Exploring the Concept of a Solar-Powered Airbus Passenger Plane (Honey Stream): A Revolutionary Approach to Sustainable Aviation

This article delves into the innovative concept of a solar-powered Airbus passenger plane, featuring an outer body entirely covered in solar cells. With a growing emphasis on sustainability in the aviation industry, this concept presents a potential solution to reduce carbon emissions and dependence on fossil fuels. The article examines the advantages and challenges associated with this groundbreaking idea, including the potential for increased energy efficiency, reduced operating costs, and environmental benefits. Additionally, it explores the technological advancements required to implement such a design, including the integration of solar cells into the aircraft’s structure and the management of power distribution. By shedding light on this concept, the article aims to contribute to the ongoing discussions surrounding sustainable aviation and inspire further research and development in this promising field.

Figure 1. Schematic of an Airbus air-plane whose entire outer body is completely covered with solar cells.

Keywords: Airbus passenger planes, Solar cell, Renewable energy, Airport compatibility, Airbus, Airplane, Solar Airplane, Technological complexities, advanced technology, High-tech

The concept of a solar-powered Airbus passenger plane, with its entire outer body covered in solar cells, represents a significant leap towards sustainable aviation. This essay explores the potential of such an aircraft, highlighting its benefits, challenges, and the implications it holds for the future of air travel. Airbus passenger planes, like any other aircraft, have their own set of disadvantages. While Airbus is a renowned manufacturer known for its innovative designs and advanced technology, it is important to consider the potential drawbacks. Here are some disadvantages associated with Airbus passenger planes:

1.   Size & capacity limitations

Airbus planes, particularly the smaller models, may have limitations in terms of passenger capacity compared to their counterparts. This can be a disadvantage for airlines that require larger seating capacities or for routes with high passenger demand.

2.    Higher operating costs

Airbus planes are often equipped with advanced technology and features, which can result in higher operating costs. These costs include maintenance, fuel consumption, and training for pilots and maintenance personnel. Airlines need to carefully consider these factors when choosing Airbus planes for their fleet.

3.   Limited airport compatibility

Some Airbus models, such as the A380, require specific infrastructure and modifications at airports to accommodate their size and unique features. This can limit the number of airports that can handle these planes, potentially restricting route options for airlines.

4.  Longer takeoff and landing distances

Due to their larger size and weight, Airbus planes may require longer runways for takeoff and landing compared to smaller This can be a disadvantage for airports with shorter runways or         those    located in         areas with geographical constraints.

5.   Higher initial investment

Airbus planes generally come with a higher price tag compared to other aircraft manufacturers. This can pose a financial challenge for airlines, especially smaller or budget carriers, when considering fleet expansion or replacement.

6. Potential for technological complexities

With advanced technology comes the potential for increased  Airbus planes incorporate sophisticated systems and automation, which may require additional training and expertise for pilots and maintenance crews. This can lead to higher training costs and potential challenges in adapting to new technologies.

Figure 2. Schematic of an air-plane whose entire outer body is completely covered with solar cells.

It is important to note that these disadvantages may vary depending on the specific model and airline requirements. Despite these drawbacks, Airbus passenger planes continue to be a popular choice for many airlines worldwide, offering a range of benefits and features that cater to different operational needs.

The necessity of using clean energy, particularly solar energy, has become increasingly evident in our efforts to combat climate change and transition towards a sustainable future. The Paris Agreement, a landmark international accord, highlights the urgency of limiting the use of carbon energy by 2030. Here’s why:

1. Mitigating climate change: The use of clean energy sources, such as solar energy, is crucial in reducing greenhouse gas emissions. Carbon energy, such as fossil fuels, releases significant amounts of carbon dioxide into the atmosphere, contributing to global warming and climate change. By transitioning to clean energy, we can significantly reduce our carbon footprint and mitigate the adverse effects of climate
2. Renewable and abundant: Solar energy is a renewable resource that harnesses the power of the sun, which is an abundant and virtually limitless source of Unlike carbon energy, which is finite and depleting, solar energy offers a sustainable solution that can meet our energy needs without harming the environment or compromising future generations’ access to energy.
3. Energy independence and security: Relying on carbon energy sources often involves importing fossil fuels from other countries, which can create geopolitical tensions and energy security concerns. By embracing clean energy, particularly solar power, nations can reduce their dependence on foreign energy sources and achieve greater energy This enhances national security and reduces vulnerability to price fluctuations and supply disruptions.
4. Economic opportunities and job creation: The transition to clean energy presents significant economic opportunities. Investing in solar energy infrastructure and technologies can stimulate economic growth, create jobs, and foster The renewable energy sector has the potential to generate employment across various skill levels, from manufacturing and installation to research and development.
5. Health benefits: The use of carbon energy sources, such as coal and oil, is associated with air pollution and adverse health by shifting to clean energy, we can improve air quality, reduce respiratory illnesses, and enhance overall public health. This transition can lead to a healthier and more sustainable living environment for communities worldwide.

Figure 3. Schematic of an air-plane whose entire outer body is completely covered with solar cells

Solar energy: Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy including solar water heating, and solar architecture. It is an essential source of renewable energy, and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power, and solar water heating to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light- dispersing properties, and designing spaces that naturally circulate air. The large magnitude of solar energy available makes it a highly appealing source of electricity. Solar energy has been cheaper than fossil fuels since 2021. In 2011, the International Energy Agency said that “the development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible, and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating global warming… These advantages are global.”

Potential: Average insolation. The theoretical area of the small black dots is sufficient to supply the world’s total energy needs of 18 TW with solar power. The Earth receives 174 peta- watts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth’s surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. Most of the world’s population live in areas with insolation levels of 150–300 watts/m2, or 3.5–7.0 kWh/m2 per day.

Figure4. Schematic of an airplane whose entire outer body is completely covered with solar cells.

Solar radiation is absorbed by the Earth’s land surface, oceans – which cover about 71% of the globe – and atmosphere. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth’s surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anticyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis, green plants convert solar energy into chemically stored energy, which produces food, wood and the biomass from which fossil fuels are derived.

The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth’s non-renewable resources of coal, oil, natural gas, and mined uranium combined.

The potential solar energy that could be used by humans differs from the amount of solar energy present near the surface of the planet because factors such as geography, time variation, cloud cover, and the land available to humans limit the amount of solar energy that we can acquire. In 2021, Carbon Tracker Initiative estimated the land area needed to generate all our energy from solar alone was 450,000 km2- or about the same as the area of Sweden, or the area of Morocco, or the area of California (0.3% of the Earth’s total land area).

Geography affects solar energy potential because areas that are closer to the equator have a higher amount of solar radiation. However, the use of photovoltaics that can follow the position of the Sun can significantly increase the solar energy potential in areas that are farther from the equator. Time variation effects the potential of solar energy because during the nighttime, there is little solar radiation on the surface of the Earth for solar panels to absorb. This limits the amount of energy that solar panels can absorb in one day. Cloud cover can affect the potential of solar panels because clouds block incoming light from the Sun and reduce the light available for solar cells. Besides, land availability has a large effect on the available solar energy because solar panels can only be set up on land that is otherwise unused and suitable for solar panels. Roofs are a suitable place for solar cells, as many people have discovered that they can collect energy directly from their homes this way. Other areas that are suitable for solar cells are lands that are not being used for businesses where solar plants can be established.

Solar technologies are characterized as either passive or active depending on the way they capture, convert and distribute sunlight and enable solar energy to be harnessed at different levels around the world, mostly depending on the distance from the equator. Although solar energy refers primarily to the use of solar radiation for practical ends, all renewable energies, other than geothermal power and Tidal power, derive their energy either directly or indirectly from the Sun.

Active solar techniques use photovoltaics, concentrated solar power, solar thermal collectors, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand-side technologies.

In 2000, the United Nations Development Program, UN Department of Economic and Social Affairs, and World Energy Council published an estimate of the potential solar energy that could be used by humans each year that took into account factors such as insolation, cloud cover, and the land that is usable by humans. The estimate found that solar energy has a global potential of 1,600 to 49,800 exa-joules (4.4×1014 to 1.4×1016 kWh) per year.

Figure 5. Schematic of an airplane whose entire outer body is completely covered with solar cells.

