A Solar Car Primer

Frontmatter

1. Introduction

Abstract

Solar car racing helps to push the development of automotive technology in new directions because it is free from the constraints by which automobile manufacturers regard themselves bound. For example, solar racers have demonstrated that it is possible to do much with far less energy than that which is lavished on commercial automobiles. Solar racing, as do other racing venues, provides a means for manufacturers to test and showcase their products. It puts a lot of young, flexible, intelligent minds to work on these difficult problems, minds that do not know what they cannot do.

Eric Forsta Thacher

2. Interactions with the Atmosphere and Road

Abstract

The interactions of a car with its environment—gravity, the atmosphere, and the road surface—create forces which act on the car, usually opposing its motion. This chapter shows how these forces are related to the characteristics of the car under the designer’s control, such as its shape and weight, and to the effort required to move it: the tractive force. A magnitude will be calculated to give the reader an idea of the importance of each interaction. The calculations will use the characteristics of actual solar racing cars to make the numbers realistic.

Eric Forsta Thacher

3. Interaction with the Sun

Abstract

This chapter focuses on three topics. First, how to estimate the rate at which solar energy strikes a planar surface, such as a solar cell, oriented at some position with respect to the sun, at a given time and location on the earth is explained. Then, a method for calculating the solar energy transmitted through a glazing is discussed. The final section explains how the solar energy irradiating a solar cell is converted into electric energy.

Eric Forsta Thacher

4. Storing Electric Energy

Abstract

All autonomous cars must use propulsive energy stored in the car. Vehicles using chemical storage run on the energy stored in gasoline or other hydrocarbon fuels. Solar energy can be stored in several ways: by sensible storage (heating a mass), by phase change storage (melting a substance), by electrochemical storage or capacitive storage (conversion to electric energy and storage in a battery of capacitor, respectively), or by flywheel inertial storage (converting electric energy to rotational kinetic energy and storing it in a spinning flywheel). Note that inertial storage is intrinsic to all vehicles because each stores kinetic energy in its own mass and the rotating masses of its wheels and drive.

Eric Forsta Thacher

5. Electric Motor Drives

Abstract

The drive is the electric motor, its controlling electronics, the speed reduction, and the driven wheel (solar racing cars usually have only one driven wheel). Figure 5.1 is a schematic of a typical drive connected to its solar-electric power source. This chapter discusses the operation of each of the drive’s components.

Eric Forsta Thacher

6. Electric Power Conversion and Distribution

Abstract

The electrical system connects the electric power sources to the high- and low-voltage loads. It is shaped by the current and voltage demands of the various loads, the requirements for grounding, switching, and electrical overload protection imposed by good practice and race rules, the need for low weight, low power loss, reliability, rapid maintenance and repair, and low cost.

Eric Forsta Thacher

7. Instrumentation

Abstract

A solar racing car cannot be managed during a race without knowledge of its speed and the state-of-charge of its battery. Other parameters are also important, such as the array current, the motor current, the main bus voltage, the motor temperature, and the cockpit temperature. The present chapter covers the means for making the foregoing measurements.

Eric Forsta Thacher

8. Solar Racer—Specification

Abstract

This chapter and the succeeding chapters draw on experience with the five solar racing cars designed and built by students at Clarkson University for the 1990, 1993, 1995, 1997, and 1999 Sunrayces.

Eric Forsta Thacher

9. Solar Racer—Concept Generation and Selection

Abstract

In this book, “conceptual design” describes the second stage of the design process in which a vehicle’s physical envelope, its boundary, is defined. Our goals are to:

1.

Select the car’s shape

 

2.

Set its major dimensions

 

3.

Estimate the gross mass and the location of the center of gravity (CG)

 

4.

Specify the main requirements for the drive

 

5.

Set the main features of the driver–car interface

 

6.

Set the main requirements for the electrical power subsystem

 

7.

Set the number of wheels

 

8.

Examine the stability

 

Eric Forsta Thacher

10. Solar Racer—Detailed Design

Abstract

This chapter continues the Shark design by developing some details or examples of procurement specifications for certain components. The components considered are: the wheels, drive, array, battery, ventilation system, and brakes. Some examples of student-produced assembly drawings for a solar car are shown to illustrate the final product.

Eric Forsta Thacher

11. Solar Racer—Construction

Abstract

Emphasis has been placed herein on the main steps in the construction process. Within this domain, most of the material focuses on construction of the composite body shell and the solar cell array. These processes are probably the most unfamiliar to the reader. Remarks on chassis and moldless shell construction, the management of construction and the skills, facilities, and equipment needed to support it have also been included.

