Hydrogeneration for Batteries?

[DaveInRI]

EDIT: turns out they’re thousands of dollars, lol. Closing that tab forever!

Morning. Has anyone ever experimented with hydrogeneration aboard a C-Dory for the purposes of charging a battery bank? My “only a couple minutes” searching online said anything being driven by a propeller will lose efficiency if using one of those systems (obviously, as it creates drag), but I’d probably be okay with that as the goal would be converting gasoline power to electrical power simultaneously with the alternator for “more bank for your buck” per hour using the outboard, and it would presumably be a minimal amount. More stuff to break than with solar panels, and a generator would work also, but it’s intriguing as a concept without knowing more.

From Yachting Monthly:

Everything you need to know about hydrogenerators - Yachting Monthly

Design developments have made hydrogenerators the most efficient form of sustainable auxiliary energy for yachts. Sam Fortescue reviews the latest

www.yachtingmonthly.com

‘Kinetic energy increases proportionally to the cube of the velocity,’ adds Andersen. ‘That means producing 300 amp-hours per day or more is a realistic prospect while cruising at 7-8 knots with a hydrogenerator fitted. And it’s the reason why more and more boat owners are now opting for water generation, although it’s still not as popular as it should be.’


By contrast, a tradewind run with a wind turbine might yield just 80 amp-hours per day, because the apparent wind on a run is lighter. Good performance might see 40W output from 10 knots apparent. Similarly, solar panels only produce a fraction of their rated output for most of the day, so you’d need a large array to match the return of a modern hydrogenerator.


A blend of all three will, of course, give the best outcome for different conditions at anchor and under way – but on passage, it’s hard to beat the benefits of a good hydrogenerator.

 

[pcg]

In theory, yes you could generate more electricity on a C-Dory this way, but it would literally be less bang for the buck, not more. The energy produced by the turbine in the water takes more fuel per watt than that produced by the alternator. Cost aside, this makes sense for a sailboat, but with a prop driven boat it doesn’t. Losses are incurred every time energy is converted from one form to another. A gasoline powered outboard motor uses power that would otherwise go to the prop, when it generates electricity from its alternator. You get a bit less mpg when the alternator is making electricity than when it is not. To then use additional power to run a turbine sitting in the water generates even more losses. The fuel from your gas tank is best utilized to make power in the most efficient manner possible which is from the outboard's alternator.

 

[Karl Konecny]

I believe it would be much more efficient to connect the generator from the hydro generator directly to the engine shaft (geared appropriately). Your propeller is fairly inefficient at transferring engine power to thrust power and the turbine that spins the hydro generator is also inefficient (even though both are designed as well as possible). Meanwhile a direct shaft connection to the engine is very efficient so the same additional load on the outboard could produce much more electricity than a hydro generator. That is pretty much what your alternator is, a 'generator' connected directly to the engine shaft. Unfortunately, alternators are not designed very efficiently (cost considerations) so they could do much better. On sail boats hydro generation may make sense because you are really trying to convert wind energy to electrical energy. I would be curious to learn how efficient hydro generation is compared to a wind turbine while tacking. The wind turbine would still be facing into the wind while the hydro generator would be aligned to the hull

 

[pcg]

Dang, the new software allows only 15 minutes for editing, half the time of the previous software. Here's slightly better version of what I'm trying to explain...
Cost aside, this makes sense for a sailboat, but with a prop driven boat it doesn’t. In theory, yes you could generate more electricity on a C-Dory this way, but it would literally be less bang for the buck, not more. The energy produced by the turbine in the water takes more fuel per watt than that produced by the alternator, because it goes through more conversions. Losses are incurred every time energy is converted from one form to another. A gasoline powered outboard motor uses power that would otherwise go to the prop, when it generates electricity from its alternator. You get a bit less mpg when the alternator is making electricity than when it is not. To then use additional power to convert the forward motion of the boat (produced by the motor, not the wind) into electricity to run a turbine sitting in the water generates even more losses. The fuel from your gas tank is best utilized to make power in the most efficient manner possible which is from the outboard's alternator.

