48-volt house bank. Next Gen for boats?

[twistedtree]

I'm kind of thinking I'd often run with both diesel and electric. So at my usual 7.5 knots instead of burning the usual 1.5 gph I'd throttle back to 1 gph and blend in 5 kw solar and maintain the same speed. Or 0.5 gph and 10 kw if I've got excess power.

Maybe this is off base, but it sounds feasible. I hang my dinghy on the transom, and don't want outboards back there as well, plus propping etc is a concern. I have a yanmar SD on my sailboat and like it.

I was looking at this guy more recently. Two 6.0 kw units. https://www.epropulsion.com/pod-drive/

I think that makes sense because the electric is coming from solar.


If the electric has been generated via a diesel, then you will have consumed more fuel than if you had just run directly off the diesel because of all the conversion losses. So it's all about WHERE the electric came from. The challenge is typically fitting enough solar on the boat to make an appreciable contribution to propulsion needs.

 

[twistedtree]

On that thought, other than not gaining anything in the maneuverability department, what about attaching one of the inboard electric motors (ELCO and Epropulsion both make them) to the shaft so the electric and diesel drive go through one prop? That gives no extra underwater drag from the setup and you'd still have prop wash over the rudder for better steering if running electric only. Only thing I'm not sure of is whether the control systems for those motors would work well with another power source on the same shaft.

That's a parallel hybrid that you have created, or at least one form of it.

 

[rslifkin]

That's a parallel hybrid that you have created, or at least one form of it.

Exactly. I'm thinking that it would likely be somewhat more efficient than having the existing shaft plus 2 more drive appendages in the water.

 

[twistedtree]

Exactly. I'm thinking that it would likely be somewhat more efficient than having the existing shaft plus 2 more drive appendages in the water.

I would expect so too. I have always understood that the larger the prop the better, so turning the main prop would be more efficient that turning a smaller aux prop. This certainly plays out with wing engines vs hydraulic or other drives that turn the main shaft. System turning the main shaft seem to go faster with the available HP (typically from one or more generators) vs a dedicated wing engine shaft & prop, I believe because the wing prop is so much smaller. Being offset doesn't help either. What you gain is redundancy of the while drive line, not just the engine that turns it. Gee, another tradeoff in a boat. Who would'a thunk?

 

[Jeff F]

I think that makes sense because the electric is coming from solar.
...
The challenge is typically fitting enough solar on the boat to make an appreciable contribution to propulsion needs.

Right. My total energy consumed is low - right now about 10 gal/day when traveling. So if I express that as 100 kwh/day, and can collect and use 30 kwh/day solar, I can reduce fuel use by 3 gal/day, or 30%.

If I travel 200 days/yr that's a savings of 600 gal/yr, by my simple calculations, which may pay for the system. Would need about 8 kw installed solar.

 

[twistedtree]

Right. My total energy consumed is low - right now about 10 gal/day when traveling. So if I express that as 100 kwh/day, and can collect and use 30 kwh/day solar, I can reduce fuel use by 3 gal/day, or 30%.

If I travel 200 days/yr that's a savings of 600 gal/yr, by my simple calculations, which may pay for the system. Would need about 8 kw installed solar.

Think you can fit 8kw of solar? I’m in the process of upgrading my home solar to about 11kw, and it’s 4 pole mounts worth of panels. It takes a lot of space.

 

[Jeff F]

I have always understood that the larger the prop the better, so turning the main prop would be more efficient that turning a smaller aux prop. This certainly plays out with wing engines vs hydraulic or other drives that turn the main shaft. System turning the main shaft seem to go faster with the available HP (typically from one or more generators) vs a dedicated wing engine shaft & prop, I believe because the wing prop is so much smaller. Being offset doesn't help either.

Interesting. This doesn't exactly match my intuition, but I won't argue. The SD(s) seem easier to install than trying to set something up on the shaft.

What you gain is redundancy of the whole drive line, not just the engine that turns it.

That's appealing. I seriously damaged my prop twice on my last long trip. I like the driveline redundancy.

 

[Jeff F]

Think you can fit 8kw of solar? I’m in the process of upgrading my home solar to about 11kw, and it’s 4 pole mounts worth of panels. It takes a lot of space.

Maybe? I've got a lot of unused space. Or maybe a frame overhead with a large array. Need to do some measurements.

This is very much up my alley. I'd find satisfaction in implementing this sort of system.

 

[Jeff F]

New system is looking like 2x6kw pods, 15 kwh batteries, 8 kw solar, a bit over $20k in parts.

 

[mvweebles]

New system is looking like 2x6kw pods, 15 kwh batteries, 8 kw solar, a bit over $20k in parts.

Am I correct that around 200W per square meter, so 8kw is 40 square meters (20 solar panels, covering 430 square feet)? Massive!!!

Question: Leaving aside practicality of such a large array on a boat, how will you clean off the seagul guano?

Peter

 

[Jeff F]

Am I correct that around 200W per square meter, so 8kw is 40 square meters (20 solar panels, covering 430 square feet)? Massive!!!

At a guess I have 250 sq ft of empty deck space now. So maybe my scheming is impractical. But I could have an overhead array and stay within my self-prescribed height restrictions. Or maybe the system is still viable with 5 kw solar. It's interesting to play within practical limits to see what's possible.

