A Review on Energy Management system of Solar Car - CiteSeerX

A Review on Energy Management system of Solar Car †2

Zahari Taha1, Rossi Passarella , Jamali Md Sah3, Center for Product Design and Manufacturing Faculty of Engineering, University Malaya, Kuala Lumpur 50603 Malaysia Email: [email protected] 1 [email protected] 2 [email protected] 3 Nasrudin Bin Abd Rahim 4 Department Electrical Engineering, Faculty of Engineering, University Malaya, Kuala Lumpur 50603 Malaysia Email: [email protected] 4

Abstract. In 1987, the first world solar challenge (WSC) was organised in Australia to trigger the development of solar powered vehicle by all researchers around the world. Since then, various technologies have emerged to make the vehicle capable to perform similar to conventional type of fuel powered vehicle. However there are still limitations on the vehicle development process especially in terms of the energy management technology which includes the photovoltaic (PV) technology and battery technology. The phrase energy management means differently to different people, for us, energy management is “the judicious and effective use of energy to maximise the system”. Generally the energy management system of a solar car includes the requirement to ensure that electrical power flow from the PV to the loads will be monitored and optimised. Load behavior significantly affects the utility planning and strategies for driving the solar cars. Hence, proper load management strategy is important to draw maximum power from the PV module. A maximum power point tracker (MPPT) device must be used between the PV module and battery to boost the battery charging rate. Some back-up ba tteries are needed in the system to eliminate unexpected system shutdown. As a result, an appropriate system should be determined at the design stage to ensure for optimum solar car energy management system. The aim of this paper is to review the solar cars energy management system that has been done and published in journals. A new system approach for second version of CPDM solar car is described. Keywords: Energy Management, MPPT, Photovoltaic, Batteries

1. INTRODUCTION

be more or equal to the current consumption rate used by the motor. However, this is not the ideal situation because

Solar car is a name given to an electric car which uses a photovoltaic (PV) unit to charge its battery. It is classified as a green vehicle since zero greenhouse gasses are emitted to atmosphere. In general, Figure 1 shows the basic energy management system that can be used for a solar car. The sunlight makes the PV electrons to be in higher state of energy and thus creates direct current (DC) electricity. This electricity is absorbed by a PV controller and stores it into a battery. The battery is used by a DC motor to generate the mechanical energy for the vehicle to move. It sounds like a simple system but in reality the energy management system is quite complicated especially when the vehicle is required to move continuously for a long period or distance where the sun is not always shining brightly. Theoretically, the charging rate of the battery must __________________________________________________ † Corresponding Author Tel : +60379675369; Fax: +60379675330 Email address: [email protected]

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APIEMS 2008 Proceedings of the 9th Asia Pasific Industrial Engineering & Management Systems Conference Figure 1. An example a solar car energy system of unpredictable weather condition and also other factors such as speed, slope, and road condition that will use more current to overcome the situation. The complexity of the system has made the solar car impractical [Pudney, 2000] unless it is possible to discover better energy management system to cater the needs for a reliable solar car. Since the introduction of World Solar Challenge (WSC) in 1987, many universities and companies have taken part and are involved in research activities to develop technologies for solar vehicle. Within 20 years, the development of solar cars is so remarkable in terms of the vehicle weight, speed and the energy management. Most of the solar cars were using 3 wheels, 2 front wheels with effective steering and suspension systems, a rear wheel with built-in DC motor, an aerodynamic body shape which is capable of reaching a top speed of 120 km/h and able to complete the 3000 km distance from Darwin to Adelaide in 4 days. As an example, in 2007 World Solar Challenge, the team from Ashiya University, Japan with their solar car ‘TIGA’ as in Figure 2 completed the race in 4 days with an average speed of 93.57 km/h (WSC, 2007).

3. RESULT AND DISSCUSION 3.1. Type of system

The energy management strategy is the most important factor to prevent energy shortage and waste in a solar car system. The energy in the system should also be properly managed in such a way that: the driver inputs (from the braking and accelerating pedals) are consistently satisfied, while the battery is sufficiently charged at all times. In practice, the electrical output from the array and electrical demand for the vehicle application are not that easy to be synchronised where the demand could be always higher than the array output, thus making the system very complicated. Thus, system optimisation is required where the size, power, reliability and cost of the solar array and battery should be able to supply the demand. In this case, it is necessary to minimize the difference between the charging rate for the battery and the charging capacity of the PV array. In order to solve this problem, it is possible to insert a DC/DC converter between the PV and the battery, which consist of a topology and control circuit. It is normally called a maximum power point tracker or well known as MPPT.

3.1.1.

Figure 2. A solar car from Ashiya University, TIGA The objective of this review is to investigate the energy management system of solar powered vehicles. The review considers studies that had been published for the last 20 years, looking for development associated with photovoltaic (PV) and battery systems.

