Constructing an innovative Bio-Hydrogen Integrated Renewable Energy System

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Constructing an innovative Bio-Hydrogen Integrated Renewable Energy System Pao-Long Chang a, Chiung-Wen Hsu b,*, Chih-Min Hsiung c, Chiu-Yue Lin d a

Dept. of Business Administration, Feng Chia University, Taichung, Taiwan Graduate Institute of Management of Technology, Feng Chia University, 100, Wenhwa Road, Seatwen, Taichung, Taiwan c Research Center for Industry and Technology Policy, Feng Chia University, Taichung, Taiwan d Dept. of Water Resources Engineering and Conservation, Feng Chia University, Taichung, Taiwan b

article info

abstract

Article history:

Hybrid Renewable Energy Systems (HRES) offer alternative energy options that deliver

Received 14 January 2013

distributed power generation for isolated loads. However, the production of energy from

Received in revised form

both wind turbines and solar PV systems is weather-dependent. In this study, we devel-

11 March 2013

oped an innovative Bio-Hydrogen Integrated Renewable Energy System (BHIRES) based on

Accepted 21 March 2013

the integration of hydrogen generation from biomass fermentation, renewable energy

Available online xxx

power generation, hydrogen generation from water electrolysis, a hydrogen storage device, and a fuel cell providing combined heat and power. BHIRES can provide electric power,

Keywords:

thermal energy, and hydrogen, with the additional function of processing biomass waste

Biohydrogen

and wastewater. As indicated by results of the economic analysis conducted in this study,

Biomass

the cost of electricity and the average energy cost of using BHIRES are both lower than

Fermentation

those for wind/PV/hydrogen HRES. Therefore, this system is ideal for users in remote areas

Hybrid renewable energy system

such as islands, and farms in mountainous areas. Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

There is a need to discuss the viability and efficiency of serving isolated loads with alternative energy options. Many areas that lack grid power tend to have abundant wind or solar energy resources, and hence renewable hybrid energy systems are popular alternatives for power generation in remote areas. Hybrid Renewable Energy Systems (HRES) are becoming popular alternative energy sources for the stand-alone power generation in remote areas. HRES combines the use of two or more renewable power generation technologies, making the best use of their operating characteristics, and obtains efficiencies that are higher than could be obtained from each

individual power source [1]. However, both wind power generation and solar power generation are dependent on the weather, and thus cannot act as all-weather electric power suppliers. The most frequently used solution is to integrate a wind power turbine, or a photovoltaic power generation module, with a diesel engine power generator [2]. However, the use of a diesel engine has drawbacks, such as additional fuel expenses, and the production of noise and exhaust pollution, which leads to adverse environmental impacts. In order to avoid such issues, the combination of a wind power turbine/photovoltaic power generation module, together with different kinds of energy storage systems, has become the main direction of research related to HRES, and among the various kinds of energy storage technologies,

* Corresponding author. Fax: þ886 4 3507 2145. E-mail addresses: [email protected], [email protected] (C.-W. Hsu). 0360-3199/$ e see front matter Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2013.03.112

Please cite this article in press as: Chang P-L, et al., Constructing an innovative Bio-Hydrogen Integrated Renewable Energy System, International Journal of Hydrogen Energy (2013), http://dx.doi.org/10.1016/j.ijhydene.2013.03.112

