Introduction

It is no secret that aircraft are gas guzzlers. They account for nearly 3% of the total C02 emissions in the United States, although not many can complain about this, as air travel is indispensable. However, what we can do is use our advances in science and technology paired with our innate curiosity, to solve this pressing issue. 

Historically, there has been a lot of research regarding the use of silicon and gallium arsenide solar cells to power aircraft, however Perovskite Solar Cells (PSCs) have been a rather recent innovation, so minimal research has been conducted in that regard. In this article, I shall discuss everything from the basics of PSCs to their potential applications in aircraft.

Basics of PSCs

When light (photons) strikes the perovskite layer, the energy of the photons energizes the electrons, thus imparting kinetic energy. This kinetic energy enables the conduction of electrons in the electron transport layer (ETL) (See fig.2). However, something interesting happens. When an electron ‘moves’ up to the ETL and conduction band, it leaves a gap in its original position. This gap is filled by a particle called a ‘hole’. Holes essentially have the opposite charge to an electron. The concept of holes stems from the Law of Conservation of Charge. The holes then migrate to the Hole Transport Layer (HTL) (See Fig.2). The electron-hole pairs generated are conductive, so they can move about in their respective layers, and moving charges produce electricity. This is the basic principle of a solar cell. 

The mesoporous Tio2 layer is engineered such that the perovskite material can be drawn into it, which increases the surface area for photon absorption, thus increasing the efficiency. The optimal thickness for PSCs is in the ballpark range of 500nm (which is almost 50X thinner than a human hair!).

Desirable properties of PSCs which make them ideal to power aircraft

PSCs are flexible and mechanically durable. This is the single most important property of a PSC, as it can withstand the stresses of flight. Research conducted into using PSCs as a wearable source of energy quantified the mechanical durability of PSCs. The researchers conducted numerous bending cycles and analyzed FEM simulations. These are the strategies they used to make PSC’s flexible which are published in the Royal Society of Chemistry Journal (Citation: Energy Environ. Sci., 2019, 12, 3182):

1. They introduced a parylene protective layer on top of the PSC, which protected the perovskite layer from scratching, contamination, etc. and shifted the neutral plane (NP) to the photon absorbing and mechanically unstable perovskite layer (See Fig.3). A neutral plane is essentially the plane where the strain is zero, as the compression and tension of bending is balanced out. Thus, shifting the NP to the mechanically sensitive layer is desirable, as no strain would be experienced.
2. Bending can reduce the conductive power of a PSC, so to find the optimal tradeoff, a gold metal mesh was introduced.

In separate research, a scaffold like structure was designed to be placed within the mechanically fragile perovskite layer, to internally reinforce the layer (See Fig.4). This ‘honeycomb’ structure divides the layer into different grids, thus isolating defects to one grid area only, and the mechanical durability imparted makes the cell resistant to the mechanically harsh environment of flight.

Fig. 5 shows a magnified section of a microcell within the honeycomb structure. As you can see, there is a continuous point of contact between the perovskite material and the scaffold wall. Since there is contact, adhesion must prevail, i.e. the two materials must be ‘glued’ together. This can be achieved by mechanical interlocking, that is the static friction between the two layers. Mechanical interlocking can be enhanced by increasing the roughness between the two surfaces.

However, a new way to increase adhesion we researched is the use of organosilicate. In a nutshell, organosilicate is a good adhesive. It also possesses extra durability as organosilicate has Si (silicon) bonded to the classic organic compound C-C bonds. Organosilicate is also a good diffusion barrier. Perovskite is highly sensitive to moisture, so organosilicate could also act as a good protective barrier/layer. These qualities make organosilicate promising for use in PSC powered aircraft.

You may have realized that a C60 layer has been added below the perovskite layer in Fig.4. But why? This has to do with the inherent salt-like weak nature of perovskite. 

As you can see in the figure above, the structure of perovskite has many     gaps/defects. These make the material fragile and the solar cell loses efficiency. Thus, to correct this, C60 (fullerene) acts as a defect filler by filling in the gaps.

On a side note, graphene is an exciting innovation that could be used to make the grid structure discussed above. Although graphene is difficult to control and harness at this stage, new research emerges every day that makes the mechanical use of graphene inch closer to us.  In fact, researchers from the University of Texas at Austin discovered that by limiting the oxygen during graphene crystal growth, much larger crystals can be obtained, which could have potential uses in flexible electronics. 

