furnace, LF, slag. They are generated, respectively,from an electric arc furnace and an AOD converter and ladle furnace in stainless steel makingprocesses, approximately one tonne of slag being generated in the production of three tonnesof stainless steel.

[0003] Slags have been used in various applications extending from production ofglass to road construction, where slags have been used as aggregate material and also ascomponents in asphalt cements. Slags have also found application as components of construction cements, where slag-based cements have been used in e.g. bridge building as such cements are resistant to chlorides and sulfates. Challenges in using slags arise from the fact that slags exhibit variability as to their chemical composition, rendering it difficult to use them in chemical processes requiring precisely defined raw materials. SUMMARY

[0004] The present disclosure relates to a system comprising at least one energyharvesting device configured to harvest radiative energy from two opposite sides of therespective energy harvesting device and a layer of a granular slag material comprising atleast 70% of calcium oxide and / or silicon dioxide between the at least one energy harvesting device and ground, whereby solar radiance to a side of each energy harvesting device not facing direct sunlight is affected by reflection from the granular slag material, and wherebycarbon dioxide is captured from the atmosphere by reacting with calcium oxide comprised in the granular slag material.

[0005] According to some aspects, there is provided the subject-matter of theindependent claims. Some embodiments are defined in the dependent claims.

[0006] According to a second aspect of the present disclosure, there is provided thegranular slag material is stainless steel slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIGURE 1 illustrates an example system in accordance with at least someembodiments of the present invention;

[0008] FIGURE 2 illustrates an example system in accordance with at least someembodiments of the present invention, and

[0009] FIGURE 3 illustrates an example system in accordance with at least someembodiments of the present invention. EMBODIMENTS

[0010] Described herein are systems which harvest energy from solar irradiation to,for example, generate electricity or to heat water. The harvesting is enhanced by using agranular slag material, such as stainless steel slag, to increase the quantity of total irradiation falling on the harvesting device, such as a solar panel or a solar water heater. The granular slag material is of a predominantly white colour, whereby it is effective in reflecting light. The granules also have irregular shapes, beneficially creating a diffuse reflected light field. The reflection from the slag material occurs from both direct sunlight, coming from the direction of the Sun, and from diffuse light which falls on the ground from a wide range of directions, in particular from blue sky but also as reflected and scattered by clouds and objects on the ground. Further benefits are obtained in some embodiments from a reduced heat load from sunlight to a surface upon which the granular slag material is placed.

[0011] FIGURE 1 illustrates an example system in accordance with at least someembodiments of the present invention. While a solar panel is illustrated, also solar waterheaters, for example, are within the ambit of the present disclosure as energy harvestingdevices. Solar panel 110 may be an isolated solar panel, or the system may comprise dozens,hundreds or even thousands of panels to form a solar power station. Solar panel 110 is abifacial solar panel, by which it is meant a solar panel which is configured to produce electrical energy from photons encountered on either of its surfaces, front or rear. Monofacial solar cells, unlike bifacial ones, produce electrical energy only when photons impinge ontheir primary side. In bifacial cells, a bifaciality factor, expressed often as a percentage, isdefined as the ratio of rear-side efficiency in relation to front-side efficiency in the sameirradiance conditions. Even if the bifaciality factor is low, energy is nonetheless harvestedalso from the non-primary side as long as it is irradiated. The front and rear sides are oppositesides of solar panel 110.

[0012] Solar panel 110 of FIGURE 1 produces electricity from the total radiativeenergy falling upon it, on both the front and rear sides. Primary irradiance 120 is usuallyprimarily direct sunlight from the Sun, and secondary irradiance 130 is also from the Sun but indirect, from one to several reflection events. Depending on the geographical location of solar panel 110, its installation and the direction of the Sun, primary irradiance 120 may fall on either side of solar panel 110. As to secondary irradiance 130, it falls usually on both sides of solar panel 110. Primary irradiance 120 also comprises some indirect irradiance, as the atmosphere scatters sunlight. In cloudy weather, primary irradiance 120 is light impinging on solar panel 110 from the sky in general. The blue colour of clear sky is a result of atmospheric scattering of sunlight, wherefore the clear sky as a whole is a multidirectional source of light, which thus does not exclusively arrive at the energy harvesting system from the direction of the Sun.