Solar energy developments

Experimental solar power: Concentrated photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the

purpose of electricity generation. Thermoelectric, or “thermo- voltaic” devices convert a temperature difference between dissimilar materials into an electric current.

Floating solar arrays: Floating solar arrays are PV systems that float on the surface of drinking water reservoirs, quarry lakes, irrigation canals or remediation and tailing ponds. A small number of such systems exist in France, India, Japan, South Korea, the United Kingdom, Singapore, and the United States. The systems are said to have advantages over photovoltaics on land. The cost of land is more expensive, and there are fewer rules and regulations for structures built on bodies of water not used for recreation. Unlike most land-based solar plants, floating arrays can be unobtrusive because they are hidden from public view. They achieve higher efficiencies than PV panels on land, because water cools the panels. The panels have a special coating to prevent rust or corrosion. In May 2008, the Far Niente Winery in Oakville, California, pioneered the world’s first floatovoltaic system by installing 994 solar PV modules with a total capacity of 477 kW onto 130 pontoons and floating them on the winery’s irrigation pond. Utility-scale floating PV farms are starting to be built. Kyocera will develop the world’s largest, a 13.4 MW farm on the reservoir above   Yamakura   Dam    in Chiba Prefecture using 50,000 solar panels. Salt-water resistant floating farms are also being constructed for ocean use. The largest so far announced floatovoltaic project is a 350 MW power station in the Amazon region of Brazil.

Perovskite solar cells

A perovskite solar cell (PSC) is a type of solar cell which includes a perovskite-structured compound, most commonly a hybrid organic- inorganic lead or tin halide-based material, as the light-harvesting active layer. Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture. Solar cell efficiencies of laboratory-scale devices using these materials have increased from 3.8% in 2009 to 25.7% in 2021 in single-junction architectures, and, in silicon-based tandem cells, to 29.8%, exceeding the maximum efficiency achieved in single-junction silicon solar cells. Perovskite solar cells have therefore been the fastest-advancing solar technology as of 2016. With the  potential of achieving even higher efficiencies and very low production costs, perovskite solar cells have become commercially attractive. Core problems and research subjects include their short- and long- term stability.

Figure 6. Schematic of an airplane whose entire outer body is completely covered with solar cells.

Solar-assisted heat pump

A heat pump is a device that provides heat energy from a source of heat to a destination called a “heat sink”. Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A solar-assisted heat pump represents the integration of a heat pump and thermal solar panels in a single integrated system. Typically, these two technologies are used separately (or only placing them in parallel) to produce hot water. In this system the solar thermal panel performs the function of the low temperature heat source and the heat produced is used to feed the heat pump’s evaporator. The goal of this system is to get high COP and then produce energy in a more efficient and less expensive way. It is possible to use any type of solar thermal panel (sheet and tubes, roll-bond, heat pipe, thermal plates) or hybrid (mono/polycrystalline, thin film) in combination with the heat pump. The use of a hybrid panel is preferable because it allows covering a part of the electricity demand of the heat pump and reduces the power consumption and consequently the variable costs of the system.

Solar aircraft

An electric aircraft is an aircraft that runs on electric motors rather than internal combustion engines, with electricity coming from fuel cells, solar cells, ultracapacitors, power beaming, or batteries. Currently, flying manned electric aircraft are mostly experimental demonstrators, though many small unmanned aerial vehicles are powered by batteries. Electrically powered model aircraft have been flown since the 1970s, with one report in 1957. The first man-carrying electrically powered flights were made in 1973. Between 2015 and 2016, a manned, solar- powered plane, Solar Impulse 2, completed a circumnavigation of the Earth.

Solar updraft tower

A solar updraft tower is a renewable-energy power plant for generating electricity from low- temperature solar heat. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines placed in the chimney updraft or around the chimney base to produce electricity. Plans for scaled-up versions of demonstration models will allow significant power generation and may allow the development of other applications, such as water extraction or distillation, and agriculture or horticulture. A more advanced version of a similarly themed technology is the Vortex engine which aims to replace large physical chimneys with a vortex of air created by a shorter, less-expensive structure.

