This article reviews current knowledge and recent advances in the development of solar-powered aircraft.
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A key development in the field of solar-powered aircraft flight took place when test flights of the Airbus Zephyr aircraft were completed, which remained in the air for a week, providing internet to people.
History of solar aviation
During the energy crisis of the 1970s, solar energy via photovoltaic panels was identified as an alternative energy source for humanity. Solar-powered airplanes have recently piqued the curiosity of the general public and the aviation industry due to their use as an environmentally friendly alternative.
Sunrise, the world’s first solar-powered airplane, took flight in 1974. Solar-powered airplanes have come a long way since then. Solar-powered airplanes, unlike ordinary airplanes, capture solar irradiance and convert it into electrical energy using photovoltaic panels.
Preference of solar-powered planes over traditional planes
Due to the inexhaustible supply of solar electricity, solar-powered aircraft have significant potential for High Altitude Long Endurance (HALE) missions. Solar-powered planes can be built to fly near space; i.e. just above the atmospheric flight region but below the spacecraft flight region (about 20-100 km).
They can sail perpetually for an extended period of time, even years, depending on the durability of the aircraft system and sunlight conditions, which conventional aircraft cannot achieve due to their operational limitations. Another major benefit is the massive reduction in emissions, with almost 80% less carbon emissions than a traditional aircraft.
Working mechanisms
The main idea is to cover a certain region of the plane with solar cells, often the wings and the tail. When exposed to sunlight, photovoltaic panels convert it into electrical energy. The amount of energy generated is determined by factors such as the orientation of the panels to the sun and the intensity of the sunlight.
A circuit with a configurable microprocessor manages the power transmission output. The electricity regulation and transmission mechanism guarantees maximum energy yield from the solar panels. The electricity produced is mainly used to propel the aircraft and on-board electronics. The excess energy is used to recharge the batteries which are used in the absence of low sunlight.
AIRBUS – ZEPHYR S | solar electric uav
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Advances in solar-powered aircraft
Photovoltaic (PV) cells, concentrated solar power (CSP), and solar thermal collectors for heating and cooling (SHC) are three main technologies used for solar energy applications. Photovoltaic technology is widely recognized as a means of generating electricity by using photovoltaic panels consisting of an array of solar cells to transform solar energy into a flow of electrons. The initial practical application of this technology was to power communications satellites and spacecraft.
Solar battery development patterns over the past century have been driven by additional energy storage needs and portable gadgets. Batteries with improved energy densities of 400 to 600 Wh/kg and more than 500 cycles at standard grade recharge rates are now available through technological improvement.
Solar fuel cells were created to generate power in stationary systems, much like other competing technological approaches. Current research and development efforts are focused on creating reliable, low cost, high performance fuel cell array elements for automotive applications.
Technological developments are rapidly being made to improve and expand the applicability of solar aviation. Organic photovoltaics and quantum dots are essential in this regard. Organic photovoltaics (OPVs) are made from diverse and adaptable organic materials, offering unlimited possibilities for enhancing a wide variety of functionalities. Organic molecules are inexpensive; they have excellent light absorption capacity, allowing coatings as thin as several hundred nm to be used for this purpose.
Quantum dots have the potential to improve the conversion efficiency of solar cells in at least two ways: by widening the energy gap of solar panels to collect more sunlight in the spectral region, and by producing more voltage from a single solar particle. Solar cells built on quantum dots could potentially transform more than 65% of the sun’s energy into electrical energy, increasing efficiency nearly twice.
Nanomaterials are also considered essential in this regard. Nanomaterials like nanowires and nanoparticles offer new potential in solar devices. Nano-sized objects have very high surface areas per unit volume, allowing the formation of very large interfacial regions.
Recent news
Zephyr, an Airbus photovoltaic unmanned aerial vehicle (UAV), was used to transmit wireless broadband during a flight test over Arizona. Airbus was evaluating the ‘High Altitude Platform Station’ (HAPS) aboard the British-built drone during an 18-day journey into the stratosphere, 76,100ft above the earth’s surface.
The successful test could lay the groundwork for a squadron of Zephyr aircraft to bring 5G and 6G mobile broadband to the world’s most remote locations, or to provide a rapid boost in transmission during a significant event in an area very populated. Capitalizing on this, the South Korean government has also approved work on a similar type of solar-powered drone.
Future challenges and prospects
Solar energy has the potential to be an important component of a potential carbon-free energy sector in aerospace. The Solar Impulse program revealed the ambition to create a new solar-powered aircraft capable of performing some of the activities normally performed by satellite.
However, scientific developments and innovations are needed to overcome the low efficiency and high cost of current systems. Keeping in mind that the generation of a solar panel fluctuates with temperature and humidity, a maximum power point tracker (MPPT) is usually needed to maximize the use of solar insolation.
Interview: Survival of microbiota on photovoltaic panel materials
Most energy conversion systems can waste energy; for example, the overall energy utilization rate of solar-powered aircraft is only 11%, implying that about 89% of solar irradiance is wasted. All current research focuses on increasing energy production and reducing its waste through the manufacture of efficient solar cells.
The updraft is an important environmental resource that is being researched. Solar-powered aircraft can reach great heights while expending little energy following an updraft. To save energy, the SoLong solar plane was piloted remotely and reached a considerable height by chasing an updraft.
In short, since the first solar-powered aerial flight in 1974, the solar-powered aviation industry has grown to meet cost and power demands while maximizing aerodynamic efficiency to perform missions effectively. Photovoltaic aircraft fly at higher altitudes for long periods of time, but with relatively limited applications, such as tiny wing loading for cargo. Subsystems such as energy, aerodynamics, propulsion systems and control mechanisms must be thoroughly researched to improve their performance and expand their range of applications.
Further reading
Jamshed, W. et al., 2021. Optimizing Thermal Expansion in Solar Airplanes Using Tangent Hyperbolic Hybrid Nanofluid: A Solar Thermal Application. Journal of Materials Research and Technology, pages 985-1006. 14(1). Available at: https://doi.org/10.1016/j.jmrt.2021.06.031
Loughran, J., 2021. Solar-powered planes flew for almost three weeks without landing. [Online]
Available at: https://eandt.theiet.org/content/articles/2021/10/solar-powered-aircraft-flyn-for-nearly-three-weeks-without-landing/
[Accessed 5 January 2022].
R Güntürkün, R. & ÇINAR, S., 2021. Use of alternative energies in aircraft. International Journal of Energy Applications and Technologies, 8(4), p. 222-227. Available at: https://dergipark.org.tr/en/pub/ijeat/issue/66272/1033611
Wu, M., Shi, Z., Xiao, T. & Ang, H., 2021. Effect of wingtip connection on flight energy and endurance performance of solar-powered aircraft. Aerospace Science and Technology, Volume 108. 106404. Available at: https://doi.org/10.1016/j.ast.2020.106404
