SOLAR SPLASH® “Handbook”
The three Handbook Chapters contain information from various Solar Splash newsletters and form a “handbook” for teams preparing to enter SOLAR SPLASH for the first time or for those getting ready for their next SPLASH.
Handbook Chapter 1 – So you want to enter the SOLAR SPLASH
Handbook Chapter 2 – Managing the Sun
Handbook Chapter 3 – Getting the Most from the Sun
Chapter 1 – So you want to enter the SOLAR SPLASH…
It doesn’t matter if this will be your first year or your fifth, most of the following relates to the creation of a team, and that has to take place, often from scratch, each year.
What do I need from the outside world to get started?
- Visit the Home Page (you already made it here!) as it contains numerous details.
- Print a copy of the Rules from the website.
Although you may have a group of people who are interested in participating, you need more. The purpose of this write-up is not to intimidate you but to pass on experience we have gained over many years of participating in and running events of this type. Keep reading and many details will follow.
ADVERTISE – Make up an announcement banner to mount on the poster to let people know the date and time of your organizing meetings and who to get in touch with and how, if someone is interested but can’t attend.
Don’t get ahead of yourselves, no matter how much experience you have, be sure to get through each step which is outlined in this write-up. They all add up to success.
Just like students, faculty advisors come with diverse perspectives. Some Advisors are very active in the program and want to remain actively involved. Others are willing to sign the Entry form and then prefer to step aside and leave the project to the students. What works best? There is no magic formula, but there are some potential pitfalls. If a Faculty Advisor holds the reins too tightly, the students may lose interest. If the students are without an Advisor, the lack of experience may hurt. Many years ago, just before leaving for Florida to put on the first Sunrayce, I (George Ettenheim) got a call from one of the Team Leaders that they had started testing and caught the car on fire. They had grossly undersized the wires which go from the controller to the motor. Perhaps, a faculty advisor might have caught this before it became a problem.
In a perfect world, having more than one advisor gives you more resources to turn to if you need them.
FORMULA FOR SUCCESS
What should we try to accomplish in our Initial Meeting?
Getting to know one another is the first and most important step. Start with each attendee. Have them introduce themselves and be sure they talk about their interests, past experience, and why they are there. Some members will have to be flexible enough to plug the holes which are bound to exist.
Socialize, have a pizza, or whatever. Team building is not just an idea, it is practiced in most work places whether in the public or private sectors.
What roles need to be filled to have a successful team?
The following is a list of “skills” and functions that your team will need. One person may do several or several people may do one.
Leadership– There is a great tendency to break up the team into groups, such as Hull, Drive train, etc., and have a leader for each. This is satisfactory if each of these people is part of a Leadership group. In recent years, we have seen that although a strong inspirational leader is needed, a great deal of success can be achieved with a facilitator who strives to reach consensus.
System Engineering– It is very important to get everyone’s ideas but there comes a time to make decisions. These need to be system driven, rather than component by component. I once visited a university that was teaming with another as the second had considerable experience with solar arrays. Through the process of asking a variety of questions, it was learned that the array group was designing for a system voltage of 120 volts while the lead team was assuming they would have 135 volts.
In the case of a boat, System Engineering is critical because the hull, motor, prop, and available energy must be very well matched. We have seen several instances where this was done but the simplest task, steering, did not get enough attention. Without good handling, there is not much value in having a good boat.
Mechanical Engineers– It is not unusual for ME’s to see the project as a mechanical one with some help needed from EE’s, or vice versa. The reality is it is neither. It is a multi-disciplinary systems problem. ME’s are needed, but so are fabricators. Hands-on experience for many of the team members is very important. In the process of pursuing the project, ME’s will gain a better understanding of the problems of others, such as the EE’s, and then the team aspect really starts to work.
Electrical Engineers– The tasks for the EE’s are many. A solar array must be designed and built. The output from the array and power from the batteries must be regulated and controllable. Motor(s) must be selected and matched to the system. Telemetry systems for monitoring the electrical and solar systems and managing a power strategy are needed.
Technical Specialties– An aerodynamicist once compared himself to a father saying he was only around for the start. There are design aspects which must be done early on, and a fluid dynamics person may not be needed throughout the project. Although some participants have a School of Naval Architecture, they may get delayed in making design decisions because there are too many ideas.
P.O.C.– It is not necessary that the Team Leader serves as the Point of Contact, but one person needs to have this responsibility. Effective communications is a two way street. Questions from the team need to be passed on to Headquarters and responses communicated back to the team. The POC is the person who should be distributing copies of the News, the Rules, etc. to the team. This person may serve as the interface with others on campus and even the outside world including the media.
