Tidal charger?

[Resolution]

Like many forumites, I have a boat which is moored in a tidal river (the Hamble) and have been looking at the ways of keeping the batteries charged up while not in use. Solar panels are a possibility but the amount of sunshine available seems limited. Wind generators seem to me to be noisy and intrusive, not very elegant mechanically.
Has anyone had experience of harnessing tidal flows for recharging purposes, other than whilst out at sea? Is there any kit that could be hung on the transom (like an outboard) when on the mooring?
All ideas welcomed.

 

[fireball]

Solar panels are a possibility but the amount of sunshine available seems limited.

We've just put a 20w panel on for 240Ah bank .... it's charging nicely! Even during the "rainy" days ...

 

[AngusMcDoon]

Like many forumites, I have a boat which is moored in a tidal river (the Hamble) and have been looking at the ways of keeping the batteries charged up while not in use. Solar panels are a possibility but the amount of sunshine available seems limited. Wind generators seem to me to be noisy and intrusive, not very elegant mechanically.
Has anyone had experience of harnessing tidal flows for recharging purposes, other than whilst out at sea? Is there any kit that could be hung on the transom (like an outboard) when on the mooring?
All ideas welcomed.

I've just been doing some calculations for lack of anything better to do.

Lets assume tide running at 1 m/s.
A cubic metre of water at 1 m/s has a kinetic energy of (mv^2)/2...
So that's 500 J.
Lets assume an impellor of 25 cm diameter.
That's an area of 0.05 m^2...
So at 1 m/s flow it takes 20 s for 1 cubic metre to pass through that area.
In that 20 s, water with kinetic energy of 500 J has passed.
So that's 25 W of power available in the water for that impellor.

Next, what is the efficiency of the system - the impellor might operate at 20% efficiency. Tidal flow rises and falls, so halve that to 10%. Then there are losses in conversion to electrical power and subsequent regulation and rectification, so halve it again. 5% of 25 W is now down to just over 1 Watt.

There are two fundamental problems here...

1) Small systems suffer from low efficiencies.
2) That v^2 term in kinetic energy. Low speed equals very low energy availability.

Better get a solar panel, I think.

 

[neale]

Like many forumites, I have a boat which is moored in a tidal river (the Hamble) and have been looking at the ways of keeping the batteries charged up while not in use. Solar panels are a possibility but the amount of sunshine available seems limited. Wind generators seem to me to be noisy and intrusive, not very elegant mechanically.
Has anyone had experience of harnessing tidal flows for recharging purposes, other than whilst out at sea? Is there any kit that could be hung on the transom (like an outboard) when on the mooring?
All ideas welcomed.

What a great idea and I'm sure there would be a market for such a device. As far as I know there is nothing available now to do this.

I seem to remember back in the early 90's when the Balkans were in conflict, locals without electricity made some tidal generators from old washing machines. Very clever but not quite the boaty image . I reckon you could use an old outboard as the basis for something like this, stripping the engine out and allowing a free flowing prop to generate power. Not sure how much you would get but it would be very consistent, unlike wind and solar, although you would need a prop with equal efficiency in both directions to get the most out of it.

 

[Evadne]

Aquair

One of the wind generator companies does just this thing. Trouble is, if you look at the figures you don't get much power at less than two knots:

 

[TiggerToo]

... I have a boat which is moored in a tidal river (the Hamble) and have been looking at the ways of keeping the batteries charged up while not in use. Solar panels are a possibility but the amount of sunshine available seems limited. Wind generators seem to me to be noisy and intrusive, not very elegant mechanically.

Whilst the musings are fun, the facts are that you have answered your question already:

"to keep the batteries charged while not in use" solar panes or a small, silent wind generator (or both) are absolutely fine.

I'll leave debates about elegance to other threads (although some of the wind jennies are items of beauty - and go well with the lines of a sleek classic sloop).

 

[Fantasie 19]

...and what happens when the large chunk of seaweed floats by and gums up the impellor/propellor....

 

[ianat182]

Tidal charger-innesker

If the propellor device was pivoted then it would also work in the reverse ebb tide as the flood ,retaining its efficiency as a propellor.This would hopefully shed the weed too?
Prepare yourself for questions on antifouling,pitch and diameter of the propellor!!!

ianat182

 

[Iota]

modify one of these?
http://www.duogen.co.uk/

I had a Solara M225 fitted earlier this year and it keeps my batteries topped up nicely. Made a big difference on holiday. I looked at wind generators but decided I would try solar first.