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Old 03-02-2014, 08:21   #1
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Solar for a Boat with a Good Diesel Generator

I've about decided to ditch the useless Rutland 914i wind generator, which I have not been able to get to make useful power.

I can fit a solar panel (or two) on a frame over my davits. I have wanted to avoid this, but nowadays I am starting to not see any alternative.

The primary mission is this: boat lives on a mid-river mooring with no shore power. When I cruise, I don't stay in marinas very often. So we are largely autonomous with power. I have a low-speed, heavy-duty Kohler 6.5kW generator driving a Victron Multiplus 70 amp (by 24v) charger; plus the main engine has a jumbo Leece-Neville school bus alternator putting out 110 amps at 24 volts. All this charges 420 amp/hours (x 24 volts) of Trojan batts.

I leave the boat for a month at a time on her mooring, as I live in a different country from my boat. As a result, the batts live their lives in a partially charged state, which is not good for them (for lead acid, anyway).

So if I have solar putting out usable power (unlike the pathetic Rutland wind turbine), I will come back to my boat to find fully charged and happy batts, unlike today's situation. Besides that, I will cover some of my consumption on the mooring and on the hook, and while sailing.

Sounds like a good deal. However, I am having some trouble thinking through the sizing. I need 72 cell panels for a 24v system. I have been looking at the Panasonic monocrystalline ones -- 240 watts each. I could theoretically put two of them on my davits, as two would roughly equal the beam of my dinghy, but this would be quite a bit uglier (I mean still uglier) than a single panel, I think. On the plus side, they would be wired in parallel, so this will give useful diversity in terms of shading.

But according to midsummerenergy.co.uk, I can only expect a little less than one kw/hour a day from one of these 240 watt panels on a typical sunny summer day in the UK, which is only about 10% of my battery bank capacity, and only what my diesel genset can put into the batts in 40 minutes or so.

So doubling this to 480 watts and 2kW/hours per day doesn't seem like it will really change my generator runs all that much -- we use quite a bit of power on my boat.

So maybe on the contrary I should find a smaller panel and not expect that much contribution to consumption, just keeping my batts topped off when away?

What do you solar wizards think?
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Old 03-02-2014, 09:05   #2
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Re: Solar for a Boat with a Good Diesel Generator

I have been researching solar a lot myself lately as we prepare for an extended voyage. The key is to determine how much power you need to generate. You seemed to answer this question when you said the only intent of the solar was to keep your batteries charged up while you were away. Are you currently going through 10% of your battery bank capacity per day when nobody is on board? Solar panels have come a long way. We have a gentleman living on board locally that says he still gets a small charge at night when the streetlight is on at the end of his dock.
Personally I do not have the power requirements you do, but I am opting for 3 240W panels to run everything on my boat 24/7.
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Old 03-02-2014, 09:15   #3
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Re: Solar for a Boat with a Good Diesel Generator

i need a good diesel for a boat with solar......
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Old 03-02-2014, 09:17   #4
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I have been researching solar a lot myself lately as we prepare for an extended voyage. The key is to determine how much power you need to generate. You seemed to answer this question when you said the only intent of the solar was to keep your batteries charged up while you were away. Are you currently going through 10% of your battery bank capacity per day when nobody is on board? Solar panels have come a long way. We have a gentleman living on board locally that says he still gets a small charge at night when the streetlight is on at the end of his dock.
Personally I do not have the power requirements you do, but I am opting for 3 240W panels to run everything on my boat 24/7.
Thanks, that's a useful data point. Three (!) 240 watt panels! That's for what size boat? How many people on board?

I go through at least 3 or 4 kW/hours a day not counting larger AC loads (which are run directly from genset) when cruising with 5 or 6 people on board.
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Old 03-02-2014, 09:21   #5
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Re: Solar for a Boat with a Good Diesel Generator

Dockhead, hard to say without some solid consumption numbers, but guessing from your other posts about equipment and boat usage, I suspect you are right that one or two 240W panels will not go a long way toward your power budget where you cruise. So, sounds like something at a "battery maintainer" level might be the way to look at things. If you have room to mount one of the 240W panels easily that still might be the way to go, it will contribute a little and be more than sufficient in the maintainer role even during the winter months. If you go significantly smaller you may find that the small panel won't even work well as a maintainer in the winter.

The other option in the maintainer role might be to get a couple of flexible panels that you can roll out somewhere when the boat is on the mooring, and then put away when the boat is in use. That gets rid of some of your aesthetic issues (although creating new storage issues) and would probably suffice for maintenance.
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Old 03-02-2014, 09:28   #6
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Re: Solar for a Boat with a Good Diesel Generator

Dockhead, it sounds like you have two different operating modes for the boat:
1-Mooring, standby
2-Cruising, active

And there's no reason why one "charging" mode should work for two different usage modes.

Surely you don't use quite as much power while moored? A/C, reefer, all systems going full blast? Or...?

I'd say that if "unattended" solar can take care of your batteries while you have abandoned the boat on the mooring, that's justification on its own for installing solar to do that job. And whatever contribution that makes to the cruising mode, is just icing on the cruising cake. So you do the best you can, and if you can put in enough solar to keep the boat happy on the mooring, isn't it better to have that job done, than to get nothing done?
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Old 03-02-2014, 09:45   #7
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Re: Solar for a Boat with a Good Diesel Generator

I think your thinking is sound.

