In July 2018, the Supreme Court of India (SCI) asked the Delhi Government and the Environment Pollution Authority (EPCA) to explore the feasibility of introducing hydrogen- fuelled buses for public transport in place of the electric buses in Delhi. The apex court made this observation in view of successful demonstration of hydrogen Fuel Cell Buses (FCBs) elsewhere. In this article, Dr M R Nouni, Rudranath Sarkhel, and Prakash Jha analyse the present status of development, advantages, and challenges associated with deployment of buses powered by H-CNG, electricity, and hydrogen.

In a time when dependence on imported petroleum is continuously increasing, when emissions from fossil fuel-powered automobiles are poisoning the air, when thousands of people are dying because of poor air quality, when stubble burning in some states is turning the northern part of the country into a gas chamber during early winters, and where keeping anthropogenic climate change at bay has become an important point of the political agenda at the global level, the demand for having a cleaner and greener public transport system is attracting attention of the public, government, judiciary, and regulators. In this background, the SCI in July 2018 asked the Delhi Government and EPCA to explore the feasibility of introducing hydrogen-fuelled buses for public transport in place of the electric buses (EBs). The SCI made this observation in view of successful demonstration of hydrogen FCBs elsewhere.

In response, the EPCA recommended to the SCI that the Indian manufacturers and oil companies are not yet ready for introduction of FCBs in Delhi and therefore, the Delhi Government may consider converting all CNG buses to H-CNG (fuel containing 18% hydrogen in CNG) in a phased manner by 2020/21 to improve Delhi’s air quality. These developments point to the growing recognition that mobility solutions of tomorrow should use new energy resources, such as electricity and hydrogen with H-CNG serving as a transitional fuel before switching to hydrogen.

H-CNG Fuel for Automotive Application

H-CNG is an automotive fuel, where hydrogen is mixed with CNG to improve its combustion characteristics. This process, increases the gravimetric calorific value, but decreases volumetric calorific value. Global H-CNG testing has demonstrated its potential to reduce emissions, such as NOx, CO2, and CO compared to traditional CNG. Studies undertaken in India led by the Society of Indian Automobile Manufacturers (SIAM) have found that 18% hydrogen in CNG provides the optimal results for different types of vehicles. Emissions of CO and total hydrocarbon were found to be lower by using H-CNG in place of CNG. The study was however, inconclusive with respect to increase/ decrease in NOx emissions.

Production of H-CNG

H-CNG blend can be produced by having either separate high pressure supplies of hydrogen and CNG with mixing in the dispenser or using a compact reformer, wherein CNG is reformed to get H-CNG of the desired blend. Such a compact reformer has been developed by R&D Centre of the Indian Oil Corporation Ltd. (IOCL), Faridabad. Earlier two H-CNG dispensing stations operated by the IOCL at Dwarka in New Delhi and Faridabad were providing H-CNG to some test vehicles by mixing hydrogen and CNG. The dispensers at these stations were configured to provide 18% hydrogen blended with CNG by volume. The compact reformer obviates the need for either transporting hydrogen to H-CNG dispensing station or producing it on-site.

Issues associated with h-CNG

Cost of H-CNG fuel is expected to be higher than CNG, but better fuel economy coupled with reduced emissions of CO and hydrocarbon, make it a better fuel than CNG. Indian automobile industry already has experience of developing H-C NG buses, which will help them in supply of H-CNG buses and modify the existing CNG buses. In retrofitted engines reduction in NOx emission is highly dependent on the adjustment of the engine retuning, which may lead to higher NOx emissions with H-CNG than CNG.

ELECTRIC BUSES

With a view to decarbonize the transport sector, which contributed about 24% of CO2 emissions of 32.3 Gt in 2015; electric vehicles (EVs) are getting wider attention with many countries adopting different promotional strategies. As a result, the total global fleet of EVs at the beginning of 2018 was about 3 million. In comparison, the total number of EBs that may be in operation at the beginning of 2018 were only about 3.73 lakh, of which about 3.70 lakh were deployed in China alone and remaining in Europe, Japan, and the USA. Some cities in China aim to completely electrify their network of buses.

