Ky 20220627094801 optimal planning for sustainable hybrid energy systems producing oxygen onsite and considering by product hydrogen for backup power in aquaculture

Ky 20220627094801 optimal planning for sustainable hybrid energy systems producing oxygen onsite and considering by product hydrogen for backup power in aquaculture

OPTIMAL PLANNING FOR SUSTAINABLE HYBRID ENERGY SYSTEMS

PRODUCING OXYGEN ONSITE AND CONSIDERING BY-PRODUCT

Nguyên Nhut Tiena, Vo Tran Thi Bich Chaub, Ryuji Matsuhashi‘

Ll Can Tho University, Can Tho, Vietnam, nntien@ctu.edu.vn

b Can Tho University, Can Tho, Vietnam, vttbchau@ctu.edu.vn

c The University of Tokyo, Tokyo, Japan, matu@enesys.t.u-tokyo.ac.jp

Abstract

This paper presents optimal planning for susta ina ble hybriđ energy systems for the aquacu Itu re sector, wh ích inherently requires intensive energỵ The designed system is energized by renewable resources to produce pure oxygen in situ through water electrolysis for oxygenation according to the changes of dissolved oxygen (00) of species under culture Moreover, the by-product hydrogen from the electrolysis process is used to generate backup power íor the eventual power tailures The mathematical models of the system were developed for simulation and optimization to assess the períormance of the system regardỉng economic and environmental aspects as multi-objective íunctions The merits of the proposed system are demonstrated at a shrimp farm Turthermore, the optimal results showed that the sustainable hybrid energy system operating in grid-connected mode, which possesses such attractive íeatures as producing onsite pure oxygen for oxygenation and utilizing the by-product hydrogen íor generating backup power, could bring sig n if icant beneíits for tarmers thanks to a notable reduction in the annualized cost of the system as well as C0 2 emission in comparison with the conventional system, which is powered by the national grid to run common paddlevvheel aerators for oxygenation.

Keyvvords

Aeration; onsite pure oxygen; electrolyzer; renewable energy; by-product hydrogen.

1 INTRODUCTION

Amongcritical economic scctors in Vietnam, thehshery, including aquaculture, which plays a vital role in the economy of the eountry, has ranked tồiirth However, aquaculture systems consume a high amount of energy, which is used to power the pumping, aeration, wastewater treatment system, heating, and cooling Intensive pumping is essential for transferring water from the sea or river to water treatment ponds, transporting clean water from storage ponds to cultured ponds, and removing wastes from cultured ponds Aeration

is necessary for providing oxygen to assure the health and survivability of species under culture because aquatic animals reared in ponds require a high amount of dissolved oxygen

in the pond, especially in intensive aquaculture systems The intense energy requirement increases the operation cost and causes overload for the power network In addition,

156 TUYỂN TẬP CÔNGTRÌNH KHOA HỌC CỦA CÁC TIẾN SĨTRẺ TỐT NGHIỆP TẠI NHẬT BẢN (2021)

power cuts írequently occur in urban and rural areas; a diesel generator is employed to operate mechanical aerators, causing CO2 emissions into the environment

In general, renevvable energy is one of the best solutions for the above problems Photovoltaic energy is supplied to control the oxygen levels in fish tanks [1] Floating and Aoating-tracking PV systems are employed for shrimp farms in Thailand, producing energy self-sufficiency with high reliability and better competitiveness by limiting energy storage systems [2] A solar-thermal aeration system in [3] is introduced to circulate oxygen to deeper layers of the pond for aquaculture in rural areas Likevvise, wind energy

is solely employed íồr small-scale fish farms in developing countries [4] and small-scale prawn farms in [5] or combined with a PV system in [6] to power the farm Renewable energy is also employed for on-shore and off-shore aquaculture with promising results [7], [8] Besides, hydrogen and lìiel cell technology have recently become an excellent altcrnative resource [9] The hydrogen, which can be stored in large volumes and generated into electricity by fueỉ cells, has dominated other storage technolơgies Proton-exchange membrane fuel cells produce power from hydrogen for aeration systems in stagnant ponds [10], [11] Notably, the local biogas vvaste at a shrimp farm in [12] is used to generatc hydrogen produccd by dry reíorming methane íồr power generation

