Decision making for the design of solar cars and basis for driving strategy General estimation of recommended mean speed for solar cars Main Subject area: Computer Engineering Author: Isac Sélea, Håkan Thorleifsson Supervisor: Rickard Nyberg JÖNKÖPING 2021 February This final thesis has been carried out at the School of Engineering at Jönköping University within Computer Engineering. The authors are responsible for the presented opinions, conclusions, and results. Examiner: Rachid Oucheikh Supervisor: Rickard Ninde Scope: 15 hp (first-cycle education) Date: 2021-08-07 i Abstract The global interest in green vehicles has been growing since it is letting out less pollution than normal internal combustion engines (ICE) and many people want to get into the ecological-friendly alternative mode of transport. The solar car is one of these types of green vehicles, which is powered by renewable energy with zero emissions. The solar car makes use of its solar panel that uses photovoltaic cells to convert sunlight into electricity to the batteries and to also power the electric motor. The state of solar cars is that it is almost exclusively for competition and when competing a strategy is needed to get the best placement. Having knowledge about how the car is behaving is a good basis for building a driving strategy. Therefore, a case study is made on World Solar Challenge (WSC) focused on the cars of JU Solar team with the use of datasets such as topographical data and solar irradiation. An optimization model is made that inputs these datasets and simulates a time period (an hour) and checks the set battery discharge rate (BDR or C rating). It is concluded that a safe BDR is between 8 to 9 % per hour (i.e. 0.08 to 0.09 C), relative to the full capacity of the battery. Results shows an improved mean speeds of the solar cars and improved finish times. The model also works very well for solar cars that are not meant for racing. Since it keeps a relatively stable state of charge for long term driving, that ensures battery longevity. With these results JU Solar team can use this model to improve their driving strategy but could also be used for economical driving for the future of commercial solar cars. This paper recommends to follow a simple procedure, to keep the BDR on 9% as long as the sun irradiation stays above 800 W/m2, and lower the BDR to 8% if irradiation goes below 800 W/m. Adjustments to increase the BDR for the end of the race is also recommended for optimal driving strategy. Keywords: solar car, world solar challenge, energy model, MATLAB, driving strategy ii Table of content Abstract .......................................................................................... ii Table of content ............................................................................ iii 1 Introduction ................................................................................. 5 1.1 SOLAR CARS ......................................................................................................... 5 1.2 JÖNKÖPING UNIVERSITY SOLAR TEAM ................................................................. 7 1.3 PROBLEM STATEMENT ........................................................................................... 7 1.4 PURPOSE AND RESEARCH QUESTIONS .................................................................... 8 1.6 DISPOSITION .......................................................................................................... 8 2 Method and implementation ..................................................... 9 2.1 DATA COLLECTION ................................................................................................ 9 2.2 DATA ANALYSIS .................................................................................................. 10 2.2.1 Power consumption ..................................................................................... 10 2.2.2 Sun irradiation data ..................................................................................... 12 2.3 THE OPTIMIZATION MODEL ........................................................................... 12 2.3.1 Sun data interpolation ................................................................................. 12 2.3.2 Simulation model ................................................................................... 13 2.4 VALIDITY AND RELIABILITY ................................................................................ 15 2.5 CONSIDERATIONS ................................................................................................ 15 3 Theoretical framework ............................................................ 16 3.1 DRIVING STRATEGY IN PREVIOUS WORK .............................................................. 16 3.1.1 Undulating roads .................................................................................... 16 3.1.2 Clouds .................................................................................................... 16 3.1.3 Other Solar Car Teams ........................................................................... 16 3.2 FORMULAS .......................................................................................................... 17 4 Results ........................................................................................ 19 iii 4.1 THE CARS OF JU SOLAR TEAM ............................................................................ 19 4.1.1 Axelent (2019) ............................................................................................ 19 4.1.2 Solveig (2017) ............................................................................................. 21 4.1.3 Solbritt (2015) ............................................................................................. 21 4.1.4 Magic (2013) ............................................................................................... 21 4.2 ANALYSIS............................................................................................................ 21 5 Discussion .................................................................................. 23 5.1 RESULT DISCUSSION ............................................................................................ 23 5.2 METHOD DISCUSSION .......................................................................................... 24 6 Conclusions and further research ............................................ 26 6.1 CONCLUSIONS ..................................................................................................... 26 6.1.1 Practical implications ............................................................................. 26 6.1.2 Scientific implication ............................................................................. 26 6.2 FURTHER RESEARCH ............................................................................................ 27 7 References ................................................................................. 28 8 Appendixes ................................................................................ 30 iv 1 Introduction The global interest in green vehicles has been growing since it is letting out less pollution than normal internal combustion engines (ICE) and many people want to get into the ecological-friendly alternative mode of transport. The world is moving into that direction because many countries have announced plans to ban the sales of ICE vehicles after 2040. The policy has the aim to reduce air pollution and greenhouse gas emissions (Fulton et al., 2019). 1.1 Solar Cars The solar car is one of these types of green vehicles, which is powered by renewable energy with zero emissions. The solar car makes use of its solar panel that uses photovoltaic cells to convert sunlight into electricity to the batteries and to also power the electric motor. Figure 1. Axelent, Jönköping University Solar Teams 2019 solar car General Motors showcased in 1958 the first solar car that a human could drive. Larry Perkins and Hans Tholstrup in 1982 made the first long distance travel in a solar car, from Perth to Sydney, Australia in 20 days. Later, a race was organized by Hans Tholstrup in Australia called the World Solar Challenge (WSC) to bring more publicity and interest in research of solar cars (Babalola & Atiba, 2021). General Motors won the event and in a response of their victory they partnered with US Department of Energy to organize a solar race in north America. These are the two most notable races of solar car racing but there are many others around the world. The interest of solar cars was in the beginning fueled by research but now it is being referred to as a “brain sport”, with the sole purpose to develop new solar cars for competition and not production. Solar car racing was made to promote interest in the vehicles and demonstrate a proof of concept. Still today it remains a sport for students but continue to improve valuable technologies that could be applied to electric vehicles to provide more efficient and cleaner alternatives over ICE vehicles. 5 An applied example is the technology in an ICE vehicle can make use of a solar panel that gives energy to a battery. This will put a load off the engine and make less of an environment impact (Connors, 2007). In 2006 a company named Venturi announced the first production solar car called Astrolab, (see figure 2). The projected range was only 110 kilometers (Astrolab - Venturi Automobiles, 2021). Figure 2. Venturi’s Astrolab solar car In 2019 the Lightyear One (see