Can PSCs power aircraft?

Now that we have discussed the properties and mechanics of PSCs, we can move forward to the actual integration of PSCs into aircraft. 

Temperature decreases as altitude increases. At such cold temperatures, the efficiency of PSCs increases, because the hysteresis energy loss is reduced considerably. Hysteresis is the resistance offered to the flow of electrons by iodine ions. At low temperatures, the movement of iodine ions is lowered, which is beneficial. Resistance due to phonons (heat particles) is also reduced.

What aircraft surfaces can harbor the solar cells?

The wings and upper fuselage surfaces. The PSCs cannot be placed on the control surfaces of aircraft such as the ailerons and flaps, but the relatively flat mid-section of the wing is suitable.

The upper part of the fuselage is displayed below:

However, because of the inherent bi-axial curvature of the fuselage, the surface is not flat, which affects the angle of incidence of sunlight. To correct this, micro lenses could be used. The material for the micro lenses needs to withstand the stresses of flight, thus organosilicate or reinforced carbon glass may be the best candidates. 

On the ground, the solar power we get on a daily basis comes from operating solar farms containing solar panels. All of these solar panels are divided into individual modules connected by conducting bus-bars. Generally, each module is connected to a micro-converter which converts DC to AC current. However, this requires a large and heavy transformer. This is not feasible for aircraft due to weight constraints, so a Super Capacitor may be used instead. Super Capacitors have high power densities as well, which is great for instantaneous thrust (bursts of power). This is achieved by placing an ion-permeable membrane between two charged plates.

Batteries will also need to be modified and enhanced for cold temperature operations, and current research is quite promising.

Current technology makes a PSC powered aircraft tricky to design. However, the field moves at a rapid pace and detailed research can be conducted into this topic. According to calculations we ran using a simple model, we can roughly suggest that PSCs, when used on the surfaces of an aircraft mentioned above, can produce approx. 10-12% of the required power of a current aircraft.

Our model accounted for the bi-axial curvature of the fuselage by including an angle x:

The aircraft we used for our calculations was a Cessna 172 Skyhawk, one of the most popular general aviation aircraft ever produced. However, do keep in mind that the Cessna was developed many decades ago. Technology has obviously advanced a lot since then, and we can design an ultra-light aircraft using lightweight composites, which could potentially fly for 30-60 minutes while being powered solely by PSCs. Such short-haul flights are very useful for logistics. For instance, Amazon is developing special drones to deliver packages. These drones could potentially be replaced by ultra-light aircraft powered by PSCs, with larger cargo capacities and higher weight limits This could be an ideal testbed to further expand this idea. 

Moreover, aircraft have APUs (Auxiliary Power Units) that are used to provide initial electrical power to the aircraft to start its engines. Aircraft also spend a large chunk of their time taxiing to the runway, which requires propulsion by the engines. So, if the APU could be enhanced to provide power for taxiing, the valuable PSC power could be conserved and used only for flying.

Conclusion

As you can probably tell, this is an exciting prospect, and PSCs do have many desirable qualities that can enable them to power aircraft. Of course, many innovations will need to be developed, however it does seem quite likely that this rather bold thought experiment can come to life within the next 20 years. Electrically powered aircraft can reduce CO2 emissions anywhere from 40 to 50X the current emission rates. This is something to look forward to. 

Works Cited

• Royal Society of Chemistry Journal (Citation: Energy Environ. Sci., 2019, 12, 3182):
• https://www.graphene-info.com/ut-austin-researchers-grow-large-graphene-crystals-exceptional-electrical-properties
• outreach.phy.cam.ac.uk
• www.ossila.com/pages/perovskites-and-perovskite-solar-cells-an-introduction
• Citation: Energy Environ. Sci., 2019, 12, 3182
• Citation: Energy Environ. Sci., 2017, 10, 2500
• science.sciencemag.org/content/367/6482/1097

About the author

Advait Harish Shirbhayye

Advait is a senior at the Hiranandani Foundation School.

The post Can Perovskite Solar Cells Power Aircraft? appeared first on Exploratio Journal.

