Hydrogen As A Sustainable Energy Source

How much electricity (in kWh) would be needed to produce the hydrogen to power a hydrogen-fuel cell car for the same total vehicle km as one litre of petrol in a typical conventional car? Assume:

1. Electricity are required to generate 1 kg of hydrogen a high pressure electrolyser and pressurised to 350 bar suitable for on-board storage in a mobile application.
2. The energy content of hydrogen (HHV) is 142 MJ/kg (~40 kWh/kg)
3. The average energy efficiency of the fuel cells used is 44% (based on HHV), and that of the electric motors 86%
4. The energy content of unleaded petrol is 34.2 MJ/litre
5. The conventional petrol car has an average energy efficiency of 20% (see the lecture materials).

a- If the hydrogen is stored as compressed gas at a pressure of 350 bar (1 bar = 101 kPa)

b- If the hydrogen is stored cryogenically as a liquid

c- If the hydrogen is stored in a metal hydride in solid form Assumptions and information required to answer this question: • Assume the same energy conversion efficiencies and energy contents as in question 2.

• Note that the following gravimetric and volumetric energy storage figures are based on 50% fuel cell energy efficiency, but the energy efficiency that you need to use (based on question 2) in order to answer this question is 44%, HHV.
• Assumptions for the volumetric and gravimetric electrical energy densities of different hydrogen energy storage options based on 50% electrical energ efficiency (HHV) for the fuel cell:

Consider just whole numbers of MH canisters and batteries. At the gravimetric energy density crossover point, how many MH canisters would the hydrogen fuel system employ and how many batteries (rounded to the nearest whole numbers)?

Using what you have learnt in this course during weeks 1-6, present a critical discussion (in about 1000 words), in a quantitative and qualitative manner, about advantages and disadvantages of using hydrogen in national and global sustainable energy strategies (think about different energy sectors). Use credible references including books, journal papers, case studies, and industry examples to back your argument. Make sure all sources used for this discussion are properly referenced using the Harvard system.

Sizing a Solar-hydrogen-battery system for a standalone household

Q.1 - A standalone household (no grid connection) with a conservative daily electrical load profile as given below this question is considering a Solar-hydrogen-battery system to supply its load. The household has been assumed to have a passive design with no heating and cooling load. Use HOMER software tool to size the system; discuss your assumptions, and demonstrate and discuss the technical and economic performance and the system.

Solution:

Here the assumption consider are load detail provided of the residential domain, same load is considered throughout the year. Heating and cooling loads are not considered here in isolated home which is supplied only by PV means with no interconnection with main grid or microgrid. Temperature of Melbourne considered by default value.

Figure 1 Schematic and Load detials in HomerThe power factor of load considered is 0.3, and no specifications are provided we assume that PV is connected with the battery as energy storage and the converter is use to convert the DC power from the battery to AC is coupled in between. Assumed temperature is 38^o C. and maximum PV capacity of 1.2 kW. Other parameter is kept as default. Results are attached in result.csv file.

Q2. How much electricity (in kWh) would be needed to produce the hydrogen to power a hydrogen-fuel cell car for the same total vehicle km as one litre of petrol in a typical conventional car?

Assume:

1. 0 kWh of electricity are required to generate 1 kg of hydrogen a high pressure electrolyze and pressurized to 350 bar suitable for on-board storage in a mobile application.
2. The energy content of hydrogen (HHV) is 142 MJ/kg (~40 kWh/kg)
3. The average energy efficiency of the fuel cells used is 44% (based on HHV), and that of the electric motors 86%
4. The energy content of unleaded petrol is 34.2 MJ/litre
5. The conventional petrol car has an average energy efficiency of 20% (see the lecture materials).

Solution:

t1 litre of petrol = 34.2MJ of energy. But the energy efficiency is 20% => 1 litre of petrol effectively = 20/100* 34.2 MJ = 6.84 MJ

Let x be MJ of energy that comes from Hydrogen. Then taking efficiencies into account, x* 0.44*0.86 = 6.84

=> x= 6.84/ ( 0.44*0.86 ) = 18.07MJ

1Kg of Hydrogen gives - 142 MJ => 18.07MJ is obtained from 18.07/142 = 0.1272Kg

to generate 1Kg of Hydrogen - 63 kWh of electricity is needed

To generate 0.1272Kg of Hydrogen - 0.1272* 63 = 8 kWh of electricity is would be needed

Q3. For storage options a, b, and c, what volume of storage tank for hydrogen would be needed for a hydrogen fuel cell car to have the same delivered transport energy (that is, total vehicle-km of travel) as a conventional car with a full 50 litre petrol tank (note that the actual volume of the tank is more than 50 litre).

