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Old 23-05-2011, 23:07   #1
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Solar Power Virgin - Be Gentle Please

I'm taking up my mid-river mooring in the Hamble - hooray! But now I have to get used to life without shore power. I'm worried for my battery bank since the boat may be left alone for up to a month at a time.

I'm thinking about istalling a small solar panel just to keep the batteries up - what do you guys think? I always shut down refrigeration and basically everything except bilge pumps when I leave the boat, but the batteries self-discharge. Will a 50 watt panel be enough to trickle charge a 440ah by 24 volt battery bank?
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Old 23-05-2011, 23:47   #2
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Re: Solar Power Virgin - Be Gentle Please

What's the output voltage of the 50W panel? Does it get up high enough to charge the battery?

Nominally, 50W would give you 2A at 24V, which is about C/220 for your bank. This is on the high end of trickle charging, but you are unlikely to get 2A in the UK! If the average was about 1A, this would put you right into the trickle charge band.

I'd consider adding a controller of some sort to set the current and voltage to be correct for your bank.
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Old 24-05-2011, 00:10   #3
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Re: Solar Power Virgin - Be Gentle Please

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What's the output voltage of the 50W panel? Does it get up high enough to charge the battery?

Nominally, 50W would give you 2A at 24V, which is about C/220 for your bank. This is on the high end of trickle charging, but you are unlikely to get 2A in the UK! If the average was about 1A, this would put you right into the trickle charge band.

I'd consider adding a controller of some sort to set the current and voltage to be correct for your bank.
So with a controller you think that's enough juice for trickle charging? The bank is 440aH by 24v. I guess it wouldn't hurt for me to try to calculate the self-discharge rate and see if 1 amp for some hours a day is enough.
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Old 24-05-2011, 00:15   #4
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Re: Solar Power Virgin - Be Gentle Please

5% per month out of a 440aH bank would be 22aH per month.

So one amp for an hour a day at perfect efficiency would be enough to make up self-discharge losses.

Say three hours a day to make up for all the inefficiencies in the system.

Sounds like a single 50 watt panel would be enough even in the UK.

Anyone have concrete experience?

Naturally, I would use a controller. Victron makes a small one which costs only 35 squids.
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Old 24-05-2011, 00:17   #5
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Re: Solar Power Virgin - Be Gentle Please

I'd have thought so - IIRC the ideal trickle charge is about C/500, but I agree, calculating the self discharge rate would be a fine way to go about it.
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Old 24-05-2011, 02:50   #6
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Re: Solar Power Virgin - Be Gentle Please

50w should be fine for your application, but if you are permanently mounting it go for the biggest one that will fit in space. Solar panels are not expensive these days, but there is a lot of hassle mounting and wiring them. A bit of extra power is always useful.
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Old 24-05-2011, 03:13   #7
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Re: Solar Power Virgin - Be Gentle Please

DH, we have one of these mounted infront of the sprayhood and under the boom.

Solara SM160M Solar Panel

Although rated at 45w, in practise with it mounted flat (at 51'n) it generates 1AH in sunshine and about half that in cloud or when the boom casts a shadow. Since we face nearly South, the shadow isn't a problem and the panel generates enough in the afternoon to keep our batteries topped up for 9 months of the year. In the depths of winter its struggling due to the conditions and lattitude, the output is low but it still kept the batteries up to 12.7v throughout the winter. Overall however, its been fantastic and we always arrive with two (110ah) full batteries.

The panel has been tested by Angus our 40kg labradoodle for strength as he regularly sits on it as it's always warm.

Barden are just down the road from us and offer a discount to the Moody Owners Association, somewhere between 5 and 10 % depending on item.

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Old 24-05-2011, 04:00   #8
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Re: Solar Power Virgin - Be Gentle Please

It's expensive and very little power! Maybe I should be thinking about wind . . .

An Air Breeze will produce 90Ah per day, according to Yachting Monthly. Or 45Ah per day at 24 volts. That's 10% of my total battery capacity or 20% of my usable capacity. I could almost live on that. Probably cut my generator runs in half, besides fulfilling the original purpose of keeping batts topped off when I'm not on board. Hmmmmmmm.