The pure oxygen prodưccd through electrolysis has been widely applied in the stee! industry, oil and metal rehning, welding, mining, paper industries, food industry, calibration, etc [13], [14] However, there are few studies about utilizing pure oxygen produced from water electrolysis for aquaculture [15], [16] Besides intensive energy demand for pumping, wastewater treatment system, heating, and cooling, the aeration system also acquires dramatically high cnergy demand Nonetheless, conventional aeration systems have low eíTìciency and high energy consumption due to atinospheric oxygenation, which accounts for 21% Using pure oxygen instead of oxygen in the atmosphere íồr aeration system might reducc energy demand and raise yield; nevertheless, the operation cost of the system is expensive due to extra transporting costs ííom suppliers to customers, which causes associated co, emissions

Given these gaps above, this paper proposes optimal planning for sustainable hybrid energy systems to satisfy these concerns The proposed system is applied for the aquaculture industry to adopt renewable energy resources to reduce dependence on conventional power resources, environmental impacts, and save energy The system could provide pure oxygen onsite from the electrolysis process tbr oxygenation according to the DO demand of species under culture Moreover the by-product hydrogen is stored

to provide the farm with backup power for the most critical devices The whole system

is optimized by multi-objective functions, such as the annualized cost of the system and carbon dioxide emission in grid-connected operation mode

TUYỂN TẬP CÔNG TRÌNH KHOA HOC CỦA CÁC TIẾN sỉ TRẺTỐT NGHIẼPTAI NHÂĨ BẢN (2021) 157

2 PROPOSED SYSTEM

2.1 System conhguration

The system components in Figure 1 are divided into power resources, power loads, and cultured ponds Power resources include wind turbines (WT), photovoltaic (PV) arrays, proton-exchange membrane fuel cells (FC), and the national grid as backup power

in on-grid operation mode Moreover, the main power load of the system is the alkaline electrolyzer, while the baseload involves illuminating loads, water treatment systetns, and water pumps

2.2 System operation

Aeration for aquaculture ponds continuously runs all day long to sustain good water quality, although it is required more at night than in the daytime During the day, the primary power extracted from solar panels and wind turbines is converted

to AC and fed into the system The baseload is supplied by stable power because the water treatment system needs steady power to produce clean water for water electrolysis and cultured ponds The remaining energy is used to run the electrolyzer for making oxygen in situ

The pure oxygen from the electrolyzer is compressed vía a short-term oxygen tank

to the microbubble system generating oxygen microbubbles at the bottom of ponds for cultivated specics The aeration system, which is oxygenated by pure oxygen microbubbles with high oxygen absorption eíĩìciency instead of oxygen from the air (21%), rcquires icss energy demand and releases fewer emissions compared to the conventional aeration system since the compressing and the stripping of a signihcant volume of nitrogen from the air is eluded

The Auctuation of DO in cultured ponds is caused by total respiration of sediment, plankton, and species under culture, photosynthesis production, and exchanges with the atmosphere The DO requirement during daytime in the pond is low due to the oxygen supplement from photosynthesis, corresponding with low power demand from the elec- trolyzer Consequently, the electrolyzer is controlled to change its input power As the proposed system is appropriately managed, the energy demand is reduced, leading to low operation costs Besides, the surplus electricity is sold to the national grid vía point of common coupling (PCC) based on feed-in-tariffs (FITs) policy

158 TUYỂN TẬP CÔNG TRÌNH KHOA HOC CỦA CÁCTIẾN sĩ TRẺ TỐT NGHIỆPTAI NHẨT BẢN (2021)

Figu re 1 ỉustainable hybrid energy system for aquaculture íarms

Aeration becomes essential at night becausc thc DO level drops signiíìcantly during the

night due to the ceased activity of photosynthesis and respiration of organisms Thereíồre

keeping suíRcient DO conccntration to protect eultured species f'rom low-oxygen mortality

is necessary In such conditions, WT systems alone might not produce enough energy for the power demand of the whole system, especially the elcctrolyzer Due to a high amount

of oxygen demand or at daylight hours, when renevvable resources cannot satisíỳ' the power load demand, a dehcieney in poxver is inevitable To compensate í'or the energy mismatch of the system, the by-product hydrogen, which is eompressed and stored in a hydrogen tank, is fed into the PEM fuel cell to regenerate electric power to supply the electrolyzer and cover the baseload However, if the power demand is higher than the capacity of the fuel cell, the system is connected to the national grid to purchase electricity

