Total energy in the world from the use of automotive, transportation and industry is about 16,000 GW4 of the average rate of energy, which is an enormous amount of energy consumption. Therefore, to reduce the emission of environmental pollution of fossil energy use, finding alternative energy sources that are environmentally friendly is essential. Solar energy is an energy source that has ample potential for the demand. If considering the efficiency of solar cell at 10% and using only 1 – 2% of the overall land area with solar panel, we still have many times more than we need to power the whole world. Since the technology of solar cells that are prevalent today is opaque solar cells produced from silicon semiconductors, a major problem of installing opaque solar panels is that the large area used to install the sufficient solar panel. The area of the solar panel installation must be a large open space, such as installing solar panels on the land area, or installing a solar rooftop. The most of installation position of solar panels on the ground or solar farms are often far from where of the actually use, that is resulting in losses in energy delivery. In addition, the installation of a solar farm may also be a threat to the use of agricultural or forest areas. And also, the installation of solar panel on the roof is not fully utilized from the surface of the building.
Transparent solar cell technology can be applied to all kinds of glass products. Therefore, it is a technology that has eliminated the limitations of installation area of traditional solar cell. Transparent solar cells can be installed with building glass, windshield of the automotive, smart mobile screen, tablet or watch. If various buildings in large cities are installed with transparent solar cells on all glass surfaces, the building will become a small power plan, which can be used to produce electricity for use in the building itself or share on the power grid. The electricity produced from the automobile glass that is a transparent solar cell can be used to lighten the load of the engine, which may help increase the mileage for several kilometers. Transparent solar cells on the screen will allow us to use mobile devices, smart phones, tablets or watches for longer during the day. And for the effects of solar farms on agricultural areas, we can also apply transparent solar cells to create greenhouses to grow plants as well.
A transparent solar cell is a glass coating technology with dye-sensitize solar cells that aims to optimize both the transmission of visible light while maximizing the wavelength selective absorption of ultraviolet (UV) and near-infrared (NIR) light spectrum for power conversion (As shown in Figure 1). Therefore, the transparent solar cells act as both glass windows and solar cell to generate electricity at the same time.
Transparent solar cells are classified into 2 types; Non-wavelength selective technologies absorb a broad solar spectrum including visible light and realize limited average visible transmission (AVT) between 0 to 50% or wavelength selective approaches according to how visible light is absorbed which achieve 50 to 90% AVT.
Table 1 below summarises each transparent solar cell based on the method of fabrication. Screen-printing
Dye-Sensitized Solar Cells (DSSC), electrophoretic deposition (EPD) and dip-coating are all methods of depositing a thin film of titanium dioxide (TiO2) on Fluorine doped tin oxide/Indium-doped tin oxide (FTO/ITO) glass. With screen printing, the transparency is controlled by the screen mesh design. For the transparent solar cell that can select wavelength, it has lower efficiency such as near-infrared organic photovoltaic (OPV) which focused on absorbing the UV and NIR light spectrum and transmitting visible light through the structure, Transparent luminescent solar cells (TLSC), Polymer solar cells have the heterojunction structure of an NIR polymer material and PCBM. Semi-transparent solar cells are suitable for applications that require low transparency, such as Quantum Dot Solar cell, Perovskite and Tandem Semi-transparent Perovskite.
Table 1 comparisons between different TPV based on process.1
Although the transparent solar cells have passed through the limitations the installation area of the former solar cells that are opaque, but theirs actual efficiency is still very low. Therefore, this very low in efficiency is an important factor that still cannot be used of the transparent solar cell in the commercial use. More than 80% of transparent solar cells technologies are still under development and need more improvements in order to be compatible with market PVs such as the following innovators;Brite Solar – are offering with the goal of changing greenhouse agriculture, Onyx Solar – offers fully customizable solar glass in stunning architectural designs that can be chose specific colors, shapes and transparency percentages, Physee – produces the PowerWindow, which sidesteps the difficulty of creating transparent solar cells by simply placing nontransparent solar paneling around the perimeter of the window. The PowerWindow allows users to charge devices directly from a USB on the window, and the system can be accessed with an app, which reports on the performance of each window and constantly monitors outside weather conditions and adapts accordingly, and Ubiquitous Energy – founded by MIT grads, aims to research and develop transparent solar cells as the thin, plastic-like material that can be placed on a window. It is expected for this technology to be ready for small applications such as electronic devices in the coming 5 years 2 Thus far, Ubiquitous Energy has succeeded at achieving 90 percent transparency with 10 percent efficiency, all in a film less than one-thousandth of a millimeter thick. 3
Pachern Jansa (Asst.Prof.) – School of Engineering, Sripatum University
1 Alaa A.F. Husain et. all “A review of transparent solar photovoltaic technologies”. Renewable and Sustainable Energy Reviews vol.94 (2018) pp.779–791
2 Edgar A. Gunther “Making PV transparent: The ultimate BIPV solution?”. Retrieved from: https://www.pv-tech.org/editors-blog/making-pv-transparent-the-ultimate-bipv-solution
3 Mona Bushnell “How Transparent Solar Panels Affect Construction Companies”. (2018) Retrieved from: https://www.business.com/articles/transparent-solar-windows-construction/
4 Richard Lunt “See-Through Solar Harvesting Surfaces”. (2015) Retrieved from: https://www.youtube.com/watch?v=5Vx59VLc98E&t=113s