The Possibility of Using Fuel Cells with Wind Turbines for Rural Electrification in Ethiopia

Post date: Dec 26, 2011 9:02:59 AM

by Moges Ashagrie Retta, Msc Thesis

Abstract

Among the common renewable options for supplying electricity to remote locations is using wind turbines coupled to diesel generators with larger battery banks. Its dependency on diesel and thus sustainability could be improved by using hydrogen storage and fuel cells. To study the performance of the system, a typical rural electric load consisting of household electricity, small business facility, health post, school and water pump is modeled along with system components. The wind resource data for two locations Addis Ababa and Nazareth have been used. Simulation and optimization of the energy system are carried out in HOMER and numerous alternative implementable system designs have been proposed. The results show that the use of fuel cells enabled enhanced energy autonomy, higher renewable energy contribution and less CO2 emission with moderate increase in net present cost. Sensitivity study on diesel price, wind speed, average electric load has also been carried out.

Key words: Fuel cells, hydrogen storage, HOMER, net present cost, renewable fraction

File attached at the bottom!!

Introduction

Hydrogen derived from renewable sources such as wind and solar is clean, self-sufficient and a permanent energy solution for sustainable development. A kilogram of hydrogen is roughly equivalent to a gallon of gasoline in energy content. [22] This makes hydrogen a technology of the future in reducing reliance on imported fuel and greenhouse gas emissions. Particularly in remote areas with plentiful renewable energy resources, but grid extension is not cost-effective and diesel cost is high because of transport, hydrogen energy systems are logical.

In rural Ethiopia where a majority of the population lives, access to electricity is very low. The people in these areas use small kerosene lamps that emit eye irritant smoke and very dim light. Lack of electricity hampered the development of various infrastructures such as basic health posts, schools, small business and telecommunication. Hydropower is the major electricity source in Ethiopia with installed capacity of 668.8MW in 2006 and a planned capacity of 4303.8MW in 2013. [2] The electrification is 15% in 2009 as reported in by international energy agency [3] and literature. [4,2] This value is well below the sub-Sahara average of 29% in 2009. [3] Further, it is argued the numbers mentioned are based on the population count near the grid and the real access is very much lower. The electrified rural areas account to 1% [2] while the potentials of renewable energy resources are; wind 10, 000MW, solar, average insolation of 5.26kWh/m2 across the country and geothermal, 700MW. [2]

Several wind hydrogen energy system researches for remote area power supply [4, 5-8] and for hydrogen production usually combined with PV [9-17] have been carried out. The researches all agree on the potentials and near term competitiveness of wind hydrogen systems.[12,13,14] However, the capital costs of components are the major hurdles in the competitiveness of hydrogen based systems. Using an updated modeling tool HYDROGEMS, the research [13] studied wind hydrogen energy system with 600KW wind turbine, 55KW hydrogen generator, 10KW fuel cell, 10Nm3/h electrolyzer and flywheel and battery storage. The study used 2005 market survey cost data with electrolyzer cost of 2500$/KW and fuel cell capital cost of 3125$/KW. It was shown that the system, although not the cheapest, would reach much higher renewable fraction of 96% and operated in 100% stand alone mode for 50% of the time. The important advantages of the system are the higher energy autonomy and more reliable power. In another study, [14] , the system could substitute diesel power plants and may be better than grid extension If strong wind resources are available.

Materials and methods

Wind energy potential assessment

An earlier study shows there is west - east and south-north increase of wind speed in the country. [15] The most recent study, [16], on four major towns in Ethiopia, Mekele, Addis Ababa, Nazareth and Debre Zeit, identified the resource in Addis Ababa and Nazareth as wind class 2. Since strong wind conditions are required for effective use with hydrogen technologies, these two towns are selected for further study. The wind profiles are shown in figure 1 and figure 2.

Figure 1 Wind speed profile of Nazareth

Figure 2 Wind speed profile of Addis Ababa

Modeling rural electric load

To make good use of economy of scale in wind-hydrogen energy system, larger size of 500 families having school, clinic, grinding facility and water pumps is considered. The electrical loads are determined as discussed below.