Abstract

The Covid-19 Pandemic has led to a decrease in carbon emissions, especially by the transportation industry. In order to sustain these reduced emissions, an increased usage of public transport is necessary. By reducing the amount of passenger vehicle emissions, there can be a steady decline in air pollution levels. However, criteria pollutants emitted by the tailpipe of many modes of public transport negatively impacts many public transport users’ health. Since a majority of public transport users are low income workers, such an issue leads to a disproportionate impact of respiratory illnesses. In order to avoid such emissions, most modes of transportation should be electrified. Moreover, electrification of vehicles eliminates any tailpipe emissions, but GHG emissions are not completely avoided. Charging electrified vehicles leads to more emissions of GHG. Therefore, decoupling from the central grid and using renewable sources of energy for electricity and fuel can lead to eliminating a significant portion of the GHG emissions from the transportation industry. 

Introduction

The unexpected pandemic due to the Sars-Cov-2 virus, popularly known as the ‘COVID-19 pandemic,’ has had a major impact on both the environment and society. At an economic level, it has led to an unprecedented economic crash, mass unemployment and the collapse of entire industries. At an environmental level, however, it has led to many positive changes in the aftereffects of climate change, and global warming. As found by the climate group Carbon Brief, because the COVID-19 pandemic effectively seized hold of China’s economy and heavy industries and caused complete shutdowns, Greenhouse Gas (GHG) emissions from the country plummeted by a record-breaking 25 percent. 

The pandemic has led to a drastic decline in many industries which would have led to the decrease in GHG emissions, however, the most notable GHG emitter and one of the areas most hit by the pandemic and the enforcement of lockdown legislation was the usage of transportation. The transportation sector generates the largest share of GHG emissions, emitting about  28.2 percent of all GHG in the atmosphere, as of 2018. In another analysis by Carbon Brief in early April, it was estimated that globally, in 2020, emissions could fall by 5.5 percent, beating the 3 percent decrease that followed the 2008 financial crash, when economies also slowed and people traveled less. The GHG emissions will inevitably increase as the economy revives itself and lockdowns are lifted, however, there may be specific precautions which could be taken to sustain these low GHG emissions. One such method could be through controlling and electrifying the transportation sector. 

As COVID cases reach their peak and cities start to open up, cars and motor vehicles are bound to enter the streets again, however, if GHG emissions coming from these vehicles can be controlled, this positive change in carbon emissions can be sustained. Another method through which a more sustainable level of GHG can be sustained is by promoting the use of public transport. This, however, may be challenging due to social distancing and the fear of shared space. Below, I will discuss the public transportation industry, the method of tackling the public’s mindset in certain places to introduce an increase in usage of public transport, the link between transportation and GHG emissions in relation to the pandemic and decoupling carbon in transportation. 

The Effect of COVID-19 on Transportation and its Repercussions on the Industry

Around the world, the transportation industry has been devastated by the introduction of lockdowns and social distancing laws related to the Coronavirus. Within the transportation industry, the COVID-19 pandemic has arguably hit the public transportation industry the hardest. According to most estimates, ridership levels are at least 70% below pre-crisis levels, with some areas losing even more, especially on longer-distance and commute-oriented services, as demonstrated by San Francisco’s BART system losing 93% of its riders. Transit agencies are struggling to maintain service levels, with many of them making cuts or planning to make cuts in the next few months, which will further have an impact on ridership. Moreover, due to the mandatory social distancing and city-wide lockdowns, the public transport industry has not been able to operate for months now. However, with businesses now opening again, it is significant for the public transportation industry to open up again, albeit, it will be challenging to do it safely. For many low income employees, public transport is the only way for workers to commute to their workplaces, however, falling sick with the virus is not an option. The question then remains whether the public transport systems will be able to return to full capacity or will suffer major consequences. This is an important consideration because the public transport industry is vital in reducing the quantity of GHG emissions globally, and should it suffer, it could impact the sustainability in the industry moving forward. 

Moreover, as people are incentivised to move away from public transport, due to legislation for social distancing and increasing fears of hygiene in a shared environment, they may move towards personalised motorised vehicles, such as cars and motorcycles. This may be devastating to the GHG levels as supporting public transportation can reduce harmful CO₂ emissions by 37 million metric tons annually. Moreover, the increased consumption of ars could, in turn, increase congestion in the streets, thereby, increasing the average time spent on the roads, and therefore, increasing the average GHG emissions per car. This raises the question of how the car, and motor vehicles, industry could be shaped to offer a more sustainable and cheaper option which could both be economically feasible, yet able to help the decrease GHG emissions.

