Building Solar Electric Propulsion (Motor Katamaran)

I'm building a cabin motor kat (6.3 m) for displacement speed and will use her in sheltered inland waterways around Berlin, Germany (Design Bernd Kohler, ECO62). She will be driven by two small electric outboard motors (trolling motors, 1,44 kW each), going silently and slowly is the goal. While it is by far not a groundbreaking thing, the examples available at the web, differ in a lot of points. So I will have to plan, to construct and to test an reasonable amount of details. As the cabin roof which is also covering the "Achterdeck" has an area of around 11 square meters there will be 12 semiflexible solar panels with 1.100 W(peak) power. 4 peaces of LiFePO4 batteries at 25,6 V, 100 Ah in parallel will build up the battery bank, together about 10 kWh (nominal) capacity.

Today I got the main battery breaker. 4 poles to cut the current under load safely in both poles.

 

This project has potential.

Can you just wire all those flex panels direct to a controller and skip the battery?

 

That would be a waste of electric energy.

To test the behaviour of the panels I temporarily mounted 6 of them to a house wall and connected them with a with a simple Ohm's resistance. Trying to keep my workshop free of frost.
The winter sun is not very strong anyway but the electric yield was very low because in this kind of set the panel is mostly not operating at its power peak.
The MPPT solar charger between the panels and the batteries (I will use 6 of them) is able to get the most out of the panels (MPPT = maximum power point tracking).

When I added the MPPT and 2 batteries to my wall installations, the yielded power was growing very much.

 

Additionally it is necessary to get electric power from the panels if not cruising and store it in the batteries. So I will able to cruise on cloudy days.

 

Your results don't surprise me.

Run a tiny battery then if it makes you feel better.
Why waste the money, weight and contribute to long term environmental impact on a storage battery?

It would be a waste of solar energy, which is wasted every day everywhere there isn't a solar panel.
Use less panels if it saves "wasted electricity".

It's a different way of thinking that's for sure.
Requires more planning, better design, and flexibility.
As you were.

 

Clever design would allow you to operate on cloudy days too.

 

Huh? How would you do that without a battery ?

 

Like I said, clever design.

 

Not really a solution.
If you have X square metres of deck, and the Panels produce Y amount of power at max, then there aren't any further design options, surely.

 

I think BlueBell is talking about a backup secondary real time Energy System being incorporated, that doesn't use storage, like wind, wave, Etc.

 

Why not use sail as primary propulsion and charge batteries from a paddle-wheel generator/motor? Sail can produce much more power per M^2 than solar panels and are less affected by contact with water. A tear in the sail is less likely to occur than a cracked solar panel, and can still be used.

 

Heimfried’s plan will work just fine, and I’m sure he has chosen to design the propulsion system the way he has in order to fulfill his intended use.

You don’t mention, but are those motors 1.4kW input or output?

 

The 1,44 kW is power input.

I'm more than 70 y. o., do have no experience as a boater and not enough physical strenght for sailing. My wife and I just would like to own a boat (which everyone can also call a "swimming coffee table") to be on the water for a day or a week. Cruising slow and silent with serenity, enjoying the nature and a sunset and a glass of wine at anchor.

I started the build 6 years ago, I like to build my boat very much - but also would like very much to hit the water with my boat before I'm dead.
(Jens, a friend of mine, building the same boat near Dresden, 10 years younger than me, fell ill and left this world two weeks ago.)

 

Heimfried,

I am sorry for your loss.
I have fond memories of Dresden.
Godspeed on your build, enjoy.

BB

 

Sounds like you have already settled on your motor selection. What are they?

Hopefully they are a brushless design with the ESC located inside the housing below the water.

If they are, they should provide about 2kW of propulsive power which should be plenty for your goal provided you keep your hull shape efficient and don’t go crazy with the superstructure which can introduce a lot of windage.

Displacement isn’t as critical with electric motors as windage. Sometimes more weight can help keep a small boat better pointed in wind and current, at the cost of reduced speeds and more sluggish maneuvering response.

A few suggestions that you may want to consider.

First, make sure you have properly sized BMS’s in the batteries with ample discharge rates. With the size motors you are using, they should be pulling around 60-70A max, so you’ll want BMS’s capable of 2X whatever the motor manufactures states is the max amount draw. Yes, the panels will help supplement this (might see 50A max), but there may be times when you want full power while your panels aren’t producing due to weather, nighttime, or failure. I imagine you will likely have some small house loads as well like USB charging, lights, maybe even an electric anchor?

Also, if you are going to be putting X4 100aH 24V batteries in parallel, make sure the manufacturer allows for this (some have limits on # in a parallel or series connection which is typically associated with the BMS design and/or internal wire gauge), and I would also recommend using battery balancers since I assume you’ll be charging the bank via your X6 MPPT wired in parallel?

Even though many LiFePo4 manufacturers claim they are unneeded, I have seen larger banks experience voltage/capacity drift. Two batteries in parallel or series is a little easier to manage, but may still require periodic balancing.

In a series connected bank it’s more a problem if one battery disconnects early due to low voltage/capacity which is what can happen if one battery never charges up completely. The advantage of course of your bank in parallel is you’ll still be able to use the capacity of the other 3 batteries if one disconnects since they are providing the system voltage needed for the motors.

On that note, this is where having a fully configurable MPPT comes in handy as you can set them up so they aren’t charging your bank up to full capacity every day which will increase their longevity. Then every month or few months, you can push them and hold them at full voltage so that they can internal balance. Meanwhile your external balancers will ensure each battery that makes up your 24V 400aH bank is balanced with the other.

Anyway, I think you have a good plan and should have no problem accomplishing your goal of quiet smooth slow speed cruising.

Now back to my solar electric cat which I’m half way finished servicing the motors and making a few other tweaks on today so I can get it back on the water for the Summer…