Household load

The households have one 60W light bulb for the main house where most of the gathering takes place and a 5W light bulb for the bedroom. The use of LED light bulbs is not considered because of the current high cost [20]. Three hours of electricity at night, 18:00 to 21:00 is assumed sufficient because normally 21:00 is the last time to go to bed in Ethiopia. The 5W Led light is assumed to stay in 1hr longer for bedroom considering time for sleep preparation.

Health post load

The RHC has a vaccine refrigerator which is compulsory for keeping vaccines for medication and two light bulbs for assumed 2 rooms. It is used to keep the vaccines in safe storage for 24hr/day at temperatures 2-8oC. Communication VHF 3W radio has been included for the RHC.

Small business load

The grinding facility has one 12kW capacity grinder and a 1.1kW capacity small grinder for special crops.

School load

In quantifying the school load, two microscopes and light bulbs for night school has been assumed. For a family size of 5 per household with 2 adults and 3 children, the community will have at maximum 1000 children and 1500 adults. Assuming a better class size of 20-40 children, 40 classrooms are required for children assuming 100% primary education cover. For adult education in night school, a maximum of the 20 classrooms should have a light bulb. It is assumed that 40W light bulb is enough for each class room for 3hr in the evening.

The total load calculated by homer is 267KWh/day and 63KW peak. A daily noise of 20% and hourly noise of 15% have been used to give a more realistic load distribution.

Figure 3 Daily load profile of the model village

The figure shows the time distribution of the load. Grinding machines consist of the major daily load and light bulbs are the major evening loads. The refrigerator is working all day and after 06:00 the grinding business starts. The school load adds up to the load to reach a peak of 17KW. At night light bulbs and radio add to the load to reach a peak of 35KW power.

Deferrable load

To increase productivity during the dry seasons, water pumping is essential. Assume 10 electrical pumps with a rating of 150W each and a capacity of 10lit/min. Assuming 100lit/day for each family, a total of 50, 000lit/day can be supplied for the households in 8hrs. Additional 5, 000lit/day safe drinking water is pumped for the school and the clinic. 12KWh/day energy is required for the households while 1.25 KWh/day is needed for the school and clinic adding up to a deferrable load of 13.25KWh/day. For a storage capacity of three days, the total energy required is 36KWh for the household and 3.75KWh for the school and clinic totaling 40KWh. The peak deferrable load (10 pumps of rating 0. 15KW) is 1.5KW.

In the rainy seasons, June, July and August, and on January schools are closed. This reduces the total deferrable load by 0.6KWh/day. During these seasons, rain is assumed to supplement the water pumping. Assuming 3 of the pumps will be out of operation at these times, the load decreases to 8.4KWh/day. Totally the load in rainy seasons is 9KWh/day. Considering these variations, the yearly load profile is as shown below.

Figure 4 Monthly deferrable load of the model village

Capital cost of equipment

The table below shows summary capital costs of equipment based on several publications between 2001-2007. [ 17,6,18,19]

Table 1 Summary of cost function of wind hydrogen subsystems

This is the best possible approximation of actual costs of the project in Ethiopia. However, because of the import of equipment, lack of local skill and many local factors, the installed project cost is expected to be higher. This could be studied in sensitivity studies.

Results and discussion

Figure 5 the monthly average electric production from wind/fuel cell/diesel system in Addis Ababa

Figure 6 the monthly average electric production from wind/fuel cell/diesel system in Nazareth

Figure 5 shows that more than 50% of the power is produced from diesel generators for most of the months except October to December. In winter season, more than 80% of the power is produced by the diesel generator. The contribution of fuel cells is visible in all the months making them useful in improving availability of power. The table below shows the full report for the system.

Figure 6 shows that more than 50% of the power is produced from diesel generators most of the year unlike that of Mekelle and Addis Ababa. Uniquely, the generator produces more than 80% of the power only on September. The contribution of fuel cells is visible in all the months contributing to better availability of power. The table below shows the full report for the system.