Along with the public transportation sector, another aspect of the transportation industry that has been drastically impacted is the aviation industry. Airline capacity in Europe reduced by almost 88 percent in 2020 as compared to 2019, a direct response to the travel restrictions placed by countries due to the COVID-19 pandemic. In the first half of 2020, Chinese passenger travel declined by approximately 87 million passengers, and by the end of May most airlines were bankrupt. However, as this is dreadful news on the economic front, environmentally, the airline industry is a large emitter of  GHG, emitting worldwide about 915 million tonnes of CO₂ in 2019.

The Transportation Industry and Trends in Criteria Pollutants 

The transportation industry has been a key contributor to pollution, but specifically in the section of air pollution. There are multiple sources which contribute to the emissions of harmful gasses, but the transportation industry is one which causes a significant amount of daily emissions. Within the broad subject of air pollutants, there are six criteria pollutants, which include carbon monoxide (CO), ground-level ozone, lead, nitrogen dioxide (NO_x), particulate matter, and sulfur dioxide (SO₂). A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year, but this number can vary based on a vehicle’s fuel, fuel economy, and the number of miles driven per year. Most car exhausts are known to emit sulfur dioxide, carbon dioxide and oxides of nitrogen. Moreover, the transportation sector alone is responsible for over 55% of NO_x total emissions inventory in the U.S.  These gases are harmful as pollutants. Carbon monoxide is a harmful gas, as breathing in low levels of the gas can cause fatigue and increase chest pain in people with chronic heart disease, while breathing in higher levels can cause flu-like symptoms such as headache and dizziness. Sulfur dioxide can, too, be extremely harmful to human health when it is breathed in, causing irritation in the nose, throat, and airways leading to coughing, wheezing, and shortness of breath. Moreover, sulfur dioxide inhalation can directly contribute to the development and progression of ischemic stroke in the brain, although there is no definite relationship has been established between the gas and symptom. 

Furthermore, increased concentrations of greenhouse gases, especially carbon dioxide, in the earth’s atmosphere have already substantially warmed the planet, causing more severe and prolonged heat waves, temperature variability, increased length and severity of the pollen season, air pollution, forest fires, droughts, and heavy precipitation events and floods, all of which put respiratory health at risk. Diesel exhaust particles (DEPs), composed of 80% ultrafine particles, and associated polycyclic aromatic hydrocarbons impact on airborne allergens, increasing exposure effects, concentration and allergenic biological activity. Several studies have demonstrated effects of ozone over respiratory symptoms, including shortness of breath, wheezing and coughing, lower respiratory tract infections, acute and transient decreases in lung function, increased airway responsiveness, airway injury and inflammation, and systemic oxidative stress.

As seen in figure 1, there is a direct correlation between the gigagrams, direct CO₂, equivalent from energy and use. As there has been an increase in the usage of  cars and other forms of vehicles, there has been a steady increase in CO₂ emissions consequently. Over 30 gigagrams of the 55 gigagrams emitted in 1990 were due to passenger cars. This shows how the increase in public transport can affect emission levels as a bus of 65 passengers, is equal to 50 cars. Figure 1 also demonstrates that emissions have increased but marginals emissions have had steady improvement

However, the issue does not come from metrics. Rather, it is a result of a larger amount of  and a larger amount of miles. These increases are functions of increased number of vehicles and miles. A statistic reports that passenger vehicles sales in India were at a record high in 2017-18 touching almost 3.3 million units, growing at 7.89 per cent driven by demand from smaller towns coupled with increasing popularity of utility vehicles. Public transport, therefore, decreases the amount of metric emissions per person. One local bus would emit about 82 grams of CO2 per kilometer whereas an average car running on petroleum would emit 180 grams.  

