A SOLAR VEHICLE BASED ON SUSTAINABLE DESIGN CONCEPT

Transcription

1 Proceedings of the IASTED International Conference Solar Energy (SOE 2009) March 16-18, 2009 Phuket, Thailand A SOLAR VEHICLE BASED ON SUSTAINABLE DESIGN CONCEPT Zahari Taha 1, Jamali Md Sah 2, Rossi Passarella 3, Raja Ariffin Raja Ghazilla 4, Norhafizan Ahmad 5, Yap Hwa Jen 6, Tuw Tze Khai 7, Zulkefle Kassim 8, Iskandar Hasanuddin 9, Mokhtar Yunus 10 Centre for Product Design and Manufacture (CPDM), Faculty of Engineering, University of Malaya, 50603Kuala Lumpur, MALAYSIA zahari_taha@um.edu.my 1, jamali@perdana.um.edu.my 2 passarella.rossi@gmail.com 3, r_ariffin@um.edu.my 4 norhafizan@um.edu.my 5, hjyap737@um.edu.my 6 tuwtzekhai8@yahoo.com 7, zulkefle@um.edu.my 8 iskandar_h@um.edu.my 9, ysmokhtar@yahoo.com 10 ABSTRACT A solar car which uses solar energy to charge its batteries has been designed and built at the Centre for Product Design and Manufacture (CPDM), University Of Malaya. The vehicle main body structure is made of aluminium. Most of the mechanical components are common parts available off-the-shelf. The electrical components such as the solar panels and batteries are available in the local market. However, the DC motor, its controller and the maximum power point trackers (MPPT) are manufactured in other countries. The process of combining these mechanical and electrical components is not an easy task especially at the design stage because of the individual part specific characteristic and function. Since the development cost is one of the major constraints for this project, the sustainable design concept was implemented. Suitable parts which can be easily recycled and re-used, with desired functions that contribute to vehicle optimum performance are properly selected. This paper describes the integration of the off-the-shelf mechanical and electrical components for the solar vehicle. The conceptual design and the performance of the prototype are also presented. KEY WORDS Off-the-shelf parts, solar vehicle, sustainable design. 1. Introduction The World Solar Challenge (WSC) has been organised in Australia since 1987 as a platform for researchers, educational institutions and automotive corporations to develop environmentally friendly type of transport as a potential vehicle of the future. The development of the solar cars that had participated in the event for the last 20 years has been so remarkable in terms of the materials used, the mechanical and electrical components, and the energy management systems implemented. Most of the solar cars used 2 front wheels with effective steering and suspension systems, a rear wheel with built-in direct current (DC) motor and aerodynamic body shape that had resulted in high speed solar cars that are capable of reaching a top speed of 120 km/h and able to complete the race of 3000 km distance form Darwin to Adelaide in 4 days [1]. However, the technologies employed required millions of dollars of investment. Several solar cars that participated in the 2007 WSC had cost more than USD 1 million. It is well understood that new technologies will involve huge capital investments but it does not mean that the solar car enthusiast is not able to develop an economical solar vehicle. The solution to this financial constraint is to use off-the-shelf components which are easier to purchase at reasonable cost. Furthermore, it is important to know that the materials and components can be recycled or re-used again after the event which will fulfill some of the sustainable product principles. In this paper, the project development activity is explained including the influential factors that resulted in the final design of the solar vehicle. The components that used in the solar vehicle are described and the performance of the vehicle is presented. 2. Solar Vehicle Design Concept Several factors must be considered when designing a product since the process involves multidisciplinary fields [2]. A design project at the early stage requires a balance consideration and compromise between four fundamental demands, namely the product cost, design cost, product performance and design time as shown in Fig. 1[3]. The material selection process however, depends on several aspects either it is design-oriented, product oriented, costoriented or environment-oriented [4]. These demands and material selection requirements have influenced the design team at the Centre for Product Design and

