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diesel green ship operating in standalone and grid-connected mode – Experimental investigation
Energy 49 (2013) 475e483
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Hybrid photovoltaic/diesel green ship operating in standalone and grid-connected mode e Experimental investigation Kyoung-Jun Lee a, Dongsul Shin a, Dong-Wook Yoo b, Han-Kyu Choi c, Hee-Je Kim a, * a
The School of Electrical Engineering, Pusan National University, Jangjeon-dong, Geumjung-gu, Busan, Republic of Korea Korea Electrotechnology Research Institute (KERI), 28-1 Seongju-dong, Changwon 641-120, Republic of Korea c The Korea Ship Safety Technology Authority (KST), Incheon, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 June 2012 Received in revised form 23 October 2012 Accepted 4 November 2012 Available online 1 December 2012
This paper presents the experimental results from the operation of a proto-type green ship in Geoje island, South Korea. As Korea is a peninsula situated between the continent and the sea, its location is ideal for utilizing PV/diesel green ship. After ground testing with a stand-alone PV (photovoltaic) generation system, this PV system was added to a conventional diesel ship. The proto-type green ship consisted of a photovoltaic (PV) generation system, diesel engine, battery energy storage, hybrid control system, and a stand-alone and grid-connected inverter. The aim of the green ship was not only to minimize fuel consumption but also to support the power grid as DG (distributed generation) connected to the smart grid (in land) and micro-grid (in island) in the near future. At the end of this paper, environmental, economic and sensitivity analysis would be discussed mainly based on experimental results. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
Keywords: Green ship Hybrid PV/diesel system Photovoltaic Grid connection Smart grid LabVIEWÔ
1. Introduction Around the world, governments have strived to increase the share of renewable green energy in power production. The main interest has mainly been energy security, increasing prices of carbon-based energy sources and minimizing global warming. Concerning the second, global shipping is a major contributor to GHG (global greenhouse gas) emissions, being responsible for approximately 3% of global CO2 emissions [1,2]. The IMO (International Maritime Organization) is now working to start GHG regulations for global shipping, and is under pressure, e.g. from the EU and UNFCCC (United Nations framework convention on climate change), to apply regulations that will have a substantial impact on emissions [3]. In addition, because global shipping is normally powered by standalone diesel generators for electricity supply, the shipping industry is affected considerably by the increase in global fuel prices. Therefore, the use of a renewable energy resource in the shipping industry would be a great advantage, particularly in reducing CO2 emissions and the dependence on the highly unpredictable diesel price [4]. The mandatory renewable energy targets
* Corresponding author. Tel.: þ82 51 510 2770; fax: þ82 51 510 0212. E-mail address: [email protected] (H.-J. Kim).
in Korea is expected to be 11.0% in 2020 compared to 2.4% in 2008, as shown Fig. 1, which shows increasing trends in the world energy policy [23]. Therefore, every possible method for increasing the proportion of renewable energy is required to meet the goals and expectations. Many studies have examined hybrid energy systems [5e15]. Among the renewable energy sources, the abundant solar energy is most applicable to conventional ships at sea [16,17]. Abdullaha et al. [24] proved that hybrid power schemes are more sustainable in terms of supplying electricity in rural area compared to a standalone PV (photovoltaic) system due to prolong cloudy and dense haze periods. The investigators presented the reliable and cost effective hybrid energy systems [25]. Therefore, a hybrid green ship (hybrid PV/diesel) might be an effective solution. This paper proposes a hybrid PV/diesel green ship operating in stand-alone and grid-connected mode. PV is the primary power source of the system to the electrical loads in the ship, and the diesel engines are used to compensate for the fluctuating electric power from the PV system. A battery bank is also installed in the hybrid system to supply stable power [18]. Unlike a conventional PV hybrid system on land, a hybrid green ship utilizes the free space on the ship. In addition, with grid-connected inverters, the overall power flow is broadened from the smart grid on land to the off-grid on the island, which is more economical than a hybrid PV (stand-
0360-5442/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2012.11.004
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2. Proposed hybrid PV/diesel green ship experimental system The operation of the hybrid PV/diesel green ship is divided mainly into modes A (at sea) and B (in port). The power ratings of the hybrid PV/diesel system were approximately 3.2 kW for the electrical loads, such as lighting, GPS (global positioning system) & Communication system and Video system, in the cruise ship (85 ton). Fig. 2 shows the block diagram of the proposed hybrid system. Table 1 provides details of the hybrid system components. In the conventional ship, two diesel powered generator (20 kW) is installed to meet the occasional peak load of winch motor to pull the ship anchor. The power rating of base electrical loads of ship is under 3 kW, which can be thoroughly covered by the PV system. 2.1. Power conversion system in hybrid green ship
Fig. 1. Renewable energy targets (%).
alone only)/diesel system. Also, Korea is a peninsula which stretches from the north to the south, located in the 33 w 43 north latitude, and in the 124 w 132 east longitude. As Korea is situated between the continent and the sea, its location is ideal for utilizing PV/diesel green ship between the continent and the sea. Therefore, the proposed hybrid PV/diesel green ship is effective in the countries with this territory characteristics. This paper reports the experimental results from the operation of a proto-type green ship in Geoje island, South Korea. After ground testing with a stand-alone PV generation system, the PV system was adopted to a conventional diesel ship. The proto-type green ship consisted of a PV (photovoltaic) generation system, diesel engine, battery energy storage, hybrid control system, standalone and grid-connected inverter. The aim of the green ship was not only to minimize fuel consumption but also to support the power grid through a smart grid in the near future. The remainder of this paper is organized as follows. Section 2 discusses the hybrid system configuration and operation mode. The stability test results for the hybrid green ship equipped with a PV system are given in Section 3. Section 4 discusses the experimental results of the hybrid green ship according to operation mode. Section 5 gives an environmental, economic and sensitivity analysis of the hybrid green ship. Section 4 summarizes and concludes the paper.
As mentioned above, there are mainly two operation modes. Mode A (at sea) is like the stand-alone mode of PV systems on land, as shown in Fig. 2. According to the status of PV power, the electrical loads in ships can be powered by either a battery bank or a diesel generator. The PV arrays on the left and right side of the roof are connected separately to a solar controller (DCeDC Converter) due to the different MPP (maximum power point). Once the cruise ship is in harbor and the battery is full charged, the extra PV power can be utilized through a grid-connected inverter. To meet the input voltage range of the grid-connected inverter, the PV arrays on the left and right are series connected, not requiring an additional power conversion unit, resulting in a doubling of the Voc (open circuit voltage). The control of the hybrid systems is summarized in Fig. 2, where SWA, SWB and SWC are the magnet contact switch controlled by a laboratory-made hybrid control panel. The ATS (auto transfer switch) is installed between the output of the DCeAC inverter (stand-alone) and the output of diesel generator to simply change the operation mode. The monitoring system for the hybrid green ship was established using the LabVIEWÔ program, as shown in Fig. 3. The monitoring system was connected to the PC through a RS232 communication, storing the acquired data in the excel file. The controller board includes an Atmel AVR ATmega 128. The prototype hybrid green ship plied between Geojedo (island) and Somaemuldo (island). Through the experiment, the validity of the hybrid green ship was confirmed.