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hydrogen energy is a solution with great potential [1]. When hydrogen is produced from wind power plants or solar photovoltaic (PV) systems, it can be stored in order to be used directly in fuel cells, or transported to users through pipelines to produce electricity. A wind/hydrogen energy systems project was started in on Utsira Island in Norway (2004), to establish a renewable energy generation system that included the use of wind power generation with a hydrogen energy application [3]. The PURE (Promoting Unst Renewable Energy) project has been operating in the UK since 2005 [4]. Similarly, a wind power generation and hydrogen generation system has been established in Keratea, Greece, for the testing of technologies related to hydrogen generation based on wind power [5]. In May 1991, Stuart Energy Systems Inc. in Canada installed a PV-powered hydrogen generator on the roof of a factory [6]. In order to further understand and evaluate the prerequisites for sustainable and energy-saving systems, Asea Brown Boveri (ABB) and Fortum have equipped an environmental information center, located in Hammarby Sjo¨stad, Stockholm, Sweden, with an alternative energy system [7]. The Hydrogen Research Institute (HRI) in Canada has conducted research on the application of an integrated renewable energy system in a remote area [8], and a standalone renewable-energy system employing hydrogen-based energy storage was commissioned within the Hydrogen and Renewable Integration (HaRI) project at West Beacon Farm, Leicestershire, U.K [9]. In 2003, the Taipower Company collaborated with the ITRI (Industrial Technology Research Institute) to establish a hybrid power generation system integrating fuel cell, PV, wind power generation, and water electrolysis hydrogen generation technologies, which was installed in Taipei County in northern Taiwan for long-term system operation. Xcel Energy and the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) have collaborated to design, install, and operate the Wind-toHydrogen (Wind2H2) project. NREL seeks to improve hydrogen production from renewable sources efficiently and costcompetitively [10]. One of the major issues that need to be addressed when designing such systems is the necessity of reducing the cost of energy. In the study by Ali and Andrews [11], the storage requirements of PV-based solar-hydrogen systems for remote area power supplies (employing PEM electrolyzers and fuel cells), to meet a range of typical daily and annual demands in remote areas, were investigated using a spread sheet-based simulation model. The result of the calculation shows that the cost of energy used in the system is about $1.37 w 2.34 kWh, based on the size of the hydrogen storage capacity. The result of research conducted by Tu¨rkay and Telli [12] shows that the cost of energy reaches $ 2.187 w 3.391 kW/h when using a combination PV/wind turbine/fuel cell stand-alone hybrid energy system. Shiroudi and Taklimi [13] evaluated the techno-economic aspects of a PV-Electrolyzer-Fuel cell system, investigating a standalone power system consisting of 10 kW PV arrays as the power supply and a 5 kW electrolyzer. The cost of energy (COE) of the proposed hydrogen system was $ 1.216 kW/h. The reason that the cost of energy in a stand-alone HRES is several times higher than that of a normal electric power load,

is the high cost equipment and the installed capacity of the wind turbine and/or PV system. In addition to a continuous reduction in cost for all the kinds of equipment used in HRES, together with the enhancement of hydrogen generation and fuel cell power generation efficiencies, the integration of other low-cost renewable energy technologies is therefore also a direction worthy of investigation. However, with the additional consumption of energy used for the generation of hydrogen from water electrolysis, the cost of power generation via a wind/PV/hydrogen HRES would be very high; this problem needs to be resolved in the future. Therefore, besides anticipating a reduction in the cost of PV/wind turbines, water electrolysis devices, hydrogen storage devices and fuel cells, a combination of other renewable energy methods is a useful direction to investigate. In addition to the usual options: wind power and solar energy, the use of biomass energy is also an important research and development direction for an HRES innovation. The electric power, or heat, generated by biomass substances, would not be affected by the weather, and could therefore be used in combination with wind turbines or photovoltaic modules, to form a composite energy system capable of allweather operation. Research performed in this field includes the use of a bio-hydrogen and PV hybrid energy system [14], a biomass gasification and wind power hybrid energy system [15], a PV/biomass gasifier-based hybrid energy system [16], a biomass gasification/solid oxide fuel cell/gas turbine hybrid energy system [17], and a PV, wind turbine, and biogas generator hybrid energy system [18]. Much research is currently being performed on potential methods for hydrogen generation from biomass, and there are three methods currently used for generation: photofermentation, dark fermentation, and a two-stage process (integration of dark- and photo-fermentation) [19]. Two types of biomass feedstock are necessary for use in these methods, for the production of hydrogen: bioenergy crops and less expensive residues or organic waste [20]. Unused, discarded lignocellulosic biomass from forestry, agriculture, and municipal sources can be considered as potential feedstock for the synthesis of hydrogen. Organic waste offers an economical, environmentally friendly source for the production of renewable hydrogen [21]. However, a major challenge to the development of biohydrogen production systems is the high cost of the feedstock (e.g., glucose-containing feedstock). Several studies have shown that the cost of producing hydrogen from biomass strongly depends on this cost [20]. The solution to this problem evidently includes the use of low-cost feedstock, renewable biomass, and biowaste. Another future commercial application of hydrogen generation from biomass fermentation would be the treatment of biomass wastes generated by households and communities [22]. The use of fermentation hydrogen generation from biomass is an emerging renewable energy application. Based on the current cost of equipment it is feasible to provide added value to organic wastewater treatment systems using dark fermentation hydrogen generation technology [23]. However, the value of the system remains relatively low if it is solely used for hydrogen generation [24]. In order to promote the development and application of hydrogen generation

Please cite this article in press as: Chang P-L, et al., Constructing an innovative Bio-Hydrogen Integrated Renewable Energy System, International Journal of Hydrogen Energy (2013), http://dx.doi.org/10.1016/j.ijhydene.2013.03.112

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 3 ) 1 e1 0

technology from biomass fermentation, we believe that an integration of the technology with other renewable energy power generation devices is worthy of further investigation and analysis. In order to develop the technology for hydrogen generation from biomass fermentation, it is necessary to search for other solutions to reduce the HRES cost of energy. We developed an innovative Bio-hydrogen Integrated Renewable Energy System (BHIRES), based on the integration of the following: fermentation hydrogen generation from biomass, renewable energy power generation, hydrogen generation from water electrolysis, a hydrogen storage device, and a fuel cell for combined heat and power (CHP). Relying completely on renewable energy, a BHIRES has the advantage of sustainability and of delivering zero carbon emissions, and as such, it is an important approach in the provision of electric power, thermal energy, and hydrogen to users in remote areas. In this present study, we propose two solutions: a new BHIRES and a wind/PV/hydrogen HRES. We then compare the energy use of these two systems, in terms of investment cost, power supply capability, and power generation cost.