2 Manufacture (CPDM) to apply the concept of sustainable products when designing the solar vehicle. One of the sustainable products principle as described by Zhou et al. [4] is to use easy recycling, easy reuse and easy degradation materials. Product cost Product performance Design cost Design time mostly from off-the-shelf parts available in the local market. For example, the solar car used photovoltaic (PV) panel that was designed for roof application; the batteries were manufactured for stand alone PV application such as for traffic lights and parking meters; the electric motor was made for the mountain bicycle; including the mechanical parts such as the wheels and tyres, and the braking systems are those used in motorcycle and car components. In the event however, the solar car had only managed to complete 30% of the total distance. The problem was due to the design of the stand alone power management system which was unable to balance the power consumption required to run the vehicle with the power generated from the PV during the daytime. Figure 1. The four fundamental market driven demands The product development activity for the solar vehicle can be considered as a one-off project. Therefore, it can be said that the design concept for the vehicle is very much dependent on the investment. Since cost is the main concern for this activity, the ability to recycle and re-use the materials and parts that have been used for the vehicle is very important. Furthermore, the selection for the materials and parts are done based on the costoriented approach. At the same time, there are several vehicle aspects that must be achieved. Using the Pugh s checklist [2], the objectives of the design work are established. The flow of the product development activity can be summarised as in Fig. 2. Recycle/Reusable materials and parts Electrical parts Mechanical parts Material for vehicle structure Design Figure 3. The first University of Malaya solar car Recently, the university has decided to participate again in the WSC 2009 with a second version of the solar car. Several of the electrical and mechanical parts will be re-used while the main chassis and body will be built using aluminium. Fig. 4 shows the lower part of the solar car where the chassis was made using 50.8 mm x 24.5 mm hollow aluminium of 3.14 mm thickness. Aluminium is used because it is lightweight, which is very important for energy saving during the race [5]. Furthermore, it can be purchased at a reasonable price and most importantly, at the end, it can be easily recycled or re-used for other applications. Some other components that can be seen in Fig. 4 are the wheels and tyres, seat, steering, suspension, battery compartment, electric motor (under the seat), the sprocket, the front fork and rear swing arm. Fabrication Figure 2. The solar car development activity 2.1 Merdeka - First solar car by University of Malaya In October 2007, University of Malaya participated in the WSC for the first time [1]. The solar powered vehicle was named Merdeka, as in Fig. 3, which also means independence from pollution and fossil fuel. It is also named in conjunction with the celebration of the 50 th Malaysia s Independence Day. The solar car was built Figure 4. The second version solar car chassis 39

3 3. Recycle/Reusable materials and parts 3.1 Electrical parts Photovoltaic (PV) system The second version of the solar car uses two pieces of 180 Watt - mono crystalline silicon PV module (Fig. 5) with the specifications described in Table 1. Table 1 Specifications of SHARP PV [6] Capacity (W) 180, Min W Voc V Vpm V Isc 8.37 A Ipm 7.60 A Encapsulated Cell Efficiency % Module Efficiency % Cell type Mono-Crystalline Silicon Number of cells (in series) 48 The PVs are connected in series in order to get the 48 V voltage rating. The PVs are sold in Malaysia for house roof application, comes with an aluminum frame (1320 mm x 1000 mm x 20 mm) and laminated with glass. It has a high-voltage output for a grid-connected system, and the output terminal uses lead wire covered by waterproof connectors. This PV module uses a bypass-diode to minimise the power drop that might caused by shades. The texture cell surface has the advantage of reducing the reflection of sunlight BSF (back surface field) and the structure is designed in such a way to improve the cell conversion efficiency up to 15.70%. Figure 5. The solar panel Length : 1.3 m Width : 1.0 m Height : 0.02 m Weight : 16 kg Solar Charge Controller Solar charge controllers can be divided into two types, systems with maximum power point tracking (MPPT) or systems without MPPT. The function of the MPPT is to maximise the solar cells capability of supplying the current and to improve the variations in the currentvoltage characteristics of the solar cells. The system with MPPT has been used by most of the participants of the WSC since 1990 and many universities have made their own MPPT to meet the specification of their system [1]. Normally, MPPT has been confined to high-end applications such as in the communications satellites and solar vehicle race events where the size of the array is somehow limited while the cost is not an issue. Therefore a specially designed MPPT is required to extract every bit of energy possible from that array. However, it is not necessary for the second version solar car to use custom made MPPT as the PVs that will be used is designed for commercial used. Hence, a suitable MPPT available in the market and with a good safety factor is the main priority. As a result, the OutBack MX60 charge controller has been chosen for the system. This MPPT unit was designed for home application. The rated output current is up to 60 Amps DC. It can be used with battery systems from 12 to 60 VDC with a PV open circuit voltage as high as 140 VOC. Detail specification of the MPPT is shown in Table 2. Table 2 Specification of Outback MX60 charge controller [7] Output Current Rating Nominal Battery Voltage Open circuit Voltage Standby power consumption Charging regulation methods Power Conversion Efficiency 60 Amps DC 2,24,32,36,48,54,60 PV 125 VDC maximum Less than 1 Watt Bulk, Absorption, Float,Silent,Equalization Amps, 60 Amps Battery The solar car uses a sealed valve regulated lead acid (VRLA) mono bloc gel battery which is maintenance free. Table 3 shows the detail specification of the battery. Table 3 VRLA Battery [9] Type of cell Cellyte TLG Bloc Gel Manufacturer SEC Industrial Battery Voltage cell 12 Volt Capacity cell 30 Ah Weight full-charged cell 11 Kg Total number cells 4 System layout cells in series (=1string) 4 Strings Total battery energy kwh Total battery weight 44 Kg According to the data sheet from the manufacturer, this battery can be used for several different applications such as the photovoltaic and solar systems, wind systems, in telecommunication systems, for bicycle, float service, wheelchair, electric vehicle, boats, marine or navigational 40

