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Old 28-08-2017, 17:23   #16
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Re: How feasible is 100% renewable electric cruising right now?

Quote:
Originally Posted by Peregrine1983 View Post
Interesting. Thanks Stu. So with that calculation though my boat is currently "massively overpowered" at 58hp.
There was a recent thread here about HP per ton that you may find interesting.
HP per tonne

and here's an older one:
Engine Sizel

(And no, I wouldn't call that massively overpowered, but it is certainly "plenty of power for pushing into adverse conditions")

Added: I'm around 11ton cruising weight and have 2 x 38HP Yanmars
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Old 28-08-2017, 17:45   #17
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Re: How feasible is 100% renewable electric cruising right now?

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Not being facetious at all.

20kW = 26 HP.
A common rule of thumb for an auxiliary engine is 2 - 4 HP per ton. 26 HP for a 10 ton vessel is reasonable and certainly not "massively under powered":

Or did you actually mean to type "over powered"?
Hi Stu,

I have the same boat and same engine which is rated 58 HP and would not call it over powered. True about 99% of the time I only use a small fraction of that 58 HP but on a couple of occasions I was glad to have every bit of that 58.

Generally happens when maneuvering in a tight marina or other restricted area with strong winds or a current running. Another time when I was a little late getting through Hell Gate on the East River in NYC (delayed because Obama was speaking at the UN) and had to buck a 2-3 kt current and get through before it increased to 5-6 kts.

HP is one of those things that I would rather have a little too much than not enough.


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There is a lot of hype about EP motors, thrust and "equivalent horsepower" where the EP proponents claim that somehow EP is different and because of the torque curve of EP somehow 1HP of EP provides the same propulsive power as much more powerful diesel engines under typical sailboat auxiliary conditions.

A typical example would be Torqueedo, who claim things like:
"10kW continuous output powerful propulsion comparable to a 20 HP combustion engine"

or OceanVolt
"Q: WHY IS THE 15KW OCEANVOLT MOTOR EQUIVALENT TO A 45HP DIESEL ENGINE?
A: The torque of Oceanvolt electric motors is significantly higher than that of a diesel engine - and they both have the same propeller.

and elsewhere:
" A 10kW Oceanvolt electric motor easily outperforms and is more powerful than a 30hp diesel engine.

Yes a lot of hype around "electric HP" vs diesel HP. There are a few valid arguments for a small differential. Electric doesn't have the parasitic loads that a diesel has to run water pumps and alternators so you gave a few HP there. The other argument is the torque curve is much better a low speeds with electric but that really only gives you a better acceleration but I don't see where that will matter at cruising speed.
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Old 28-08-2017, 17:46   #18
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Re: How feasible is 100% renewable electric cruising right now?

When FULL SPECTRUM solar panels come out, (currently solar only use ultraviolet) I'm all over the electric switch.
Until then, in my case it makes no financial, speed or weight sense.
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Old 28-08-2017, 18:31   #19
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Re: How feasible is 100% renewable electric cruising right now?

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% of capacity, that means you need 25kWh or storage
(about twenty 12V, 100Ah batteries).

Stu thanks for those calcs.

How do the batteries you suggest above compare to say Trojan T-105s in terms of the big three - size, weight and cost?
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Old 28-08-2017, 18:34   #20
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Re: How feasible is 100% renewable electric cruising right now?

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I've been very impressed with how much juice I can get from the sun to run all sorts of things on my boat without ever plugging in or running the motor - my wife's 2000 watt 110v hair dryer being the thing I'm probably most proud of.

Some folks in my owner's group are re-powering with Electric Yacht's Quiet Torque 20 motor with supposedly great results.

That hair dryer may just push the boat by itself.

I would be interested to hear their thoughts on RY vs Torqueedo 40-80 Hp touted replacement motor.
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Old 28-08-2017, 18:45   #21
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Re: How feasible is 100% renewable electric cruising right now?

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When FULL SPECTRUM solar panels come out, (currently solar only use ultraviolet) I'm all over the electric switch.
Until then, in my case it makes no financial, speed or weight sense.
That's news to me.

Visible spectrum wavelengths = 400-700nm. Ultraviolet is10 - <400nm, Infrared is 700-1000 nm

Spectral Response | PVEducation
This graph is in microns, multiply by 1000 for nanoeters




The spectral response of a silicon solar cell under glass. At short wavelengths below 400 nm the glass absorbs most of the light and the cell response is very low. At intermediate wavelengths the cell approaches the ideal. At long wavelenghts the response fall back to zero. Silicon is an indirect band gap semiconductor so there is not a sharp cut off at the wavelengh corresponding to the band gap (Eg = 1.12 eV).