3 MULTÌ-OBJECT1VE OPTIMIZATION FOR THE HYBRID SYSTEM

3.1.0bjectivefunctions

3.1.1 Annualized cost ofsystem (ACS)

The annualized cost of the system, composed of the annualized cost of components

in the system C ACC, the total cost of purchasing clectricity C G p , the total cost of selling electricity CGS , and the total selling cost of dumped hydrogen CHS , is eomputed as follows:

TUYỀN TẬP CÕNG TRÌNH KHOA HỌC CỦA CÁC TIÊN SĨTRẺTỐT NGHIỆP TẠI NHÁT BÁN (2021) 159

3.1.2 Carbon dioxide emission (EMI)

The total amount of' co, emission from the national grid in case of grid-connected operation mode is minimized by the second obịective íunction and expressed as:

(2)

/=1

where EMI is the amount of co, emission of the system during a year (t-CO,), /ị is the power bought from the national grid (W), ande yis the grid emission factor (g-CO,/kWh)

3.2Powerload model

The electric powerPA7Z (W) acquired to run the electrolyzer to keep stable DO in the pond according to the Auctưation of DO is computed by [16]:

PaM = 2Xn-80,^Xa(t), QM = 0,6999 X M (3)

where n H is the number of electrons transíerred per hydrogen molecule, F is the Faraday’s number (96485 c/mol),ợ reprcsents the cell's actual voltage (V), ?7Frefers

to Faradic eíRciency, Qo refers to the total oxygen flow rate produced from electrolyzer (NmVh), TODis the total demand of oxygen for a pond (kg/h), and )] indicates the oxygen absorption eíĩìciency generated by the microbubble system

To compare the íeaturcs of the proposed system with the conventional system run

by mechanical aerators in terms of Acs and EMI , the electrical power requirement for mechanical aerators is taken into account and calculated by the following expression [17]:

“ ma ~ r

AE

w \ iqĩq P ma is the electric power demand of the mechanical aerator (W) and4£ refers

to the aeration efficiency of the aerator (kg/kWh)

3.3 Constraintỉ

The optimization problem attempts to achieve the optimal values of six decision variables, including tilt angle/7,(°), azimuth angle/a(°), PV peak capacity Ppy ak(W ),

WT rated capacity P i y ‘ ì ‘ld (Wr), FC rated capacity Ppc ed (Wr), and the rnass of HT m:unk (kg) The constraints of the variables should be met:

160 TUYẾN TẬP CÔNGTRÌNH KHOA HỌC CỦA CÁCTIẾN sĩ TRẺ TÔT NGHIỆP TẠI NHẬT BẢN (2021)

0 < /3, < 90", - 180" < < 180" 0 < Pl^ < PrP

0 < PWd < Pwi! 0 < Prc" < PĨF. 0 < m llink <

(5)

where Ppv\ Pìvr Pĩc\ and m^âenote the maximum values of PV capacity, WT capacity, FC capacity, and the mass of HT, respectively

3.4 Implementation of nondominated sorted genetic algorithm (NSGA-II)

The optimization simulations are developed in the Matlab environment NSGA-1I, which

is a robust multi-obịective evolutionary algorithm based 011 Pareto-optimal solưtions is utilized to tìnd the optimal system contìguration A lầst non-dominated sorting technique

is employed in NSGA-II to sort the population into various non-dominated levels Furthermore, the obtained Pareto-optimal solutions in this algorithm comprise a set of optimal solutions called the Pareto front

4 RESULTS AND ANALYSIS 0F CASE STUDY

4.1 Case data introduction

The proposcd sustainable hybrid energy system and its optimal planning are applied

to a shrimp fann located at Vinh Chau, Vietnam, situated 9.42° north latitude, 106.7° east longitude, and -8 m elevation The investigated shrimp íầrm consists of ihree grow-out ponds, one pond for storing vvater, and another pond for water treatment Each grow-out pond has a depth of 1.2 m and a surtầce area of 1400 m2

Tabie 1 B iophysica I characteriỉtics of grow-out ponds

Suríace area of grow-out pond (m2 ) 1400

Average water temperature (°C) 30

The total oxygen requirement in grow-out ponds, which have biophysical characteristics presented in Table 1, determines the operation mode of the electrolyzer The power consumption of the electrolyzer changes during the day according to losses

TUYỀN TẬP CÕNG TRÌNH KHOA HỌC CỦA CÁC TIẾN síTRÉ TỐT NGHIÊP TAI NHÃT BÁN (2021)_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Ị6[

of oxygen due to the respiration of organisms in ponds and oxygen production by photosynthesis, reaching the highest valuc at night when the photosynthesis activity stops,

as illustrated in Figure 2 Thus, the load proíìle of the system, followed by the pattern of the electrolyzer, demands more electricity at night