• If the hydrogen is stored as compressed gas at a pressure of 350 bar (1 bar = 101 kPa)
• If the hydrogen is stored cryogenically as a liquid
• If the hydrogen is stored in a metal hydride in solid form

Solution:

Given tank capacity containing petrol tank is =50 liter

Electricity required to produce hydrogen for a fuel cell car

Transport energy in hydrogen fuel cell car= transport energy in conventional car

In the form of compressed gas

V=50 lit x 0.35 kWh/lit=17.5 kWh

In the form of cryogenic hydrogen

V= 50 lit x 0.89 kWh/lit =44.5 kWh

In the form of metal hydride

V=50 lit x 0.5 kWh/lit =25 kWh

Q4. A small electrical energy storage system is based on a 30-W PEM fuel cell (mass 285 g, efficiency based on HHV of 50%) and a number of metal hydride hydrogen storage canisters each capable of storing up to 1.2 wt% hydrogen with an uncharged mass of 134 g (NB 100% includes mass of canister plus hydrogen here). At what minimum total electrical energy delivery capacity would this system have a system gravimetric energy density advantage over a battery bank based on a number of lithium polymer batteries, each weighing 88 g and rated at 1800 mAh with a nominal voltage of 7.4 V? Assume an 80% depth of discharge for each battery and a 12% drop in voltage, linear with usage, during discharge. Consider just whole numbers of MH canisters and batteries. At the gravimetric energy density crossover point, how many MH canisters would the hydrogen fuel system employ and how many batteries (rounded to the nearest whole numbers)?

Solution:

Given that

A small electrical energy storage system is based on a 30-W PEM fuel.

(mass 285 g effi=50%)

Capable of storing 1.2 wt

Uncharged mass of 13kg

(NB 1007. Includes mass of canister plus hydrogen)

L1 each weigting 85 gm

Rated at 1800 mAh with a nominal voltage of 7.4

 depth % of discharge =80%

drop in voltage g=12%

according   MH canisters

Transport energy in Hydrogen fuel cell=transport energy in conventional

• In composed gas

V= 50 x 0.35 kWh/ltr

   =17.5 kWh

• The cryogentic hydrogen

V=50 x 0.89 kWh/ltr

 =25 kWh

• Form of metal hydride

V=50 x 0.5 kWh/ltr

 =25 kWh

1. At constant pressure condition

Volume

1. At constant pressure condition

Volume

1. At constant pressure condition

Q5. Using what you have learnt in this course during weeks 1-6, present a critical discussion (in about 1000 words), in a quantitative and qualitative manner, about advantages and disadvantages of using hydrogen in national and global sustainable energy strategies (think about different energy sectors). Use credible references including books, journal papers, case studies, and industry examples to back your argument. Make sure all sources used for this discussion are properly referenced using the Harvard system.

Solution:

The use of hydrogen started in 1962 by John Bockris he proposed the supply of electricity to US major cities with solar based energy with use of hydrogen. Later on, number of articles and research work has been done on the same domain. Hydrogen. The production of hydrogen can be done with variety of processes. With the use of natural gas and steam, electrolysis of water and oxygen etc. The by product of most processes is the CO2.  The efficiency of conversion and storage in the case of AC-AC system is 20-45%. The response time of hydrogen fuel cell is very quick towards the corrective action suggested by the controller.  The key component of hydrogen conversion process is electrolysis, storage tank, compressor or the liquefier.

Volume of storage tank required for a hydrogen fuel cell car

Figure 2 Application field wise

The hydrogen having unique properties, but also its very dangerous material if not handled properly. The boiling point of hydrogen is -253^o C and melting point -259^o C. So, it is having very low boiling temperature which makes storage of hydrogen very challenging.

Fuel cell is a device which uses hydrogen and oxygen and generates electricity by an electrochemical process.  The main advantage of using hydrogen as energy storage batteries need only recharging while fuel cell needed to be refueled. Many researchers stated that 1kg of hydrogen is equivalent to the 1 gallon of gasoline fuel which delivers power density of 200-600 Wh/lit [1]. Also, at the same time conversion of water to hydrogen efficiency ranges from 60-70%. The best way to produce hydrogen is the use of RES, or the harvested energy can be use, why producing and storing it properly can be utilizing for later usage.  

Applications:

• Mobile applications (bike, car, scooters, buses, trucks)
• Stationary applications (building, tower etc.)