Business Majors– Quite a number of business majors have gotten some very good experience raising money for the team and finding “in kind” contributions. The project is an ideal way to get out into the local business community and become known. There is also a need for financial backing, and this should be right up their alley.
Communications major– If you can get a communications major, it can be very helpful to get a story on local radio or TV. It should be a part of the overall Public Relations aspect of the team representing your University.
Do we really need Meetings and what kind?
It has been our experience that weekly meetings are mandatory. They are a vital part of the Team concept. This is the time to have each person report on progress, future tasks, and, more importantly, find out where gaps or needs exist.
One common theme which is vital is the schedule. The Time Line needs to be updated and, if it is done as a group, everyone can easily understand their interdependence.
Hold meetings in the same place at the same time. In this way, everyone always knows where they need to be and when. Have an agenda. It can be the same one, but have a list of topics which get covered each meeting and don’t let the meeting stray too far from the agenda.
End all meetings with action items. Be very clear as to who will do what by when!
Why do we have difficulty staying on Schedule?
There are many reasons for falling behind schedule, but here are three strategies which may help you do better.
- Create an initial schedule and include contingencies for delays.
- Make decisions and stick to them. Often, there are things you would like to do but everyone has to be realistic. Maybe some things get saved for “next year”.
- Maximize the available time.
How can this be accomplished? First, set an absolute deadline of Christmas break to fix the design. In order to do this, many decisions must be made. These milestones need to be defined and met. This is where team members need to have time to present their ideas, but must also be willing to accept the fact that there are not sufficient resources in time, labor, or money, to have a reasonable chance of success this year.
Next, when are most team members available? Evenings, weekends, vacations? Although the temptation may be great to take the entire Christmas/semester break off, it is probably the longest time with the fewest other commitments in the entire school year.
Finally, be sure to have contingency plans. Don’t get hung up on one task or part. Keep an active list of projects that need to be tackled in a prominent location so if someone has some time, they can go to the list and choose something. The list of projects should include an estimate of how long each might take and enough details to make the assignment clear.
Where should all of this happen?
Ideally, you should have a space which is used exclusively for the Splash project where fabrication or assembly can take place. It is best if it includes a meeting area and a bulletin board as the minimum.
What else do we need?
- Computer access to contact the Hotline and team members, and to access the website.
- The support of the Department. This may be your Faculty Advisor, Department Head or the Dean. Who can be of the most help? Maybe all of
- Commitment, Commitment, Commitment!
Chapter 2 – Managing the Sun
Over the history of the Solar Splash, much has been written on the subject of energy. From incoming and how it is measured to storage and consumption. Some is in the form of Rules, some as Hotline questions, and some in News stories. The following is an attempt to compile all of this into one chapter of the “Handbook”.
Like electric cars, electric boats have been around for a century. Whether a launch or a submarine, the drive systems of these craft are typically simple, reliable, and energy efficient. Although an enormous amount of energy is available in one gallon of gasoline, it is not renewable. On the other hand, most boats are outdoors most of the time and often are not in use for many hours a day. Using that down time to let the sun charge on-board batteries is an excellent use of solar energy. This is why the only energy source for the Solar Splash is direct incoming “Sunlight”.
Why 480 watts?
Solar Splash is intended to be a competition that draws attention to a practical application of Solar Energy. It is hoped that having stimulated the interest of many, others will use solar energy to whatever extent is practical from a one square foot panel on a kayak to power a laptop computer to a sight-seeing boat where the entire roof is covered with solar panels.
The first solar car competition, the Tour de Sol, held in Switzerland, developed the rule limiting solar panel output to 480 watts under one-sun conditions. This rule has been adopted for the Splash as it minimizes any advantage a team would have if they could afford very efficient solar cells. It is also true that with the dimension limits for the boats, 480 is a rather practical limit in terms of size and weight.
How is the Output of the Solar Array Measured?
Prior to 2014, a calibrated cell was used to measure the incoming solar radiation, and a solar panel testing system was used to measure the output of the array. Beginning in 2014, the specs of the cells (in the case of student-built panels) or the specs of the panel (in the case of commercially-built panels) will be used to determine the maximum output of the array. The power output may not exceed 480 watts, although a 10% allowance is given for student-built panels.
There are several reasons that storage batteries are allowed. Should the day be cloudy, it is not very practical to be limited to incoming energy. The batteries are a storage unit for energy, coming from the sun when the boat is not in use. Even on a sunny day, there may be a need for more energy than is currently available directly from the sun. For the Splash, the two hour Endurance event presents the opportunity for 960 watt-hours to be accumulated under ideal conditions. Prior to 2014, a nominally equal amount of energy, 1000 watt-hours, was chosen for the storage capacity of the batteries in the Endurance event, which resulted in a weight limit of 31 kg (68.2 lb). With rule changes for 2014, the weight limit for all events in the competition was increased to 45.5 kg (100 lb).