Space-based solar power

For either photovoltaic or thermal systems, one option is to loft them into space, particularly geosynchronous orbit. To be competitive with Earth-based solar power systems, the specific mass (kg/kW) times the cost to loft mass plus the cost of the parts needs to be $2400 or less. I.e., for a parts cost plus rectenna of $1100/kW, the product of the $/kg and kg/kW must be

$1300/kW or less. Thus for 6.5 kg/kW, the transport cost cannot exceed $200/kg. While that will require a 100 to one reduction, SpaceX is targeting a ten to one reduction, Reaction Engines may make a 100 to one reduction possible.

Figure 7. Schematic of an air-plane whose entire outer body is completely covered with solar cells.

Artificial photosynthesis

Artificial photosynthesis uses techniques including nanotechnology to store solar electromagnetic energy in chemical bonds by splitting water to produce hydrogen and then using   carbon    dioxide    to    make methanol. Researchers in this field are striving to design molecular mimics of photosynthesis that use a wider region of the solar spectrum, employ catalytic systems made from abundant, inexpensive materials that are robust, readily repaired, non-toxic, stable in a variety of environmental conditions and perform more efficiently allowing a greater proportion of photon energy to end up in the storage compounds, i.e., carbohydrates (rather than building and sustaining living cells). However, prominent research faces hurdles, Sun Catalytix a MIT spin-off stopped scaling up their prototype fuel-cell in 2012, because it offers few savings over other ways to make hydrogen from sunlight.

Thermal energy 

Solar thermal technologies can be used for water heating, space heating, and space cooling and process heat generation.

Early commercial adaptation

In 1878, at the Universal Exposition in Paris, Augustin Mouchot successfully demonstrated a solar steam engine, but couldn’t continue development because of cheap coal and other factors. In 1897, Frank Shuman, a US inventor, engineer and solar energy pioneer built a small demonstration solar engine that worked by reflecting solar energy onto square boxes filled with ether, which has a lower boiling point than water and were fitted internally with black pipes which in turn powered a steam engine. In 1908 Shuman formed the Sun Power Company with the intent of building larger solar power plants. He, along with his technical advisor A.S.E. Ackermann and British physicist Sir Charles Vernon Boys, developed an improved system using mirrors to reflect solar energy upon collector boxes, increasing heating capacity to the extent that water could now be used instead of ether. Shuman then constructed a full-scale steam engine powered by low-pressure water, enabling him to patent the entire solar engine system by 1912.

Shuman built the world’s first solar thermal power station in Maadi, Egypt, between 1912 and 1913. His plant used parabolic troughs to power a 45–52 kilowatts (60–70 hp) engine that pumped more than 22,000 litres (4,800 imp gal; 5,800 US gal) of water per minute from the Nile River to adjacent cotton fields. Although the outbreak of World War I and the discovery of cheap oil in the 1930s discouraged the advancement of solar energy, Shuman’s vision, and basic design were resurrected in the 1970s with a new wave of interest in solar thermal energy. In 1916 Shuman was quoted in the media advocating solar energy’s utilization, saying: We have proved the commercial profit of sun power in the tropics and have more particularly proved that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the Sun.

Water heating

Solar hot water systems use sunlight to heat water. In middle geographical latitudes (between 40 degrees north and 40 degrees south), 60 to 70% of the domestic hot water use, with water temperatures up to 60 °C (140 °F), can be provided by solar heating systems. The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.

As of 2015, the total installed capacity of solar hot   water   systems   was   approximately 436 thermal gigawatts (GWth), and China is the world leader in their   deployment   with 309 GWth installed, taken up 71% of the market. Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. In the United States, Canada, and Australia, heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GWth as of 2005.

Heating, cooling and ventilation

In the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ/yr) of the energy used in commercial buildings and nearly 50% (10.1 EJ/yr) of the

energy used in residential buildings. Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy. Use of solar for heating can roughly be divided into passive    solar concepts    and active solar concepts, depending on whether active elements such as sun tracking and solar concentrator optics are used.

Thermal mass is any material that can be used to store heat—heat from the Sun in the case of solar energy. Common thermal mass materials include stone, cement, and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However, they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, day lighting, and shading conditions. When duly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment.

A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated, causing an updraft that pulls air through the building. Performance can be improved by using glazing and thermal mass materials in a way that mimics greenhouses.