The table below summarizes the fuel cell based systems performance in all locations.

Table 2 summary of simulation results for the four cities

About 43% of the annual demand can be met from renewable using wind/gen/battery system as shown in table 2.(Row 2) This system can be a very good candidate for implementation because of its high renewable proportion. This benefit could be enriched with integration of the hydrogen storage system.(Row 1) The net present cost increased by about 8% for the same operating cost over the system in row 1. It can be a good alternative if considerations are given to other related issues such as future price trend of components and unprecedented rise in diesel price. Compared to the least cost system where the contribution of the diesel generator is 83%, the annual CO2 emission is around 74 ton. It excels both the100% fossil fuel (diesel/battery) system, which has CO2 emissions of 108ton/yr and the least cost system (94ton/yr). (See Appendix)

For the model society around the vicinity of Nazareth, using wind/gen/battery system shown in row 5, about 42% of the annual demand can be met from renewable This benefit could be enriched with integration of hydrogen storage system as shown in row 4 with only 5% increase in NPC for the same operating cost. This system could also be implemented if there is a motive to use the available wind resource. The least cost system shown in row 6 produces only 14% renewable fraction.

So far, the wind resource alone has been used. But the selected locations have also excellent solar resources [20]. This section deals with utilization of solar energy and its impacts on the energy system. The wind and solar profile of Addis Ababa has been taken for illustration. The mean solar radiation in Ethiopia is 5.2KWh/m2.[1] For the purpose of understanding the system performance, solar radiation has been varied from 5-7Kwh/m2 and the wind speed is varied from 3-5m/s. The cost of PV cells is 6000$/KW. [20] The figure below shows the results of the simulation.

Figure 7 Comparison of solar and wind with hydrogen storage

In location with wind speed above 4m/s the wind/FC/Gen system is the least cost option. This is mainly because of the current high capital cost of PV cells. The PV/FC/Gen system is preferable in locations with limited wind resource as could be the case of Dire Dawa. The hybrid Wind/PV/FC /Gen system becomes the least cost option in locations with wind speeds between 3.0-3.8m/s. In conclusion, the use of solar or hybrid solar/wind comes to picture in locations with low to moderate wind conditions.

Conclusion

The performance of a wind hydrogen energy system in powering a model rural village of 500 families having a small business facility, school, health post and water pump has been presented. The wind resource potential of Addis Ababa and Nazareth has been used in the analysis.

While battery based systems provide the least cost option, hydrogen storage systems enabled much higher energy autonomy at low to moderate cost increase. The stored hydrogen can sustain the average electric load for 3-8days as opposed to up to 1 day possible using large number of batteries.

Also, hydrogen storage help is large scale renewable development where the size of battery becomes very high. In this case, the hydrogen storage enables cost effective and long term storage. Environmentally as well, hydrogen based systems have the least pollutant emissions compared to equivalent battery based systems. In conclusion, integration of hydrogen systems enhances the energy autonomy highly with low to moderate cost increase.

The cost of electricity is found to be 30-40 cents/KWh for highly renewable hydrogen based systems. This is much higher than hydro power price (less than 5cents). However, considering the low access to electricity, its environmental advantages, its contribution to development of sustainable society and better life style, the future trend of fossil fuels and equipment costs, this cost should not be considered as high.

Therefore, the use of fuel cells with wind turbines contributes to sustainable development by improving the renewable energy use, reducing emissions and reducing diesel dependency. If due emphasis is given for renewable development, the system must be a priority option.