4 aids, and golf buggy car [9]. It is obvious that the reason for choosing this type of battery for the solar car is because it can be re-used later for other applications Motor and Controller The motor and controller were made by Cyclone Taiwan [10] for use on a bicycle. This type of motor was chosen because of the reasonable price, low maintenance, and also easy to purchase because the motor and controller is sold in several European and Asian countries and also in Australia. It is a DC brushless type of motor; the operating voltage is 48 Volt; and maximum current of 35 Amp. The maximum power rating is 1050 W with maximum speed of 3223 r.p.m. The weight of the motor is 4.8 Kg. The controller uses pulse width modulation (PWM) signal to control the motor. Based on the estimated weight of the solar vehicle, it has been decided to use 2 units of motor in order to generate enough torque especially when it is required to climb a slope of 20 o. 3.2 Mechanical Parts Wheel, tyre and front fork The wheels and tyres are standard bicycle motocross (BMX) parts. The diameter of the tyres is 500 mm. The front two wheels are supported by the BMX steel forks while the rear wheel is supported by aluminium swing arm which has been specially designed and fabricated. Both front forks are attached to the chassis by means of a suspension system. There are 2 units of spring suspension used for each wheel in order to isolate vibration due to road roughness Steering The steering system comes from one of the sedan cars which is manufactured in Malaysia. However, slight modification to the steering system was done to fit with the overall size of the vehicle Suspension The suspension system uses the standard BMX spring suspension where the spring stiffness is 650 lbs per inch. There are 6 spring suspension used for the vehicle Sprocket and chain The sprocket for the rear wheel was specially made using mild steel. The diameter is approximately 450 mm with 96 number of teeth. It is designed to accommodate the motorcycle chain that is being used. design of the seat will increase the comfort level for the driver. 3.3 Material for body and chassis The vehicle main chassis structure was made using 50.8 mm x 25.4 mm hollow aluminium of 3.14 mm thickness. The body frame of the vehicle was made using round tubing aluminium of 22 mm and 1.5 mm diameter and thickness respectively. The round tubing aluminium is also used for the safety roll bar, which was built to protect the driver. The body of the vehicle was made using 1 mm thickness aluminium plate. 3.4 Solar Car Conceptual Design The conceptual design of the solar vehicle was very much dependent on the dimension and profile of the electrical and mechanical components that are being used. For example, the top area of the vehicle was designed to accommodate the 2 solar panels. The chassis was designed to cater the load and to accommodate all the electrical and mechanical components as shown in Fig. 4. Finally, the body was designed for simplicity, lightweight and easy maintenance. Figure 6. Assembly view of the chassis, body and PV Fig. 6 shows the assembly view of the chassis and body of the solar car. The shape of the solar car is made as simple as possible in order to accommodate the shape of the solar panel. The body of the solar car is designed based on the components obtained off-the-shelf Braking system The vehicle uses BMX disc brakes on both front wheels. However, the braking system uses callipers and pumps that are normally used for a motorcycle Seat It is a bucket type seat which is designed for racing car. It is light and seat belts can be easily installed on it. The Figure 7. Exploded view of the solar car 41