[0013] Most solar modules are produced from crystalline silicon solar cells made ofpolycrystalline or monocrystalline silicon. So-called third-generation solar panels use thin-film cells, which achieve high-efficiency conversion for a lower cost compared to other solarenergy technologies. On the other hand, high-cost, high-efficiency, and close-packedrectangular multi-junction cells are usually used in solar panels on e.g. spacecraft, as they offer the highest ratio of generated power per kilogram of solar panel. Multijunction cells are compound semiconductors made of gallium arsenide and other semiconductor materials. Systems in accordance with solutions described herein may use a wide range of solar paneltechnologies, such as third generation solar panels or multi-junction cells. In particular,bifacial photovoltaic modules with different architectures for their cells are currentlyavailable. These include passivated emitter rear contact, PERC, passivated emitter rearlocally-diffused, PERL, passivated emitter rear totally diffused, PERT, heterojunction withintrinsic thin-layer, HIT, and interdigitated back contact, IBC, cells.

[0014] In terms of secondary irradiance 130, radiative energy absorbed by the groundor other surface upon which solar panel 110 is installed is energy lost to the energy harvesting process. Thus reducing the fraction of radiative energy absorbed by the surface by increasing reflection from that surface will have the result of increasing energy yield of the energy harvesting system. In principle a mirror-like surface under solar panel 110 would solve the question of absorbed radiative energy, however a mirror surface is not ideal for various reasons, which include the resource cost of building it, its tendency to break, glare and its handling of rainwater.

[0015] Disclosed herein are systems which comprise a layer of a granular slag materialunder the energy harvesting device(s), such as solar panel 110. In particular, the slag may be stainless steel slag which is a by-product of stainless steel production, thus this material is generated with no separate expenditure of energy or raw materials. Furthermore, the slag needs to be disposed of somewhere in any case, wherefore its use as a reflection-enhancing layer in radiative energy harvesting solutions is particularly beneficial.

[0016] The main components in both EAF, AOD and ladle furnace stainless steel slagare calcium oxide CaO, silicon dioxide SiO2, magnesium oxide MgO and aluminium oxideAl2O3. CaO and SiO2 may compose nearly 80% of these slags. For example, the slag maycomprise at least 60%, 70% or 75% of calcium oxide and / or silicon dioxide, by which it ismeant that the combined proportions of CaO and SiO2 by weight are at least 60%, 70% or75% of the weight of the slag, respectively. CaO is white, while SiO2is either white orcolourless, giving the slag overall a reflective property. It is of note, that the slag need notbe completely white for its use to being a technical benefit, rather, an irradiance benefit isobtained as long as the slag is more reflective than the surface it covers. In outdoor systems the surface covered by the slag may be the ground, in other words gravel or grass, for example.

[0017] A specific example of slag composition is provided in the following Table 1:CaO 50%SiO225% MgO 10%Al2O3 5% Cr2O3 2% Table 1

[0018] The presence of the layer of slag may have the effect, that no, or nearly no,sunlight reaches the ground. The absence of sunlight will prevent the growth of grasses which would otherwise absorb radiative energy, causing radiative losses in the energy harvesting process.

[0019] FIGURE 2 illustrates an example system in accordance with at least someembodiments of the present invention. Like numbering denotes like structure as in FIGURE 1. Primary irradiance 120 falls on solar panels 110 and on the layer 210 of granular slag material. As the slag material is granular, it reflects incoming light into a broad range of directions, and secondary irradiance 130 thus falls partly on solar panels 110, in particularthe rear faces of solar panels 110. As solar panels 110 are bifacial, this secondary irradiance130 will enhance their efficiency by increasing their total irradiance, generating additionalelectricity. In case the harvesting devices are solar water heaters, similar considerations apply. In realistic use scenarios, using stainless steel slag layer 210 enhances production ofelectricity by 10 – 15% in mid-latitude and arctic areas, compared to normal gravel or grassunder solar panels 110. As noted above, the layer 210 of granular slag material may compriseat least 70% of calcium oxide and / or silicon dioxide. The granular slag material layer 210has a higher reflectance than grass and the reflection of the granular slag material affects thesolar radiance to the side of each solar panel 110 not facing direct sunlight by increasing theoverall solar radiance falling on these bifacial solar panels.