Fig. 2. Block diagram of hybrid PV/diesel green ship.
K.-J. Lee et al. / Energy 49 (2013) 475e483 Table 1 System component parameters. 200 W under 1 sun (100 mW/cm2), 25 C Voc ¼ 33.2 V, Isc ¼ 8.09 A Module number 4(Ns) 2(Np) 2(group) ¼ 16 Power rating 200 16 ¼ 3.2 kW Battery Cell unit 12 V/100AH Cell number 2(Ns) 8(Np) ¼ 16 Capacity 19.2 kWh Rated voltage 24 V Power DCeDC converter Power rating 1.6 kW conversion (solar controller) 2(group) ¼ 3.2 kW system (MSB; Maximum solar input 150 VDC main switch Output 24 VDC board) DCeAC inverter Power rating 4 kW (stand-alone) Input 22.5e30.8 VDC Output 220 VAC DCeAC inverter Power rating 4 kW (grid-connected) Input 100e370 VDC Output 220 VAC NFB 2P-20A, 2P-30A, 2P-175A MC (magnet MC-32 contact) ATS (auto transfer DMH20 switch) MCU (micro Atmega 128 controller unit) Diesel generator Power rating 20 kW Number 2 Load Basically used Power rating 3 kW electrical loads of ship (lighting, GPS & communication system and video system) Occasionally used Power rating 20 kW electrical loads of ship (winch motor)
PV array
Module unit
2.2. Implementation of the hybrid green ship After the verification experiment of the hybrid PV/diesel system on land in 2010, the proposed system was installed as an 85 ton level of the cruise ship in 2011, in Geoje island. After searching for
477
a suitable ship, a conventional ship was renovated according to the proposed design mentioned above. Unlike the PV plants on land, the total weight of the PV generation system and the wind pressure on the PV arrays are the main concerns regarding the safety of a ship at sea. Approved by the KST (Korea Ship Safety Technology Authority), PV systems were installed on a conventional cruise ship and controlled by a hybrid control panel. 3.2 kW (200W/16 EA) of PV arrays were installed on the back side of the ship, as shown in Fig. 4. A battery bank was installed in the basement of the ship considering the stability of the ship. Section 3 provides details of the safety problems. 3. Stability of hybrid green ship The selected ship for the experiment is a normal passenger ship (85 ton, 263 Passengers). Stability is one of the greatest concerns for a passenger ship. The back side of the dock was renovated according to the design, as shown in Fig. 5, considering the mean height of the passengers, wind pressure and maintenance. During the verification experiment of the hybrid PV/diesel system on land in 2010, the power production of the PV system was measured by changing the tilt angle of the solar panel. The results showed that the group with a 0 tilt showed poor power production due to dirt on the solar panels. In this study, a 15 tilted solar panel was installed instead of the awning of a conventional ship. A polycarbonate sheet, which is a transparent plastic material with outstanding impact resistance, was also installed under the PV arrays for passenger safety. To evaluate the stability of the hybrid green ship, the weight of the each component was checked and assessed by the KST (Korea Ship Safety Technology Authority). The main objective of the KST is to inspect vessels in accordance with the Ship Safety Act to prevent exposing the vessel and crew to any unpredictable dangers that may occur at sea. According to article 28 (Keeping Stability) of the Ship Safety Act in Korea, the owner of a ship that falls in any of the following subsections shall maintain Stability according to the criteria determined/publicly announced by the Minister, provided that in the event a ship determined by the Ordinance of the Ministry of Land, Transport and Maritime Affairs, such as a passenger ship
Fig. 3. Monitoring system for hybrid green ship (LabVIEWÔ program).
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Fig. 4. Proto-type of hybrid PV/diesel green ship (Geoje Island, South Korea/34.7269 N, 128.6042 E).
whose length is 12 m or longer. In connection with Stability under article 28, an owner of a ship shall submit the materials for Stability to the Minister for approval as to whether or not the Stability is appropriate, and shall provide all the necessary materials approved for Stability to the captain of the ship [19]. In this study, a conventional ship was modified to a hybrid green ship without changing the main frame size of the ship. The KG (vertical center of gravity) and LCG (longitudinal center of gravity) were affected slightly by the removal and installation of the components, such as PV arrays, power conversion units and polycarbonate sheets. An authorized inspector checked the
renovated hybrid green ship, and identified an increase in the LIGHT WEIGHT (approximately 1.154 tons, 1.38% increase), displacement of the KG (0.033 m increase) and LCG (0.029 m to the bow of a ship). The renovated hybrid green ship passed the stability inspection by the KST, as shown in Table 2, showing a displacement of LIGHT WEIGHT between 0.5% and 2.0% with an increase in KG. In the proposed green ship, total increased weight is 1.154 ton, which is the 1.3% of the total weight of ship and 7% of the total weight of the maximum number of passengers with the average weight of an adult human (62.0 kg), which did not impact energy saving potential.
Fig. 5. Installation drawing of PV arrays.
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Table 2 The stability assessment of the hybrid green ship (LCG and KG). Inspection sheet 1. New light calculation Item Old light Deduction Addition New light 2. New LIGHT WEIGHT & KG displacement (1) LIGHT WEIGHT displacement: (2) KG displacement: (3) LCG displacement: 3. Result (under the Ship Safety Act) KG (increase) The displacement of LIGHT WEIGHT (W) (%)
KG (decrease)
The displacement of LIGHT WEIGHT (W) (%)
Weight [t] 83.333 0.032 1.186 84.487
LCG [m] 1.224 6.700 0.672 1.195
Moment [T m] 101.936 0.214 0.797 100.925
1.154 0.033 0.029
[t] Increase (approximately 1.38%) [m] Increase [m] Increase to the bow of the ship
W < 0.5 0.5 W < 2.0 W 2.0 W < 1.5 1.5 W < 2.0 W 2.0
KG [m] 1.513 6.150 3.996 1.546
Moment [T m] 126.091 0.197 4.739 130.633
Exemption of stability test Ship stability calculation with (displaced LCG, original KG value) Retest Exemption of stability test Ship stability calculation with (displaced LCG, original KG value) Retest
*Decision: evaluated LIGHT WEIGHT (KG increased, the displacement of LIGHT WEIGHT (W)(%) is between 0.5% and 2.0%. Deduction item Item Weight [t] LCG [m] Tent 0.032 6.700 Total 0.032 6.700 Addition item Item Weight [t] LCG [m] Steel structure 0.187 6.700 PV arrays 0.306 6.700 Polycarbonate sheets 0.143 6.700 Battery bank 0.400 9.750 Inverter, converter 0.028 9.750 Control panel 0.122 7.250 Total 1.186 0.672
Moment [T m] 0.214 0.214
KG [m] 6.150 6.150
Moment [T m] 0.197 0.197
Moment [T m] 1.253 2.050 0.958 3.900 0.273 0.885 0.797
KG [m] 6.250 6.250 6.250 0.500 0.500 4.500 3.996
Moment [T m] 1.169 1.913 0.894 0.200 0.014 0.549 4.739
The experimental results presented in this section were recorded after an inspection by the KST and obtaining permission of ship operation by the Korean Maritime Police. The experiment was conducted according to the operation mode, as mentioned in Section 2. First, in stand-alone mode, the output of the PV arrays and the battery bank were checked with only the DC loads turned on, such as lighting, communication and GPS (global positioning system) equipment. Fig. 6 presents the PV array voltage of the left side (VPV_Left), the PV array current of the left side (IPV_Left), the battery voltage (VBatt) and battery current (IBatt) to the DC loads. In Fig. 5,
VPV_Left ¼ 107.26 V and IPV_Left ¼ 2.38 A, resulting in a power of 255 W to the solar controller. In addition, the battery voltage was 25.7 V, which is equal to the output of the solar controller, and the battery current was 2.401 A during charging. In this case, the power to the loads was less than the power from the PV arrays. Fig. 7 shows the battery voltage (VBatt), battery current (IBatt), voltage of the stand-alone inverter (vINV) and current of the standalone inverter (iINV) to electrical loads in the operation of the passenger ship between Geojedo (island) and Somaemuldo (island). Unlike Fig. 6, during the course, the electrical loads included the DC and AC loads. In the experiment, a PWM (pulse width modulation) modified sine wave type was used for the standalone mode inverter, as shown in Fig. 7, resulting in a square
Fig. 6. Experimental waveforms at PV arrays.