Drivers of EVs

EVs for road transport boost energy efficiency, require no direct fuel combustion, and rely on electricity, a versatile and diversified energy carrier. Adoption of EVs enhances energy security to nations and offers better air quality and less noise. Apart from stricter emission regulations, factors, such as lower battery costs, expanding infrastructure for fast charging, increasing consumer acceptance, and better total cost of ownership are also contributing to faster adoption of EVs.

Broad design features of EBs in global market

There are two principal parameters that determine the design of an EB: materials used for construction of bus body and the recharging strategy. Typical conventional bus body is built using steel frame, ensuring good structural stability at low cost. Some EBs make use of lighter materials, like aluminium or carbon fibre to ensure lower kerb weight, resulting in reduced energy consumption for propulsion of bus. Typical EBs using aluminium frame have kerb weight of 10.5–12 tonnes in comparison to about 14 tonnes with steel frame. The propulsion energy consumption of these types of EBs are around 90 kWh/100 km and 110–130 kWh/100 km, respectively. EBs can be designed to operate for a full day of operation with overnight recharging at a bus depot using slow chargers. This design requires batteries in excess of 250 kWh to satisfy range requirements. The alternative charging strategy, known as opportunity charging, relies on fast chargers at the terminals or along a bus route. This strategy requires a much smaller battery (around 80 kWh) which results in a lower purchase price, lower fuel consumption, and more space for passengers. Li-ion batteries are heavy due to low gravimetric energy density and it results in increasing the kerb weight of the EBs. A specific challenge of EBs is requirement of meeting auxiliary loads for heating, ventilation, and air conditioning particularly in cold climates. The majority of EBs sold to date have been made by Chinese manufacturers with a battery capacity of around 330 kWh, which enables it to travel more than 250 km per charge.

Manufacturing of EBs in India

While electric cars may be the preferred option in Europe and America, for India EBs are more relevant as public transport is more sustainable from environmental perspective. Even NITI Aayog has prioritized EBs amongst different EVs for deployment in India. Introduction of EBs in India is in a nascent stage. Goldstone-BYD, Tata Motors Ltd. (TML), and Ashok Leyland are some of the active manufacturers of EBs in India. Regular operation of EBs commenced in Himachal Pradesh and Mumbai with buses supplied by Goldstone-BYD, a couple of years back. Ahmedabad, Bengaluru, Guwahati, Hyderabad, Indore, Jaipur, Jammu, Kolkata, and Lucknow are the nine cities in India that have decided to procure 530 EBs from the above mentioned bus manufacturers.

Acquisition and operating cost of EBs

The upfront cost of an EB is significantly higher in comparison to other alternatives, except FCB. The cost of an EB quoted by the suppliers for the ten cities referred above was in the range of `0.77–`1.7 crore. However, procurement cost of an EB will depend on the specifications of the bus and especially the batteries used. The reported cost of an AC low-floor EB could be as high as `2.5 crore. Under FAME-India Scheme, launched in 2015, EBs with maximum energy consumption of 175 kWh/100 km were included for financial assistance of 60% of purchase cost or a maximum of ` 1 crore subject to at least 35% local content.

The cost contribution of Li-ion batteries to the total cost of the EB may be up-to 40%. The price of the Li-ion battery during 2017 was estimated at about $209/kWh and is expected to reduce to about $100/kWh by 2025. In India, cost of these batteries is high due to their import presently. Many companies have announced their plans to manufacture Li-ion batteries locally. However, Indian companies will have to largely depend on import of Li and Co and the prices of these materials are increasing due to increased global demand and only few countries controlling the supply chain.

It is economical to operate an EB in comparison to a conventional bus due to low maintenance cost on account of fewer moving components, high fuel efficiency, low cost of power and option of utilizing off-peak power during night. Besides, EBs could make use of renewable electricity as its penetration in the grid increases. During daytime, the buses owned by educational institutions usually remain unutilized for longer duration and can be used for storing excess solar electricity for feeding a part of it into the grid in the evening.