The Forms of Public Transport and Their Impact

Within the public transportation sector, there are many different forms of public transport ranging from motorised vehicles such as buses and pooled vans to vehicles such as trains and aeroplanes, which operate on high efficiency engines. When compared to aviated vehicles, motorised vehicles emit a comparatively lower amount of greenhouse gas emissions. Motorised forms of public transport also contribute to the reduction of greenhouse gas emissions, as it can encourage a reduction in the usage of individual vehicles. Moreover, if a commuter shifts from a personalised vehicle such as a car to public transport, they can deliver a 65% reduction in emissions during peak times and a 95% reduction in emissions during off peak times. This shift can also be demonstrated through the comparison that one typical passenger car, carrying one person, gets 25 passenger miles per gallon, while a conventional bus, at its capacity of 70 (seated and standing), gets 163 passenger miles per gallon. Therefore, public transit substantially reduces fuel use and greenhouse gas emissions, further making it a wise public investment in a new, carbon-constrained economy. Moreover, the fuel savings yield commensurate cuts in CO₂ emissions. Furthermore, a passenger car carrying one person emits 89 pounds of CO₂ per 100 passenger miles, while a full bus emits only 14 pounds per person. 

Railway systems are also an efficient way of introducing public transport to reduce emissions. Some may argue that rail systems are a more sustainable option, as, generally, these systems have lower levels of emissions per passenger kilometer than other means of transport. Calculations for high speed rail using the average European electricity mix, a load factor of 75%, and the consumption of an Alstom train show emissions of around 17 gCO₂/PKM, much lesser than compared to 30 gCO₂/PKM for a bus. Rail systems are also often large consumers of electricity themself. At present, the railways consume 18.5 billion units of electricity every year. The emissions avoided by passengers using rail systems are higher than the emissions caused by rail systems themself, therefore resulting in a positive outcome. Moreover, for railways, transport turnover mix accelerated the decoupling process and the increasingly active role of the transport turnover mix effect raised the likelihood of decoupling. Rail systems are not only integrated throughout cities like New York and Mumbai, which enables people to avoid using single passenger vehicles on a daily basis, but also are an efficient way of long distance traveling which may be tedious in a bus. Therefore, rail systems allow the various different sorts of travel, which can replace the use of a short-term bus or a long-term aeroplane. Rails also allow for intra city travel which proves to be more efficient than buses as they often get stuck in traffic and at stop signs whereas subway systems are built underground, allowing them to avoid all congestion. Trains scale better than buses. Each traincar can hold more people than a bus, and trains can be run at long lengths and at higher frequencies than buses. The number of buses required to fully replace the capacity of a full subway line at rush hour frequencies exceeds one per minute. It’s ungridded cities where the ability of trains to cut under the street network becomes critical to providing service to major destinations, which may not be anywhere near the wide streets.  Creating an underground railway system requires a certain amount of infrastructure and funds which may not be available in rural areas. Moreover, it is challenging to build such a facility without the presence of underground tunnels already. However, Mumbai is a populated city which is dependent on its light rail system as well. Consequently, its metro system is completely operational and overground. The rail system was built as late as 2006, and was introduced in full scale to the city in 2013.

Vehicles such as aeroplanes also use jet fuel, which is a refined version of petroleum classified as kerosene, which emits more carbon dioxide than regular fuels. However, it is important to note that the GHG emissions rely heavily on the fuel use and emissions are dependent on the fuel, aircraft, and engine type, and other factors such as the engine load and flying altitude, which vary from aircraft to aircraft. 

The Realities of the COVID-19 Pandemic

Due to the current state of the pandemic, an increase in the use of public transport cannot be implemented in most places. With regards to the direction in which the pandemic is going, COVID-19 cannot completely disappear until a vaccine is found. Many scientists predict that the pandemic will last until February 2021. Others think it may even extend till longer. It is clear now that summer does not uniformly stop the virus, but warm weather might make it easier to contain in temperate regions. In areas that will get colder in the second half of 2020, experts think there is likely to be an increase in transmission. With many countries having a decline in COVID-19 cases like New Zealand and others, like India, which have not possibly hit their peak yet, the pandemic is not playing out in the same way from place to place. If the virus induces short-term immunity — similar to two other human coronaviruses, OC43 and HKU1, for which immunity lasts about 40 weeks — then people can become reinfected and there could be annual outbreaks. New York, a city which is popularly known for its widespread use of public transport and walking population, has recently reported the fact that many New Yorkers have bought their first car, due to coronavirus.  Although most major cities in the UK have opened up, a poll that surveyed a mix of 482 business leaders and employees, conducted by Breathe, Posture People and HR Centra, reported nearly nine in ten employees (about 88 per cent) said they would not be comfortable commuting to work on public transport at all during the rest of 2020. 