As you can see, current silicon cells effectively use the visible and infrared portions of the spectrum, tno the ultraviolet.

Recent developments on Gallium etc will allow cells to capture the lost energy between 1000 nm and 25,000 nm ( so called full spectrum) .

But note that much of the energy in the solar spectrum is contained in the visible and infrared ranges where Si cells are already reasonably efficient, so don't expect to see a doubling of maximum potential efficiency through this technology. Maybe 20-30% improvement?

It's only the energy above the trough at around 1100 on the graph below that will be added. All the red and green below that is being captured fairly effectively now ("effectively" given certain limitations of the theoretical efficiency of single junction cells)

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Old 28-08-2017, 18:51   #22
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Re: How feasible is 100% renewable electric cruising right now?

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Stu thanks for those calcs.

How do the batteries you suggest above compare to say Trojan T-105s in terms of the big three - size, weight and cost?
Lithiums are roughly half the weight, many times the price of flooded lead acid, but since they can be discharged more deeply, you don't need as many Ah of storage.

So it very roughly works out that for equivalent usable Ah. that they are 1/3 the weight and 3 times the price overall.
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Old 28-08-2017, 20:02   #23
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Re: How feasible is 100% renewable electric cruising right now?

A no-fuel cruiser sounds optimistic, not to say unrealistic.

Extended range, dependability (day/night, in foul weather,...) and power-hungry appliances are to be considered..
I love the idea of hybrid systems:
A smaller main engine coupled to a power alternator (200A) charging lithium engine bank.
Or
A massive DC generator

Problem is power, proportional to the electric system V.
Beyond 70V any hazard is lethal. Thus system should be designed waterproof and to a level of accuracy which makes it all uneconomic

Big ship propulsion is usually electric, with diesel engines used for producing electricity. More efficiency, control, no gear- box...
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Old 28-08-2017, 20:40   #24
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Re: How feasible is 100% renewable electric cruising right now?

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Originally Posted by StuM View Post
That's news to me.

Visible spectrum wavelengths = 400-700nm. Ultraviolet is10 - <400nm, Infrared is 700-1000 nm

Spectral Response | PVEducation
This graph is in microns, multiply by 1000 for nanoeters




The spectral response of a silicon solar cell under glass. At short wavelengths below 400 nm the glass absorbs most of the light and the cell response is very low. At intermediate wavelengths the cell approaches the ideal. At long wavelenghts the response fall back to zero. Silicon is an indirect band gap semiconductor so there is not a sharp cut off at the wavelengh corresponding to the band gap (Eg = 1.12 eV).

As you can see, current silicon cells effectively use the visible and infrared portions of the spectrum, tno the ultraviolet.

Recent developments on Gallium etc will allow cells to capture the lost energy between 1000 nm and 25,000 nm ( so called full spectrum) .

But note that much of the energy in the solar spectrum is contained in the visible and infrared ranges where Si cells are already reasonably efficient, so don't expect to see a doubling of maximum potential efficiency through this technology. Maybe 20-30% improvement?

It's only the energy above the trough at around 1100 on the graph below that will be added. All the red and green below that is being captured fairly effectively now ("effectively" given certain limitations of the theoretical efficiency of single junction cells)

I read it on the internet, so it must be true.

Upon further research, there are different curves depending on if your boat's solar panels are at sea level or the TOA ( Top Of Atmosphere), but I will admit your research appears to be more accurate especially at 100,000 feet and above !
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Old 28-08-2017, 21:00   #25
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Re: How feasible is 100% renewable electric cruising right now?

With the battery banks required for electric propulsion, what happens if one battery in the bank goes bad? Do you then need to replace all of the batteries in that bank, so that they all have a similar charging & discharge history? That way when you're charging that bank, they then all accept a charge at the same rate. As, in theory at least, that's how you do it with conventional lead-acid batteries. And if you have to do this on a battery bank of this size, with the newer gen. batteries, it surely would take a bite out of your wallet. Maybe even enough $ to cover a full diesel rebuild (or more).
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Old 28-08-2017, 21:41   #26
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Re: How feasible is 100% renewable electric cruising right now?