Challenges associated with EBs

Factors, such as high initial cost, dependency on imported Li-ion batteries, absence of charging infrastructure, operational range, and long charging time are attributed to slow adoption of EBs. Bus depots could in fact, make use of the vacant land and roof area for installation of solar charging systems. Procurement of buses and installation of dedicated power generation capacity may require additional funds, which may be a constraint with government-owned bus transport corporations.

HYDROGEN-FUELLED BUSES

Hydrogen can be used for powering buses using either Internal Combustion Engine (ICE) or Fuel Cells (FC) technologies. A Hydrogen ICE (HICE) bus uses hydrogen as fuel in place of diesel/CNG. Hydrogen is the lightest element with density of about 0.0898 kg/m3. Therefore, it requires on-board storage at very high pressure (350 bar/700 bar) in composite cylinders for storing enough hydrogen to provide desirable operational range. Compressing hydrogen to such high pressures may consume up to about 13% of energy. An FCB is an electric bus that makes use of FC stack for generating direct current through electrochemical reaction between hydrogen and oxygen for running it. Energy conversion efficiency of an FC may be as high as 60% with no emissions except water vapour and heat. HICE bus may produce some emissions in the form of NOx and traces of particulates resulting from combustion of lubricating oil. Even NOx emissions can be eliminated by using after treatment processes.

Energy density of hydrogen and Li-ion batteries

Gravimetric energy density of hydrogen is in the range of 1.47–1.83 kWh/kg, depending on the volumetric capacity of the storage vessel used and storage pressure. In comparison, energy density of Li-ion batteries is in the range of 100–265 kWh/kg. Therefore, for storing same amount of energy, Li-ion based storage system would be about ten times heavier. Thus, for a given driving range, hydrogen storage system will be lighter than Li-ion batteries. Coupled with it, hydrogen vehicles can be refuelled as quickly as similar petrol/diesel vehicles with hydrogen filling rate of about 1 kg/minute in comparison to several hours taken by EBs. Hydrogen vehicles, therefore do not pose any ‘range anxiety’ fears but finding a Hydrogen Refuelling Station (HRS) is going to be a big concern till infrastructure for HRSs is developed.

Infrastructure for hydrogen

EVs have advantage over hydrogen vehicles as the electricity infrastructure is fairly well developed. The only incremental building block required to be put in place is regarding charging infrastructure. In contrast, infrastructure for production, storage, transportation, and dispensing of hydrogen for automotive sector is non-existent. Hydrogen for road transport vehicles can be produced in a centralized facility with distribution through either pipeline or trucks. Hydrogen so produced will be economical with high delivered cost that depends on transportation distance. On the other hand, on-site hydrogen can be easily produced using electrolysers though at a higher cost than centralized production but will have almost negligible transportation cost. The cost of HRS ranges from $2.1–3 million in California, USA for average daily hydrogen supply of 120–180 kg. On an average, the California Alternative and Renewable Fuel and Vehicle Technology Programme is providing about $1.5 million in grant for construction of a HRS. Japan, Germany, the USA, and other countries in Europe have set up about 330 HRSs so far. Japan alone has more than 100 stations. So far as India is concerned, two stations with on-site electrolytic hydrogen production are currently in operation at Faridabad and Gwalpahari, Gurugram. There are 32 operational chlor-alkali units in the country that are producing by-product hydrogen and a significant proportion of it can be utilized for powering hydrogen vehicles in their vicinity to minimize transportation cost.

Types of Electrolysers

For on-site hydrogen production, two types of electrolysers are used—alkaline and PEM. Alkaline electrolysers are extensively used and is a proven technology. Its efficiency is of the order of about 65% and efforts are currently underway to further improve it. On the other hand, PEM electrolysers are compact and more efficient with efficiency of about 75% that may improve upto 80%. However, PEM electrolysers aremore expensive, and have low footprint and better load response. With increasing penetration of variable solar and wind power generation in the grid and problem of power-curtailment from such sources, hydrogen production using electrolysers would become attractive.