Deciduous trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building in the northern hemisphere or the northern side in the southern hemisphere, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter. Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating. In climates with significant heating loads, deciduous trees should not be planted on the Equator-facing side of a building because they will interfere with winter solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain.

Electricity production

Solar power is the conversion of renewable energy from sunlight into electricity, either directly using photovoltaics (PV), indirectly using concentrated solar power, or a combination. Concentrated solar power systems use lenses or mirrors and solar tracking systems to focus a large area of sunlight into a small beam. Photovoltaic cells convert light into an electric current using the photovoltaic effect. Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. Since then, as the cost of solar electricity has fallen, grid-connected solar PV systems have grown more or less exponentially. Millions of installations and gigawatt-scale photovoltaic power stations have been and are being built. Solar PV has rapidly become an inexpensive, low-carbon technology.

The International Energy Agency said in 2021 that under its “Net Zero by 2050” scenario solar power would contribute about 20% of worldwide energy consumption, and solar would be the world’s largest source of electricity. China has the most solar installations. In 2020, solar power generated 3.5% of the world’s electricity, compared to under 3% the previous year. In 2020 the unsubsidized levelized cost of electricity for utility-scale solar power was around $36/MWh and installation cost about a dollar per DC watt.

Photovoltaics

Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially utilized for electricity generation and as photosensors.

A photovoltaic system employs solar modules, each comprising a number of solar cells, which generate electrical power. PV installations may be ground-mounted, rooftop-mounted, wall- mounted or floating. The mount may be fixed or use a solar tracker to follow the sun across the sky.

Some hope that photovoltaic technology will produce enough affordable sustainable energy to help mitigate global warming caused by CO2. Solar PV has specific advantages as an energy source: once installed, its operation generates no pollution and no greenhouse gas emissions, it shows simple scalability in respect of power needs and silicon has large availability in the Earth’s crust, although other materials required in PV system manufacture such as silver will eventually constrain further growth in the technology. Other major constraints identified are competition for land use and lack of labor in making funding applications. The use of PV as a main source requires energy storage systems or global distribution by high-voltage direct current power lines causing additional costs, and also has a number of other specific disadvantages such as unstable power generation and the requirement for power companies to compensate for too much solar power in the supply mix by having more reliable conventional power supplies in order to regulate demand peaks and potential undersupply. Production and installation do cause pollution and greenhouse gas emissions and there are no viable systems for recycling the panels once they are at the end of their lifespan after 10 to 30 years.

Photovoltaic systems have long been used in specialized applications as stand-alone installations and grid-connected PV systems have been in use since the 1990s. Photovoltaic modules were first mass-produced in 2000, when German environmentalists and the Eurosolar organization received government funding for a ten thousand roof program.

Decreasing costs has allowed PV to grow as an energy source. This has been partially driven by massive Chinese government investment in developing solar production capacity since 2000, and achieving economies of scale. Much of the price of production is from the key component polysilicon, and most of the world supply is produced in China, especially in Xinjiang. Beside the subsidies, the low prices of solar panels in the 2010s has been achieved through the low price of energy from coal and cheap labour costs in Xinjiang, as well as improvements in manufacturing technology and efficiency. Advances in technology and increased manufacturing scale have also increased the efficiency of photovoltaic installations. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries. Panel prices dropped by a factor of 4 between 2004 and 2011. Module prices dropped 90% of over the 2010s, but began increasing sharply in 2021. In 2019, worldwide installed PV capacity increased to more than 635 gigawatts (GW) covering approximately two percent of global electricity demand. After hydro and wind powers, PV is the third renewable energy source in terms of global capacity. In 2019 the International Energy Agency expected a growth by 700 – 880 GW from 2019 to 2024. In some instances, PV has offered the cheapest source of electrical power in regions with a high solar potential, with a bid for pricing as low as 0.01567 US$/kWh in Qatar in 2020.

Concentrated solar power

Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists; the most developed are the parabolic trough, the concentrating linear Fresnel reflector, the Stirling dish, and the solar power tower. Various techniques are used to track the Sun and focus light. In all of these systems, a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.

