Engineering is at the forefront of the search for new products for a more sustainable world. Renewable energy is key, with electricity generation being responsible for 42.5% of CO2 emissions worldwide. Solar glass is amongst those new technologies, developed as an alternative to existing solar panels which offer a relatively poor output relative to the space they require. Solar glass belongs to the building-integrated photovoltaic technology, which aims to replace traditional construction materials with products that generate energy. Solar glass can potentially be used as roof tiles, windows in houses and workplaces, car sunroofs, or even in cell phones in order to generate electricity. The technology is already a key element of the building industry’s pledge to carbon neutral buildings. For example, the Museum of London, advised by Arup’s sustainability experts, in its endeavour to achieve an outstanding BREEAM rating for its new home (the old Smithfield’s Market), counts 236 sqm of photovoltaic panels on the roof as one of the key drivers.

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Mono-crystalline and polycrystalline solar panels

Currently, two kinds of solar panels are produced, mono-crystalline and polycrystalline [1].  Different carbon footprints apply to each category. Mono-crystalline solar panels feature a distinctive black colour and are related to the glossy, modern appearance of high-end solar panels.  Silicon is also used to make polycrystalline solar cells. The production procedure is different. Polycrystalline modules are made by fusing silicon crystals collectively, as opposed to being derived from a silicon block. It consumes a lot of energy to do this. As a result, the emissions produced during this operation must be taken into account when calculating the solar carbon footprint.

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Relative carbon footprint and cost of made in Europe vs made in China

The research team concluded that European-made goods had the lowest carbon footprint when taking into account CO2 emissions from the production, shipping, and use of solar modules as compared to China and Germany.  Compared to modules imported from China, CO2 emissions from PV modules made in the EU are reduced by 40%. While the energy needed to manufacture the solar modules accounts for between 50 and 63% of total CO2 emissions. the emissions that occur from shipping the PV modules from China to Europe only make up around 3% of those emissions. Statistical estimations by the Fraunhofer ISE, glass-glass PV modules produced in the EU have 420 kg of CO2 equivalents per kW of output and 480 kg of CO2 equivalents per kW of output for EU-made glass-backsheet solar modules. The researchers calculated values of 520 and 580 kg of CO2 equivalents per kW of electricity respectively for industries in Germany. In comparison, 750 kg of CO2 equivalents are created for every kW of electricity when PV modules are made in China. The fact that glass-glass solar modules don't need an aluminium frame account for their higher pricing. Additionally, compared to their glass-film equivalents, glass-glass PV panels have a higher operational lifespan and are prone to less deterioration, which also reduces their carbon impact. According to the researchers, glass-glass module generates 22 to 27 % lower CO2 emissions per kWh than the glass-backsheet module. Large portions of PV manufacturing have recently moved from Europe to China. China generated 71% of the solar modules, 68% of the world's polysilicon, 76% of the solar cells and 96% of the wafers in 2019 [2].

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Figure 3: Glass-Backsheet vs Glass-Glass PV Module [2]

It should therefore be encouraged to build PV manufacturing chain in Europe due to the reduced CO2 emissions and the continued rise in demand for more environmentally friendly PV modules globally.

According to market research firm PV InfoLink, quotations for PV glass increased throughout November and December 2020 to approach a price of $6.64/m2, with some small-scale vendors even proposing rates as high as $7.72/m2. In Europe, there have been around 200% more PV patent applications in the last 10 years, especially those for solar glass. Chinese industries names such as Flat Group, Xinyi Solar, Caihong Group, CSG Holdings and CNBM appear to be driving the hunt to move solar PV glass into mass manufacturing and commercialisation. The rise of Chinese patents and engagement in solar glass might be justified by the ‘Made in China 2025’ policy which has designated 10 technological sectors that it aims to foster activity and development in for local enterprises, which includes PV and solar glass specifically. Aside from pandemic related supply inefficiencies problems, solar glass is still not technically mature since suppliers cannot yet guarantee the technology's efficacy, which would then gain more investments and lower its cost to an economically viable level. 

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Key players and technologies

The top supplier of solar glass for structures is Onyx Solar well-known Spanish corporation founded in 2009[3]. It has completed over 70 projects in 25 nations while winning 30 top awards globally. They have constructed the world's first walkable solar pavement. Platio follows suit and manufactured solar pavers, which weigh 8.6 kg and are solar tiles used to create pavements and run them at safer lower voltages having a power output of 186 W per square meter. They are constructed up of a layer of composite recycled polymer, anti-slipping reinforced laminated glass and solar cell array.

