I am reporting to you all today as a proud member of the University of Rochester Solar Splash team (URSS).
The whole team, myself included, worked hard all year to attend this annual competition. As a freshman, it was my first year in attendance so I spent much of that time learning. I hope to share some of that knowledge with you by explaining this competition, what it’s about, and what it takes to enter, in hopes of expanding this competition to new parts of the country or even the globe.
What Exactly Is Solar Splash?
According to the Solar Splash website, Solar Splash's official name is "an international intercollegiate solar/electric boat regatta." It is a five-day event centering around the intercollegiate competition of solar/electric boats. The boats, themselves, are built in the months before the competition. A technical report for each boat must be submitted before the week of the event.
Day one is reserved for technical inspections and the other four are spent on the water. There are five total events: the qualifying events for both speed and maneuverability, the Solar Slalom, the Solar Endurance, and the 300-meter sprint. Points are earned in seven categories: the technical report, an assessment of visual display, an assessment of workmanship, and scores in the qualifying, slalom, sprint, and endurance events.
What this means, in reality, is that safety inspections are done to ensure requisite equipment is in hand (visual and auditory warnings, fire extinguisher, paddle, dead-man’s switch, etc.) Then, points are awarded for different events, four based on boat performance - qualifying, sprint, slalom, and endurance - and three separate categories for Visual Display (on-site display of information about the boat and design process), Workmanship (a completely subjective assessment of the overall build quality of the boat/design) and Technical Reports (fully detailed report of all design components and decisions that went into your team’s boat).
Unlike other competitions, Solar Splash is all about moving every team forward, and it isn’t cutthroat at all.
Each team’s visual display is available for other teams and attendees to peruse at their leisure and the best five technical reports are always posted online for all teams to view. Thanks to the efforts of my team, our technical report was given 85/90 points and is one of those available for you to read if you wish to give it a glance. [6/22/16: Currently the 2015 reports are still up, but 2016 will soon be available at the same page linked above.]
These allow for teams to all share knowledge and help to level the playing field so nobody has an extreme advantage over other teams. In fact, at the competition, I was personally invited by this year's champion, Cedarville, to take a look at their boat by their advisor. He shared some tips with me and some other teams' members about choosing and testing batteries, including the exact details of their own sprint battery set. He even provided guidance for getting sponsorships!
Rules and Design Restrictions
Another important aspect of Solar Splash that differs from other large-scale engineering competitions such as SAE Mini Baja and Formula SAE, which are more widely held in the US, is the open design restrictions. A simple glance at a few boats will show you what I mean:
The design restrictions mainly limit the length and width of the boat and permit only the use of up to 100 pounds of SLA batteries to power the drive system.
You also cannot operate the drive system at over 36 volts nominal. However, if you decide to utilize one big motor at 36 volts, or power four smaller ones at 24 volts, or any other combination you like; that’s totally valid.
Our boat utilized a hybrid design with an airboat-inspired bow and trimaran hull. Many other teams used longer canoe-like boats, or other hybrid designs. Almost any material is allowed too, from simple cedar wood plank to composite weaves of fiberglass, carbon fiber, and Kevlar. You are also allowed to use supercapacitors or even flywheels without a weight restriction, so long as the open system still operates at no higher than 52 VDC or VAC, and drive is still nominal at 36 volts. (Nobody has successfully used flywheels yet, but last year’s competition saw one boat attempt to use a capacitor bank!) This is in stark contrast to Mini Baja, where all vehicles are required to use the same exact motor, and thus extremely similar drive systems, and they all look more or less the same since they have the exact same kind of suspension, nearly the same wheels, are required to be basically the same size... Need I go on?
Images courtesy of Motorworks UK (left) and Eastar Battery Co. (right).
As long as drive system batteries are all lead acid, they are permitted. That said, teams are allowed two sets of SLA batteries, each up to 100 pounds, to swap between endurance and sprint/slalom heats. The reason for the SLA restriction is because if lithium batteries were allowed, it would basically give a massive advantage to whomever could spend the most money on batteries, and using them at all would be prohibitively expensive for teams like mine with less than $1000 to spend on batteries. A full look at the rules from this year’s competition is available here.
This competition is very different from solar cars on land because the boats never operate directly on solar energy. Solar power recharges the batteries and provides an extra boost during the two hour endurance heats, but the sprint and slalom events are usually run without panels on the boat to be lighter and more aerodynamic. This is due to the current technology limitations of solar panels. Our boat utilized some of the best panels available, running even slightly above the panel wattage limit of 480 watts, but we would need to supply over 35 amps to our motor to run even at low speeds and at 36 volts, 480 watts provides less than half of that power, and only while there is full sun on the panels. In contrast, a typical electric motor scooter can easily safely operate on 350 watts on land.
While smaller trolling motors might be able to operate at that power level indefinitely, they would be too weak to be competitive in Solar Splash. Thus, having a very efficient solar charger and efficient drive system is imperative. Recharging during daylight hours is necessary, hence the competition being held over multiple days.
Obviously, the need for high-efficiency systems is one of the driving design decisions for this competition, as it is a requirement for everything from choosing motors and motor controllers to the type and pitch of propeller utilized, and saving weight everywhere possible is a huge priority. Some teams even design their own custom motors, propellers, and motor controllers and have them professionally machined for their boat! These aren't your average $50 PCBs either, these components will often need to handle kilowatt levels of power, easily tens of horsepower at peak, with current draw continuously higher than 250 amps in sprint heats.
This is the motor/controller pair used in our boat. We were the only team to utilize a 3-phase AC motor at this year's competition. Image courtesy of ThunderStruck Motors.
Lining up for the first Endurance heat.
I couldn't in good conscience dedicate just one article to an event that I dedicated a so much of my free time to. Plus, I have barely scratched the surface of the nitty-gritty details of how the competition works. That’s why I’m going to give you all an exposé on my team’s design, and all of the hard work we put into our boat this past year. Although we may not have performed as well as we would have liked, it was a real learning experience for me, and it can be for you too!