Hi,
No experiences, but a few comments......
An exception to the difficulty in getting enough returns might be if
there was an ability to moor in a tidal or river flow.
As far as tuning for regen, apparently as far as wind power goes, those
old wind pumps on US farms , with many blades, would turn when a flea
breathed against them, but had speed limitation. Certainly, I have this
gut feeling that a 'solid' disc of blades would be a way to get masses
of torque, and fits in with what was said a week or so ago, that paddles
would be efficient at propulsion.
The fact is though, water is 'thick', and has lots of power once moving.
I see the main ultimate issue as being one of deciding to move the boat
at a practical speed, or do the charging by creating massive drag that
is directly proportional to the power produced. Again, the smaller the
battery bank, (and the bigger the sailboat), the more practical it
becomes.
John
3b. Re: Experiences with Sail-powered Regeneration?
Posted by: "Eric" ewdysar@yahoo.com ewdysar
Date: Fri Mar 25, 2011 5:49 pm ((PDT))
Jak,
You already have reasonable experience with regen while sailing. If you
stop and think about your towed generator, it is optimized for power
generation and it produces about 80W (13.5V x 6A) at 6kts, probably
considerably less at 5kts. I would not plan on doing any better than
that with a system that is designed for propulsion, the regen has to be
a secondary consideration.
So you need to ask yourself, how much of the time do you expect your 26'
boat to be able to sail at 6kts? We'll assume that your 7kW motor is
driven with 48V, that means that your max power will be around 145A. If
your drive is somehow as efficient as your towed generator, then your
max regen will be 1.5A at 6kts. I think that this is optimistic, but
we'll go with that number for now.
We have no idea where on earth you sail, but let's assume that you'll be
satisfied with a capacity of only 1 hour at 4kts under power or a
practical range of 4nm. You'll probably need about 2kWh of usable
energy to cover this distance. So how long will it take to recharge
2000Wh with an 80W charger? The answer is 25 hours of sailing at 6kts
to recharge from 1 hour powering at 4kts. That assumes no other
electrical load during the recharging period, house loads will make the
recharging process take longer.
So far we've been estimating with best case scenarios, in practice, your
results will probably be somewhat less due to prop inefficiencies, drive
train friction, controller losses and charging losses going into the
batteries.
Larger (faster) boats can do more with regen, there are a number of 40'+
catamarans that are pretty successful at collecting power at sailing
speeds around 8kts and faster, but your 26' boat won't be able to do
that. 8kts is hull speed for a 45' waterline length in a displacement
keelboat.
So I would guess that Niki was getting as much regen as the laws of
physics allow for, which is nowhere near the expectations that drive
manufacturers set when they say "you can recharge your batteries while
you're sailing". I find electric drive manufacturers to be disingenuous
when they pitch regen in small (less than 30') sailboats
Therefore, I think that it is pretty safe to say that 2kWh of regen is a
theoretical maximum for 24 hours of 6kt speeds, regardless of the size
of the boat. In practice, the results will probably be somewhat less.
I want regen as much as you do (maybe more), so please, somebody, prove
me wrong.
Fair winds,
Eric
Marina del Rey, CA
1964 Cheoy Lee Bermuda 30 ketch
5.5kW Propulsion Marine drive, 8kWh LiFePO4 batteries
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