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Figure 1: Walkable Solar Pavement [4]

In order to capture light from the sun and transform it into electricity, Onyx Solar employs PV glass as a construction material. These panels are constructed of sheets of heat-treated reinforced glass that may maintain the same acoustic and thermal insulation as traditional structural glass while still allowing for the same amount of ambient light transmission as standard glass. These solar glass panels filter radiation from both the UV (up to 99%) and infrared (up to 95%) spectrum [5]. As a result, photovoltaic glass panes are a better alternative to regular glass. Furthermore, these glass panels might be added to a number of already existing structures, enhancing them from a visual and energy perspective. It allows structures to significantly increase their energy savings, cut operating and maintenance costs, and lessen their carbon footprint by offering the same thermal insulation as ordinary glass while having the ability to produce free clean power from the sunlight. There are currently two commercially available varieties of solar glass. The first category is a long-standing class of thin-film PV modules that are mostly orange in colour and are therefore are only up to 20% transparent since they are constructed of amorphous silicon. The second form of solar panel has a black appearance and came up with 50% transparency. It could be placed in walls, roofs, terraces, or other places in addition to regular windows. Companies including clean-tech Poly solar which is an England-based firm are working on another new form of PV solar glass having organic polymer technology that, based on the angle of placing, might function with as little as 10% sunlight [6]. New Energy Technologies, a united states firm, has invented an almost transparent photovoltaic fluid that can be applied to any clear surface. Transparent Luminescent Solar Concentrators (TLSC) are used to filter invisible UV and infrared energy to accomplish this liquid that uses the principle of total internal reflection[5]. 

Figure 2: Transparent Luminescent Solar Concentrators [7]

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The industry is anticipated to have potential growth because of the increasing trends for renewable energy, nevertheless the global solar PV glass market has not yet reached its full potential. The United States alone have between 5 and 7 billion square meter of glass exterior in different forms at present, which, when combined with solar panel technology, could possibly meet around 40% yearly energy requirements [8]. Overall, the sector is moving forward positively, with design teams and experts aiming to maximise energy efficiency in buildings to produce clean electricity locally and eventually reduce the carbon footprint of the structure. Additionally, the appropriate regulations have been implemented to achieve the global objectives for reducing greenhouse gas emissions and energy consumption.

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References

[1] Inc. Cool Effect, “Carbon Footprint of Solar Panel Manufacturing | Cool Effect,” Jun. 01, 2021. https://www.cooleffect.org/solar-carbon-footprint (accessed Oct. 02, 2022).

[2] Sandra Enkhardt, “Frameless glass-glass solar modules made in Europe have the best CO2 footprint,” PV magazine International, Sep. 24, 2021. https://www.pv-magazine.com/2021/09/24/frameless-glass-glass-solar-modules-made-in-europe-have-the-best-co2-footprint-fraunhofer-ise-says/ (accessed Oct. 02, 2022).

[3] Onyx Solar, “Onyx Solar - Photovoltaic Glass for Buildings,” 2022. https://www.onyxsolar.com/ (accessed Oct. 02, 2022).

[4] Emiliano Bellini, “Solar pavement for outdoor applications – pv magazine International,” Apr. 23, 2020. https://www.pv-magazine.com/2020/04/23/solar-pavement-for-outdoor-applications/ (accessed Nov. 05, 2022).

[5] I’MNOVATION, “Solar glass: a clean and transparent energy ,” 2022. https://www.imnovation-hub.com/energy/solar-glass-a-window-to-the-future-of-energy/?_adin=02021864894 (accessed Oct. 02, 2022).

[6] Analysis, “The state of solar glass - Power Technology,” Feb. 02, 2021. https://www.power-technology.com/analysis/the-state-of-solar-glass/ (accessed Oct. 02, 2022).

[7] Dricus De Rooij, “Luminescent Solar Concentrator Cells,” 2022. https://sinovoltaics.com/learning-center/solar-cells/luminescent-solar-concentrator-cells/ (accessed Nov. 05, 2022).

[8] Laura Rodríguez, “Solar glass buildings: Greatest achievable idea or science-fiction? — RatedPower,” Apr. 14, 2021. https://ratedpower.com/blog/solar-glass-buildings/ (accessed Oct. 02, 2022).

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