References

[1] Projekt-Consult GmbH, Dipl.-Ing. Detlef Loy, 2007,” Energy-policy Framework Conditions for Electricity Markets and Renewable Energies A 23 country analysis”, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH Division Environment and Infrastructure, Germany

[2] International energy agency (OECD/IEA), 2009,” World energy outlook”, IEA publications, Paris

[3] Wold-Ghiorgis W., 2002, “Renewable energy for rural electrification in Ethiopia: The case for new energy policies and institutional reform”, Energy Policy, 30(2002) 1095-1105, pp.3

[4] Andrew M., Said Al-H., 2004,” Simulation of hydrogen-based hybrid systems using Hybrid2”, International journal of Hydrogen energy, 29 (2004) 991 – 999, pp.1-9

[5] Christopher J. G., Magnus K, Arne T. H., 2007,” A Norwegian case study on the production of hydrogen from wind power”, International journal of Hydrogen energy, 32 (2007) 1500 – 1507, pp. 1-8

[6] Christopher J. G., Magnus K, Arne T. H., 2007,” A Norwegian case study on the production of hydrogen from wind power”, International journal of Hydrogen energy, 32 (2007) 1500 – 1507, pp. 1-8

[7] Shin’ya O., 2007,” Analysis of a fuel cell micro-grid with a small-scale wind turbine generator”, International journal of Hydrogen energy, 32 (2007) 323 – 336, pp. 1-14

[8] Sonia L., Dario Z., 2009,” Hybrid renewable energy-fuel cell system: Design and performance evaluation”, Electric power systems research, 79 (2009) 316–324, pp.1-9

[9] Kamaruzzaman S., Mohd Z., Wan R., Mohd Y., Baharuddin Y., Nowshad A., 2009, “Performance of a PV–wind hybrid system for hydrogen production”, International journal of Hydrogen energy, 34 (2009) 1973–1978, pp.1-6

[10] Magnus K., Christopher J. G., 2008,” Opportunities for hydrogen production in connection with wind power in weak grids”, Renewable energy, 33 (2008) 1199–1208, pp. 1-10

[11] Ricardo J. M., Herna´n D., 2008,” Hydrogen production from idle generation capacity of wind turbines”, International journal of Hydrogen energy, 33 (2008) 4291 – 4300, pp. 1-10

[12] M.J. Khan, M.T. Iqbal, 2005,” Prefeasibility of stand-alone hybrid energy system for remote applications in Newfoundland”, Renewable energy, 30 (2005) 835–854, pp.3

[13] Øystein U., Torgeir N., Arnaud E., 2009, “The wind/hydrogen demonstration system at Utsira in Norway: Evaluation of system performance using operational data and updated hydrogen energy system modeling tools”, International Journal of Hydrogen Energy, doi:10.1016/j.ijhydene.2009.10.077, pp.4

[14] Leonidas N, Chariton K, Zissis S, Konstantinos P, 2005, “A wind-power fuel-cell hybrid system study on the non-interconnected Aegean islands grid”, Renewable energy, 30 (2005) 1471–1487,pp.1-15

[15] Yacob M., Frances D, 1997,” Assessment of solar and wind energy resources in Ethiopia. II. Wind energy”, Solar energy, S0038-0992X (96)00074-6, pp.1-6

[16] Getachew B., Bjorn P.,”2009”, Wind energy potential assessment at four typical location in Ethiopia”, Applied energy, 86(2009)388-396, pp.6

[17] SØren K., Poul E., Shimon A., 2009, “The economics of wind energy”, European wind energy association, Brussels

[18] A.Kashefi K, G.H. Riahy,SH.M Kouhsari,2009,” Optimal design of a reliable hydrogen based standalone wind/PV generating system, considering components outages”, Renewable enrgy, 34(2009) 2380-2390, pp.5

[19] Christopher J., Magnus K, Arne T., 2007,”A Norwegian case study on the production of hydrogen from wind power”, International journal of hydrogen energy, 32(2007) 1500-1507, pp. 6

[20] Getachew B, Palm B, 2009,” Feasibilty study for standalone solar-wind based hybrid energy system for application in Ethiopia”, Applied energy [2009], doi:10.1016/j.apenergy.2009.06.006

[21] Johanna L., Margaret K.M, Robert M., Annelia M, 2007, ”An analysis of hydrogen production from renewable electricity sources” Solar energy, 88(1) 773-780,pp.3