Fig. 7. Experimental waveforms in the stand-alone mode (before the cruise).
4. Experimental results of hybrid PV/diesel green ship
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Fig. 8. Experimental waveforms in the stand-alone mode (during the cruise).
waveform voltage and current with 60 Hz. During the measurement, the power supplied to the loads was approximately 773 W. Fig. 8 shows the logged data of PV production and power to the loads during the cruise. The passenger ship began to cruise at 10:24 AM (21 July, 2011) from Geojedo (island) to Somaemuldo (island). There was a difference in power output between the PV array of the left side and the PV array of right side. This is because the PV arrays were tilted 15 (See Fig. 4) and the passenger ship was affected by the movement of rolling, pitching and yawing. On the other hand, to solve the problem of different MPP, the solar controllers were connected separately to the PV arrays in each side, tracking the MPP per arrays. The electrical loads were varied arbitrarily by the captain of a ship. When the output power of the PV arrays was higher than the electrical loads, the battery bank was charged by the excess amount for later use. On the contrary, the battery bank supported the shortage when the output power from the PV arrays was less than the connected electrical loads. In this study, a grid-connected mode was implemented when the ship was at anchor in the harbor. The PV arrays were series connected using a simple change in magnet switches, resulting in Ns (Number of series connections) ¼ 8, Np (Number of parallel connections) ¼ 2. The open-circuit voltage of the PV arrays in gridconnected mode was 265.6 V, which satisfies the input voltage range of a DCeAC inverter (grid-connected). In the case of grid faults, such as the grid over/under voltage, grid over/under frequency, over current and ground fault, the grid-connected inverter will wait 5 min prior to restarting. Fig. 9 shows the
Fig. 10. Power output of the hybrid PV/diesel systems.
voltage of the PV arrays (VPV_Total), current of the PV arrays (IPV_Total), AC grid voltage (vGrid_INV) and AC grid current (iGrid_INV) at Geojedo (island). The output voltage of the PV arrays in the gridconnected mode was increased to 224 V, which is the voltage at maximum power point (Vmpp). The injected active power to the grid was approximately 600 W at 3:20 PM (27 Sep, 2011) in Fig. 9. The injected grid current includes low-order harmonic components due to the effect of the weak and distorted grid at Geojedo (island), requiring an improvement in power quality using a SAPF (shunt active power filter) in the near future. The performance of the hybrid PV/diesel operation was evaluated by changing the electrical loads arbitrarily when the ship was at anchor in the harbor (31 Oct, 2011), as shown in Fig. 10. During the performance test, a change in operation mode occurred three times from PV mode to diesel mode and vice versa. It takes 8e10 s for the diesel generator to reach normal operation. However, the power from the battery bank supported the transient stability, including critical loads, such as a GPS navigator, LADAR (light detection and ranging) and lighting. 5. Environmental and economic analysis of the proposed hybrid PV/diesel green ship The Korean government has introduced a number of new incentives and support programs, such as “1 million green homes” program. Korea’s electricity prices are cheaper than in Europe and Japan but they are likely to rise in the near future. This will trigger the installation of PV systems on rooftops. On the other hand, these support programs for PV systems are limited to the ground-mount type or roof-top type and a lack of space will be a severe limitation to PV installation. Therefore, the hybrid PV/diesel green ship can be an alternative solution, particularly in the countries with small
Table 3 Annual CO2 emissions and fuel savings for hybrid PV/diesel green ship.
Operating days (annually) Operating hours of the diesel engine (daily) Diesel consumption rate (liter/hr) Diesel (DM grade): density (kg/m3) Diesel (DM grade): % of carbon Emission of carbon (ton) Carbon to carbon dioxide (44/12) Emission of carbon dioxide (ton) Avoided emission of carbon dioxide (ton/yr) Fuel saving (kiloliter) Fig. 9. Experimental waveforms in the grid-connected mode.
Diesel only
70% PV penetration
150 6 3 830 85 1.905 3.667 6.984 e e
150 1.8
0.571 2.095 4.889 1.6
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Table 5 The cost analysis of the hybrid PV/diesel green ship. Percentage of PV penetration Initial investment cost (A) Fuel price (B) Diesel consumption rate (C) Operation of hybrid PV/diesel green ship (D) Operation hours of stand-alone mode (E) Operation hours of grid-connected mode (F) Electricity bill (G) Power rating of PV system (H) Total efficiency of PV system (I) Carbon credit (J) Avoided emission of carbon dioxide (K) Payback period (X)
Fig. 11. Emission of CO2 and fuel saving potentials according to the PV penetration (%).
5. territorial dimensions. In addition, remote areas, such as islands are greatly affected by the increase in global fuel price [4]. Consequently, a hybrid PV/diesel green ship would be of great benefit in these locations.
6.
5.1. Environmental analysis
7.
The proposed hybrid PV/diesel green ship could reduce 3.5 tons of GHG equivalent of CO2 annually. In addition a total of 70 tons of GHG could be avoided during the lifetime of 20 years. The reduction of GHG in 70% PV penetration was compared with diesel only powered ship, given in Table 3. The reduction in CO2 with increasing PV penetration of 30, 50 and 70% is depicted in Fig. 11 which shows positive impact on CO2 and fuel savings potential of the green ship.
8.
9. 10.
70% 31,360 $ 1.7 $/L 3 L/hr 150 day 3 hr/day 1.2 hr/day 0.1 $/kWh 3.2 kW 0.94 20 $/ton 4.889 ton/yr 11.87 yr
fossil fuel prices have increased. This would reduce the payback period.) The utilization PV energy will result in earning carbon credits (J) of around 20 $ for each ton of GHG [20,21]. (South Korea starts emissions trading in 2015. Carbon pricing would reduce the payback period.) Operation hours of stand-alone mode per day (E) include the supply of electricity to the ship and island. Operation hours of grid-connected mode per year (F) include the supply of electricity to the power grid. Electricity bill (G) is assumed to 0.1 $/kWh in Korea) Maximum operation days of hybrid PV/diesel system is set to 150 days/yr. Maximum operation hours of hybrid PV/diesel system is set to 6 h/day (¼E þ F) No financial support from the government, such as tax incentives. (This factor would reduce the payback period.) The loan rate [22] offered from the lending institution for initial investment cost is not considered.