2.

BHIRES

2.1.

System structure

(3)

(4)

(5)

In order to establish an energy supply system with an allweather electric power supply capability, we propose an innovative BHIRES structure consisting of the major parts listed below (as shown in Fig. 1): (1) Renewable energy generation devices: Users can choose from wind turbine and/or PV power generation systems, according to the local geographic and climate conditions. (2) An electrolysis-based hydrogen generation device: When the electric power generated by the renewable energy

(6)

3

generation device(s) is more than the power load demand of the system, the surplus electric power will be used for the generation of hydrogen from water electrolysis. Device for hydrogen generation using biomass fermentation: Biomass waste can be used as the raw material for CO2, and hydrogen generation using fermentation technology, and high-purity hydrogen can then be obtained using separation and purification devices. Possible source materials include agricultural waste, kitchen waste, and organic wastewater. Solid biomass waste requires effective pre-treatment before entering the fermentation process. The choice of fermentation approaches include: dark fermentation, light fermentation, and lightedark composite fermentation. Electric power is needed for the pretreatment device, fermentation tank, gas separation and purification devices during the process of fermentation hydrogen generation from biomass, and this can be provided by the BHIRES itself. A hydrogen storage device: The hydrogen generated by water electrolysis and the biomass fermentation process can be stored in a hydrogen storage device. Currently there are various approaches used for hydrogen storage, such as compressed hydrogen storage, liquid hydrogen storage, and metal hydrides [25]. A fuel cell: When the electric power (generated by the renewable energy power generation device) is insufficient to meet the demand requirements, the hydrogen can be converted to electric power through a fuel cell. In addition to electric power generation, the fuel cell can also be used as a heat source for hot water and gas heating. Currently, the kinds of fuel cells used for CHP devices include low temperature proton exchange membrane fuel cells (LT PEMFC), high temperature proton exchange fuel cells (HT PEMFC), and solid oxide fuel cells (SOFC) [26]. An electric power output and control device. The purpose of such a device includes: direct current (DC)/alternating current (AC) conversion, stabilization of electric power

Fig. 1 e Bio-Hydrogen Integrated Renewable Energy. Please cite this article in press as: Chang P-L, et al., Constructing an innovative Bio-Hydrogen Integrated Renewable Energy System, International Journal of Hydrogen Energy (2013), http://dx.doi.org/10.1016/j.ijhydene.2013.03.112

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output, electric power security, and the operation and control of all kinds of power generation devices. Chargers and battery modules can be installed in the electric power output and control device, to reduce the risk of a system power outage.

2.2.

System functionalities

(1) Electric power: The electric power, generated by the renewable energy generation device and fuel cell, can provide DC and AC power that meets local voltage standards, and can be used by external loads through the electric power output and control device. In addition, the electric power needed for the operation of this energy system itself, can also be provided by these DC and AC power sources. (2) Thermal energy: Based on the operating temperature of the CHP device, the thermal energy generated can be used to produce hot water or steam for applications such as indoor heating and hot water. (3) Hydrogen: In addition to providing electric power and thermal energy through the CHP fuel cell, the hydrogen generated by the renewable energy in BHIRES can also be used as fuel for fuel cell vehicles (fuel cell cars and scooters). (4) Biomass waste treatment: Another important functionality of BHIRES is to help with the treatment of regional biomass waste, including agricultural waste (such as sawdust, rice husks, tree branches and plants rich in fiber), kitchen waste, and organic wastewater. These types of biomass waste can be converted into usable energy through fermentation hydrogen generation processes that would also reduce the economic and environmental costs of the original waste treatment. (5) Byproducts for other system applications: During the biomass fermentation for hydrogen generation, other byproducts, such as CO2 and CH4, are generated in addition to hydrogen.

3.

Economic analysis

In order to verify the advantages of BHIRES, in terms of energy supply and power generation costs, we compared a BHIRES solution with a wind/PV/hydrogen HRES solution. The assumptions for the power requirement scenario are as follows: - a daily peak electric power load of less than 10 kW; - an average daily electricity consumption of 80 kWh, and thus a total annual electricity consumption of 29,200 kWh. This is roughly the annual electricity consumption for 5e6 households, or for 16e18 people in Taiwan.