2. METHOD Search for papers on energy management systems was done through several electronic databases which are available in University of Malaya such as Science Direct and Springer Link and also from the internet. Electronic searches used several combinations of the following terms: Energy management, solar car, solar panel, solar controller and battery performance.

Maximum Power Point Trackers (MPPT)

The use of MPPT is particularly important to maximise the PV produced current. In 1993, University of New South Wales used 26 MPPT to cater for 1800 cells, each MPPT weights 270 gram and an efficiency of 97% over most of its range. It was designed such that 14 MPPT were used to generate the total power of 45 Watts from the cells, and the remaining 12 MPPT generated the total power of 90 Watts from the cells (Inge Skaale, et al. 2001). Tesseract, the solar car made by Massachusetts Institute of Technology’s (MIT) used 12 MPPT during the North American Solar Challenge (NASC) 2005, to boost the maximum power from the array during the whole race day (III-Vs Review, 2005). Nuna II, Technical University of Delft, Holland solar car, which was the winner at World Solar Challenge (WSC) 2003, had an average speed of 97 km/h when travelling across Australia of 2,998 km distance, needing 30 hours and 54 minutes to complete the race. It also used MPPT to boost more power from the solar cells to the battery (Refocus, 2003). However, details of the MPPT systems were not explained. 3.1.2.

Non MPPT

Merdeka Solar Car 2007 from University of Malaya, Kuala Lumpur, Malaysia used a single Solar Controller PLASMATRONIC PL-40 which is capable of charging a

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APIEMS 2008 Proceedings of the 9th Asia Pasific Industrial Engineering & Management Systems Conference battery with the maximum current of 40A. The controller is a passive system which means it does not boost up the power gained from the PV to charge the battery i.e. whatever value of the output current from the PV, the controller will charge the same value of current to the battery. 3.2. Type of Battery Batteries used in solar powered vehicles perform three main functions: (i) to store electricity gained from the PV during daytime; (ii) to supply direct current when it is required; (iii) as a medium to smoothen the fluctuation of the current and voltage output from the array into the loads. In this review, it was found that there are three classes of battery which are widely used for the storage of electricity for the solar powered vehicles. 3.2.1.

Lead Acid Battery

There are several different types of lead acid battery being manufactured. Automotive batteries are widely used in cars, trucks, boats, aircraft, etc. to start the engine and other purposes. Usually, they are not over used or too much discharged and under this condition they last longer for several years. Leisure batteries, as used in caravans, boats, etc. to supply the electricity for “house appliances” may be discharged moderately. Industrial batteries are used for uninterruptible power supplies in many different situations. Tubular-plate traction batteries are used to power electric vehicles while ‘valve-regulated’ (or ‘sealed’) lead acid batteries are getting more important for solar vehicles since they do not require regular maintenance and may be used in any orientation. One example of the valve regulated type of battery is “gel” type, which was used by Merdeka Solar Car from University Malaya in 2007 WSC. The performance of the gel batteries is good but some of the disadvantages are it is too heavy and big for a solar powered vehicles. 3.2.2.

Lithium Ion

Tamagama University Solar/Hydrogen Fuel Cell used lithium ion battery and a capacitor unit to collect and store the excess electricity generated by the PV and electricity from the PV will be used directly when the car is traveling at low speed (Fuel Cells Bulletin, 2004). The ‘iSun’ solar car from McGill University used 25 lithium ion batteries, each of it is capable to store more than 40 Ampere per hour; while Solar Miner III from University of Missouri-Rolla used 459 lithium ion batteries (Photovoltaics Bulletin, 2003). 3.2.3.

Alkaline batteries

Nickel-cadmium batteries was used by team Simon in World Solar Rally at Akita Japan (Andy Shacklock et al. 1999), with 204 number of cells of total voltage 115.6 Volt. Though the performance is good but one of the