Cost not much more than two of those tiny solar panels, and easier to mount.
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Old 24-05-2011, 04:18   #9
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Re: Solar Power Virgin - Be Gentle Please

Yes agreed, we are paying for convenience of having something mounted on the deck so no frames or moving parts in the case of wind. Its task is to keep the batteries topped up, although when on board it generates about 10AH a day towards our usage. This could be improved upon by changing location and angle but the area in front of the spray hood doesn't get used for anything so it's convenient.

If you are thinking of wind and therefore a pole, the Barden rigid panels with a frame would be a better comparison. Personally Viv and I don't like noise even from quiet wind generators and we are in a sheltered location so solar for us.

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Old 24-05-2011, 04:25   #10
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Re: Solar Power Virgin - Be Gentle Please

Does the Moody have 12v start batteries? If so I have an idea....

I have mounted a 135w panel on the double backstay of my none Moody and a panel on the pushpit port and stb. I run them through a mppt controller and that takes care of the 24v side. The 12v side is also charged at the same time by a 15a charger that begins 12v charging when the 24v batteries have a voltage around 26 and stops at around 25v.

This way the solar takes care of both the 24v and 12v batteries.

I have a big 24v alt on my engine and no 12v alternator as the 15a charger takes care of everything on the 12v start batteries.
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Old 24-05-2011, 05:12   #11
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Re: Solar Power Virgin - Be Gentle Please

Dockhead,

Go on e-Bay and buy a VW solar panel for around $30. I use these every winter and it keeps both my house and starter batteries topped off.

Haul Out, On The Hard, Antifoul & Winter Storage
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Old 24-05-2011, 05:50   #12
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Re: Solar Power Virgin - Be Gentle Please

Unless the batteries are really old or have been cycled far too hard and too low, it seems to me that 130 watt or even 50 watt panel is too large for a simple trickle charge. Are you trying to recharge after use... or are you just trying to maintain full charge when not using the boat?

Self discharge is a bit exponential. The battery will discharge faster the lower the voltage gets... so often even a very small amount of current (hence trickle charge) can maintain a nice high voltage and curb or drastically reduce the self discharge all together... and might save you a lot of money. A 5 watt is typical for this application and being smaller it is easier to mount and find a spot that doesn't get affected by shade as easily.

Might be a cheaper experiment anyway before you break out the big bucks.

Good luck.
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Old 24-05-2011, 06:20   #13
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Re: Solar Power Virgin - Be Gentle Please

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A 5 watt is typical for this application

Good luck.
Except the OP is in the UK and has the equivalent (@12v) of 880 AHrs in batteries
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Old 24-05-2011, 06:29   #14
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Re: Solar Power Virgin - Be Gentle Please

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Yes agreed, we are paying for convenience of having something mounted on the deck so no frames or moving parts in the case of wind. Its task is to keep the batteries topped up, although when on board it generates about 10AH a day towards our usage. This could be improved upon by changing location and angle but the area in front of the spray hood doesn't get used for anything so it's convenient.

If you are thinking of wind and therefore a pole, the Barden rigid panels with a frame would be a better comparison. Personally Viv and I don't like noise even from quiet wind generators and we are in a sheltered location so solar for us.

Pete
Hmmm, decisions, decisions. I also hate noise but you can shut down the wind generator when you don't want to listen to it. You've got more options for when to run it because unlike solar it works day and night.

Do I understand you place your solar panel in front of your spray hood, and stow it when you're sailing?

That's an interesting idea -- avoids the whole problem of installing them permanently somehow.
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Old 24-05-2011, 06:57   #15
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Re: Solar Power Virgin - Be Gentle Please

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I also hate noise but you can shut down the wind generator when you don't want to listen to it. You've got more options for when to run it because unlike solar it works day and night.
Wind: you need a windy place. There are 2 sets of moving parts: the one that does the propellor bit and one that faces the prop into the wind.
Solar has no moving parts and is 'set and forget'. Forever.

My thought would be that you need a propper array so you can power the fridge while on the boat. Too much electricity is no problem.

In England in winter to trickle charge a 440 amp hour bank at 24 volts.... sound like 150 watts to me, not 50. And then when you go to a marina you will never need to hook up again
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