A single 240w panel will recharge your batteries back up to 100% while you are away and easily keep up with the self discharge.
This will prolong the life of your battery bank. I think you will find it a worthwhile addition.

To make a significant difference to your generator run time would require a much bigger solar array as well as a total redesign of your boats electrical equipment.(to reduce demand)

If you were based in a sunnier climate installing two solar panels instead of one might be justifiable in economic terms in reducing generator running costs, but even then I suspect the weight on the davits and aesthetic problems would not justify the slightly reduced long term running costs.

240w (or even less) will achieve your goals.
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Old 03-02-2014, 10:56   #8
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Re: Solar for a Boat with a Good Diesel Generator

Dockhead:


3-4 KW per day on the hook is a lot and you are not likely to get a useful contribution to that kind of load with solar. So focus on maintaining the batteries at the mooring.


In the US at least 200+ watt, 34 V panels are cheap per watt, but cost a fortune to ship one. That is because they can't be shipped by UPS.


So, if I were here in the US I would be thinking about two 17V panels wired in series. The shipping cost is reasonable. The wattage depends on what loads need to be compensated for while you are on your mooring. Usually that isn't much- maybe a 1/2 an amp or so (at 12 V) for smoke detectors, incandescent (yes some are still incandescent) panel lights, bilge pump use (not much one hopes), etc.


And I would try to find a cheap 24V, pulse width modulation- ie non MPPT, controller. Just buy a few more watts to compensate for the limited benefits of MPPT.


I do understand the aesthetics of davit mounting. I had a 135 watt, 17 V panel mounted on my davits and it looked relatively good. But you have the problem of 24 V which either means two 17 V panels or one 34 V panel which is expensive (at least in the US) and you may not be able to find an inexpensive 34 V input, 24 V output PWM controller.


David
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Old 03-02-2014, 11:23   #9
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Re: Solar for a Boat with a Good Diesel Generator

Dockhead, here's some good info including mounting and sizing.

Solar Systems: Selection, Installation & Controllers by Maine Sail SUPERB

Installing A Small Marine Solar System Photo Gallery by Compass Marine at pbase.com
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Old 04-02-2014, 08:27   #10
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Re: Solar for a Boat with a Good Diesel Generator

Get yourself a Honda 2000, use it whenever you need electrical power, keep your batteries fully charged, and disconnect your batteries when you leave the boat. If your batteries are low when you return, charge them. If they don't take a charge, get new batteries.
England is a cold dark place where the sun doesn't shine, that's how we became white. Solar won't work there.
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Old 04-02-2014, 10:33   #11
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Get yourself a Honda 2000, use it whenever you need electrical power, keep your batteries fully charged, and disconnect your batteries when you leave the boat. If your batteries are low when you return, charge them. If they don't take a charge, get new batteries.
England is a cold dark place where the sun doesn't shine, that's how we became white. Solar won't work there.
Actually, solar gives real yields in summer in the UK more than in Florida. Longer days plus lower temperatures (solar loses efficiency rapidly with higher temperatures).
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Old 04-02-2014, 16:28   #12
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Re: Solar for a Boat with a Good Diesel Generator

That would be maybe 10 weeks of the year.
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Old 05-02-2014, 06:18   #13
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Re: Solar for a Boat with a Good Diesel Generator

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Thanks, that's a useful data point. Three (!) 240 watt panels! That's for what size boat? How many people on board?

I go through at least 3 or 4 kW/hours a day not counting larger AC loads (which are run directly from genset) when cruising with 5 or 6 people on board.
3 or 4kw/hours a day means only one thing.... rip out your fridge and freezer and replace them with a built in energy efficient installation.... I seem to remember that Jedi posted a very good writeup on this some time ago. Just so we don't have to reinvent the wheel.

I don't use that much and I have no gas, an induction double hob, a combination microwave grill and fan oven. Water boiled in an electric kettle.

Forget sizing your solar for use while onboard until you have got your consumption down.

For maintaining the batteries using solar while off the boat you need only a single panel and a good reliable regulator.

The solar charging parameters for this senario are very different from the solar charging parameters for an array to suppliment the diesel generator and also the main engine for the short runs in and out of harbour.
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Old 05-02-2014, 07:22   #14
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Re: Solar for a Boat with a Good Diesel Generator

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Forget sizing your solar for use while onboard until you have got your consumption down.

For maintaining the batteries using solar while off the boat you need only a single panel and a good reliable regulator.
I think a common problem with these type of threads is that there are two distinct types of boat electrical management.

The first uses a generator to produce most of their power. Electrical efficiency is not a great concern, and daily consumption is high.

The second uses solar/wind to generate most of the power. Electrical efficiency needs to be considered with each piece of equipment. The advantage is freedom from the reliability/cost/noise/heat issues associated with a generator.

It is difficult to convert a boat from one mode of operation to the other. In many ways it even more difficult to covert the thinking of the owner.

The OP (Dockhead) does not want a solar, self sufficient powered boat, he only wants to cover the requirements while the boat is unused and to raise the charge level of the batteries to 100% (which is not practical under generator). This requires very different planning. There is little need to implement energy reduction. The goals are achievable with a small solar panel.
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Old 05-02-2014, 07:34   #15
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Re: Solar for a Boat with a Good Diesel Generator

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Get yourself a Honda 2000, use it whenever you need electrical power, keep your batteries fully charged,
I get a reversed polarity light when I connect my portable generator. How do I correct that?
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