[0020] Solar radiance to a side of each solar panel 110 not facing direct sunlight isaffected by reflection from the granular slag material 210. It is affected in the sense that it isincreased compared to a situation when the granular slag material layer 210 is absent, inother words, the layer of granular slag material reflects more than a layer upon which the granular slag material layer 210 is placed. This may in particular involve, in the case of solar panels, reflectance in the frequency band or bands where the solar panel produces electricity from light.

[0021] The system of FIGURE 2 further comprises a water-impermeable barrier 220,such as, for example, a plastic or metal layer. This barrier is useful as it will prevent rainwater from flowing through slag layer 210 to the ground, potentially leaching chemicals from the slag into the ground. Barrier 220 may have a sloped arrangement to convey rainwater from the granular slag material to a spot where it may be disposed of safely, such as to a rainwater channel or drain. In some embodiments, barrier 220 is absent. Barrier 220 may be absent, for example, in case the energy harvesting system is on a nonpermeable surface, such as rockor concrete, for example, or in case the slag is of a type which doesn’t leach chemicals.

[0022] In some embodiments, the slag is spread on a roof of a building to enhancereflectivity of the roof and reduce the quantity of energy needed for active cooling of the building, for example by air conditioning or remote cooling. Then the energy harvestingdevice is optional. In some of these embodiments, the solar panel 110 of FIGURE 1 or 2 isplaced on the roof, such that energy efficiency is enhanced in several ways: firstly, the solar panels shade the roof, secondly, the solar panels generate electricity for air conditioning, thirdly, the slag cools the building down by reflecting solar irradiance away from structures of the building, and fourthly, some of the reflected solar irradiance falls on the solar panels, enhancing their yield.

[0023] In these embodiments there is provided a building comprising a layer of thegranular slag material comprising at least 70% of calcium oxide and / or silicon dioxide on the roof. For example, the slag may be stainless steel slag, that is, slag which is a by-product of stainless steel production. There may be an energy harvesting system as described herein on the layer of the granular slag material, the energy harvesting system comprising at least one energy harvesting device configured to harvest radiative energy from two opposite sides of the respective energy harvesting device, such that solar radiance to a side of each energy harvesting device not facing direct sunlight is affected by reflection from the granular slag material. It is affected in the sense that it is increased compared to a situation when the granular slag material is absent, in other words, the layer of granular slag material reflects more than a layer upon which the granular slag material is placed.

[0024] In addition to the increase in overall irradiance falling on the energy harvestingdevices, use of slag, such as, for example, stainless steel slag, provides a further technical benefit in terms of weathering. In detail, carbon capture from the atmosphere takes place as a distributed arrangement, such as a layer 210, of CaO and MgO bearing slag interacts withair. The reaction CaO + CO2→ CaCO3captures carbon dioxide from the atmosphere,whereby it is possible to arrive at a carbon-negative electricity generation process by usingslag layer 210 in the energy harvesting system. The energy harvesting system may thus bothproduce electricity and capture carbon in the form of carbon dioxide from the atmosphere. Weathering takes place faster as the slag is spread into a layer 210, compared to a case where the slag is stored in a heap, where access to air and water is slower. Layer 210, on the other hand, exposed a large surface area of the granular slag to wind and rainfall. The calcium carbonate, CaCO3, may in turn be used as a building material, or in the purification of iron from iron ore in a blast furnace, for example. Calcium carbonate in fact has a wide range of uses, from paint extenders to use as a calcium supplement for human consumption. The reaction CaO + CO2 → CaCO3 is reversible by heating to about 1000 degrees Celcius. Thefollowing CO2 uptake potential of Table 2 was measured in research published in thepublication “La Plante, E. C.; Mehdipour, I.; Shortt, I.; Yang, K.; Simonetti, D.; Bauchy, M.;Sant, G. N. Controls on CO2 Mineralization Using Natural and Industrial Alkaline Solidsunder Ambient Conditions. ACS Sustain. Chem. Eng. 2021, 9 (32), 10727–10739.Stoichiometric CO2 uptake [CO2 mass-%] potential equation 1 & equation 2 [ton of CO2 / tonof slag] Stainless steel slag 0,52 51,03Table 2