Sailing UMA is doing it - Sailing Uma

They only use the motor leaving or arriving, so they are reliant on the wind for most of their crusing. Their YouTube is vey addictive.
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Old 28-08-2017, 21:52   #27
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Re: How feasible is 100% renewable electric cruising right now?

Our Electric Motor (Electro-Beke, part 1) Sailing Uma

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Old 28-08-2017, 21:54   #28
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Re: How feasible is 100% renewable electric cruising right now?

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Originally Posted by senormechanico View Post
I read it on the internet, so it must be true.

Upon further research, there are different curves depending on if your boat's solar panels are at sea level or the TOA ( Top Of Atmosphere), but I will admit your research appears to be more accurate especially at 100,000 feet and above !
I think that if you compare my previous graph to the following, you will see that the previous one equates to "Radiation At Seal Level" shown, not TOA.

(Note: the troughs in the Sea Level spectrum result from the absorption bands of various atmospheric gases)
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Old 29-08-2017, 04:43   #29
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Re: How feasible is 100% renewable electric cruising right now?

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Sailing UMA is doing it - Sailing Uma

They only use the motor leaving or arriving, so they are reliant on the wind for most of their crusing. Their YouTube is vey addictive.

Given our propulsion system, I'm really always an outsider to conversations like this...

But FWIW, that seems like an OK use case assuming one is willing to work the boat that way. I understand Columbus and Magellan and so forth sailed similarly in open waters, i.e., depending on wind alone.

But... even if that's the paradigm a user adopts... a situation that would seem to be critical is about any need for motoring in heavy weather, if necessary to maintain steerage, power nav equipment, whatever. The calculation of how long batteries might last relative to how long dangerous weather might last... seems to me like a big deal.

And of course, budget. Cost of a boatload of LFP batteries and related systems versus cost of a new (or maybe a rebuild) diesel? (I don't have a clue what that specific comparison would be like for OP's boat/engine, but doing that analysis may be useful if not already done...)

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Old 29-08-2017, 05:08   #30
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Re: How feasible is 100% renewable electric cruising right now?

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Originally Posted by Peregrine1983 View Post
I've been very impressed with how much juice I can get from the sun to run all sorts of things on my boat without ever plugging in or running the motor - my wife's 2000 watt 110v hair dryer being the thing I'm probably most proud of.

I have a Pearson 424 (22,000lb disp). Some folks in my owner's group are re-powering with Electric Yacht's Quiet Torque 20 motor with supposedly great results. I'm not sure if they're doing hybrid (diesel generator) or all electric. There will probably come a day where I too will have to replace my good old W58 motor. Our boat lives on a mooring, and when we cruise we either anchor or pick up a mooring - so we never plug in.

If I remove the motor and diesel tank, I now have a massive empty engine bay - roughly 5'x4'x4' and the space where an 80 gal diesel tank was (about 5'x4'x3') behind that. The electric yacht QT 20 will supposedly fit where my old V-drive was under the cabin sole. So, I have a ton of space for batteries. I imagine weight would likely be my limiting factor for batteries, not space.

For experiment's sake, let's say on average I have to motor my boat for 2 hours every day at 6 knots with the Electric Yacht QT 20. Let's also say I'm in a sunny, windy place at low latitude - say Curacao.

Assuming these things, how much solar, hydro-generator, and wind charging wattage do I need to be a completely "off the grid" yacht?
Well, let's sort it out the scientific way:

The QT20 has 20kW power draft. You want to go for 2 hours per day, that means 40kWh or 40.000Wh a day. A Solar Panel with 200Wp has a footage of 1.5m with no shade and can produce in average 800Wh per day, so you need an area of solar panels to re-charge the batteries of 40.000 / 800 = 50 x 200W Solar panels and an area of 25m or 270ft.

Well, you won't put the pedal to the metal, so there will be some excess power for your electronics.

Lets see, what battery you'll need: With 12V LiFeYPO4 you would need 4.000Ah - with single 1.000Ah cells you'll need 16 prismatic blocks 1.000Ah each for a total price of 1.329,00 € each + a BMS so round about 23.000€ or 27.000$.
The solar array contributes with 200€/panel with another 10.000€ + the controller / charger, let say another 2.000€

So total for the setup: 40.000€ + the engine and regulators...

The batteries will weight 560kg (1cell is about 35kg). The solar panels round about 800...1.000kg (one panel is about 15-20kg+some fixing)

It's a lot of diesel you can buy for just 2 hours daily cruising...
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