Designs need to account for the risk of a dust storm, hail, or another extreme weather event that can damage the fine glass surfaces of solar power plants. Metal grills would allow a high percentage of sunlight to enter the mirrors and solar panels while also preventing most damage.

Architecture and urban planning

Darmstadt University of Technology, Germany, won the 2007 Solar Decathlon in Washington, DC with this passive house designed for humid and hot subtropical climate. Sunlight has influenced building design since the beginning of architectural history. Advanced solar architecture and urban planning methods were first employed by the Greeks and Chinese, who oriented their buildings toward the south to provide light and warmth.

The common features of passive solar architecture are orientation relative to the Sun, compact proportion (a low surface area to volume ratio), selective shading (overhangs) and thermal mass. When these features are tailored to the local climate and environment, they can produce well-lit spaces that stay in a comfortable temperature range. Socrates’ Megaron House is a classic example of passive solar design. The most recent approaches to solar design use computer modeling tying together solar lighting, heating and ventilation systems in an integrated solar design package. Active solar equipment such as pumps, fans, and switchable windows can complement passive design and improve system performance.

Urban heat islands (UHI) are meteropolitan areas with higher temperatures than that of the surrounding environment. The higher temperatures result from increased absorption of solar energy by urban materials such as asphalt and concrete, which have lower albedos and higher heat capacities than those in the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white and to plant trees in the area. Using these methods, a hypothetical “cool communities” program in Los Angeles has projected those urban temperatures could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving estimated total annual benefits of US$530 million from reduced air-conditioning costs and healthcare savings.

Agriculture and horticulture

Agriculture and horticulture seek to optimize the capture of solar energy to optimize the productivity of plants. Techniques such as timed planting cycles, tailored row orientation, staggered heights between rows and the mixing of plant varieties can improve crop yields. While sunlight is generally considered a plentiful resource, the exceptions highlight the importance of solar energy to agriculture. During the short growing seasons of the Little Ice Age, French and English farmers employed fruit walls to maximize the collection of solar energy. These walls acted as thermal masses and accelerated ripening by keeping plants warm. Early fruit walls were built perpendicular to the ground and facing south, but over time, sloping walls were developed to make better use of sunlight. In 1699, Nicolas Fatio de Duillier even suggested using a tracking mechanism which could pivot to follow the Sun. Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure. More recently the technology has been embraced by vintners, who use the energy generated by solar panels to power grape presses.

Greenhouses convert solar light to heat, enabling year-round production and the growth (in enclosed environments) of specialty crops and other plants not naturally suited to the local climate. Primitive greenhouses were first used during Roman times to produce cucumbers year-round for the Roman emperor Tiberius. The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad. Greenhouses remain an important part of horticulture today. Plastic transparent materials have also been used to similar effect in poly- tunnels and row covers.

Transport

Development of a solar-powered car has been an engineering goal since the 1980s. The World Solar Challenge is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometers (1,877 mi) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winner’s average speed was 67 kilometers per hour (42 mph) and by 2007 the winner’s average speed had improved to 90.87 kilometers per hour (56.46 mph). The North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles. Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.

In 1975, the first practical solar boat was constructed in England. By 1995, passenger boats incorporating PV panels began appearing and are now used extensively. In 1996, Kenichi Horie made the first solar-powered crossing of the Pacific Ocean, and the Sun21 catamaran made the first solar-powered crossing of the Atlantic Ocean in the winter of 2006–2007. There were plans to circumnavigate the globe in 2010.

In 1974, the unmanned AstroFlight Sunrise airplane made the first solar flight. On 29 April 1979, the Solar Riser made the first flight in a solar-powered, fully controlled, man-carrying flying machine, reaching an altitude of 40 ft (12 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaics. This was quickly followed by the Solar Challenger which crossed the English Channel in July 1981. In 1990 Eric Scott Raymond in 21 hops flew from California to North Carolina using solar power. Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios which set the altitude record for a non- rocket-propelled aircraft at 29,524 meters (96,864 ft) in 2001. The Zephyr, developed by BAE Systems, is the latest in a line of record- breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights were envisioned by 2010. As of 2016, Solar Impulse, an electric aircraft, is currently circumnavigating the globe. It is a single-seat plane powered by solar cells and capable of taking off under its own power. The design allows the aircraft to remain airborne for several days.

