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Old 24-03-2011, 17:20   #1
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Solar Panel: Too Big ?

I am trying to wrap my head around solar charging systems. Of course the old 'slap marine on it and double the price' idea is holding strong, so I have been looking all over the place for panels. I have a 27ft pocket cruiser and my plan is to build a removable arch on top the stern push and mount a solar panel there. The most cost and space efficient route seems to be get the biggest solar panel I can fit on there and just do one, with possibly a couple softies put up at anchor.

What I can't seem to figure out is will this (Sharp NU-U235F1 - Sharp NU-U235F1 235 Watt Solar Module) 20v 235 watt solar panel work with a charge controller on our dual bank deep cycle system? Or is it too much and designed for residential use? I am really new to this so some clarification would be very helpful. It just seems if I can get a 120 watt panel for the same price as this fella and I don't mind the size difference, why wouldn't I? Thank you!
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Old 24-03-2011, 18:23   #2
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Re: Solar Panel, too big?

I am not an expert in this, but it looks like that panel is 37 volt. I don't think you can find a controller to match it to your 12 volt system.
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Old 24-03-2011, 18:38   #3
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Re: Solar Panel, too big?

Depends on what you plan to run off the batteries. Just basic stuff, 100 watts should do it but if you have a lot of stuff to run, more to much more watts.
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Old 24-03-2011, 19:40   #4
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Re: Solar Panel, too big?

That's about 16 amp max output for the panel..
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Old 25-03-2011, 01:18   #5
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Re: Solar Panel, too big?

Quote:
Originally Posted by Velocir View Post
I am trying to wrap my head around solar charging systems. Of course the old 'slap marine on it and double the price' idea is holding strong, so I have been looking all over the place for panels. I have a 27ft pocket cruiser and my plan is to build a removable arch on top the stern push and mount a solar panel there. The most cost and space efficient route seems to be get the biggest solar panel I can fit on there and just do one, with possibly a couple softies put up at anchor.

What I can't seem to figure out is will this (Sharp NU-U235F1 - Sharp NU-U235F1 235 Watt Solar Module) 20v 235 watt solar panel work with a charge controller on our dual bank deep cycle system? Or is it too much and designed for residential use? I am really new to this so some clarification would be very helpful. It just seems if I can get a 120 watt panel for the same price as this fella and I don't mind the size difference, why wouldn't I? Thank you!
Fit the biggest wattage you can is a good philosophy.
The Sharp panel will need an MPPT regulator to convert the voltage, but with a suitable regulator (not all MPPT regulators will be OK) it will be fine.
It will be difficult to fit such a large panel on your boat without shading on some part of the panel. 2 smaller panels of the same total wattage would give you more output.
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Old 25-03-2011, 02:52   #6
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Re: Solar Panel, too big?

Two thoughts, firstly that panel weighs 20 kgs, so that is going to be quite a substantial frame on the stern of a 27 foot yacht. The frame will also be very heavy if its stainless steel.

Secondly, the efficiency is only 14.4%, which isn't great and the latest panels are more like 19% which suggests its an old design, hence the cheap price.

Rather than just plonk a large panel on the stern, you need to know how many amps hours you use each day at anchor. Without this information, you will either have too big a panel and waste money or end up with something that is too small.

One of the modern battery charging monitors ought to be the first thing to fit. For example, Viv and I use about 30 AH a day at anchor. That's made up of low power lights, small fridge, laptop and phones etc in NW Europe during the summer. This is a tiny amount and down to the fact we have a dog so get up at dawn in the summer and fall asleep when the sun goes down.

We have a 45w panel that came second hand from e bay. Keeps the batteries topped up during the winter and gives us 10AH a day in the summer at anchor reducing the time we need to run the genny to charge up. Before we installed the battery monitor it was all guess work and I suspect we wasted time and fuel. Now with a battery monitor I know how much time I need to charge.

Like you we would like another panel and are considering a stern frame but it’s an expensive exercise. The other option is to have it loose, so prop it up against the mast, angled towards the sun when stationary and put it away when sailing.

As a rough estimate for a 12v boat in ideal conditions, a 1/3rd of the max watts = the amp hours each day. We are 51 north so a 45w panel in less than ideal conditions gives us 10AH.

However, you need to calculate your charging requirements first or risk wasting hard earned dollars.

Pete
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Old 25-03-2011, 05:56   #7
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Re: Solar Panel, too big?