5 Fig. 7 shows the exploded view of the solar car. The body of the solar car is built on top of the chassis, while two solar panels are mounted on the body of the solar car. 4. Result and Discussion According to NASA surface meteorology and solar energy as in Table 4 and Fig. 8 [8], University Malaya at latitude 3.5 and longitude should have an average energy absorption of 4.36 kwh/m 2 /day in the month of October. However, the experiment that was conducted shows that the maximum power recorded was 3.3 kwh, using the MPPT. The graph in Fig. 9 shows the recorded results. Table 4 Monthly averaged energy absorbed on a Horizontal Surface (kwh/m 2 /day) [8] acceleration was measured at 4 different wheel speeds. The vertical r.m.s. acceleration results are shown in Fig. 10. All the readings recorded were less than 10 m/s 2, the value that may be assumed hazardous to the driver [11]. The used of the suspension system had resulted to significant reduction to the r.m.s. acceleration at the four points compared to the rear wheel r.m.s. acceleration. r.m.s Graph for Z axis rear wheel seat back seat floor steering 10 kmph 25 kmph 40 kmph 50 kmph Figure 10. Graph of r.m.s. acceleration vs measurement points for Z axis On November 19, 2008, the solar car was tested for speed evaluation. The test was done at the Shah Alam stadium with the total distance of approximately 5 km. The pressure of the front and rear tyres were set to 70 psi. The average speed recorded was 40 km/h with a maximum speed of 45 km/h. There were only 4 strings of battery used during the test which produced an output of 48 Volt and 30 Ah. Figure 8. Daily average energy absorbed on a horizontal surface, for lat: 3.5, long: 101.5, at University of Malaya, Kuala Lumpur [8] Figure 11. The second University of Malaya solar car Figure 9. The graph of absorbing energy from the PV recorded in MPPT on 29 October 2008 Figure 11 shows the 95% completed solar car that has been fabricated at the department according to the drawing as shown in Fig. 6. In general, the specification of the vehicle can be described according to Pugh s checklist as given in Table 5. A lab test was conducted to investigate the vibration characteristics of the vehicle [5]. Vibration acceleration was measured at 5 points at the rear wheel, seat backrest, floor and steering. The rear wheel was placed on a test rig that produced vibration input to the rear wheel. The 42

6 Table 5 Pugh s checklist for the solar car Performance Max speed 45 km/h Environment No gas pollution Maintenance Low Target product cost Less than USD10,000 Size and weight Length : 3 m Width : 1.5 m Height : 1.6 m Weight : 180 kg Materials Aluminium, off-the-shelf parts Standards International standard according to each part Safety Built-in roll bar Re-use, recycling, disposal Almost zero waste 5. Conclusion A solar vehicle has been constructed using off-the-shelf parts based on the sustainable product concept. Even though the total investment involved can be considered as small compared to other solar cars, the performance is similar to the expectation. The use of the design methods had given many advantages to the design team. Most of the electrical and mechanical parts are able to be recycled and reused after the WSC 2009 event. For example, the PV and the MPPT can be re-used for home applications. The DC motor and the controller can be attached to a bicycle. The aluminium parts can be recycled or re-used. This sustainable concept which has been implemented will result in almost zero waste once the vehicle is required for disposal. However, there are limitations that need some considerations. The freedom to design the solar vehicle is restricted. The combination of readily made parts does not guarantee competitive performance but has greater commercial potential. products: artificial neural networks and genetic algorithm approach, Materials and Design, 30, 2009, [5] Z. Taha, S. Z. Md Dawal, R. Passarella, Z. Kassim, J. Md Sah, Study of lightweight vehicle vibration characteristics and its effects on whole body vibration, Proceeding 9 th Asia Pacific Industrial Engineering and Management System Conference, Bali, 2008, [6] NUS0E3E&show=specifications Opened on December 3 rd [7] ntrollers/flexmax/, opened on October [8] ep=1&lat=3.5&lon=101.5&ms=1&ds=1&ys=1983&me= 12&de=31&ye=2005&daily=swv_dwn&submit=Submit, opened on December 2008 [9] Opened on December 3 rd [10] on December [11] M.J. Griffin, Handbook of Human Vibration (Academic Press, London, 1990). References [1] Z. Taha, R. Passarella, J. Md Sah, N. Abd Rahim, A review on energy management system of a solar car, Proceeding 9 th Asia Pacific Industrial Engineering and Management Systems Conference, Bali, 2008, [2] N.F.M. Roozenburg and J. Eekels, Product design: fundamentals and methods (West Sussex, England: John Wiley & Sons Ltd, 1995). [3] M.J. Hall, A framework for efficient product design, Concurrent Engineering - Getting it Right First Time, IEE Colloquium on June1995, Page(s): 5/1-5/3, IEEE Xplore. [4] C.C. Zhou, G.F. Yin, X. B. Hu, Multi-objective optimization of material selection for sustainable 43