A solar balloon is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands, causing an upward buoyancy force, much like an artificially heated hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high.

Fuel production

Solar chemical processes use solar energy to drive chemical reactions. These processes offset energy that would otherwise come from a fossil fuel source and can also convert solar energy into storable and transportable fuels. Solar induced chemical reactions can be divided into thermochemical or photochemical. A variety of fuels can be produced by artificial photosynthesis. The multielectron catalytic chemistry involved in making carbon-based fuels (such as methanol) from reduction of carbon dioxide is challenging; a feasible alternative is hydrogen production from protons, though use of water as the source of electrons (as plants do) requires mastering the multielectron oxidation of two water molecules to molecular oxygen. Some have envisaged working solar fuel plants in coastal meteropolitan areas by 2050 – the splitting of seawater providing hydrogen to be run through adjacent fuel-cell electric power plants and the pure water by-product going directly into the municipal water system.

Hydrogen production technologies have been a significant area of solar chemical research since the 1970s. Aside from electrolysis driven by photovoltaic or photochemical cells, several

thermochemical processes have also been explored. One such route uses concentrators to split water into oxygen and hydrogen at high temperatures (2,300–2,600 °C or 4,200–4,700°F). Another approach uses the heat from solar concentrators to drive the steam reformation of natural gas thereby increasing the overall hydrogen yield compared to conventional reforming methods. Thermochemical cycles characterized by the decomposition and regeneration of reactants present another avenue for hydrogen production. The Solzinc process under development at the Weizmann Institute of Science uses a 1 MW solar furnace to decompose zinc oxide (ZnO) at temperatures above 1,200 °C (2,200 °F). This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen.

Energy storage methods

Thermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or inter-seasonal duration. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements.

Phase change materials such as paraffin wax and Glauber’s salt are another thermal storage medium. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C or 147 °F). The “Dover House” (in Dover, Massachusetts) was the first to use a Glauber’s salt heating system, in 1948. Solar energy can also be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity, and can deliver heat at temperatures compatible with conventional power systems. The Solar Two project used this method of energy storage, allowing it to store 1.44 terajoules (400,000 kWh) in its 68 m³ storage tank with an annual storage efficiency of about 99%. Off-grid PV   systems have   traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid, while standard grid electricity can be used to meet shortfalls. Net metering programs give household systems credit for any electricity they deliver to the grid. This is handled by ‘rolling back’ the meter whenever the home produces more electricity than it consumes. If the net electricity use is below zero, the utility then rolls over the kilowatt-hour credit to the next month. Other approaches involve the use of two meters, to measure electricity consumed vs. electricity produced. This is less common due to the increased installation cost of the second meter. Most standard meters accurately measure in both directions, making a second meter unnecessary.

Pumped-storage hydroelectricity stores energy in the form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water, with the pump becoming a hydroelectric power generator.

Beginning with the surge in coal use, which accompanied the Industrial Revolution, energy consumption has steadily transitioned from wood and biomass to fossil fuels. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum.

The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world. It brought renewed attention to developing solar technologies. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan.

Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).

Commercial solar water heaters began appearing in the United States in the 1890s. These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels. As with photovoltaics, solar water heating attracted renewed attention as a result of the oil crises in the 1970s, but interest subsided in the 1980s due to falling petroleum prices. Development in the solar water heating sector progressed steadily throughout the 1990s, and annual growth rates have averaged 20% since 1999. Although generally underestimated, solar water heating and cooling is by far the most widely deployed solar technology with an estimated capacity of 154 GW as of 2007.

The International Energy Agency has said that solar energy can make considerable contributions to solving some of the most urgent problems the world now faces:

The development of affordable, inexhaustible, and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible, and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating climate change, and keep fossil fuel prices lower than otherwise. These advantages are global. Hence the additional costs of the incentives for early deployment should be considered learning investments; they must be wisely spent and need to be widely shared. In 2011, a report by the International Energy Agency found that solar energy technologies such as photovoltaics, solar hot water, and concentrated solar power could provide a third of the world’s energy by 2060 if politicians commit to limiting climate change and transitioning to renewable energy. The energy from the Sun could play a key role in de- carbonizing the global economy alongside improvements in energy efficiency and imposing costs on greenhouse gas emitters.