Eric Forsta Thacher

12. Testing

Abstract

This chapter discusses ways of measuring the characteristics of a vehicle and that of some of its components. Emphasis has been placed on methods that are straightforward and economical. Wind tunnel testing of models is not economical unless the team can obtain the wind tunnel time as part of a sponsorship. Nevertheless, a section documenting the construction and test of a quarter-scale model of the Table Top concept has been included. It will be useful, should an opportunity to test in a wind tunnel arise.

Eric Forsta Thacher

13. Energy Management

Abstract

This chapter emphasizes energy management. But this skill is not practiced alone; it is practiced within the context of race management, and it is influenced by the preparations for the race. The fastest racing system wins. Therefore, to put energy management in its proper context, these topics will be touched upon as well. For an alternative view of energy management, readers may wish to study the variational calculus-based method reported in MacCready et al. (1990). A complete description of the theory of this method is beyond the mathematical scope of this book. Wright (1997) describes an energy management strategy used by a 1995 Sunrayce^TM team. Shimizu et al. (1998) give a description of the energy management strategy and its supporting energy management system used by the winner of the 1993 World Solar Challenge.

Eric Forsta Thacher

14. Fund Raising and Public Relations

Abstract

Experience shows that developing a racing system from scratch and competing in a cross-country race, such as the American Solar Challenge, costs $ 50,000–190,000, in cash and in kind, over a 2-year period. Most schools cannot afford this expense. Therefore, the solar car team must seek sponsorships from individuals and agencies, principally businesses, outside the school. However, this is on balance a good thing because it provides an opportunity to involve students in yet another phase of real work. And if the university has a business school, then seeking sponsorships is made to order for that school’s marketing majors.

Eric Forsta Thacher

15. A Solar Car-Based Learning Community

Abstract

Most of the ideas in this chapter are originally from Thacher and Compeau. That material is copyrighted by Roskilde University Press and is used with permission. I gratefully acknowledge the contributions of Dr. Larry Compeau, my collaborator for several years, and co-advisor of Clarkson University’s Solar Car Team.

Eric Forsta Thacher

16. American Solar Challenge™ Regulations

Official Version April 30, 2001.

Abstract

The fundamental missions of the American Solar Challenge™ are to promote and celebrate educational excellence and engineering creativity. Fuelled by the spirit of friendly competition and teamwork, the American Solar Challenge (ASC) champions the creative integration of technical and scientific expertise across a range of exciting disciplines.

Eric Forsta Thacher

17. The Drag Build-up Method

Abstract

A way of making an estimate of the drag area is to model the car as a composite of shape elements which have known drag coefficients. The drag areas of these shape elements are added to give the drag area of the car at a particular speed. This is called the drag build-up method.

Eric Forsta Thacher

18. Ventilation System Analysis

Abstract

The ventilation system influences the cockpit comfort conditions and removes battery-evolved gases and battery-heated air from the battery compartment at a specified minimum rate.

Eric Forsta Thacher

19. Performance Simulation

Abstract

This chapter suggests a method by which the performance of a solar–electric car over a route may be simulated. The motivation for writing such a simulation is to study the battery energy consumed as a function of the speed, the road course, or the parameters of the car.

Eric Forsta Thacher

20. Rolling Resistance Calculation

Abstract

This chapter provides a means for estimating the rolling resistance coefficient of a wheel. This information has two uses: it can assist the designer in choosing among candidate wheels and bearings, and it provides rolling resistance coefficients to be used in energy consumption analysis.

Eric Forsta Thacher

21. Stability Calculations

Abstract

This appendix shows how to investigate certain critical stability limits of a solar car as a function of important design parameters, such as the location of the carʼs center of gravity. The aim is to present calculations that may be done by hand on a digital calculator or on an electronic spreadsheet. The calculations are therefore based on simplified models. The results still capture the relative importance of the main parameters. However, the errors thus introduced are not always conservative. These errors are qualitatively discussed in each section. For convenience, the notation for moments and forces has been changed from that of Chap. 2.

Eric Forsta Thacher

22. Structural Load Estimation

Abstract

This chapter suggests ways to establish design structural load sets for the cruise condition (including remarks on transport of the solar car by trailer) and emergency maneuvers. These load sets can be used by the designers to calculate the loads in the members of the suspension, steering, and frame of the car. The chapter also provides some guidance for the design of the structure under collision loadings.

Eric Forsta Thacher

23. Nomenclature

Abstract

This chapter provides the nomenclature related to “A Solar Car Primer”.

Eric Forsta Thacher

Backmatter