3.1.

BHIRES composition, cost, and energy analyses

3.1.1.

System composition

In accordance with the electric power demand scenario, the system composition of the BHIRES is as shown below:

(1) One set of wind turbines with a nominal power output of 10 kW; one set of photovoltaic power generation devices rated at 10 kW. (2) An alkaline water electrolysis hydrogen generation module, with a nominal power of 5 kW and an electrolysis efficiency of 0.65. (3) The dark fermentation hydrogen generation module consists of pre-treatment equipment, a fermentation tank, and a hydrogen separation and purification device (with hydrogen purity reaching 99.99%). The volume of the fermentation tank ¼ 1 m3, the hydrogen generation rate ¼ 18 m3/day (assuming the concentration of incoming feedstock ¼ 20 g COD/L), and the hydraulic retention time ¼ 7 h [24]. (4) The fuel cell CHP module, based on PEMFC, has a nominal power output of 10 kW. The power conversion efficiency of the CHP device ¼ 40%, while the thermal energy conversion efficiency ¼ 50%, based on the calculation of hydrogen’s low heating value (LHV). (5) The compressed hydrogen storage capacity ¼ 12 kg and the hydrogen storage pressure ¼ 10 bar. (6) The electric power output and control device include a 15 kW DC/AC inverter, and other necessary control equipment.

3.1.2.

Cost analysis

A cost analysis of the energy supply system is shown below: (1) Wind turbine: A 10 kW wind turbine is regarded as a small wind turbine (SWT), with an equipment investment that is cost dependent on the wind turbine maker and the installation area. In the USA, the installed cost of a SWT ranges from 3000 to 6000 USD/kW. In contrast, the installed cost of a SWT in China averages approximately 10,000 CHY (1580 USD)/kW [27]. In this study we use statistics employed by the Ministry of Economic Affairs (MOEA) of Taiwan, for the calculation of the renewable energy feed-in tariff, where the installation cost of a wind turbine rated below 10 kW ¼ NTD 130,000/kW (USD 4333/ kW, NTD/USD ¼ 30), and the annual O&M cost ¼ 1.5% of the installation cost (USD 65/kW) [28]. The equipment cost of a 10 kW wind turbine is ¼ USD 43,330. The annual amortization cost ¼ USD 2,167, based on a lifetime of 20 years. The annual O&M cost ¼ USD 650. (2) PV power generation device: In 2010 the installation cost of solar PV was around USD 4.59/W (commercial rooftop) and USD 5.71/W (residential rooftop) [29]. In this study we use the mean value of USD 5.15/W, while the annual O&M cost ¼ 0.5% of the installation cost with a lifetime of 20 years [30]. The equipment cost of a 10 kW PV system ¼ USD 51,500, and the annual amortization cost ¼ USD 2,575, based on a lifetime of 20 years. The annual O&M cost ¼ USD 258. (3) Water electrolysis hydrogen generation device: Currently, commercialized water electrolysis hydrogen generation devices can be divided into two categories, alkaline and PEM. The former uses a more mature technology, has lower equipment costs and a longer lifetime, yet the installation volume is larger owing to a lower electrolysis efficiency. PEM electrolysis devices are a relatively new

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technology with a compact size and high electrolysis efficiency. However, the current market for products in this category is still facing issues related to the high prices and short product lifetime. The results of NREL research have indicated that the equipment cost of a PEM electrolyzer is around USD 5000/kW [31] when the installation size is less than 10 kg/day. Therefore, in this study we choose an alkaline electrolyzer with an electrolysis efficiency of 0.65, where the cost ¼ 1290 V/kW (USD 1568/kW, V/USD ¼ 1.2156), the lifetime is 10 years, and the annual O&M cost ¼ 21 V/kW (USD 26/kW) [32]. The equipment cost of a 5 kW alkaline electrolyzer ¼ USD 7840. The annual amortization cost ¼ USD 784, based on a lifetime of 10 years. The annual O&M cost ¼ USD 130. (4) Dark fermentation hydrogen generation device: Since there have not been any commercialized dark fermentation hydrogen generation systems available at this point, it is rather difficult to establish specific cost information. In the research by Chang and Hsu [24], a value analysis of a dark fermentation hydrogen generation system with the material sources of sucrose-containing wastewater and solid biomass waste was conducted in a fermentation tank with a volume of 10 m3. For this study, we have used a lot of different cost information listed in that particular literature, as the basis for establishing the cost of a hydrogen generation system with a 1 m3 fermentation tank in a proportional manner. Based on the consideration of higher unit prices for smaller systems, we have added an extra 20% to the cost estimation. For example, if the equipment cost of a 10 m3 fermentation hydrogen generation system ¼ USD 133,333, the cost of 1 m3 hydrogen generation system should be USD 16,000. The breakdown of the cost of a dark fermentation hydrogen generation device is as shown below: A. The cost of pre-treatment equipment ¼ USD 4800, and the annual amortization cost ¼ USD 320, based on a lifetime of 15 years. B. The cost of a fermentation hydrogen generation tank ¼ USD 16,000, and the annual amortization cost ¼ USD 1067, based on a lifetime of 15 years. C. The cost of gas separation and hydrogen purification equipment ¼ USD 14,800, and the annual amortization cost ¼ USD 1480, based on a lifetime of 10 years. D. The annual O&M cost for the aforementioned equipment ¼ USD 1600. (5) Fuel cell CHP module: CHP modules based on fuel cells are emerging products and as such, the prices vary by manufacturer. According to the analysis by James et al. [33], the cost of a home LT PEMFC system (after mass production) ranges from USD 3620/kW (with an annual production of 1000 sets) to USD 2768/kW (with an annual production of 10,000 sets). However, the actual cost remains high, owing to the small production volume. By referencing research studies by other scholars [34], in this study we assume the cost of CHP PEMFC ¼ USD 5000/kW, with a lifetime of 4 years [23], and the O&M cost is 1% of the equipment cost. Therefore, the equipment cost of a 10 kW CHP PEMFC ¼ USD 50,000, with an annual amortization cost of USD 12,500, and an annual O&M cost of USD 500.