“The strength of solar is the incredible variety and flexibility of applications, from small scale to big scale”.

Figure 8. Schematic of the interior of an airplane whose entire outer body is completely covered with solar cells.

The Paris Agreement, signed by nearly all countries, sets a target to limit global warming to well below 2 degrees Celsius above pre- industrial levels and to pursue efforts to limit the temperature increase to 1.5 degrees Celsius. To achieve this, it is crucial to reduce carbon emissions and transition to clean energy sources by 2030. By doing so, we can align with the goals of the Paris Agreement, mitigate climate change, and create a sustainable future for generations to come.

1.   Harnessing Solar Energy

The integration of solar cells on the outer body of an Airbus passenger plane allows for the direct conversion of sunlight into electrical energy. These solar cells, also known as photovoltaic cells, capture and store solar energy, providing a renewable and clean power source for the aircraft.

2.   Advantages of Solar-Powered Flight

• Environmental Benefits

By relying solely on solar energy, the solar- powered Airbus significantly reduces its carbon footprint, as it produces zero greenhouse gas emissions during flight. This contributes to mitigating climate change and improving air quality.

• Cost Savings

Solar energy is a free and abundant resource, eliminating the need for traditional fuel sources. This translates into substantial cost savings for airlines, potentially reducing ticket prices for passengers.

• Extended Flight Range

With an infinite potential to fly on solar energy, the solar-powered Airbus can extend its flight range without the need for refueling stops. This opens up new possibilities for long-haul flights and reduces the reliance on fossil fuels.

3.   Technological Challenges

• Energy Storage

One of the main challenges of solar-powered flight is the efficient storage of excess energy generated during daylight hours. Advanced battery technologies or alternative energy storage methods need to be developed to ensure a continuous power supply during nighttime or cloudy conditions.

• Weight and Efficiency

The integration of solar cells on the entire outer body of an Airbus plane adds weight, potentially impacting its overall efficiency and performance. Innovations in lightweight materials and aerodynamic design are crucial to optimize the aircraft’s energy efficiency.

4.    Implications for the Future

• Sustainable Aviation

The     solar-powered    Airbus    represents    a significant step towards achieving sustainable aviation. It sets a precedent for the industry to prioritize renewable energy sources and reduce its environmental impact.

• Technological Advancements

The development of a solar-powered aircraft necessitates advancements in solar cell efficiency, energy storage, and lightweight materials. These advancements can have broader applications in various industries, driving innovation and progress.

• Public Perception and Adoption

The successful implementation of a solar- powered Airbus can inspire public confidence in renewable energy and encourage the adoption of sustainable practices in other sectors.

Figure 9. Schematic of the interior of an air-plane whose entire outer body is completely covered with solar cells.

The solar-powered Airbus, with its entire outer body covered in solar cells, holds immense potential for revolutionizing air travel. While there are challenges to overcome, such as energy storage and weight considerations, the benefits of reduced emissions, cost savings, and extended flight range make it a promising concept. As technology continues to advance, the solar-powered Airbus represents a significant step towards a more sustainable future in aviation.

Acknowledgement

This research was supported by “P.Z.I.R.I.G (Pourya Zarshenas International Research- Industrial Group)”, Geneva, Switzerland. We thank our colleagues, who provided insight and expertise that greatly assisted the research, although they may not agree with all of the interpretations/conclusions of this paper.

I would also like to show our gratitude to the A.C. Milligram Institute, Geneva, Switzerland for sharing their pearls of wisdom and for their laboratory and computer research facilities and artificial intelligence, as well as their financial support with me during  the course of this research,   and   we   thank   2   “anonymous” reviewers for their so-called insights.

We are also immensely grateful to Dr. Isabella Lopez, Head of the “A.C. Milligram” International Scientific Institute and Head of “Alhambra Constant” Scientific Research Group and Dr. Ji-hye Kim Head of Hanbok Enzyme Scientific Group, for their comments on an earlier version of the manuscript, although any errors are our own and should not tarnish the reputations of these esteemed persons.