In the past few years, solar panels have made vast improvements in terms of costs and efficiency so that nowadays many homes can afford to install them on rooftops and save money. However, when the sky is overcast or other circumstances prevent sunlight from reaching the surface of the earth, this otherwise valuable energy source cannot be harnessed properly.
Now (2020), a way to circumvent the intermittency of solar energy has been found by harvesting invisible ultraviolet light that is always present regardless of the weather. A student at Mapua University in Manila has created an innovative design for walls and windows that might enable the use of buildings as “vertical solar farms”. The innovative system is called AuREUS, and has won the Sustainability Award of the James Dyson Award 2020. It employs upcycled crop waste to absorb stray UV light from sunlight and transforms it into renewable electricity. The designer, Carvey Ehren Maigue, drew his inspiration from the natural light display called the Aurora Lights. Instead of using conventional PV cells and producing electricity directly from UV light, the system first degrades solar wind radiation to low-energy lights and then captures the photons. The captured visible light is then converted to direct current electricity. Regulating circuits are used to control the voltage output, facilitating battery charging, storage, or the direct utilisation of electricity. At first, quantum dot technology was chosen as a suitable candidate for light degradation, but proved to be too costly and would take a long time to launch onto the market. By chance, inspiration came to Carvey Maigue in the form of glowing neon plates when exposed to blacklight. In 2019 he wrote a full academic thesis and designed several prototypes proving that the concept was feasible. In 2020, the possibility of using local fruit and vegetable dyes as key particles for the design was researched, with 78 types of local crops having been tested and 9 having shown high potential.
There are two AuREUS devices, Borealis Solar Window and Astralis Solar Wall, which use the same principle derived from the phenomenon that governs the northern and southern lights where high energy particles are absorbed by luminescent particles and re-emitted as visible light. A similar type of luminescent particles (produced from certain fruits and vegetables) was suspended in a resin substrate and used as the core technology on both devices. When exposed to UV light, the particles absorb and re-emit visible light along the edges due to internal reflectance. PV cells are placed along the edges to capture the visible light emitted.
Research for harnessing UV light as an energy source seems to have mainly been carried out in the field of PV solar cells, so far. In 2010, a team of scientists created a prototype of a new type of photovoltaic (PV) cell that generated electricity from visible, infrared and ultraviolet light with the aim of developing a highly-efficient PV cell, without needing multijunction cells. The team constructed a 10 mm square PV cell consisting of elements such as manganese (Mn) or cobalt (Co) and the transparent semiconductor material gallium nitride (GaN). After the elements had been added, the absorption coefficient of GaN was higher, enabling a much wider spectrum of light to be absorbed, including infrared, visible and ultraviolet light.
In 2016, scientists were able to produce photo induced motion (photomotility) in monolithic polymer films made from azobenzene-functionalized liquid crystalline polymer networks (azo-LCNs). Leveraging the twisted-nematic orientation, irradiation with broad spectrum ultraviolet–visible light (320–500 nm) transformed the films from flat sheets to spiral ribbons, which subsequently travelled large distances with continuous irradiation on an arbitrary surface. The motion was the result of a complex interplay of photochemistry and mechanics.
In 2019, a team of Korean scientists succeeded in developing hybrid flexible copper indium gallium selenide (CIGS) thin-film solar cells that could transform all ultraviolet, visible and infrared sunlight into electric energy. The researchers created CsPbBr3 perovskite high-efficiency fluorescents that were able to light up visible light bands by absorbing the light in the ultraviolet region and applied them to the transparent photoelectric layer of CIGS solar cells. The result was CIGS-perovskite hybrid flexible thin-film solar cells that could transform various kinds of sunlight, which included not only visible and infrared light, but also ultraviolet light, into electricity.
The advantages of harnessing UV light as an energy source are the following: it enables better access to solar energy, which supports climate change mitigation as well as the local agriculture industry through upcycling crops that would otherwise be utilised. As with aurora lights, where high energy rays (gamma, UV) are degraded to low energy states (visible light) by luminescent particles in the atmosphere, the technology uses particles which can transform UV light in a similar way. Buildings covered on all sides with AuREUS can be turned into vertical solar farms. AuREUS even works when not directly facing the sun as it can harness UV scattering through clouds as well as UV light bouncing along walls, pavements, other buildings. This is highly applicable for skyscrapers in urban settings. As opposed to glass cladding on buildings that use special films which reflect UV away from the building, AuREUS absorbs UV light, protecting people both indoors and outdoors.
The next step will be to launch a pilot project using the UV panels on a larger scale. The first installation will be at a small medical clinic on the remote island of Jomalig, a four-hour boat ride from the Philippine mainland. Carvey Maigue hopes that in future the fibre will also be used in many other applications, as the resin can be processed to create power-generating fabrics, for example. This, along with putting UV-harnessing panels in windows and walls, may prove a valuable contribution to increasing people’s awareness for the potential of renewable energy.