5

(6) Inverter: Inverters are mature products with a cost of USD 1350/kW, a lifetime of 20 years, and a zero O&M cost [34]. The cost of a 20 kW inverter ¼ USD 27,000, with an annual amortization cost of USD 1350. (7) Water expenses: If solid biomass waste is used as the feedstock, it must be mixed with water during pretreatment. The resulting annual water consumption is 1 m3  24 h/day/7 h (retention time)  365 day ¼ 1251 m3. If we assume the cost of water ¼ USD 0.25/m3 (based on water bills in Taiwan), the annual water bill will be USD 313. (8) Other expenses: Other expenses include the cost of the basic infrastructure required by the energy system and the control systems, which are not included in any of the aforementioned modules. In this study, we assume that the total value of such expenses is equal to 10% of the total equipment cost listed in the aforementioned items (1)e(6), which ¼ USD 233,270. The annual amortization cost will be USD 1166, for 20 years. Based on the aforementioned calculation results, the total annual cost of this BHIRES system ¼ USD 27,850 (as shown in Table 1).

3.1.3.

Amount of energy supplied

(1) Wind power generation In actual application, the total annual electric power that can be generated by a wind turbine depends on the regional wind power characteristics and the installation site of the wind turbine. Taking Taiwan as an example, the average annual full-load power generation time can reach 2300 h (6.3 h/day) [35] in the west coastal areas with strong winds. In this study, we use statistics used by MOEA of Taiwan for the calculation of the renewable energy feed-in tariff, and we calculated the amount of electric power generation from the wind turbine based on an average annual full load power generation time of 2000 h (5.48 h/day) [28]. In a BHIRES system, if the amount of power generated is more than the external load demand, the surplus electricity will be used for hydrogen generation by water electrolysis. If 10% of the annual electric power generated by the wind turbine has been used for hydrogen generation, the actual annual electric power that can be used will be: A. The total annual power generation by a 10 kW wind turbine is 10 kW  2000 h ¼ 20,000 kWh. B. With a 10% ratio of hydrogen generation electricity consumption, the electricity consumption by hydrogen generation is 20,000 kWh  0.1 ¼ 2000 kWh. C. With an electrolysis efficiency of 0.65, the electric power required for producing 1 kg of hydrogen is 39.42 kWh/kg/ 0.65 ¼ 60.65 kWh/kg, where the 39.42 kWh/kg is the high heating value of hydrogen. Therefore, the total annual hydrogen generation is 2000 kWh/60.65 kWh/kg ¼ 33 kg. D. If we assume the power generation efficiency of the fuel cell CHP module is 0.4, and a heating efficiency of 0.5, the electric power which can be generated by 33 kg of hydrogen is 33 kg  33.31 kWh/kg  0.4 ¼ 439 kWh, where

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Table 1 e Cost analysis of the BHIRES. Device

Unit cost (A) (USD/kW)

Capacity (B) (yr)

Lifetime (LT)

ICC(A  B)

ICC/LT

O&M

Annual cost

4333 5150 1568 1500 5000

10 kW 10 kW 5 kW 12 kg 10 kW

20 20 10 20 4 15 15 10

43,330 51,500 7840 18,000 50,000 4800 16,000 14,800

2167 2575 784 900 12,500 320 1067 1480

650 258 130 90 500

1350

20 kW

20

27,000

1350

2817 2833 914 990 13,000 320 1067 1480 1600 1350 313

Wind turbine Solar PV Electrolyzer Hydrogen Storage FC CHP Bio-H2-E1a Bio-H2-E2b Bio-H2-E3c Bio-H2 O&M Inverter Water for Bio-H2