disadvantages is that it is heavy compared to lithium ion batteries. 3.3. Type of PV The science and technology of solar panel is advancing rapidly (M.D. Archer et al, 2001). In recent years, the efficiency of silicon solar cells has improved steadily and the cost of photovoltaic modules has fallen as the manufacturing facility to produce the PV has developed dramatically. The principal application for solar powered vehicle is to move the car by using PV as an independent electricity supply or stand alone mode. To optimise the output from photovoltaic array is also quite sophisticated. It depends on the latitude of the sun which determines the angle of the array to the sun. The sunlight intensity will also affect the electricity output from the PV which is normally not consistent throughout the day. Another critical factor is whether the array can be adjusted or steerable to follow the latitude of the sun during the day in order to get constant right angle between the PV surface and the sunlight. A steerable array is more expensive to construct but it gives better electrical output than the fixed array. Apollondine Solar Vehicle from Tamagama University, used polycrystalline silicon solar cells which able to supply a maximum power of 480 W to the electric motor and provides enough electricity for the car to reach a top speed of 110 km/h (Fuel Cells Bulletin, 2004) In WSC 2003, the Alpha Centauri Team from Holland built Nuna II at Technical University of Delft. They used the triple junction gallium-arsenide (GaAs) solar cells which is also used by SMART-1 satellite that was launched to the moon on 2003 (Refocus, 2003). In the same year the winner of NASC 2005, Solar Miner III from University of Missouri-Rolla used 2800 GaAs cells with cell efficiency of 20% (Photovoltaics Bulletin, 2003). The ‘iSun’ solar car from McGill University was powered by polycrystalline silicon PV cells. The array produces over 1 kW of power on a sunny day. A solar car made by Auburn University used monocrystalline silicon cells with an efficiency of 16%. Kansas State University used Emcore solar cell with total unit of more than 3500 cells with an average efficiency of 26%.University of Waterloo also used the Emcore solar cell with total area of 8 m2 with 22% efficiency (Photovoltaics Bulletin, 2003). 3.4. Driving strategy Proper driving strategy is important especially to control the speed that based on road profile, weather condition, batteries condition, and sun radiation. Cruising strategy is one of the methods where the idea is to generate as much power as possible under fluctuation weather condition while cruising at highest speed possible with minimal motor current consumption. The Honda team during the third WSC had implemented the system that consists of three base elements: supervision support,


APIEMS 2008 Proceedings of the 9th Asia Pasific Industrial Engineering & Management Systems Conference cruising simulation and powder/speed optimizing control (Yasuo Shimizu et al, 1998).

4. CONCLUSION The solar car racing has great implications on the development of electric vehicles and has raised the interest as research topics and energy issue in the public domain. System testing and understanding the characteristic of the vehicle electrical system is critical in order to achieve the best system optimisation especially for the battery power management. The most important criteria for solar vehicle battery selection are listed below: a. Weight More weight will increase the rolling resistance and more power will be needed. b. Capacity Batteries capacity should be enough to absorb the current from the PV during the day and should not be easily damaged. c. Voltage Choice of total battery voltage must be decided early at design stage. It must be suitable to be used with the photovoltaic array and the operating voltage of the motor and controller. Nowadays the photovoltaic technology is rising rapidly and the application has expanded widely. Yet, for any application, system cost and efficiency are the critical factors that should be considered. In March 2008, Centre of Product Design and Manufacturing, University of Malaya completed the prototype of 2nd version of solar car ‘Merdeka 2’ for participation in 2009 World Solar Car Challenge. A number of improvements has been decided which include lighter body structure and better suspension system to improve the driving comfort. More instrumentation will be used to improve the energy management system such as monitoring system that is able to give continuous performance evaluation throughout the race. Figure 3 show the basic concept system that will be used for Merdeka 2 solar car. The PV is directly connected to the MPPT. The MPPT will be used to charge 4 sets of batteries, 1 set of battery (48V) will be charged at a time and will be switched to another battery once the battery is fully charged. The DC motor will be connected only to the fully charged battery and this rotation system will help to prevent the DC motor from having direct connection with the MPPT due to safety reason. The management system will monitor the battery management system (BMS), the MPPT and the DC motor so that the solar car will be able to move at suitable speed and more distance coverage. The solar car uses the lithium ion battery, an Outback MPPT as the charge controller and a mono-crystalline silicon PV module.

Figure 3. Basic concept system of stand alone PV for Merdeka 2 solar car.

REFERENCES III-Vs Review, Momentum is a winner, Volume 18, issue 7, September- October 2005, page 35 Andy Shacklock, Mike Duke, Nigel Burgess (1999), The 1998 World Solar Rallye: Akita, Japan, Journal of Power Sources 80, pages 199-206. Fuel Cells Bulletin, Solar/Hydrogen Fuel cell car crosses Australia, Volume 2004, Issue 2, February 2004, Page 8. Inge Skaale,Dean J. Patterson, Howard Pullen (2001), The development of new maximum power point tracker for a very high efficiency, compound curve photovoltaic array for a solar powered vehicle, Renewable Energy 22:295-302 M.D. Archer, R.Hill (2001.), Photoconversion of solar energy, Vol 1, Clean Electricity from Photovoltaics , Imperial College Press, London, Uk, Peter Pudney, Phil Howlett (2002), Critical speed control of solar car. Optimization and engineering, 3:97107 Photovoltaics Bulletin, PV cars race across the US- The 2003 American Solar Challenge, Volume 2003, Issue 8, August 2003, Pages 7-9. P.G. Howlett, P.J. Pudney, Tania T, David Gates (1997), Optimal driving strategy for solar car on a level road, IMA Journal of Management Mathematics 8(1):59-81 Refocus, Solar Car Averages 97 km/h to cross a continent, Volume 4, Issue 6, November-December 2003, Page 12 WSC organization (2007). http://www.wsc.org.au. Access date on 12 November 2007 at 09.00 am Yasuo Shimizu, Yasuyuki Komatsu, Minoru Torii, and Masato Takamuro (1998), JSAE Review, 19, pages 143-149.