[0025] Further clarifying the good reactivity of the slag in CO2 capture, which is dueto the fact that the majority of the CaO in the slag is specifically in certain polymorphs ofdicalcium silicate (gamma-dicalcium silicate, γ-C2S, and beta-dicalcium silicate, β-C2S),which are highly reactive with CO2. The carbonation reaction mechanisms of the γ-C2S andβ-C2S differ. Upon carbonation of β-C2S, the carbonation reaction occurs via hydration(CaO∙SiO2 + CO2 + H2O ↔ Ca(OH)2 + SiO2 + CO2 ↔ CaCO3 + SiO2 + H2O). Due tothe weak hydraulic reactivity of the γ-C2S polymorph, the carbonation reaction of γ-C2S does not form an intermediate product, but the CaO directly reacts with CO2 via carbonicacid, forming CaCO3 with notably higher reaction rate (CO2 + H2O → H2CO3, 2CaO∙SiO2 + 2H2CO3 →CaCO3 + SiO2 + 2H2O).

[0026] There are differences in the reactivity of these calcium silicate phases withCO2, and the slag according to the invention contains the right phases for this, as well assome phase that requires water to react.

[0027] Concerning the granular slag material itself, this material may have an averagegranular diameter in the range of 0,1 to 6 cm, or, for example from 1 to 10 cm. By averagegranular diameter it is meant a diameter such that half of the mass of the slag is in granules of at most this diameter. This range provided the benefit, that wind doesn’t scatter the granules, and on the other hand a large surface area of the granules is exposed to air to enhance carbon capture. This grain size range can also effectively block sunlight from penetrating layer 210. The size distribution of the granular slag material may be as described in Table 3, for example, which provides the benefit, that wind doesn’t scatter the granules, and on the other hand a large surface area of the granules is exposed to air to enhance carboncapture. Layer 210 of the granular slag material may be between 10 and 30 centimetres, cm,thick, for example. The thickness of layer 210 may be selected to optimize the capture of carbon from the atmosphere. Another example of the thickness is between 15 and 25 cm. By thickness it is meant an average thickness. The thickness of layer 210 may be selected to optimize the capture of carbon from the atmosphere, the thicker the layer is the less efficient is the carbon capture owing to a smaller relative proportion of the slag which is directly subject to wind and rain. On the other hand if the layer is too thin, its reflectivity will be inferior to a thicker layer as the ground may be imperfectly covered.Granule diameter Cumulative size distribution Content per size, up tostated figure 31,5 millimetres, mm 100%22,4 mm 100%16 mm 90%11,2 mm 55%8 mm 30%5,6 mm 15%4 mm 5% 1 – 45%2 mm 3% 1 – 45%1 mm 2 % 1 – 40%0,063 mm 0,5% < 5%Table 3: Granule size distribution

[0028] The granular slag material may, in particular, have the size distribution ofTable 3 and the composition of Table 1. As another example, the granular slag material mayhave the composition of Table 1 and a size distribution where less than 5% of the slag’s massis in particles of less than 4mm diameter and 90% of the mass is in particles of less than 16mm in diameter. As a third example, the granular slag material may have a composition of at least 60%, 70% or 75% of calcium oxide and / or silicon dioxide and a size distributionwhere less than 5% of the slag’s mass is in particles of less than 4mm diameter and 90% ofthe mass is in particles of less than 16 mm in diameter.

[0029] FIGURE 3 illustrates an example system in accordance with at least someembodiments of the present invention. Like numbering denotes like structure as in FIGUREs 1 and 2.