1600 0

Other costs

1166

Total annual cost

27,850

a Fermentation equipment. b Gas separation and purification equipment. c Gas separation and purification equipment.

the 33.31 kWh/kg is the LHV of hydrogen. The thermal energy which can be generated by 33 kg of hydrogen is 33 kg  33.31 kWh/kg  0.5 ¼ 549 kWh. The actual annual electric power available is (1  0.1)  20,000 kWh þ 439 kWh ¼ 18,439 kWh. The calculation results of actual annual electric power and thermal energy available from a wind turbine with hydrogen generation electricity consumption ratios of 10%e50%, are shown in Table 2.

the average amount of annual power generation per kW of installed capacity of 1200 kWh (3.29 kWh/d/kWp) [30] to calculate the amount of electric power generated by the photovoltaic power generation system. The calculation results of actual annual electric power and thermal energy available from a 10 kW photovoltaic power generation system, based on different ratios of hydrogen generation electricity consumption, are shown in Table 3. The calculation approach is similar to that for the aforementioned wind power generation system.

(2) PV power generation

(3) Dark fermentation hydrogen generation

Similar to the wind power generation analysis, the actual annual power generation of the PV power generation device depends on the intensity and time of sun irradiation at the installation site. Taking Taiwan as an example, the capacity of solar PV systems is 2.66e3.98 kWh/d/kWp [36], meaning that every day an average of 2.66e3.98 kWh of electric power can be generated by every kW of installed PV equipment. In this study, we use statistics used by MOEA of Taiwan for the calculation of the renewable energy feed-in tariff, and we use

The calculation approach for the electric power and thermal energy that can be generated annually by the dark fermentation hydrogen generation module, is shown below: A. The annual hydrogen production is 1 m3  18 m3/(m3day)  365 day ¼ 6570 m3, which is equivalent to 591 kg (the specific mass gravity of hydrogen is 0.09 kg/m3). B. If we assume the power generation efficiency of the fuel cell CHP module is 0.4 and a heating efficiency of 0.5, the

Table 2 e Actual annual electric power and thermal energy available from a 10 kW wind turbine. Energy produce

Electricity consumption for hydrogen generation (kWh) Annual amount of hydrogen generation (kg) FC power generation (kWh) Annual electric power available (kWh) Annual thermal energy available (kWh)

Ratio of hydrogen generation electricity consumption (%) 10

20

30

40

50

2000

4000

6000

8000

10,000

33

66

99

132

165

439 18,439

879 16,879

1318 15,318

1758 13,758

2197 12,197

549

1099

1648

2197

2746

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Table 3 e Actual electric power and thermal energy available annually from a 10 kW photovoltaic power generation system. Energy produce

Electricity consumption for hydrogen generation (kWh) Annual amount of hydrogen generation (kg) FC power generation (kWh) Annual electric power available (kWh) Annual thermal energy available (kWh)

Ratio of hydrogen generation electricity consumption (%) 10

20

30

40

50

60

1200 20 264 11,064 330

2400 40 527 10,127 659

3600 59 791 9191 989

4800 79 1055 8255 1318

6000 99 1318 7318 1648

7200 119 1582 6382 1977

electric power which can be generated by 591 kg of hydrogen is 591 kg  33.31 kWh/kg  0.4 ¼ 7878 kWh, and the thermal energy that can be generated by 591 kg of hydrogen is 591 kg  33.31 kWh/kg  0.5 ¼ 9848 kWh. C. According to research by NREL, 4.1 kWh of electric power will be consumed for generating 1 kg of hydrogen by the dark fermentation process (including purification and storage) [37]. Because there are different ways to handle the pre-treatment procedure and different amounts of electric consumption are used in the processing of biomass waste, this study assumes that it takes 2 kWh of pre-treatment to product 1 kg hydrogen in the process of dark fermentation. Therefore, the production of 591 kg of hydrogen will consume a total of 3605 kWh. D. The available annual electric power generated by the dark fermentation hydrogen generation module will therefore be: 7878 kWh  3605 kWh ¼ 4273 kWh. (4) Annual available electric power In this study, we assume that in our BHIRES system, the electricity consumption ratio of annual hydrogen generation by the wind turbine is 30%, and the electricity consumption ratio of annual hydrogen generation by the PV power generation module is 10%. Based on the results in Tables 2 and 3, the available power generated by the wind turbine and PV power generation module are 15,318 kWh and 11,064 kWh, respectively. Therefore, the total available annual power generation by the BHIRES is 15,318 þ 11,064 þ 4273 ¼ 30,655 kWh, which is more than the 29,200 kWh needed for the power consumption scenario. (5) Total annual heat generation Based on the results of Tables 2 and 3, the annual amounts of heat generated by the wind turbine and PV power generation modules, are 1648 kWh and 330 kWh, respectively. Therefore, the total annual heat generated by the BHIRES is 1648 þ 330 þ 9848 ¼ 11,826 kWh.