Status of deployment of hydrogen-fuelled buses

Technically ready for the marketplace, hundreds of FCBs have undergone extensive demonstration in many cities in Europe and the USA. Japan is planning to showcase FCB technology during the 2020 Tokyo Olympics, where about 100 buses are expected to be deployed. China has plans to deploy a large number of FCBs in the next five years. TML has developed FCBs in India using some imported components. These buses will be ready for introduction after their extensive field trials. The SCI has taken these developments into account, while asking the Delhi Government to explore introduction of FCBs in the capital.

Safety issues related to hydrogen

Hydrogen requires very low ignition energy of 0.02 mJ for initiating combustion. Besides, hydrogen is combustible in air in a very wide range of concentrations from 4%-75% by volume, indicating combustion of very lean to very rich mixtures of hydrogen and air, which is not the case with conventional auto-fuels. These properties of hydrogen make it a fuel that needs safe handling. Since hydrogen has high diffusivity in air, it would get dispersed very quickly, whenever there is any leakage. In the event of hydrogen ignition resulting from its leakage, the flame travels vertically up rather than spreading and therefore, safety issues with hydrogen are similar to other auto-fuels.

Cost of hydrogen and hydrogen-fuelled vehicles

Cost of hydrogen varies considerably depending on the process by which it is produced, purity of hydrogen, capacity of the production facility, and transportation distance between production and delivery stations apart from other factors. Its cost in India may vary from `200–`800/kg based on the above-mentioned factors. Internationally, FCBs are expensive at present with their unit cost in the range of `6–`7 crore. As per indications provided by the TML, the cost of producing FCBs in India may be half of the international cost. The cost of HICE bus is expected to be significantly lower compared to FCBs due to their lower import content.

Hydrogen-fuelled buses: fC versus ICE

Globally, FCBs have been preferred to HICE buses in view of high energy conversion efficiencies and no tailpipe emissions. In contrast, India, while working out its priorities for development of hydrogen-fuelled vehicles, opted for HICE technology, mainly on account of: (i) ICE can use hydrogen as a fuel with few inexpensive modifications in the existing engine technology; (ii) HICE vehicles have higher efficiency compared to petrol vehicles and also lower emissions in comparison to petrol/diesel engines; (iii) existing manufacturing facilities can continue to be utilized for manufacturing of HICE and thereby requiring no new capital investment; and (iv) HICE could act as a bridging technology for making transition from fossil fuelled to FC vehicles. Mahindra & Mahindra in association with IIT-Delhi have already developed HICE-based three-wheelers and mini buses, which have undergone partial field trials. Initial results have been encouraging and these vehicles can be introduced in the market on completion of field trials. High cost and durability of FC make FC vehicles unattractive to users presently. Keeping this in view, HICE buses may have relevance in the Indian context in the coming years and therefore, must be a part of any strategy to decarbonize the transport sector.

Comparison of energy utilisation in EV and fC vehicles

Figure 1 compares availability of energy to wheels in an EV and an FC vehicle considering 100 units of grid electricity. After considering different losses in the various sub-systems of the two options, it may be seen that while about 52.24 kWh energy is available to wheels in an EV, only about 22.21 kWh energy is available in the case of an FC vehicle. Therefore, in terms of energy utilization, an EV is far better than an FC vehicle.

CONCLUSIONS

For de-carbonizing transport sector, both electric mobility and hydrogen- fuelled vehicles, especially FC vehicles have relevance, though the latter may be somewhat behind in terms of readiness for commercial introduction in India. Both the solutions can make use of renewable energies for production of the two versatile energy carriers— electricity and hydrogen, thereby, reducing the dependence on fossil fuels to begin with and ultimately eliminating their use. In terms of fuel, shifting to H-CNG from CNG and thereafter to hydrogen will certainly help in improving the air quality. In terms of vehicles, HICE could be the intermediate technology before making transition to FCBs. EBs can be introduced in city public transport quickly, provided the charging infrastructure can be developed in bus depots. Overall, it will be in the interest of the urban population in India, if these clean public transport options are deployed at the earliest.

Dr M R Nouni, Mr Rudranath Sarkhel, and Mr Prakash Jha, National Institute of Solar Energy, Gwalpahari, Gurugram, Haryana