Velocir,

You may want to check out the Sunpower 238 panel.
Its 61” x 31” and only 33 lbs

http://us.sunpowercorp.com/residential/products-services/products/panels.php

Solar Panels and Associated Systems

The controller handles the higher solar panel voltage and only outputs a 12 volt charging voltage.
Always use a MPPT controller.

Mark
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Old 25-03-2011, 06:43   #8
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Re: Solar Panel, too big?

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Originally Posted by noelex 77 View Post
Fit the biggest wattage you can is a good philosophy.
The Sharp panel will need an MPPT regulator to convert the voltage, but with a suitable regulator (not all MPPT regulators will be OK) it will be fine.
It will be difficult to fit such a large panel on your boat without shading on some part of the panel. 2 smaller panels of the same total wattage would give you more output.
Can anyone give me a quick rundown on the different types of regulators/charge controllers? MPPT As opposed to?

I originally wanted to go with two 80 watt panels, but the most cost effective route by far seems to be one large panel. The obese weight (which I had not noticed, thank you.) coupled with its comparatively low efficiency lead me to cool down on that particular panel. Any recommendations?

I do have a battery monitor, not yet installed, and I would love to get it all together and then figure out the amp hours I will be needing, but alas time constraints are forcing me to guess. So, if I have to guess I will go big and have an overabundance of power.
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Old 25-03-2011, 07:27   #9
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Re: Solar Panel, too big?

MAXIMUM POWER POINT TRACKING (MPPT)
MPPT technology can extract more power and increase charge current up to 30% or more compared to conventional controllers. The principal operating conditions which affect current boost performance are PV array temperature and battery voltage. At constant solar intensity, available PV voltage and power increase as PV temperature decreases but it takes an MPPT controller to access this extra power. When PV voltage is sufficiently high in Bulk for MPPT to operate, a constant power output is delivered to the battery. Since output power is constant a decrease in battery voltage produces a further increase in charge current. This means that the MPPT controller provides the greatest charge current increase when you need it most, in cold weather with a discharged battery. In cool comfortable temperatures most systems see about 10 – 20% increase. Charge current increase can go to zero in hot temperatures, whereas charge current increase can easily exceed 30% with a discharged battery and freezing temperatures.
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Old 25-03-2011, 07:50   #10
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Re: Solar Panel, too big?

There are guides to calculating your power usage around. They don't have to be detailed or complicated depending how you use the boat. Large boat, full time cruising, night passages, and a freezer are one extreme. At the other none of the above and 20 watts more than enough particularly since you will be doing some motoring. In between I know of boats where 60 watts is enough to run a refrigerator etc.
It also depends on how big the battery banks are.
It doesn't make much sense to fit a big panel without working out what you need.
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Old 25-03-2011, 07:58   #11
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Re: Solar Panel, too big?

Solar Panels Too Big? NEVER!
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Old 25-03-2011, 08:10   #12
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Re: Solar Panel, too big?

capngeo,

Those are all SunPower panels on the Turanor PlanetSolar.
Will go around the world on just Solar power. Just amazing
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Old 25-03-2011, 08:10   #13
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Re: Solar Panel, too big?

Quote:
Originally Posted by Velocir View Post
I do have a battery monitor, not yet installed, and I would love to get it all together and then figure out the amp hours I will be needing, but alas time constraints are forcing me to guess. So, if I have to guess I will go big and have an overabundance of power.
If I had to guess your usage for a 27 foot boat with a fridge, lights and entainment (laptop, radio or small TV) etc then your not going to be using much more than us at 30 AH a day, you just don't have the space for freezers and watermakers. So how about 40AH a day, although note; you may use more at sea if you are using a tiller pilot. Also you need to think about LEDs for lights and good insulation on any fridge.

40 AH will need a minimum 120w, so how about a 135w panel (or your original 2 x 80) which will be lighter and smaller than the big one you were looking at. If you have a 300 amp (ish) house bank then even if rains for a couple of days your batterries won't be going down to far.

Pete
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Old 25-03-2011, 08:17   #14
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Re: Solar Panel, too big?

You mentioned a dual bank system. On a small yacht, keep it simple (KISS) is probably for the best, space and weight will limit the size of any battery bank.

How about a removeable panel sitting horizontal on the boom whilst at anchor? and a second 135w on the stern whilst underway.

Pete
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Old 25-03-2011, 08:29   #15
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Re: Solar Panel, too big?

So do most MPPT controllers account for overcharge situations? What happens if the batteries are fully charged but the solar panel is still putting out amps?
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