3.1.4.

Electricity and energy costs

In Table 1, the total annual cost of the BHIRES ¼ USD 27,850, with a total annual electricity generation of 30,655 kWh. Therefore, the electricity cost ¼ USD 27,850 per 30,655 kWh ¼ USD 0.908/kWh. If the use of thermal energy is included, the average cost of the energy supplied by the BHIRES will be USD 27,850/(30,655 kWhe þ 11,826 kWht) ¼ USD 0.656/kWh. Because the fermentation hydrogen generation from biomass remains in the developmental stage, the

equipment cost is still quite high. In the future, therefore, further cost reductions related to equipment and the power generation costs of BHIRES would be made, when both the technology and product have become more mature.

3.2.

Wind/PV/hydrogen HRES

3.2.1.

System composition

Based on the electric power demand scenario, the system composition of the HRES is shown below: (1) One set of wind turbines with a nominal output power of 10 kW, and one set photovoltaic power generation devices rated at 30 kW. (2) An alkaline water electrolysis hydrogen generation module, with a nominal power demand of 10 kW and an electrolysis efficiency of 0.65. (3) The same fuel cell CHP module and compressed hydrogen storage device as for the BHIRES. (4) Electric power output and control device include a 40 kW DC/AC inverter and other necessary control equipment.

3.2.2.

Cost analysis

The cost analysis of the energy supply system is shown below: (1) Wind turbine, compressed hydrogen storage device, and inverter: The annual costs for these devices are the same as that for the BHIRES. (2) Photovoltaic power generation device: The equipment cost of a 30 kW PV system ¼ USD 154,500, with an annual amortization cost of USD 7725 and an annual O&M cost of USD 773. (3) Water electrolysis hydrogen generation device: The equipment cost of a 10 kW alkaline electrolyzer ¼ USD 15,680, with an annual amortization cost of USD 1568 and an annual O&M cost of USD 260. (4) The cost of a 40 kW inverter ¼ USD 54,000, with an annual amortization cost of USD 2700. (5) Other expenses: The calculation principle for other expenses is the same as for the BHIRES, and 10% of the total cost of the HRES equipment ¼ USD 335,510 with an annual cost of USD 1678. Based on all of the aforementioned calculation results, the total annual cost of such an HRES ¼ USD 31,510 (as shown in Table 4).

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Table 4 e Cost analysis for the wind/PV/hydrogen HRES. Device

Unit cost (A) (USD/kW)

Wind turbine Solar PV Electrolyzer Hydrogen storage FC CHP Inverter

4333 5150 1568 1500 5000 1350

Capacity (B) 10 30 10 12 10 40

kW kW kW kg kW kW

Lifetime (LT) (yr)

ICC(A  B)

ICC/LT

O&M

Annual cost

20 20 10 20 4 20

43,330 154,500 15,680 18,000 50,000 54,000

2167 7725 1568 900 12,500 2700

650 773 260 90 500 0

2816 8498 1828 990 13,000 2700

Other cost

1509

Total annual cost

3.2.3.

31,510

Amount of energy supplied

After the installation of the 30 kW PV system, the calculation results of actual electric power and thermal energy annually available, based on different hydrogen generation electricity consumption ratios, are shown in Table 5. In this study, we assume that in the HRES, the annual electricity consumption ratio of the hydrogen generation by the wind turbine is 50%, and the annual electricity consumption ratio of hydrogen generation by the photovoltaic power generation module is 60%. The combined capacity of these two devices is 40 kW, which is far beyond the 10 kW needed for peak load. Therefore, the consumption ratio for the hydrogen generation electricity will be increased. Based on the results in Tables 2 and 5, the available electric power generated by the wind turbine and PV power generation module are 12,197 kWh and 19,146 kWh, respectively. Therefore, the total electric power available annually, using the HRES, is 31,343 kWh. The amount of heat generated by the wind turbine and PV power generation modules annually are 2746 kWh and 5932 kWh, respectively, such that the total annual thermal energy generation is 8408 kWh.

3.2.4.

Electricity and energy costs

Based on the results in Table 4, the electricity cost ¼ USD 31,510/ 31,343 kWh ¼ USD 1.005/kWh. If the production of thermal energy is included, the average cost of the energy supplied by the HRES is USD 31,510/(31,343 kWhe þ 8408 kWht) ¼ USD 0.793/ kWh.