Why only Lead-Acid Batteries?
Only electrically rechargeable, lead-acid batteries are allowed due to their relatively low cost, ease of availability, and generally long life. It turns out that the capacity of such batteries is very closely related to their weight. Since weight is easy to measure, especially compared to capacity in watt-hours, weight limits are set for the competition.
Due to the availability and relatively low cost of commercially manufactured lead-acid batteries, they are used in many marine applications and the Splash. In time, as sophisticated batteries are developed, primarily for electric cars, it is likely that the limitation on lead-acid will be changed.
We could go faster if we were not limited to a “source” voltage of 36 volts.
This is true but safety is of paramount concern to the organizers. In the mid 90’s, an international safety standard for DC voltage was established at 52 volts. Since the array must have an output of higher voltage than the battery source, and since battery outputs are nominally in 6 volt increments, the 36 volts represents both a safe and practical value. Deep cycle batteries are usually used as they are not damaged by discharging them to a rather low level of charge.
Recharging of Batteries.
To be consistent with the concept of the Sun being a renewable energy source, only recharging from the solar panels is allowed for the Splash. From the standpoint of practicality, the limit of 480 watts means that no one can get an unfair advantage by having extra panels.
Another major consideration is the time table of events. Using the same two sets of batteries for all events (new for 2014) will require careful planning, charging, and strategies based on expected sun conditions.
Inspection of Batteries
In 1997, with teams allowed to choose their own batteries, it was discovered that battery weight is somewhat inconsistent with manufacturers’ specs. Starting in 1998, batteries may be weighed and checked against the Manufacturers’ specifications, which must be submitted with the Technical Reports. No exceptions to the weight limits will be allowed without Manufacturers’ specifications.
Other than output, what else should we consider when designing our array?
There are some rather obvious factors such as weight, durability, and configuration. The effect of weight depends greatly on the size and type of hull you are using. Generally, the penalty for a small amount of unnecessary weight is less on water than it is on land. The problem that is more important is the effect of the weight of the panels on the boat’s center of gravity. The boat may be very stable without the array but unsatisfactorily unstable with them.
In making these tradeoffs, durability is very important. Panels must be handled quite a bit over the course of the entire event, not to mention testing and transport before arriving on-site. Physical damage to a panel usually results in a loss of output. Finally, although the panels are not on the boat for the Sprint, their configuration can be very important. The panels should generally conform to the hull. If they extend well past the sheer of the boat, they may catch the wind and cause instability on the course. Their configuration should also be considered for launching and retrieval. It is acceptable to add the panels after the boat is launched but then it is extremely important to have an easy, positive way of hooking them up electrically, and securing them in place on the deck.
Suitably large and rugged connectors are far more important than trying to save an ounce or two. They may get wet, and if slippery, may be hard to handle. You should also take into account the use of the array when recharging batteries.
Finally, Maximizers or Peak Power Trackers can be very important. Typically, there may be one of these circuit cards for each panel of the array. The purpose is to maximize the output of any one panel, and then combine these outputs. If this isn’t done, the output of the array may be no greater than the output of the weakest component.
Battery Selection Considerations.
There is no doubt that the two primary considerations when selecting batteries are System Voltage and Capacity, but what about other factors? The location of the batteries is one option that allows you a huge amount of leeway in establishing the center of gravity of the boat. It is not just stability, but also the angle of attack or planing once the boat is up to speed.
Safety is of major concern. Many inexpensive batteries cannot take the high rate of discharge required for the Sprint. There are ventilation requirements which must be considered. One location may be ideal but may be directly in front of the skipper, thus requiring a barrier for acid and gas. All of these factors need to be considered in the selection and layout process.
Why are Battery and Motor switches required?
There is a natural tendency to assume that a Motor shut-off switch would be adequate. In most cases, it is not. Depending on the circuit, the output of the array may power the boat even if the batteries are turned off. In recent years, it has become more common to use a relay, rather than long runs of large diameter cable, to accomplish the switching and thus reduce the size and weight of switches and cables. It is still vitally important to size cables correctly for anticipated current.
Is there a need for a great deal of instrumentation?
It depends on many things. Just like an airplane, the boat can be operated with a bare minimum of instruments or use a telemetry system which is quite sophisticated. Much depends on your operating strategy. You must consider the tradeoffs in reliability, weight, and complexity.
What is your Energy Management Strategy?
For the Sprint, it is most likely “give it all it can take!” but the Endurance is another matter. Generally, the circuit philosophy is to have all of the output from the array go to the motor and then add power from the batteries as conditions dictate. Key questions are how much and when. Certainly, knowing the discharge characteristics of the battery pack is critical but what about the weather? A good forecast of solar energy is very important. Where do you stand with respect to your nearest competitor? How much time is left in the Heat? Since distance is measured to the nearest 1/4 lap, where do you expect to finish? These are just some things worthy of consideration.
