I plotted the output of a solar battery to show the need for a DC-DC C [ direct current to direct current converter ]. As the graph shows ,max power will occur when solar is loaded down to 28V @ 20.8A = 582W which is about half power for motor. Solar directly connected to motor might load solar to close to 28V, now at 28V , battery can supply current,bringing up motor voltage, which reduces power from solar, so we raise solar V with converter. Limit battery current to 1/2C, to make 2hr @ 10A. Now is battery V high enough to supply current ? Quite a ballancing act.
On test: peak power 886.2 mW, 76mA, 11.7V scalled up to full-sized collector .

 

thumb-nail did'nt make it bedfore.
Solid line is current vs voltage, dotted line is power.

 

Another thought. You are using a battery that has the advantage of being light weight (and so used in scale models) for a full scale project? In that case just go with lead acid batteries.

because in our project weight is very important. In the rules of this it is said that everyone uses the same capacity (no matter what battery you are using).

And if you want to use the max capacity possible with an LiPo battery, you have a weight of 6kg, but when you are using the lead acid battery you have a total weight of 25kg, that's almost 20kg more than the Lipo which is a huge difference because a boat of a contester from last race total weight was only 90kg.

so LiPo batteries are really the best solution for us.

 

? at the beginning of each day are you allowed charge your battery on shore? ? any restrictions on positioning solar pannel while under way?

 

I see you are under certain rules that force you to play the game a certain way. And, I think you're right. Use LiPo batteries. Light weight for a given power. You might want an aluminum flash shield to protect you from a possible fireball from what I read. Good luck!

I've wondered about using the solar panels as a wind sail. On a windy day this would be quite useful. On the other hand on a still day you want to point your panels right at the sun. I'm sure you're aware of this. But the wind sail idea might be your last resort so having a pronounced keel or a centerboard on your boat might be useful.

 

About the LiPo batteries we are going to use a BMS system so don't worry about a possible fireball. Everything has to happen so safe as possible.

About using the solar panels as a wind sail, that is not allowed. We may change the angle of the solar panels but this is only in an angle of 15degrees. We were thinking about using some mirrors to concentrate the sunlight but we have to see the effectivnes from those mirrors when we are actually going to build the boat.

We can charge the batteries whenever we want by the way, there is no restriction about that. before the race, after the race that is all allowed.