4.

Discussion

By meeting specific power load conditions (80 kWh per day with peak loads lower than 10 kW), the power generation cost

of the wind/PV/hydrogen HRES is USD 1.005/kWh, as a result of the above analysis. By using the BHIRES, this cost can be lowered by 9.6%, to USD 0.908/kWh. The average cost of energy supplied (including electric power and thermal energy), the HRES costs USD 0.793/kWh and the BHIRES costs USD 0.656/kWh, with a cost reduction of 17.3%. This shows that the BHIRES introduced in this study can provide electric power and thermal energy at a lower cost than the wind/PV/ hydrogen HRES. It is clear from the cost composition, that the cost of solar PV equals a large portion of the annual HRES cost in this study, at 27%. By combining this with use of the BHIRES and the fermentation hydrogen generation from biomass, BHIRES could provide electricity to the external system loading when the PV and wind turbines shut down during unexpected weather conditions. Although the installation cost of fermentation hydrogen generation from biomass technology for use in the BHIRES would initially be high, the final cost would be less than that of the HRES by 11.6%. As the improvements in manufacturing and application increase, the cost of solar PV will decrease, which would reduce the total cost of the HRES and subsequently reduce the cost of energy. The technology for hydrogen generation from biomass fermentation is still improving and developing. There is much room here for reducing cost, and the promotion of the application of BHIRES could foster technological development for hydrogen generation from biomass fermentation and subsequently lower the cost of related equipment. In addition, a huge amount of CO2 by-product will be generated during the dark fermentation hydrogen generation process, which can be used for various industrial purposes such as the production of food and beverages. Therefore, if we include the revenue from CO2, the total annual cost of the BHIRES can be further reduced.

Table 5 e Actual electric power and thermal energy available annually from a 30 kW PV power generation system. Energy produce

Electricity consumption by hydrogen generation (kWh) Annual amount of hydrogen generation (kg) FC power generation (kWh) Annual electric power available (kWh) Annual thermal energy available (kWh)

Ratio of hydrogen generation electricity consumption (%) 10

20

30

40

50

60

3600 59 791 33,191 989

7200 119 1582 30,382 1977

10,800 178 2373 27,573 2966

14,400 237 3164 24,764 3955

18,000 297 3955 21,955 4943

21,600 356 4746 19,146 5932

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5.

Conclusions

In response to climate change, carbon-free or low-carbon energy applications are important issues, which are being addressed in the field of international development. With respect to the development of emerging technologies, it is now crucial to consider the high cost of development and maintenance. Wind/PV/hydrogen HRES represent a very important part of the possible solution of supplying power to areas with no connection to the power grid. In this study, in order to reduce the power generation cost of wind/PV/ hydrogen HRES and to promote the development and application of hydrogen generation technologies based on biomass fermentation, we have developed an innovative BHIRES based on the integration of fermentation hydrogen generation from biomass and a wind/PV/hydrogen HRES, to provide electric power, thermal energy, and hydrogen with the additional functionality of processing biomass waste and wastewater. The BHIRES introduced in this study can be used to provide electric power, thermal energy, and hydrogen to farms, small communities, schools, and resorts in remote areas, as well as islands, and mountainous areas. The results of this study can also serve as an economic and technical verification of a hydrogen energy application, and we hope they can be used as a feasibility analysis for actual utilization in the future. After an economic assessment for costs involved in the generation of electricity and heat, it was proved that BHIRES delivers a cost advantage in comparison with a general PV/ wind/hydrogen hybrid energy system. Because the BHIRES is a novel concept, there are many details in relation to the design problems, which need to be confirmed and solved before practical application can be carried out. To simplify problems, this study designed the BHIRES and the HRES, based on assumed external electricity load and the ratio of hydrogen generation from the PV/wind turbine. When they are utilized, both the BHIRES and the HRES could potentially be affected by factors such as a variation of external loading and the capacity of the PV/wind turbine generation. Accurate ratios of electricity consumption for hydrogen generation would be able to be obtained when an exact location is confirmed for the system device, along with further information such as a greater than long-term (at least more than one year) loading, and historical weather data. In order to further reduce the cost of energy supply, it is also necessary to optimize the capacity of photovoltaic, wind turbine, water electrolysis, biomass fermentation device, hydrogen storage devices, and fuel cells in relation to the external loading demand and applicable environmental conditions. We consider that it is important that such issues be addressed in further research when developing the BHIRES.

Acknowledgments The authors appreciate the financial support from the National Science Council of Taiwan (NSC 101-3113-P-035-001; NSC 101-3113-P-035-002; NSC 99-2632-E-035-001-MY3).

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