Low income workers are heavily dependent on public transport to commute to work and now that businesses have started to open up again, a failure to arrive at work could directly lead to employment termination. Almost all businesses have suffered due to the coronavirus, and the crash of the economy has laid off millions of workers. In March 2020, total nonfarm payroll employment fell by 701,000, and the unemployment rate rose to 4.4 percent, as reported by the U.S. Bureau of Labor Statistics. Job security is at an all time low and the issue with using public transport may affect it further. With these restrictions on public transportation, low income workers can only commute to work through motorised vehicles such as cars. However, as mentioned before, the steady decline in the economy has affected the financial status of many low income workers. Consequently, they cannot afford to purchase a personal vehicle even if they had the savings for it prior to the pandemic. A third of New Orleans residents who commute via public transportation live in poverty, compared to only 9 percent of those who drive cars. In the United States, commuters driving alone to work report median earnings $4,314 higher than those taking public transportation. This also leads to another issue, air pollution has twice the impact on lung function for members of lower-income households, research has suggested, and it increases their risk of developing chronic obstructive pulmonary disease (COPD) by three times. The mainstream cigarette smoke contains approximately 500 μg of NO generated per cigarette. Second hand smoking is known to have adverse effects on people who live with or spend time around smokers. The average CO2 emission for the buses is 822 g / km. This shows how much harm can be implemented upon low income workers by just being around public transport which does not have safe sources of sustainable energy. As seen though figure 2, middle income and low income workers are at a higher risk for the majority of respiratory illnesses and other diseases in comparison to the high income population.  This is inherently flawed as this portion of the population has less access to health care and treatments.

The disproportionate impacts of ground source emissions is a growing issue which worsens with the increase of greenhouse gas emissions in the transportation industry. Especially in the current state of  a global medical emergency due to COVID-19, the effects of such respiratory illnesses are more relevant than ever as the Sars-Cov-2 virus attacks the walls and linings of the air sacs in the lungs. People with respiratory illnesses are at high risk of mortality from the Sars-Cov-2 virus. 

Electrification of vehicles 

Conventional vehicles with an internal combustion engine produce direct emissions through the tailpipe, as well as through evaporation from the vehicle’s fuel system and during the fueling process. Conversely, EVs produce zero direct emissions. Electrified cars eliminate tailpipe emissions completely, however are still not completely emission-free.  Overall, despite the mode differences, a weak decoupling state appeared between 1990–1995 and 2000–2010, offering empirical evidence for the decoupling of transport carbon emission from transport output. The decoupling index indicated the transport energy efficiency factor stimulated the decoupling in the observed period. Transportation has not successfully moved to decoupling miles from petroleum. Due to the electrification of transportation, the electric power industry has reduced carbon dioxide emissions 27 percent below 2005 levels as of 2018, nearly the lowest level in three decades, while the transportation sector is now the leading source of emissions. More than one-third of the United State’s electricity comes from carbon-free sources (nuclear energy and hydropower and other renewables).  In the Base GHG scenario, the study estimates that, by 2050, the electricity sector could reduce annual greenhouse gas emissions by 1030 million metric tons relative to 2015 levels, a 45% reduction. Electric buses are essential to minimising all emissions coming from transport. As well as, it will improve the public transport industry and make it even more sustainable. Electric buses sales have increased over the years, however, roughly 98 per cent of the electric buses in the world are deployed in Chinese cities. Introducing electric buses to countries like the United States can lead to a more efficient transportation sector and decrease the pollution. India (70,000 buses sold in 2017) is a market with big potential, when even a small part of the orders will be electric. By 2025, the research company Interact Analysis forecasts that India will account for more than 10% of the total annual demand for electric buses globally, which is more than Europe and North America combined. One of the most popular types of electric buses nowadays are batteryelectric buses. Battery electric buses have the electricity stored on board the vehicle in a battery. As of 2018 such buses can have a range of over 280 km with just one charge, however extreme temperatures and hills may reduce range. Electric buses require charging systems in multiple locations for regular charging. However, such infrastructure does not exist in developing countries like India. Ironically, these countries are the ones with larger populations which are heavily dependent on public transport such as buses. Battery-electric vehicles’ biggest problem has always been range. At the dawn of the automobile age, electric cars competed with gasoline and steam-engined vehicles: In 1900, 38 percent of U.S. cars were battery-powered, and only 22 percent boasted internal combustion engines.