According to these principles, the payback period was calculated using the following equation:
5.2. Economic and sensitivity analysis The total costs of each component of the hybrid PV/diesel green ship including mainly PV module, solar battery bank and power conversion unit are shown in Table 4. Economic analysis was performed this section to encourage the installation of the hybrid PV/diesel system on a ship. To simplify the cost analysis, the following principles and equations were used to calculate the payback period: 1. Initial investment cost (A) includes the components of the PV systems and renovation construction cost in a conventional ship. 2. The maintenance cost is not involved in the calculation because it is negligibly small in PV systems. 3. Fuel consumption in a diesel generator is 3 L per hour. 4. Fuel prices (B) and PV panel prices are assumed to be constant. (Recently, however, the PV panel prices have been falling and Table 4 The cost analysis of the hybrid PV/diesel green ship. Component
Unit price (USD)
EA
Price (USD)
PV module (200 W) Solar controller Solar battery DCeAC inverter (stand-alone) DCeAC inverter (grid-connected) Hybrid control panel Construction cost (frame) Construction cost (electrical works) Initial investment cost (A)
660 800 100 1000 1600 3000 8000 4000
16 2 16 1 1 1 1 1
10,560 1600 1600 1000 1600 3000 8000 4000 31,360
X ¼
A D ðB C E þ F G H IÞ þ J K
(1)
The payback period of proposed hybrid PV/diesel green ship is 11.87 yr according to the assumption of Table 5. The payback period decreases with increasing operating hours of the stand-alone mode and the possible operation day of PV/ diesel green ship. Also, the stand-alone and grid-connected mode (including the operation in land and island) within 6 h of maximum operation per day show potential supply of electricity to the power grid, as shown in Fig. 12. When the electricity bill is increased, the payback period of hybrid PV/diesel green ship is reduced, which is the denominator part of equation above. South Korean electricity prices remain much lower than those in other developed countries, as shown in Fig. 13. Eventually South Korea raised electricity prices twice in 2012 to help the country’s monopoly power distributor cover higher fuel costs [26]. The payback period is expected to be reduced more due to the decreasing PV module costs, increasing diesel fuel costs and CO2 emission regulations [20e22]. The choice of the hybrid PV/diesel green ship is mainly dependant on the diesel price, being feasible if the price is more than $1.05/L [4]. As the diesel price on the market in Korea is already above the $1.05/L, as shown in Fig. 14, the hybrid PV/diesel green ship is not expected to be sensitive to the variation of the diesel price [27]. Although the hybrid PV/diesel green ship will ultimately be cost-effective, a government subsidy is still essential for its widespread use.
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Fig. 12. Payback period according to the operation hours of hybrid PV/diesel green ship and electricity price.
4. The hybrid PV/diesel green ship passed the stability assessment test by the authorized department (KST in this project) 5. The payback period of initial investment can be reduced due to the decreasing PV module costs, increasing diesel fuel costs and CO2 emission trading system. 6. The hybrid PV/diesel green ship will decrease the dependence on fossil fuels and might be one solution for extending the energy flow from land (smart grid) to island (remote areas). 7. The hybrid PV/diesel green ship is expected to be commercialized and adopted widely to a range of diesel-powered ships. As a conclusion, the hybrid PV/diesel green ship has potential use in countries of peninsular or of many islands, especially in upgrading existing stand-alone diesel powered ship under 100 ton due to GHG regulations. Fig. 13. Residential electricity bill of Korea (Year 1994e2008).
References
Fig. 14. Diesel price of Korea (Year 1994e2011).
6. Conclusions This paper proposed that the hybrid PV/diesel green ship operates not only in a stand-alone mode but also when connected to a smart grid. To commercialize the proposed green ship in the near future, a conventional passenger ship was fitted with a 3.2 kW PV system and operated during the project. The operating strategy of the hybrid PV/diesel system, stability assessment and economic analysis was discussed and the following conclusions were made: 1. A 3.2 kW PV arrays were fixed on the top of the green ship with a tilt of 15 , considering the cost of installation, maintenance cost and stability against wind. 2. The stand-alone mode and grid-connected mode were controlled automatically or manually by the captain of the ship. 3. The hybrid PV/diesel operation was stable with the battery bank during mode changes.
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K.-J. Lee et al. / Energy 49 (2013) 475e483 [14] Agbossou K, Kolhe M, Hamelin J, Bose TK. Performance of a stand-alone renewable energy system based on energy storage as hydrogen. IEEE Trans Energ Convers Sep. 2004;19(3):633e40. [15] Nelson DB, Nehrir MH, Wang C. Unit sizing and cost analysis of stand-alone hybrid wind/PV/fuel cell systems. Renew Energ Aug. 2006;31(10):1641e56. [16] Enslin JHR, Snyman DB. Combined low-cost, high-efficient inverter, peak power tracker and regulator for PV applications. IEEE Trans Power Electron Jan. 1991;6(1):73e82. [17] Jain S, Agarwal V. A new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems. IEEE Power Electron Lett Mar. 2004;2(1):16e9. [18] Wang Caisheng, Nehrir MH. Power management of a stand-alone wind photovoltaic fuel-cell energy system. IEEE Trans Energ Convers Sep. 2008;23(3):957e67. [19] Ship Safety Act, Enforcement Date 06. Feb, 2009, Act No.9446, 06. Partial Amendment, http://law.go.kr; Feb. 2009. [20] Rehman S, Al-Hadhrami L. Study of a solar PV-diesel-battery hybrid power system for a remotely located population near Rafha, Saudi Arabia. Energy Aug. 2010;35:4986e95. [21] Nandi SK, Ghosh HR. Prospect of wind-PV-battery hybrid power system as an alternative to grid extension in Bangladesh. Energy Mar. 2010;35:3040e7. [22] Li Z, Boyle F, Reynolds A. Domestic application of solar PV systems in Ireland: the reality of their economic viability. Energy Sep. 2011;36:5865e76. [23] Korea Energy Economics Institute (KEEI) [Internet]. Available from:. [24] Abdullaha MO, Yunga VC, Anyia M, Othmana AK, Hamida KBA, Taraweb J. Review and comparison study of hybrid diesel/solar/hydro/fuel cell energy schemes for a rural ICT Telecenter. Energy 2010;35(2):639e46. [25] Prasad AR, Nataraajn E. Optimisation of integrated photovoltaic-wind power generation systems with battery storage. Energy 2006;31(12):1943e54. [26] Korea Electric Power Corporation (KEPCO) [Internet]. Available from: www. kepco.co.kr/eng/. [27] OPINET [Internet]. Available from: http://www.opinet.co.kr/index.do?cmd¼main.
