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Old 14-04-2020, 23:22   #1
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Solar recommendations

Hi all,

How much solar power and what brand do you recommend for the system below:

25' length at waterline, 8' beam
~8000 lbs displacement
10.5kW electric motor
48V 450 amp controller
4 x 12V deep cycle lead-acid batteries

Optimally need to motor approx. 30-40 mins at 3-4 kts.

Thanks.
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Old 14-04-2020, 23:39   #2
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Re: Solar recommendations

Quick answer is going to be as much as you can. Sailing Uma give some good figures in their videos and whilst slightly bigger at 36ft, I am guessing your yacht is 28-30ft, it will give you some ideas.

However, if you drain those batteries down to 50% in 40 minutes well that's 2500w depending on the size of the batteries. Now ask yourself how long it will take to charge them back up with 300 - 400w of solar?

Have you already converted this yacht or are you just at the planning stage?

Pete
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Old 15-04-2020, 00:00   #3
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Re: Solar recommendations

Thanks for your quick response. Yes, you are correct. 28' LOA.

We have just begun the electric conversion. Our '77 Yanmar diesel gave us nothing but problems. I've read a bit into the "Electric vs. Diesel" debate and yielded to electric. Sailing Uma was a big inspiration for us. Great, informative website and YouTube channel!

We have everything purchased except solar. We live in Hawaii, so the sun is abundant. We are also considering a wind generator, but I have yet to do proper research. We only plan on motoring in and out of our tricky channel.

Currently we are considering 2 x 240W solar panels in series at 24V to hit 48V. More than that and our yacht would be overrun with solar panels I think. Do you think this a good place to start?
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Old 15-04-2020, 00:04   #4
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Re: Solar recommendations

I think you mean 2 x 240w panels.

That is probably as much as you can fit to a 28ft yacht. We have 300w on a 31ft yacht and whilst we might be able to squeeze some more on the life lines, for the stern arch that's about the sensible limit. 300w of solar weighs 18kgs and the frame another 10kgs. Add 11kgs of dinghy engine to the stern and that's a lot of weight permanently on the very back of the boat. Deflated dinghy is now kept forward of the mast for obvious reasons.

I think the YT channel "Rigging Doctor" said they can motor at 2 knots just on the solar during the day, which gives you another marker.

Be interesting to see your project, do keep us informed with some updates as you go along.

Pete
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Old 15-04-2020, 00:09   #5
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Re: Solar recommendations

Yes! That is what I meant.

Your setup sounds exactly like ours. Deflated dingy on the bow, 5hp outboard on the stern. Granted, our 220lb engine is being replaced by an 80lb electric motor, so we have some poundage to spare. Batteries are likely going to have to be in a central location due to space restrictions. Do you have an electric motor?
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Old 15-04-2020, 00:44   #6
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Re: Solar recommendations

Quote:
Originally Posted by monstera View Post
We are also considering a wind generator, but I have yet to do proper research.
Slightly off topic but: My advice is to deploy all the solar you can - every square possible inch - before considering a wind gen.

Wind generators are uniformly disappointing in output, only generate usable current in a gale, have moving parts that wear out, and make lots of annoying noise.
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Old 15-04-2020, 02:03   #7
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Re: Solar recommendations

I did some sums a few weeks back and it just wasn't feasible. New 25hp engine about 6000. Good electric drive option like Sailing Uma 18,000. It could be done cheaper but would be a lash up. The deciding factor was the need to be back to work on Monday mornings. If retired then that changes the need to sail to a timetable, but it's still an expensive science project.

However, we have just upgraded to 300w of solar from 150 to run a small portable freezer, ice to go with the Gin is so important Wifey experimenting more with the slow cooker powered by solar, so perfected how made rice pudding, which is much nicer than the tinned stuff.

Haven't worked out how to run an induction hob. The power surge is probably too much for our 2 x 12v type 24 batteries at the moment, but its under consideration.

However, we need to be obsessive with weight, just too easy to overload a small yacht with stuff, so small inflatable dinghy, little honda 2.3hp outboard, sail with half empty tanks and fill up on arrival etc.

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Old 15-04-2020, 02:20   #8
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Re: Solar recommendations

Growling Bear on here has a electric yacht, you might look at his experience over the last few years.

We did meet a solo Dutch yacht about 26ft with electric drive a couple of years ago, but I think it was a cheap DIY project with a couple of small 100w panels. However, he only used it to get out of the harbours and sailed when the wind suited him. Seemed very happy in his retirement slowly sailing up and down the English channel. I could do that
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