4.2 Resultỉ and analysis

The Pareto front optimized in on-grid mode with the total support from the national grid as the secondary backup power system is presented in Figure 3 The increase in the /4GS leads to a signihcant decrease in co, emission, reaching the minimal value at 124.32 tCO, with the/tcsat 152,386 USD Nevertheless, the/icshas negative values indicating that the proposed system is able to procure revenues from selling both surplus electric power to the national grid and dumped hydrogen to local fertilizer ĩactories

Tigure 2 The relationship betvveen oxygen production and consumption rate with power demand at the farm

The optimal solutions from the Pareto front are divided into two groups The group with orange solutions in Figure 3 has .4CS vaỉues lower than/íCS of the conventional sys- tem (CS) run by paddlewheel aerators On the contrary, the costs of the group with purple solutions are higher than those of the cs

A comparison amongst two solutions of interest from orange solutions and the cs povvered by the national grid is illustrated in Table 2 Solution 1 (Sol 1) corresponds

to the lowest value of/tcsand the highest amount of CO; emission among orange solutions, while Sol 2 is the intermediate solution, of which values are nearly equal to the average values of all orange solutions in terms of ẨCS and EM! Hovvever, designers could choose one of the orange solutions in real applieations based on their preíerences

162 TUYỀN TÃP CÔNG TRÌNH KHOA HOC CÙA CÁC TIÊN sĩ TRẺ TÓT NGHIẼP TAI NHẬT BÀN (2021 )

Tigure 3 Pareto íront íor on-grid operation mode.

Table 2 Characteristics of two solutions of interest and conventional aeration system.

-Wind turbine capacity (kW r ) 999.09 998.96

The capacity of PV and WT of Soi I reaches the maximum available values while

the FC is not employed for backup power, which is totally purchased from the national grid Thus, besides selling surplus eleetric power to the national grid, all of the dumped hydrogen from the electrolysis process is collected and sold to fertilizer plants, producing revenues for tầnners of about 9,112 USD in a year By contrast, the amount of emission

released from the grid is high (231.35 tCO,) compared to Sol 2 (208.01 tCO,)

With the utilization of FC as backup power in Sol 2, the amount of co, emission declines considerably compared to Sol 1 and cs (23.34 tCO, and 53.95 tCO,, respectively) The utilization of FC often coincides with HT 111 combination, the extra cost associated with such contìguration is inevitable Although the system cost of Sol 2 is considerably higher than Sol I, it is still signihcantly lower than cs (7.160 USD and 35,090 USD, respectively); hence, íầrmers could save about 27,930 USD per year

TUYÊN TÃp CÔNG TRÌNH KHOA HOC CỦA CÁC TIÊN sĩ TRẺ TỐT NGHIÊP TAI NHẬT BÀN (2021) 163

5.

CONCLUSION

Optimal planning on a sustainable hybrid energy systcm for the aquaculture industry

is proposed in this work The designed system is quite different from the traditional systems for aquaculture in the conbguration and operation To assess pertbrmance and validate results, the simulation and optimization models were developed The optimal results of the proposed system were compared with the cs regarding economic and environmental aspects An excellent avouchment íồund in optimal outcomes shows that when properly designed and operated, the proposed system energized by green energy resources could prodưce pure oxygen in sitii for oxygenation based on the DO demand of species under culture and the by-product hydrogen used to generate backup power The designed hybrid system presents economic and environmental bencbts in comparison with the cs In other words, íàrmers could save operation costs by reducing energy demand and contributing

to environmental protection by limiting co, emissions for their system in the aquaculture industry Moreover, the outcomes from the paper can be guidelines to instruct optimal design and operation for aquaculture farms in Vietnam and other countries

ACKNOVVLEDGMENT

This work is supported by Vietnam Association of Japan Alumni (VAJA) and Toshiba International Foundation (T1FO)

REEERENCES

1 Hahn, F., & Pérez, R (2015) Design and evaluation ot'a dissolved oxygen controller for solar powered fish tanks. Brìtish Journal of AppliedScience & Technology, 5(2), 173.

2 Campana, p E., Wăsthage, L., Nookuea, w., Tan, Y., & Yan, J (2019) Optimization and assessment of tìoating and Aoating-tracking PV systems integrated in on-and off-grid hybrid energy systems Solar Energy, 177, 782-795.