Nomenclature Voc: open circuit voltage, V Isc: short circuit current, A
KG: vertical center of gravity, m LCG: longitudinal center of gravity, m W: displacement of LIGHT WEIGHT, % VPV_Left: PV array voltage of the left side, V IPV_Left: PV array current of the left side, V VBatt: battery voltage, V IBatt: battery current, A vINV: voltage of the stand-alone inverter, V iINV: current of the stand-alone inverter, A VPV_Total: total voltage of PV arrays of right and left side, V IPV_Total: total current of PV arrays of right and left side, A vGrid_INV: AC grid voltage, V iGrid_INV: AC grid current, A Vmpp: voltage at maximum power point, V A: initial investment cost, $ B: fuel price, $/L C: diesel consumption rate, L/hr D: operation of hybrid PV/diesel green ship, day E: operation hours of stand-alone mode, hr/day F: operation hours of grid-connected mode, hr/day G: electricity bill, $/kWh H: power rating of PV system, kW I: total efficiency of PV system J: carbon credit, $/ton K: avoided carbon emission, ton/yr X: payback period, yr List of abbreviations PV: photovoltaic DG: distributed generation GHG: global greenhouse gas IMO: International Maritime Organization UNFCCC: United Nations framework convention on climate change MPP: maximum power point KST: Korea Ship Safety Technology Authority GPS: global positioning system PWM: pulse width modulation SAPF: shunt active power filter LADAR: light detection and ranging
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Contents lists available at SciVerse ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Hybrid photovoltaic/diesel green ship operating in standalone and grid-connected mode e Experimental investigation Kyoung-Jun Lee a, Dongsul Shin a, Dong-Wook Yoo b, Han-Kyu Choi c, Hee-Je Kim a, * a
The School of Electrical Engineering, Pusan National University, Jangjeon-dong, Geumjung-gu, Busan, Republic of Korea Korea Electrotechnology Research Institute (KERI), 28-1 Seongju-dong, Changwon 641-120, Republic of Korea c The Korea Ship Safety Technology Authority (KST), Incheon, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 June 2012 Received in revised form 23 October 2012 Accepted 4 November 2012 Available online 1 December 2012
This paper presents the experimental results from the operation of a proto-type green ship in Geoje island, South Korea. As Korea is a peninsula situated between the continent and the sea, its location is ideal for utilizing PV/diesel green ship. After ground testing with a stand-alone PV (photovoltaic) generation system, this PV system was added to a conventional diesel ship. The proto-type green ship consisted of a photovoltaic (PV) generation system, diesel engine, battery energy storage, hybrid control system, and a stand-alone and grid-connected inverter. The aim of the green ship was not only to minimize fuel consumption but also to support the power grid as DG (distributed generation) connected to the smart grid (in land) and micro-grid (in island) in the near future. At the end of this paper, environmental, economic and sensitivity analysis would be discussed mainly based on experimental results. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
Keywords: Green ship Hybrid PV/diesel system Photovoltaic Grid connection Smart grid LabVIEWÔ
1. Introduction Around the world, governments have strived to increase the share of renewable green energy in power production. The main interest has mainly been energy security, increasing prices of carbon-based energy sources and minimizing global warming. Concerning the second, global shipping is a major contributor to GHG (global greenhouse gas) emissions, being responsible for approximately 3% of global CO2 emissions [1,2]. The IMO (International Maritime Organization) is now working to start GHG regulations for global shipping, and is under pressure, e.g. from the EU and UNFCCC (United Nations framework convention on climate change), to apply regulations that will have a substantial impact on emissions [3]. In addition, because global shipping is normally powered by standalone diesel generators for electricity supply, the shipping industry is affected considerably by the increase in global fuel prices. Therefore, the use of a renewable energy resource in the shipping industry would be a great advantage, particularly in reducing CO2 emissions and the dependence on the highly unpredictable diesel price [4]. The mandatory renewable energy targets
* Corresponding author. Tel.: þ82 51 510 2770; fax: þ82 51 510 0212. E-mail address: [email protected] (H.-J. Kim).
in Korea is expected to be 11.0% in 2020 compared to 2.4% in 2008, as shown Fig. 1, which shows increasing trends in the world energy policy [23]. Therefore, every possible method for increasing the proportion of renewable energy is required to meet the goals and expectations. Many studies have examined hybrid energy systems [5e15]. Among the renewable energy sources, the abundant solar energy is most applicable to conventional ships at sea [16,17]. Abdullaha et al. [24] proved that hybrid power schemes are more sustainable in terms of supplying electricity in rural area compared to a standalone PV (photovoltaic) system due to prolong cloudy and dense haze periods. The investigators presented the reliable and cost effective hybrid energy systems [25]. Therefore, a hybrid green ship (hybrid PV/diesel) might be an effective solution. This paper proposes a hybrid PV/diesel green ship operating in stand-alone and grid-connected mode. PV is the primary power source of the system to the electrical loads in the ship, and the diesel engines are used to compensate for the fluctuating electric power from the PV system. A battery bank is also installed in the hybrid system to supply stable power [18]. Unlike a conventional PV hybrid system on land, a hybrid green ship utilizes the free space on the ship. In addition, with grid-connected inverters, the overall power flow is broadened from the smart grid on land to the off-grid on the island, which is more economical than a hybrid PV (stand-
0360-5442/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2012.11.004
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2. Proposed hybrid PV/diesel green ship experimental system The operation of the hybrid PV/diesel green ship is divided mainly into modes A (at sea) and B (in port). The power ratings of the hybrid PV/diesel system were approximately 3.2 kW for the electrical loads, such as lighting, GPS (global positioning system) & Communication system and Video system, in the cruise ship (85 ton). Fig. 2 shows the block diagram of the proposed hybrid system. Table 1 provides details of the hybrid system components. In the conventional ship, two diesel powered generator (20 kW) is installed to meet the occasional peak load of winch motor to pull the ship anchor. The power rating of base electrical loads of ship is under 3 kW, which can be thoroughly covered by the PV system. 2.1. Power conversion system in hybrid green ship
Fig. 1. Renewable energy targets (%).
alone only)/diesel system. Also, Korea is a peninsula which stretches from the north to the south, located in the 33 w 43 north latitude, and in the 124 w 132 east longitude. As Korea is situated between the continent and the sea, its location is ideal for utilizing PV/diesel green ship between the continent and the sea. Therefore, the proposed hybrid PV/diesel green ship is effective in the countries with this territory characteristics. This paper reports the experimental results from the operation of a proto-type green ship in Geoje island, South Korea. After ground testing with a stand-alone PV generation system, the PV system was adopted to a conventional diesel ship. The proto-type green ship consisted of a PV (photovoltaic) generation system, diesel engine, battery energy storage, hybrid control system, standalone and grid-connected inverter. The aim of the green ship was not only to minimize fuel consumption but also to support the power grid through a smart grid in the near future. The remainder of this paper is organized as follows. Section 2 discusses the hybrid system configuration and operation mode. The stability test results for the hybrid green ship equipped with a PV system are given in Section 3. Section 4 discusses the experimental results of the hybrid green ship according to operation mode. Section 5 gives an environmental, economic and sensitivity analysis of the hybrid green ship. Section 4 summarizes and concludes the paper.