Renewable energy and its limitations 

If we look at centralised and non-renewable systems, namely, large-scale plants using fossil fuels as oil and coke, they are environmentally unsustainable because they are based on exhausting resources, so forth fastening resources depletion. Furthermore, these exhausting resources result in high greenhouse gases emission (CO2 emissions), through several processes along their life cycle, which determine global warming. Without a doubt, these operations require very costly and large-scale centralised structures, which limit the conceivable outcomes of direct and democratized access to energy production and utilization. Throughout time, people have had low control over their own fate which prompted a widened gap (as far as disparity) among rich and poor, which has been pursued in time perpetuating a centralised energy production. Renewable energy is without doubt a better option for energy consumption as it avoids greenhouse gas emissions unlike the use of petroleum fuels. However, renewable energy comes with its own challenges. One of the biggest concerns in the field of renewable energy is power generation depending on natural resources that are uncontrollable by humans.The uncertainty in energy production in renewable energy technologies is making integration more complex. High power quality is expected to guarantee security and high productivity of the system. The nature of the force gracefully permits the framework to function ably with high unwavering quality and lower costs. On the other hand, poor power quality can have major damaging consequences for the power grid and industrial processes. Furthermore, Most sustainable power source plants that share their vitality with the network require large zones of space. By and large, sustainable power sources are directed by areas which can be off-putting to clients. Of course, some sustainable power sources are just not accessible in various locations Additionally, the distance between the renewable energy source and the grid is a major aspect in term of cost and efficiency.

Looking at trends between India and the United states by the table below (Figure 3), the energy consumption of the two  countries can be compared.

As it can be seen, the energy consumption in the United States is comparatively higher than India on a daily basis. This is due to the fact that the United states is a developed country and has a larger population using transportation as compared to India. The implementation of renewable energy in areas such as India will be substantially different in comparison to an area such as the United states due to their varying levels of energy consumption. However, even though the United States has a larger amount of electric consumption, it would possibly be easier to introduce renewable energy to transportation there as the country is more developed and more likely to be able to fund such a project whereas India is a developing country with possibly not enough resources to sustain a renewable power line.

Decoupling from the central grid

The grid relied primarily on large fossil-fuel facilities to generate electricity, and an inefficient collection of cables, poles, and wires that transports this electricity over large distances. To avoid the emissions of dangerous greenhouse gases, renewable energy must become the primary source of energy for all industries, including electric transportation.  The energy grid structure that most commonly still exists in urban areas, even the areas transitioning to renewable energy, relies on large centralized power generation facilities that transmit and distribute generated energy across long transmission lines. The integrated green urban grid has four key segments: energy efficiency, demand response, distributed generation, and distributed energy storage. By adequately incorporating these four segments, the new urban green grid can decrease the amount of air pollution, including GHG emissions, while keeping up unwavering quality of the electrical framework. The kinds of renewable energy that could be utilized as distributed generation assets are advanced technologies which can be downsized and sited close to stack necessities, for example, wind, sun powered, and geothermal. A large portion of the circulated generation is solar as it can be readily sited on roofs and other available urban areas. Distributed fuel cells are likewise picking up prominence, however because the vast majority of them depend on petroleum derivatives, their advantages identified with environmental change and contamination are more restricted than different assets, for example, wind and sun oriented. Distributed energy storage resources are an essential component of a green urban grid. Consequently, the new green urban grid will rely on distributed renewable generation resources such as solar photovoltaic systems on residences. Wind and solar renewable resources are considered variable or intermittent because the sun does not always shine and the wind does not always blow.

The ultimate goal  or the transportation industry would be to become less tied to the central grid and achieve renewable charging for electric vehicles. The only viable method of decoupling transportation from fossil fuels would be through the urban green grid as it eliminates the need for depending on the centralised grid as well as allows the consumption of renewable sources of energy, therefore providing vehicles with an alternative for fossil fuels. If electric cars and buses were able to decouple from fossil fuels, there would be an extreme reduction in GHG emissions from the transportation industry and, coming out of the pandemic, the inevitable rise of air pollution can be avoided. 