[0030] In the system of FIGURE 3, each one of the energy harvesting devices has acentre point 310 at least 0,5 or 1,5 metres above the layer of the granular slag material. Centrepoint 310 is the centre point of the energy harvesting part of the harvesting device, forexample, in the case of a solar panel the centre of the panel itself. This distance to ground isillustrated in FIGURE 3 as distance 320. Further, when the energy harvesting systemcomprises plural of the energy harvesting devices, wherein neighbouring energy harvestingdevices may be separated from each other by a distance within the range of 0,5 to 2 metres.This distance between harvesting devices is illustrated in FIGURE 3 as distance 330. This distance enables irradiance of the layer of granular slag material, increasing the enhancement of yield owing to secondary irradiance 130, as described herein above.

[0031] In systems which are solar power stations, solar panels may be placed in amatrix formation which comprises rows and columns, when seen from above. In these cases a first inter-panel distance may separate solar panels of a same column from each other, and a second inter-panel distance may separate columns of solar panels from each other, these two distances being either the same, or different from each other.

[0032] It is to be understood that the embodiments of the invention disclosed are notlimited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0033] Reference throughout this specification to one embodiment or an embodimentmeans that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to the same embodiment. Wherereference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0034] As used herein, a plurality of items, structural elements, compositionalelements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0035] Furthermore, the described features, structures, or characteristics may becombined in any suitable manner in one or more embodiments. In the preceding description,numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0036] While the forgoing examples are illustrative of the principles of the presentinvention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0037] The verbs “to comprise” and “to include” are used in this document as openlimitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwiseexplicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, asingular form, throughout this document does not exclude a plurality.

[0038] As used herein, “at least one of the following: <a list of two or moreelements>” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. INDUSTRIAL APPLICABILITY

[0039] At least some embodiments of the present invention find industrialapplication in harvesting solar energy.ACRONYMS LISTAOD argon oxygen decarburisationEAF electric arc furnaceHIT heterojunction with intrinsic thin-layerIBC interdigitated back contactLF ladle furnacePERC passivated emitter rear contactPERL passivated emitter rear locally-diffusedPERT passivated emitter rear totally diffusedREFERENCE SIGNS LIST110 Solar panel120 Primary irradiance130 Secondary irradiance210 layer of granular slag material220 water-impermeable barrier310 centre point320 distance330 distance

Claims

CLAIMS:

1. A system comprising:^ at least one energy harvesting device configured to harvest radiative energy from twoopposite sides of the respective energy harvesting device; ^a layer of a granular slag material comprising at least 70% of calcium oxide and / orsilicon dioxide between the at least one energy harvesting device and ground,whereby solar radiance to a side of each energy harvesting device not facing direct sunlight is affected by reflection from the granular slag material, and whereby carbondioxide is captured from the atmosphere by reacting with calcium oxide comprised in the granular slag material.

2. The system according to claim 1, wherein the granular slag material is stainless steel slag.

3. The system according to claim 1 or 2, wherein the at least one energy harvesting devicecomprises at least one bifacial solar panel and / or at least one solar water heater.

4. The system according to any of claims 1 – 3, further comprising a water-impermeablebarrier between the ground and the layer of the granular slag material.

5. The system according to claim 4, wherein the water-impermeable barrier is has a sloped arrangement to convey rainwater from the granular slag material.

6. The system according to any of claims 1 – 5, wherein the granular slag material has anaverage granule diameter in the range of 0,1 to 6 centimetres.

7. The system according to any of claims 1 – 6, wherein each one of the at least one energyharvesting device has a centre point at least 0,5 metres above the layer of the granular slag material.

8. The system according to any of claims 1 – 7, wherein the at least one energy harvestingdevice comprises plural of the energy harvesting devices and wherein neighbouring energyharvesting devices are separated from each other by a distance within the range of 0,5 to 2metres.

9. The system according to any of claims 1 – 8, wherein the layer of the granular slag materialis at least 10 centimetres thick.

10. The system according to any of claims 1 – 9, wherein the granular slag material has ahigher reflectance than grass and the reflection of the granular slag material affects the solar radiance to the side of each energy harvesting device not facing direct sunlight by increasing the solar radiance.

11. A method comprising obtaining energy from sunlight using a system according to oneof claims 1 – 10.

12. A building comprising a roof whereon a system according to one of claims 1 – 10 isinstalled.

Images