It also may be helpful to have a cloud cover forecast for re-charging in the Paddock area. How full are your sets of batteries? Do you have a “top off” strategy?
Can you monitor key systems to know that they are performing properly? If the output of part of your system is not up to expected, do you have a strategy team to deal with the questions which arise?
The purpose of this section is not to tell you what to do or how to do it. The purpose is to give you a reference on some of the philosophy behind the rules and, to perhaps give you a source from which you can develop a check list of items you need to research or cover in your preparations for the event. It is very important to remember that the energy system is probably not much better than the weakest link.
Chapter 3 – Getting the Most from the Sun
During the 1999 Solar Splash, David Luneau of the University of Arkansas at Little Rock and Technical Manager of the Splash gave two talks on the subject of maximizing the power from the sun. This chapter is centered on the content of those talks and expands the principles to include some of the system tradeoffs that are relevant.
In analyzing the competitors’ systems for the World Solar Challenge, Chester Kyle explains, “Somewhere in between the open-circuit voltage and the short-circuit voltage, the cell will develop its maximum power output. This peak power point will change according to the illumination, the temperature, the cell design and its load or power demand.” It is not uncommon to find that the voltage of the Peak Power Point (PPP) is not the same as the system voltage of the boat. Since the Endurance Event is run on a closed course, the sun angle is constantly changing, as are other factors such as the variability of clouds and their effects on the amount of energy reaching the Endurance course. “For this reason, peak power point trackers that will automatically operate each part of the panel at its maximum power level can significantly improve performance. Power trackers oscillate about the peak power point, locating it by taking frequent samples of the cell’s transient properties.”
From Figure 1, the PPP can easily be seen. If this were a 24 volt system, the value of trackers would be significant. How important is it in the overall design considerations of the craft?
If we go back to the late 80’s when solar cars were being raced in Europe, the most successful designs tended to be aerodynamically clean, with the arrays mounted on tilting or adjustable structures usually on the top of the car. It is important to understand that these races were relatively short sprints from one city to another in relatively complex terrain. When the first World Solar Challenge was announced in 1987, AeroVironment did extensive evaluations of various design concepts and concluded that the increase in incoming energy resulting from tilting the array was more than offset by the significant aerodynamic drag. In that event, the course was essentially a North-South line of 3000 km with the sun changing position as the day passed. Sunraycer was designed by AeroVironment to minimize aerodynamic drag and, with the utilization of power trackers, to optimize the power from the array as one side tended to be shaded in the morning and the other in the afternoon.
The applicability of these lessons to the Solar Splash is interesting to examine. Speeds during the Endurance event are sufficiently low that one does not need to be very concerned about the aerodynamic drag of the array, but the effect of wind on this structure may have a significant effect on the stability and handling of the craft. It is also important to note that the Endurance heats are run within approximately 3 hours of solar noon. This, combined with the relatively low sensitivity of solar cells to sun angle, makes one stop to consider the various tradeoffs. Weight, simplicity of fabrication, and the stability of the boat often lead to the conclusion that a flat, horizontal array has many advantages.
It is also interesting to review the applicable meteorology. In the absence of clouds, the geometry is rather straightforward, but the Endurance heats are run over a period of about 6 hours and in that time, conditions can be highly variable. Although several unusual conditions had been anticipated for the race across Australia, the circumstances under which the maximum incoming solar radiation was measured were unforeseen. The actual peak, well above clear conditions, was a text book altocumulus cloud formation in which the individual cells and spaces created lens-like quality and thus scattered more radiation from a larger area of the sky than essentially one point. At another time, the sun reflected off a large cumulonimbus, and thus the strongest radiation was coming from two rather different directions.
Whether the array is fixed or tiltable, there seems to be no doubt that the addition of power trackers would be a valuable addition to any system design. But, are they mandatory? No. It can be argued that a manual system will work. In the 1990 World Solar Challenge, the winner, Honda, chose a manual system, even though the next 9 finishers all had trackers.
Certainly, over the years, we have seen significant success from a number of the Splash participants who have stuck with the KISS principal (keep it simple, stupid) and those who have built a more reliable system. Another important lesson learned is that one must start somewhere and build on success. Re-designing the entry from scratch each year only leads to new problems. Do as many things as well as possible but do not hesitate to set realistic goals and leave some things for future teams.
As always, we are here to be of assistance to anyone. We will not make decisions for you, but perhaps our many years of experience can provide some help.
Remember, if you have questions, do not hesitate to contact Headquarters at firstname.lastname@example.org.