Further analysis and research recommendations

Personally, I began writing this paper with the perspective that encouraging public transport will be the solution to sustaining low carbon emissions post the COVID-19 pandemic. However, through research I soon discovered the true complexities of the issue with transportation and GHG emissions. Although public transport is the first step towards a more sustainable society and currently is the easiest as it is already a functional system, the real issue can only be resolved once all modes of transport can be successfully electrified and decoupled from fossil fuels.  Public transport decreases per-person carbon emissions. However, the primary users of public transport are low income workers and due to the pollutants which buses and rail systems emit, they are impacted on a disproportionate scale by respiratory illnesses. Public transport reduces the number of vehicles on the road, and therefore, reduces the amount of emissions, however public transport vehicles themselves do produce harmful pollutants. To achieve a ‘0 emission’ vehicle, decoupling from the central grid and moving towards the idea of an ‘urban green grid’ is necessary. Moreover, public transport is currently not a viable solution as the recent pandemic has urged for social distancing and most people may not find utilising buses and subways as ‘safe’. Although there are many disadvantages to using passenger vehicles, if electric cars and motorcycles can operate by the use of renewable energy, cities can come out of this pandemic with a colossal decrease in GHG emissions from the transportation industry and a safe environment where people can continue practising social distancing until necessary. 

Further research recommendations would include going more in depth on the different constraints of renewable energy and the actual process of implementation of it in transportation. Moreover, linking such research with the decoupling of transportation from the central grid will provide appropriate answers to the challenges of such a project and how to go about imposing it on our society. Another field of research would surround the COVID-19 pandemic itself. Although there has been a visible decrease in the amount of GHG emissions, there have also been many factors contributing to environmental issues such as the newfound abundance of medical waste (surgical masks, gloves, etc). From an environmental perspective, do the pros of this pandemic outweigh the cons? Now with businesses and the economy reopening, is the situation becoming worse than before due to the fact that more people are inclined to using personal vehicles rather than a form of public transportation? This pandemic could have possibly crushed the entire public transport industry, as the aviation industry has arguably been hit the hardest. 

There are many possible discussions regarding public transport as well. Public transport has been around for a long time, and although there has been an increase in the usage of public transport over the years, many countries have failed in implementing this system into their cities. What may be the cause of this? What are the restrictions with public transport? How long would it take to completely reinvent public transport and make it completely electrified and renewable? With a concentration on electrification, further research on the electrification of transportation can be done. This may include researching the quantitative values, physical process or environmental impacts. 

Conclusion

The COVID-19 pandemic unintentionally caused a significant decline in carbon emissions from the transportation industry. However, sustaining this change has proved to be very challenging. Utilising modes of public transportation can contribute significantly to reducing emissions, however, it cannot completely eliminate this issue as most modes of public transport do emit criteria pollutants which leads to low income workers being affected by respiratory illness in a disproportionate manner. Moreover, public transportation is not a viable option due to the nature of the COVID-19 pandemic which restricts any sort of public contact. Moreover, this issue can be solved from the root of the problem — the tailpipe emissions of GHG from vehicles. In order to tackle such an issue, all modes of transport ought to be electrified. As well as, energy sources must be renewable. All these ideas are highly interdependent. The idea of having electrified public transport essentially tackles the issues with having too many single passenger vehicles, as well as having criteria pollutants emitted through the tail pipes of vehicles. Although electrification of vehicles is beneficial itself, decoupling from the central grid is necessary for electrified vehicles to be ‘all clean’. By promoting the urban green grid, electrified vehicles can be successfully introduced without adding to emissions from non renewable charging methods. 

Ideally, the priority of policy makers should be to find a safe way to promote public transport post the pandemic. If many passenger vehicle users can be persuaded to use public transport, there will be a significant decline in air pollution and congestion on roads. Although decoupling from the central grid will inherently minimise all emissions, it is still a long process which cannot be done in the midst of a medical emergency. Therefore, increased usage of public transport is the best way to tackle this issue. Since most people have lost savings during this economic crisis, many low income workers may not be able to afford new cars, and with job security at an all time low, public transportation is their only option. If the government can successfully optimise the experience of using public transport by taking safety precautions at every step, there will be a potential transition for many car users and will successfully lead to a more public transport dependent economy. Thus, potentially sustaining this decrease in GHG emissions post the COVID-19 pandemic. 

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Mentor: Mr. Kurt Teichert, Brown University

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About the author

Manya Mehta

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