Solar Boat Race

[yuandrew]

http://www.mwdh2o.com/mwdh2o/pages/education/solar_cup_01.html

My school (Chino Hills High) will be participating in this event this year. We've constructed a hull already and are awaiting the solar panels and a motor. Now one thing I have to help out with is the battery bank.

Our electrical system voltage will be 24 volts and we will need to power a trolling motor. The maximum weight of our battery pack is 55 pounds and the batteries can only be lead acid.

I'm planning on Concord Lifeline or Chairman batteries but are there any other brands I can use? This will be for a 200 M Sprint competition. 2 12 volt batteries will be used for 24 volts to the motor

 

[Brock]

So how much of this is going to be run off freshly charged batteries /ubbthreads/images/graemlins/wink.gif Seriously though optima spiral wound sealed lead acid will get you the most amperage out of the batteries the fastest. They should be more then enough to catch and hold 320w of solar. I would also suggest looking at a good mttp controller like the Outback MX-60 or building a similar unit. A 320w array at a nominal 24v will give you 8 amps of useable power, but if you use an mppt controller you can suck just over 12 amps out of the array. A nice improvement in power output.

 

[Minjin]

I think I'd run two different panels. A 100w panel to act as your minimum for endurance race and a 220w for additional shore charging. I really don't see any point in using the full 320w of panels when racing. Seems to me like it would just add unneeded weight when you consider the length of the races. I guess you'd have to do the math...

You need to find out what 'sets' of batteries means. That will determine what voltage and how many batteries you can run (since there is a 55lb weight limit).

Mark

 

[yuandrew]

Great guys. Anyway, I found out more today. We are actually going to use four 80 watt panals by BP Solar. They will be hooked up in series/parallel with 2 each in series to double the voltage and both sets of 2 in parallel for a total of 320 watts.

Our science teachers finally decided to use Concord Sun-Xtender batteries rated 25 amp-hour. We will hook 2 up in series for 24 volts. They will primarly run a trolling motor and get charged by the solar. I still have to find a charge controller and what gauge of wire to use.

 

[cobb]

You need to email someone here by the name darrell about this and get his advice.

I would suggest a charge booster so you can get what bit of USABLE energy from your cells in low light situations, as for batteries, *I* would look for the one with the highest capacity and in my experience plain old lead acid wet floodd cells. Also make sure to cycle them 12 times or so to break them in and try to keep them charged or topped off before the event.

 

[yuandrew]

Ok, where's Darell when I might need him?

 

[Darell]

Darell's been under a rock for a while.... Researching more tools that have (gasp) nothing to do with flashlights!

I can't think of much to add to what Brock has said. Your budget will determine much of this stuff. When I purchased my panels, I could have had 80W all the way up to 160W - all from the same size panel! I opted for 120W as a good ballance between surface area and cost. If cost is no object, you can shove lots more power into the same size space! I think the Optima batteries are going to be your best bet here because of their energy density. I wish I could get you one of the Advanced Panasonic packs from my EV1 for this! About twice the density of the Optimas!

 

[yuandrew]

Yeah, I wished too. If we didn't have a weight restriction for the batteries (55 pound max for the entire pack) and type restriction (Sealed Lead Acid only), I would have used electric vehicle batteries. Anyway, how many volts is each pack for an EV1? We have a max nominal voltage of 24 VDC as well

If I wasen't restricted to using only SLAs, I would have used batteries from this electric vehicle

http://www.altfuels.org/events/testdriv/altra.html

 

[cobb]

I hope this is not too late. See what the graph for that motor is. In my experience with electric wheelchairs and scooters is that they perform best at 75% top speed. If you go wide open they suck power and go slower, it just takes longer to get somewhere, but 75% of the wide open gets you the best speed per power used.

May want to look into a PWM controller, this way you can control the amps drawn and help you tell what your run time will be. May also want to add an amp meter to the motor and solar cells so you know what is going in and out to better estimate run time.