As mentioned above, there are mainly two operation modes. Mode A (at sea) is like the stand-alone mode of PV systems on land, as shown in Fig. 2. According to the status of PV power, the electrical loads in ships can be powered by either a battery bank or a diesel generator. The PV arrays on the left and right side of the roof are connected separately to a solar controller (DCeDC Converter) due to the different MPP (maximum power point). Once the cruise ship is in harbor and the battery is full charged, the extra PV power can be utilized through a grid-connected inverter. To meet the input voltage range of the grid-connected inverter, the PV arrays on the left and right are series connected, not requiring an additional power conversion unit, resulting in a doubling of the Voc (open circuit voltage). The control of the hybrid systems is summarized in Fig. 2, where SWA, SWB and SWC are the magnet contact switch controlled by a laboratory-made hybrid control panel. The ATS (auto transfer switch) is installed between the output of the DCeAC inverter (stand-alone) and the output of diesel generator to simply change the operation mode. The monitoring system for the hybrid green ship was established using the LabVIEWÔ program, as shown in Fig. 3. The monitoring system was connected to the PC through a RS232 communication, storing the acquired data in the excel file. The controller board includes an Atmel AVR ATmega 128. The prototype hybrid green ship plied between Geojedo (island) and Somaemuldo (island). Through the experiment, the validity of the hybrid green ship was confirmed.
Fig. 2. Block diagram of hybrid PV/diesel green ship.
K.-J. Lee et al. / Energy 49 (2013) 475e483 Table 1 System component parameters. 200 W under 1 sun (100 mW/cm2), 25 C Voc ¼ 33.2 V, Isc ¼ 8.09 A Module number 4(Ns) 2(Np) 2(group) ¼ 16 Power rating 200 16 ¼ 3.2 kW Battery Cell unit 12 V/100AH Cell number 2(Ns) 8(Np) ¼ 16 Capacity 19.2 kWh Rated voltage 24 V Power DCeDC converter Power rating 1.6 kW conversion (solar controller) 2(group) ¼ 3.2 kW system (MSB; Maximum solar input 150 VDC main switch Output 24 VDC board) DCeAC inverter Power rating 4 kW (stand-alone) Input 22.5e30.8 VDC Output 220 VAC DCeAC inverter Power rating 4 kW (grid-connected) Input 100e370 VDC Output 220 VAC NFB 2P-20A, 2P-30A, 2P-175A MC (magnet MC-32 contact) ATS (auto transfer DMH20 switch) MCU (micro Atmega 128 controller unit) Diesel generator Power rating 20 kW Number 2 Load Basically used Power rating 3 kW electrical loads of ship (lighting, GPS & communication system and video system) Occasionally used Power rating 20 kW electrical loads of ship (winch motor)
PV array
Module unit
2.2. Implementation of the hybrid green ship After the verification experiment of the hybrid PV/diesel system on land in 2010, the proposed system was installed as an 85 ton level of the cruise ship in 2011, in Geoje island. After searching for
477
a suitable ship, a conventional ship was renovated according to the proposed design mentioned above. Unlike the PV plants on land, the total weight of the PV generation system and the wind pressure on the PV arrays are the main concerns regarding the safety of a ship at sea. Approved by the KST (Korea Ship Safety Technology Authority), PV systems were installed on a conventional cruise ship and controlled by a hybrid control panel. 3.2 kW (200W/16 EA) of PV arrays were installed on the back side of the ship, as shown in Fig. 4. A battery bank was installed in the basement of the ship considering the stability of the ship. Section 3 provides details of the safety problems. 3. Stability of hybrid green ship The selected ship for the experiment is a normal passenger ship (85 ton, 263 Passengers). Stability is one of the greatest concerns for a passenger ship. The back side of the dock was renovated according to the design, as shown in Fig. 5, considering the mean height of the passengers, wind pressure and maintenance. During the verification experiment of the hybrid PV/diesel system on land in 2010, the power production of the PV system was measured by changing the tilt angle of the solar panel. The results showed that the group with a 0 tilt showed poor power production due to dirt on the solar panels. In this study, a 15 tilted solar panel was installed instead of the awning of a conventional ship. A polycarbonate sheet, which is a transparent plastic material with outstanding impact resistance, was also installed under the PV arrays for passenger safety. To evaluate the stability of the hybrid green ship, the weight of the each component was checked and assessed by the KST (Korea Ship Safety Technology Authority). The main objective of the KST is to inspect vessels in accordance with the Ship Safety Act to prevent exposing the vessel and crew to any unpredictable dangers that may occur at sea. According to article 28 (Keeping Stability) of the Ship Safety Act in Korea, the owner of a ship that falls in any of the following subsections shall maintain Stability according to the criteria determined/publicly announced by the Minister, provided that in the event a ship determined by the Ordinance of the Ministry of Land, Transport and Maritime Affairs, such as a passenger ship
Fig. 3. Monitoring system for hybrid green ship (LabVIEWÔ program).
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Fig. 4. Proto-type of hybrid PV/diesel green ship (Geoje Island, South Korea/34.7269 N, 128.6042 E).
whose length is 12 m or longer. In connection with Stability under article 28, an owner of a ship shall submit the materials for Stability to the Minister for approval as to whether or not the Stability is appropriate, and shall provide all the necessary materials approved for Stability to the captain of the ship [19]. In this study, a conventional ship was modified to a hybrid green ship without changing the main frame size of the ship. The KG (vertical center of gravity) and LCG (longitudinal center of gravity) were affected slightly by the removal and installation of the components, such as PV arrays, power conversion units and polycarbonate sheets. An authorized inspector checked the
renovated hybrid green ship, and identified an increase in the LIGHT WEIGHT (approximately 1.154 tons, 1.38% increase), displacement of the KG (0.033 m increase) and LCG (0.029 m to the bow of a ship). The renovated hybrid green ship passed the stability inspection by the KST, as shown in Table 2, showing a displacement of LIGHT WEIGHT between 0.5% and 2.0% with an increase in KG. In the proposed green ship, total increased weight is 1.154 ton, which is the 1.3% of the total weight of ship and 7% of the total weight of the maximum number of passengers with the average weight of an adult human (62.0 kg), which did not impact energy saving potential.
Fig. 5. Installation drawing of PV arrays.