 

[twistedtree]

At a guess I have 250 sq ft of empty deck space now. So maybe my scheming is impractical. But I could have an overhead array and stay within my self-prescribed height restrictions. Or maybe the system is still viable with 5 kw solar. It's interesting to play within practical limits to see what's possible.

As a reference point, my new home arrays are 10' x 14' (140 sq ft) and rated at 5kw. So on paper you might be able to do 8kw in 250 sq ft. But when I put panels on my flybridge hardtop, I left about a 1' "walkway" so I could get to other stuff, including tipping up the panels (they are hinged and pinned) to get under them for cleaning, and to get to stuff outboard of them. So utilization of the available space was not very good. Plus I have a lot of shading issues. Your boat looks more open, so I expect you will be able to do better, but be sure you can still get around the boat, clean it, etc.

 

[Jeff F]

Thanks for comments. I'll get out with a measuring tape this week. Cold snap has broken here.

I've got a 12x18(?) area aft of the PH that I really don't use, plus the forward cabin top. Could build a frame above the aft area and get to 300 sg ft probably.

 

[MacPhid]

The other issue is flat mounted panels are derated based on angle of the sun. At noon they are close to rated output but once you’re an hour either side of noon output drops off. Install 8 and count on 5!

James

 

[Jeff F]

The other issue is flat mounted panels are derated based on angle of the sun. At noon they are close to rated output but once you’re an hour either side of noon output drops off. Install 8 and count on 5!

Yep, understood. I'm curious about what optimum placement would look like. I had a chat recently with another TF member who suggested 15 degrees off horizontal was optimal. My intuition says flat may be as good as it gets, in a boat that's moving.

In my case I'm just concerned with daily yield rather than maximum current at midday.

 

[twistedtree]

Yep, understood. I'm curious about what optimum placement would look like. I had a chat recently with another TF member who suggested 15 degrees off horizontal was optimal. My intuition says flat may be as good as it gets, in a boat that's moving.

In my case I'm just concerned with daily yield rather than maximum current at midday.

In this part of the world, nearly flat is optimal in the summer. In the winter, nearly vertical. And always facing due south, which becomes the problem on a boat. You never know which direction is south, so pretty much the only thing you can do is mount them flat and live with it.


I've seen some instances where the panels on one side of the boat are tilted a bit that way, and the opposite on the other side. That will improve output from one side if it's facing south, but be worse for all other sides. Flat compromises all panels equally, but makes the boat direction not matter, other than for shading issues. I think it would be a pretty complicated analysis to figure out if one is better than another.


Power production over the course of a day is a bell curve, as the sun arcs across the sky. Daily production is typically measured/quoted in "full hours of equivalent sunlight", which how much daily power you can expect over the course of the whole day, expressed as hours of full output (think noon time). There are tables where you can look up what is expected for your location. 4-5 hrs is pretty typical for summer in North America, and of course it varies by season.


I don't recall for certain, but I think there is derating of the panels involved as well. The nameplate rating is based on full sun exposure, but also on a relatively low temperature. In the summer, panels get very hot and production drops quite a bit. What I don't recall is whether this derating in included in the tables for full hrs equivalency, or if it needs to be added in.


Ironically, I have seen the highest solar production in the winter, on cold sunny days. Where I am located the sun barely rises mores than 20 deg above the horizon, and is only up for 8 hrs or so. But it's COLD. Just the other day I had my highest output ever at 19kwh for the day from 3.6kw of panels. That's 5.3 full sun equivalent. More typical is 4.5 or so. This also illustrates why you need to design for 125% of the max possible output, because on sunny cold days, it will happen.

 

[MacPhid]

Jeff, Optimal placement on a boat for me means as close to horizontal utilizing available space while not restricting any normal function of the boat.
There are a number of apps that help with panel alignment, I use Simply Solar, it helps calculate and more importantly set the correct angle. Of course on a boat at anchor as TT says it is almost impossible to maintain.
It's interesting that one has to design a system for a boat to compensate for less output than rated (oversize) but also for over production on cold sunny days! Of course cold on a boat is relative, but if you were to use solar in your winter berth it could be an issue.

James

 

[rslifkin]

The panels on my forward cabin top follow the deck camber. So they're tilted slightly outwards and slightly forward. That helps water drain off them better, which likely keeps the panels a little cleaner. The angle does have a small impact on output, but not enough to worry much about. I get a little better output if the boat is facing south.

 

[mvweebles]

The panels on my forward cabin top follow the deck camber. So they're tilted slightly outwards and slightly forward. That helps water drain off them better, which likely keeps the panels a little cleaner. The angle does have a small impact on output, but not enough to worry much about. I get a little better output if the boat is facing south.

I have four 1m x 1m square panels (200w ea) on my hardtop. Hardtop has a significant camber so the panels are separated into two strings - port and starboard. I have very little tracking data, but was surprised yesterday when they both registered almost exactly the same amount of thru-put - about 0.6kw each.

Ensenada is dusty in general, and a boatyard is worst-of-the-worst. I suspect my panels will need a weekly cleaning while here. Less frequently out cruising of course, but will still require cleaning. I forget if it was this thread or another, but someone was thinking about making a rack system to slide panels into rather than a support structure that could support a person. Don't forget access to clean the panels from time to time.

Peter