 

[robhwa]

Generating electricity with a hydroturbine under power will clearly be a no-gainer due to the laws of thermodynamics (i.e. the parts that allow no perpetual motion machine). However, for a motor-powered vessel, one thing you might consider in this discussion is anchoring or mooring during tidal exchange or anchoring in rivers rather than using the speed of the vessel under power. If you spend considerable time "on the hook" where there are currents or tides, you could generate net power with a hydroturbine and store it or use it immediately onboard. On the hook, I've often thought of the possibility of getting something useful out of that energy source. For instance, just north of me, the Tacoma Narrows has tides >5 mph, sometimes higher. You could also put out a more substantial turbine under those conditions than you would while sailing since you are not worried about slowing your speed.

 

[Tom Hruby]

As mentioned previously going from a gas engine to a propeller and then back from a propeller to a generator is very inefficient. Rob, suggests anchoring in a tidal current to provide the force for the generator. It is hypothetically possible but not really workable in a small boat. First the tidal currents have to quite strong to provide any significant power, and I know from experience that it is almost impossible to anchor in a strong current and expect the boat to stay in place. Anchors will often drag in currents more than a few knots. And, if you actually manage to get a firm hold on the bottom, it puts a severe strain on your boat. I was slightly involved in trying to set up tidal power generation in Scotland and the biggest issue was how to anchor the system since currents of 7-10 knots were needed to make the system worthwhile.

As Rob says, the laws of thermodynamics always win... Anytime one transfers energy from one type to another there is a loss (its called entropy). The more times energy is transferred, the more loss there is. So, if you are using gasoline as your energy source to create electrical energy, the fewer times the energy is transferred from one type to another, the better. There are already enough steps in a gas generator - first gas to heat, then to rotational/mechanical - to magnetic - to electrical.

As suggested wind is also a potential option, but again the amount power you get will barely power a fridge during the day. A 500W turbine (about a 4' diameter turbine) will only get you 100 W at a 13 mph wind.

 

[Karl Konecny]

How I remember the three laws of thermodynamics:
1) You can't win
2) You can't break even
3) You can't quit

 

[pcg]

Generating electricity with a hydroturbine under power will clearly be a no-gainer due to the laws of thermodynamics

Nitpicking here, but generating electricity with a hydroturbine under power from a gasoline-powered outboard IS a gainer (it gains you more electricity albeit at a higher cost), and it doesn't violate any laws of thermodynamics. If you need more electricity, this will give you more. It's just not as efficient as using the outboard's alternator. Now, if he had an electric outboard and wanted to use that electricty to power the electric outboard, then the 2nd law would make that inviable.

 

[DaveInRI]

All of this is true, and.... I didn't mind paying $20 a gallon from the hardware store (or whatever) for TrueFuel for my small gas kicker on my daysailer because it saved me the time of draining carb bowls, cleaning jets, etc. (ethanol is required where I live), and lasted me more than an entire season. I was viewing it in a system overall. For the original "hey what if" thought bubble I had, it was about a way to charge a battery faster in a given amount of time, despite it being less efficient from an energy perspective (to continue the True Fuel metaphor, "I don't care that I'm going through gasoline faster in my outboard, I need the batteries charged before nightfall and it's cheaper and quieter than a generator"-- or something like that, it was not even fully "half baked", just a thought cloud). Until I learned they cost $5k+ of course.

Tom, so what you're saying is I need a wind turbine on top of my C-Dory to power my fridge. Great idea! (note, I don't even have a fridge on my boat, ha)

 

[thataway]

I have done this on long passages with my sailboats--you have to be moving at least 7 knots to be worthwile as far as usable amount of power. I have not used wind or solar power back in the 1980's and 1990's. I put 200 amp heavy duty alternators belt driven on the main engine and generator both belt driven. There are other disadvantages to trolling power, from fouling by seagrass, plastics, to being attacked by sharks.

Several of the communities in Alaska use hydropower. I have friends who live off the grid who use only hydro, solar and wind power (plus very large battery banks) to run their homes' demands.

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