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Table 2 The stability assessment of the hybrid green ship (LCG and KG). Inspection sheet 1. New light calculation Item Old light Deduction Addition New light 2. New LIGHT WEIGHT & KG displacement (1) LIGHT WEIGHT displacement: (2) KG displacement: (3) LCG displacement: 3. Result (under the Ship Safety Act) KG (increase) The displacement of LIGHT WEIGHT (W) (%)
KG (decrease)
The displacement of LIGHT WEIGHT (W) (%)
Weight [t] 83.333 0.032 1.186 84.487
LCG [m] 1.224 6.700 0.672 1.195
Moment [T m] 101.936 0.214 0.797 100.925
1.154 0.033 0.029
[t] Increase (approximately 1.38%) [m] Increase [m] Increase to the bow of the ship
W < 0.5 0.5 W < 2.0 W 2.0 W < 1.5 1.5 W < 2.0 W 2.0
KG [m] 1.513 6.150 3.996 1.546
Moment [T m] 126.091 0.197 4.739 130.633
Exemption of stability test Ship stability calculation with (displaced LCG, original KG value) Retest Exemption of stability test Ship stability calculation with (displaced LCG, original KG value) Retest
*Decision: evaluated LIGHT WEIGHT (KG increased, the displacement of LIGHT WEIGHT (W)(%) is between 0.5% and 2.0%. Deduction item Item Weight [t] LCG [m] Tent 0.032 6.700 Total 0.032 6.700 Addition item Item Weight [t] LCG [m] Steel structure 0.187 6.700 PV arrays 0.306 6.700 Polycarbonate sheets 0.143 6.700 Battery bank 0.400 9.750 Inverter, converter 0.028 9.750 Control panel 0.122 7.250 Total 1.186 0.672
Moment [T m] 0.214 0.214
KG [m] 6.150 6.150
Moment [T m] 0.197 0.197
Moment [T m] 1.253 2.050 0.958 3.900 0.273 0.885 0.797
KG [m] 6.250 6.250 6.250 0.500 0.500 4.500 3.996
Moment [T m] 1.169 1.913 0.894 0.200 0.014 0.549 4.739
The experimental results presented in this section were recorded after an inspection by the KST and obtaining permission of ship operation by the Korean Maritime Police. The experiment was conducted according to the operation mode, as mentioned in Section 2. First, in stand-alone mode, the output of the PV arrays and the battery bank were checked with only the DC loads turned on, such as lighting, communication and GPS (global positioning system) equipment. Fig. 6 presents the PV array voltage of the left side (VPV_Left), the PV array current of the left side (IPV_Left), the battery voltage (VBatt) and battery current (IBatt) to the DC loads. In Fig. 5,
VPV_Left ¼ 107.26 V and IPV_Left ¼ 2.38 A, resulting in a power of 255 W to the solar controller. In addition, the battery voltage was 25.7 V, which is equal to the output of the solar controller, and the battery current was 2.401 A during charging. In this case, the power to the loads was less than the power from the PV arrays. Fig. 7 shows the battery voltage (VBatt), battery current (IBatt), voltage of the stand-alone inverter (vINV) and current of the standalone inverter (iINV) to electrical loads in the operation of the passenger ship between Geojedo (island) and Somaemuldo (island). Unlike Fig. 6, during the course, the electrical loads included the DC and AC loads. In the experiment, a PWM (pulse width modulation) modified sine wave type was used for the standalone mode inverter, as shown in Fig. 7, resulting in a square
Fig. 6. Experimental waveforms at PV arrays.
Fig. 7. Experimental waveforms in the stand-alone mode (before the cruise).
4. Experimental results of hybrid PV/diesel green ship
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Fig. 8. Experimental waveforms in the stand-alone mode (during the cruise).
waveform voltage and current with 60 Hz. During the measurement, the power supplied to the loads was approximately 773 W. Fig. 8 shows the logged data of PV production and power to the loads during the cruise. The passenger ship began to cruise at 10:24 AM (21 July, 2011) from Geojedo (island) to Somaemuldo (island). There was a difference in power output between the PV array of the left side and the PV array of right side. This is because the PV arrays were tilted 15 (See Fig. 4) and the passenger ship was affected by the movement of rolling, pitching and yawing. On the other hand, to solve the problem of different MPP, the solar controllers were connected separately to the PV arrays in each side, tracking the MPP per arrays. The electrical loads were varied arbitrarily by the captain of a ship. When the output power of the PV arrays was higher than the electrical loads, the battery bank was charged by the excess amount for later use. On the contrary, the battery bank supported the shortage when the output power from the PV arrays was less than the connected electrical loads. In this study, a grid-connected mode was implemented when the ship was at anchor in the harbor. The PV arrays were series connected using a simple change in magnet switches, resulting in Ns (Number of series connections) ¼ 8, Np (Number of parallel connections) ¼ 2. The open-circuit voltage of the PV arrays in gridconnected mode was 265.6 V, which satisfies the input voltage range of a DCeAC inverter (grid-connected). In the case of grid faults, such as the grid over/under voltage, grid over/under frequency, over current and ground fault, the grid-connected inverter will wait 5 min prior to restarting. Fig. 9 shows the
Fig. 10. Power output of the hybrid PV/diesel systems.
voltage of the PV arrays (VPV_Total), current of the PV arrays (IPV_Total), AC grid voltage (vGrid_INV) and AC grid current (iGrid_INV) at Geojedo (island). The output voltage of the PV arrays in the gridconnected mode was increased to 224 V, which is the voltage at maximum power point (Vmpp). The injected active power to the grid was approximately 600 W at 3:20 PM (27 Sep, 2011) in Fig. 9. The injected grid current includes low-order harmonic components due to the effect of the weak and distorted grid at Geojedo (island), requiring an improvement in power quality using a SAPF (shunt active power filter) in the near future. The performance of the hybrid PV/diesel operation was evaluated by changing the electrical loads arbitrarily when the ship was at anchor in the harbor (31 Oct, 2011), as shown in Fig. 10. During the performance test, a change in operation mode occurred three times from PV mode to diesel mode and vice versa. It takes 8e10 s for the diesel generator to reach normal operation. However, the power from the battery bank supported the transient stability, including critical loads, such as a GPS navigator, LADAR (light detection and ranging) and lighting. 5. Environmental and economic analysis of the proposed hybrid PV/diesel green ship The Korean government has introduced a number of new incentives and support programs, such as “1 million green homes” program. Korea’s electricity prices are cheaper than in Europe and Japan but they are likely to rise in the near future. This will trigger the installation of PV systems on rooftops. On the other hand, these support programs for PV systems are limited to the ground-mount type or roof-top type and a lack of space will be a severe limitation to PV installation. Therefore, the hybrid PV/diesel green ship can be an alternative solution, particularly in the countries with small
Table 3 Annual CO2 emissions and fuel savings for hybrid PV/diesel green ship.
Operating days (annually) Operating hours of the diesel engine (daily) Diesel consumption rate (liter/hr) Diesel (DM grade): density (kg/m3) Diesel (DM grade): % of carbon Emission of carbon (ton) Carbon to carbon dioxide (44/12) Emission of carbon dioxide (ton) Avoided emission of carbon dioxide (ton/yr) Fuel saving (kiloliter) Fig. 9. Experimental waveforms in the grid-connected mode.
Diesel only
70% PV penetration
150 6 3 830 85 1.905 3.667 6.984 e e
150 1.8
0.571 2.095 4.889 1.6
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Table 5 The cost analysis of the hybrid PV/diesel green ship. Percentage of PV penetration Initial investment cost (A) Fuel price (B) Diesel consumption rate (C) Operation of hybrid PV/diesel green ship (D) Operation hours of stand-alone mode (E) Operation hours of grid-connected mode (F) Electricity bill (G) Power rating of PV system (H) Total efficiency of PV system (I) Carbon credit (J) Avoided emission of carbon dioxide (K) Payback period (X)
Fig. 11. Emission of CO2 and fuel saving potentials according to the PV penetration (%).
5. territorial dimensions. In addition, remote areas, such as islands are greatly affected by the increase in global fuel price [4]. Consequently, a hybrid PV/diesel green ship would be of great benefit in these locations.