3 Mahmoud, A., Quang, T N., Pavlov, E., & Bilton, A (2015, October) Developrnent of a solar updraíì aeration system for pond aquaculture in resource-constrained environments.

In 2015 IEEE Global llumamtariarì Technology Conference (GỈ1TC) (pp 306-313). IEEE.

4 Mahmudov, K., Mahmoud, A., Sur, s., Cruz, F c., & Bilton, A M (2019) Peasibility of a wind-powered aeration system for small-scale aquaculture in developing countries Energy for Sustainable Development, 51, 40-49.

5 Lai, c M., & Lin, T H (2006) Technical assessment of the use of a small-scale wind power system to meet the demand for electricity in a land aquafarm in Taiwan Renewable

Energy, 31(6), 877-892.

6 Nookuea w„ Campana, p E., & Yan, J (2016) Evaluation of solar PV and wind altematives tbr self renewable energy supply: Case study of shrimp cultivation. Energy Procedia, 88,

462-469.

164 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ TUYỂN TẬP CÔNG TRÌNH KHOA HỌC CỦA CÁC TIẾN sỉ TRÉ TỐT NGHIỆP TAI NHẬT BẢN (2021)

7 Menicou, M., & Vassiliou, V (20 10) Prospective energy needs in Mediterranean oíĩshore aquaculture: Renewable and sustainable energy solutions. Renevvable and Sustainable Energy Reviews, 14(9), 3084-3091.

8 Ferreira, J G., Saurel, C., e Silva, J L., Nunes, J p., & Vazquez, F (2014) Modelling of interactions between inshore and oíTshore aquaculture. Aquaculture, 426, 154-164.

9 Das, H s., Tan, c w., & Yatim, A H M (2017) Fuel cell hybrid electric vehicles: A review on power conditioning units and topologies. Renewable and Sustainable Energy Reviews, 76, 268-291.

10 Doaa, M., Faten, H., & Ninet, M (2012) Ahmed ANew Control and Design of PEM Fuel Cell System Powered Diíĩused Air Aeration System. TELKOMNIKA Indonesian Journaì of Electrical Engữieering, 10(4), 291-302.

11 Atia, D M., Fahmy, F H., Ahmed, N M., & Dorrah, H T (2011) Design and Control OÍPEM Fuel Cell DiíTused Aeration System using Artiíìcial Intelligence Techniques Internatỉonal Journal of Electrical cmd Computer Engineering, 5(9), 1191-1198.

12 Shiratori, Y., Sakamoto, M., Nguyên, T G H., Yamakawa, T., Kitaoka, T., Orishima, H.,

& Dang, c M (2019) Biogas Power Generation with SOFC to Demonstrate Energy Circulation Suitable íồr Mekong Delta, Vietnam.Fuel Cells, 19(4), 346-353.

13 Hurskainen, M (2017) Industrial oxygen deiĩiand in Finland VTT, Jyvăskylă.

14 Kato, T., Kubota, M Kobayashi, N., & Suzuoki, Y (2005) EíTective utilization of by- product oxygen from electrolysis hydrogen production. Energy, 30( 14), 2580-2595.

15 Tien, N N., Matsuhashi, R., & Chau, V T T B (2019) A sustainable energy model for shrimp farms in the Mekong Delta. Energy Procedia, 157, 926-938.

16 Nguyên, N T., & Matsuhashi, R (2019) An optimal design on sustainable energy systcms for shrimp íầrms. IEEE Access, 7, 165543-165558.

1 7 Kuinar, A., Moulìck, s., & Maỉ, B c (2013) Selection of aerators for intensive aquacultural pond.Aquacultiiral Engineering, 56, 71-78.

ABOUTTHE AWARDEE

Electrical Engineering, Can Tho University, Vietnam He received the B.s degree in electrical engineering from Can Tho University, Can Tho, Vietnam, in 2009, the M.s degree in electrical engineering and iníòrmation technology from Otto-von-Guericke University Magdeburg, Magdeburg, Germany, in 2015, and Ph.D degree in electrical engineering and iníồrmation systems at the University of Tokyo, Tokyo, Japan, in 2020 In 2009, he joined the Department of Electrical Engineering, College of Engineering Technology, Can Tho University, as a lecturer His research interests include power system stability and control, optimization for microgrids, renevvable energy generation technology