Advantages:

• The use of hydrogen provides low or zero emission
• The operation of the process is bit quiet
• The requirement of maintenance is very low
• Running cost of the hydrogen energy storage is very low

Disadvantage

• The construction and initial cost still a bit expensive
• The Hydrogen infrastructure such as storage, handling, conversion equipment not well developed yet
• the need of safety standard
• Social acceptance of the process is not much compared to other systems
• Lifetime of the installation need improvement

Electricity conversion from hydrogen to electrolysis process is best suitable solution towards the environmentally friendly and cost-effective solution. Use in the form of input fuel and application toward fuel cell base vehicles, mobile energy storage, and station energy storage is very common form of energy utilization. Though efficiency of hydrogen fuel is less but due to higher storage capacity compared to other it’s still best solution. Storage of hydrogen in pressurized vessels normally at 100-300 bar and in the form of liquid at -423 F, to store it in high density can be stored in solid metal hydrides or nano-tubes. Many government and private project initiatives has been taken towards the hydrogen energy storage applications namely few from Xcel Energy, NREL wind to hydrogen project. House at National technology near Boulder, Colorado etc. uses the PV with electrolyzer which produces hydrogen and stored in compressed form for later use.

Kigim et. al and moreover in [1] has proposed operation of hydrogen production from the use of RES (renewable energy sources). The proposed model delivers the energy in residential sector.

Figure 3 Hydrogen conversion process [1]

Figure 3 represent the power and hydrogen flow which is based on the RECSR project presented in (Nigim, 2015, p. 473) The key component of the system is Energy Management Dispatcher (EMD), which control the central hub and receive signal from smart sensing devices which are connected across the power lines.  Use of electrolyzer also important with the help of two discretely controlled hogenm each of them can generate 0.6 s-ltr/m. Moschetto et. al and moreover  presented study on modelling of integrated RES supported hydrogen storage. Below in figure represented IRES scheme which is suitable for off grid electrification means in isolated residential purpose it is best suitable also provide less environmental effects. Other benefit of high capacity and log term energy storage battery bank also offers cost effective and environmental friendly solution.

Figure 4 Electrolyser and storage configuration[2]

In (Moschetto, 2007, p. 2088) laboratory setup and simulation has been carried out and suggested further improvement of photovoltaic model which is stochastic in nature. VI characteristic also analyze and variable temperature and wind speed effect on photovoltaic presented.

Figure 5 Electric Bus connection

References

Nigim, K., McQueen, J. and Persohn-Costa, M., 2015, October. Operational modes of hydrogen energy storage in a micro grid system, Electrical Power and Energy Conference (EPEC),  IEEE pp. 473-477

Moschetto, A., Giaquinta, G. and Tina, G., 2007, Modelling of integrated renewable energy systems supported by hydrogen storage Power Tech,  IEEE Lausanne,  pp. 2088-2092

Givler, T. and Lilienthal, P., 2005, Using HOMER Software, NREL's Micropower Optimization Model, to Explore the Role of Gen-sets in Small Solar Power Systems; Case Study Sri Lanka  National Renewable Energy Lab., Golden, CO (US).

bin Othman, M.M. and Musirin, I., 2010, June. Optimal sizing and operational strategy of hybrid renewable energy system using homer Power Engineering and Optimization Conference (PEOCO), 2010 4th International  pp. 495-501

Lambert, T., Gilman, P. and Lilienthal, P., 2005, Micropower system modeling with HOMER. Integration of alternative sources of energy, pp.379-418.

Granovskii, M., Dincer, I. and Rosen, M.A., 2006, Economic and environmental comparison of conventional, hybrid, electric and hydrogen fuel cell vehicles Journal of Power Sources, 159(2),  pp.1186-1193.

Jacobson, M.Z., Colella, W.G. and Golden, D.M., 2005, Cleaning the air and improving health with hydrogen fuel-cell vehicles’ Science, 308(5730), pp.1901-1905.

Bugler, J.W., 2007, The determination of hourly insolation on an inclined plane using a diffuse irradiance model based on hourly measured global horizontal insolation.  Solar Energy, 19(5), pp.477-491.

Chen, H., Cong, T.N., Yang, W., Tan, C., Li, Y. and Ding, Y., 2009, Progress in electrical energy storage system: A critical review, Progress in natural science, 19(3), pp.291-312.

Fellay, C., Dyson, P.J. and Laurenczy, G., 2008, A viable hydrogen?storage system based on selective formic acid decomposition with a ruthenium catalyst, Angewandte Chemie International Edition, 47(21), pp.3966-3968.