6.
5.1. Environmental analysis
7.
The proposed hybrid PV/diesel green ship could reduce 3.5 tons of GHG equivalent of CO2 annually. In addition a total of 70 tons of GHG could be avoided during the lifetime of 20 years. The reduction of GHG in 70% PV penetration was compared with diesel only powered ship, given in Table 3. The reduction in CO2 with increasing PV penetration of 30, 50 and 70% is depicted in Fig. 11 which shows positive impact on CO2 and fuel savings potential of the green ship.
8.
9. 10.
70% 31,360 $ 1.7 $/L 3 L/hr 150 day 3 hr/day 1.2 hr/day 0.1 $/kWh 3.2 kW 0.94 20 $/ton 4.889 ton/yr 11.87 yr
fossil fuel prices have increased. This would reduce the payback period.) The utilization PV energy will result in earning carbon credits (J) of around 20 $ for each ton of GHG [20,21]. (South Korea starts emissions trading in 2015. Carbon pricing would reduce the payback period.) Operation hours of stand-alone mode per day (E) include the supply of electricity to the ship and island. Operation hours of grid-connected mode per year (F) include the supply of electricity to the power grid. Electricity bill (G) is assumed to 0.1 $/kWh in Korea) Maximum operation days of hybrid PV/diesel system is set to 150 days/yr. Maximum operation hours of hybrid PV/diesel system is set to 6 h/day (¼E þ F) No financial support from the government, such as tax incentives. (This factor would reduce the payback period.) The loan rate [22] offered from the lending institution for initial investment cost is not considered.
According to these principles, the payback period was calculated using the following equation:
5.2. Economic and sensitivity analysis The total costs of each component of the hybrid PV/diesel green ship including mainly PV module, solar battery bank and power conversion unit are shown in Table 4. Economic analysis was performed this section to encourage the installation of the hybrid PV/diesel system on a ship. To simplify the cost analysis, the following principles and equations were used to calculate the payback period: 1. Initial investment cost (A) includes the components of the PV systems and renovation construction cost in a conventional ship. 2. The maintenance cost is not involved in the calculation because it is negligibly small in PV systems. 3. Fuel consumption in a diesel generator is 3 L per hour. 4. Fuel prices (B) and PV panel prices are assumed to be constant. (Recently, however, the PV panel prices have been falling and Table 4 The cost analysis of the hybrid PV/diesel green ship. Component
Unit price (USD)
EA
Price (USD)
PV module (200 W) Solar controller Solar battery DCeAC inverter (stand-alone) DCeAC inverter (grid-connected) Hybrid control panel Construction cost (frame) Construction cost (electrical works) Initial investment cost (A)
660 800 100 1000 1600 3000 8000 4000
16 2 16 1 1 1 1 1
10,560 1600 1600 1000 1600 3000 8000 4000 31,360
X ¼
A D ðB C E þ F G H IÞ þ J K
(1)
The payback period of proposed hybrid PV/diesel green ship is 11.87 yr according to the assumption of Table 5. The payback period decreases with increasing operating hours of the stand-alone mode and the possible operation day of PV/ diesel green ship. Also, the stand-alone and grid-connected mode (including the operation in land and island) within 6 h of maximum operation per day show potential supply of electricity to the power grid, as shown in Fig. 12. When the electricity bill is increased, the payback period of hybrid PV/diesel green ship is reduced, which is the denominator part of equation above. South Korean electricity prices remain much lower than those in other developed countries, as shown in Fig. 13. Eventually South Korea raised electricity prices twice in 2012 to help the country’s monopoly power distributor cover higher fuel costs [26]. The payback period is expected to be reduced more due to the decreasing PV module costs, increasing diesel fuel costs and CO2 emission regulations [20e22]. The choice of the hybrid PV/diesel green ship is mainly dependant on the diesel price, being feasible if the price is more than $1.05/L [4]. As the diesel price on the market in Korea is already above the $1.05/L, as shown in Fig. 14, the hybrid PV/diesel green ship is not expected to be sensitive to the variation of the diesel price [27]. Although the hybrid PV/diesel green ship will ultimately be cost-effective, a government subsidy is still essential for its widespread use.
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Fig. 12. Payback period according to the operation hours of hybrid PV/diesel green ship and electricity price.
4. The hybrid PV/diesel green ship passed the stability assessment test by the authorized department (KST in this project) 5. The payback period of initial investment can be reduced due to the decreasing PV module costs, increasing diesel fuel costs and CO2 emission trading system. 6. The hybrid PV/diesel green ship will decrease the dependence on fossil fuels and might be one solution for extending the energy flow from land (smart grid) to island (remote areas). 7. The hybrid PV/diesel green ship is expected to be commercialized and adopted widely to a range of diesel-powered ships. As a conclusion, the hybrid PV/diesel green ship has potential use in countries of peninsular or of many islands, especially in upgrading existing stand-alone diesel powered ship under 100 ton due to GHG regulations. Fig. 13. Residential electricity bill of Korea (Year 1994e2008).
References
Fig. 14. Diesel price of Korea (Year 1994e2011).
6. Conclusions This paper proposed that the hybrid PV/diesel green ship operates not only in a stand-alone mode but also when connected to a smart grid. To commercialize the proposed green ship in the near future, a conventional passenger ship was fitted with a 3.2 kW PV system and operated during the project. The operating strategy of the hybrid PV/diesel system, stability assessment and economic analysis was discussed and the following conclusions were made: 1. A 3.2 kW PV arrays were fixed on the top of the green ship with a tilt of 15 , considering the cost of installation, maintenance cost and stability against wind. 2. The stand-alone mode and grid-connected mode were controlled automatically or manually by the captain of the ship. 3. The hybrid PV/diesel operation was stable with the battery bank during mode changes.
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Nomenclature Voc: open circuit voltage, V Isc: short circuit current, A
KG: vertical center of gravity, m LCG: longitudinal center of gravity, m W: displacement of LIGHT WEIGHT, % VPV_Left: PV array voltage of the left side, V IPV_Left: PV array current of the left side, V VBatt: battery voltage, V IBatt: battery current, A vINV: voltage of the stand-alone inverter, V iINV: current of the stand-alone inverter, A VPV_Total: total voltage of PV arrays of right and left side, V IPV_Total: total current of PV arrays of right and left side, A vGrid_INV: AC grid voltage, V iGrid_INV: AC grid current, A Vmpp: voltage at maximum power point, V A: initial investment cost, $ B: fuel price, $/L C: diesel consumption rate, L/hr D: operation of hybrid PV/diesel green ship, day E: operation hours of stand-alone mode, hr/day F: operation hours of grid-connected mode, hr/day G: electricity bill, $/kWh H: power rating of PV system, kW I: total efficiency of PV system J: carbon credit, $/ton K: avoided carbon emission, ton/yr X: payback period, yr List of abbreviations PV: photovoltaic DG: distributed generation GHG: global greenhouse gas IMO: International Maritime Organization UNFCCC: United Nations framework convention on climate change MPP: maximum power point KST: Korea Ship Safety Technology Authority GPS: global positioning system PWM: pulse width modulation SAPF: shunt active power filter LADAR: light detection and ranging
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