How to choose a solar panel ?

[sailaboutvic]

We do not use anywhere nearly as much as you and certainly not over night when the fridge door is not opened as often. We also do not have a separate freezer. Our fridge draws 4A; with a 30% cycle rate in our northern clime, that works out to about 16A over a 12 hour period.
300W of solar should, in theory, deliver about 1200W on average per day in our cruising latitude.
Having, pre solar, struggled to keep our banks charged we are suitably neurotic about the use of power and anything of importance has been converted to LED and we often use candle light in the evenings.

Our longest and most arduous drain on our batteries was when we sailed non-stop from Ijmuiden to Dieppe in 35hrs. This was done under sail only, running an electric pilot continuously, nav equipment and tablet (for Navionics), running lights, Webasto (at night), fridge (as usual, 24/7) water system etc The first day was overcast, the second sunny, sea conditions for the pilot, lively - there never was even the slightest hint of an electrical power shortage.

Once again I not saying what you post isn't correct .

Thanks that clearer .
So basically your 300w is enough to keep up with you using 16ah and a little more give say for light and get your batteries back up to float by 10am
Here in the Med my panels are give me around 5A AT 8 am just looked now as I am writing this its a very sunny morning . So by 10am in my case I would had put 10A back in without whats taken between 8 and 10 am out plus a bit more as the morning goes on the panels would produce a bit more .
So my 400w panels wouldn't put back in the 16a plus the extra power needed to get my batteries to fully charge , although it may had replace the 16a that's been taken out .

I think when it comes to power management/solar panel it would be more help full it people said what batteries AH and usage they use over the day or at less over night .
I been reading on ybw how some people been getting some wild amount of amps out of the panels and been scratching what between my legs how they do and because of that I later been messing around with my panels getting them to the right angles to the sun for days and hours and can't get anything like that .
But the more and more cruiser who I speak to people as myself are all say the same ,and some have got some very expenses panels, you be lucky to get 2/3 out of a panel , which is what I found .
If I stay on anchor and not move so I am not using any other equipment,
I have to run my Gen for an hour each morning at this time of year In the Med on sunny days which probably amount to UK summer days to put back into my batteries whats been used since last fully charge ( when the panel stop charging last) plus what I been using during the time my panels been given me power on that day. And as I said its not till late afternoon my batteries go on float and there was a period for many days this didn't happen although I did replace the amps that been used ,
Which is not the same as the batteries being fully charged.

 

[sailaboutvic]

So here three reading taken this morning in bright sun light , two panels tilt at the sun two flat , no shading panels and in parallel.
08.30 09.1510.15 LT .
As you can see at 0915 it was only still 7A going into the batteries and not till after 10am did I see any real increase.
Here figures are the best I seen within them time , there was period when they drop below the top figures I shown.
I cant imagine back in the UK I would get anymore , so in reality in two hour or say three hours even here in the Med if say my panels started charging at 7am I not going to get much more then 18 ah in my batteries considering the first hour it may only average 3a the second 5a and the third 10a and thats without taken in consideration whats being taken out in the three hour period

 

[chubby]

The jury seems in favour of rigid panels which is fine for a gantry where it is out of harms way but if it is to go on a coach roof where inevitably it will get fenders and warps dropped on it if not intentionally trodden on, are the semiflexible ones more robust? some are sold as having self repairing surfaces for minor knocks and as scratch resistant. Do the rigid ones suffer from the glass shattering?

The jury also seems in favour of MMTP controllers but the ones sold by recognized marine electrical suppliers like mastervolt and victron are a lot more than generic e bay offering: do you get more functionality or reliability in the marine environment?

In general is it best to go via chandlers as providing marine equipment, specialist suppliers like Barden or cheapest off the internet?

How about mounting; I have read that an air-gap is better than being directly fixed to the deck?

I am looking at something in the 50 to 100 watt range to go one the aft cabin coach roof of a centre cockpit ketch as a top up to batteries rather than as a main supply for live aboards.

 

[Laminar Flow]

The jury seems in favour of rigid panels which is fine for a gantry where it is out of harms way but if it is to go on a coach roof where inevitably it will get fenders and warps dropped on it if not intentionally trodden on, are the semiflexible ones more robust? some are sold as having self repairing surfaces for minor knocks and as scratch resistant. Do the rigid ones suffer from the glass shattering?

The jury also seems in favour of MMTP controllers but the ones sold by recognized marine electrical suppliers like mastervolt and victron are a lot more than generic e bay offering: do you get more functionality or reliability in the marine environment?

In general is it best to go via chandlers as providing marine equipment, specialist suppliers like Barden or cheapest off the internet?

How about mounting; I have read that an air-gap is better than being directly fixed to the deck?

I am looking at something in the 50 to 100 watt range to go one the aft cabin coach roof of a centre cockpit ketch as a top up to batteries rather than as a main supply for live aboards.

I went through a lot of the same thoughts.

Rigid panels have to meet certain levels of impact resistance in the EU, such as tempered glass for hail proofing. Smaller panels use the same frames as larger ones and would, logically, be stiffer. Mine are mounted on the wheelhouse roof and I was worried about accidentally stepping on them when sailhandling; I have done so now, many a times, it appears less of a problem than I had thought. At 35 Euro a pop, I would not have to slit my wrist if one of them did break.

Our MPPT charger is a non - marine EPEVER 40A. It lives in the wheelhouse where it has, faultlessly, done it's duty for 3 years and where it is easily viewed so that I may obsess over it's display. Proximity to the panels also keeps the leads short and avoids unnecessary voltage drop.



Having back venting is important as panel efficiency drops dramatically when they heat up in the full sun. ( I always felt this was somehow strangely counter productive). I mounted mine on aluminum angles - easy. I really have now idea how the flexible type can operate efficiently, in this regard, when glued to the deck.

 

[Pete7]

The jury seems in favour of rigid panels which is fine for a gantry where it is out of harms way but if it is to go on a coach roof where inevitably it will get fenders and warps dropped on it if not intentionally trodden on, are the semiflexible ones more robust? some are sold as having self repairing surfaces for minor knocks and as scratch resistant. Do the rigid ones suffer from the glass shattering?

The jury also seems in favour of MMTP controllers but the ones sold by recognized marine electrical suppliers like mastervolt and victron are a lot more than generic e bay offering: do you get more functionality or reliability in the marine environment?

In general is it best to go via chandlers as providing marine equipment, specialist suppliers like Barden or cheapest off the internet?

How about mounting; I have read that an air-gap is better than being directly fixed to the deck?

I am looking at something in the 50 to 100 watt range to go one the aft cabin coach roof of a centre cockpit ketch as a top up to batteries rather than as a main supply for live aboards.

Fenders and warps shouldn't be a problem, but a rigid panel isn't going to take walking on. Did have a suitcase folding rigid panel that slipped and smashed.

If you buy a cheap MPPT off e bay, how will you know it is actually an MPPT and not a cheap on / off switch type of regulator or PWM disguised as an MPPT. The extra functionality of a well known make like Victron was enough for me to pay the extra. My Victrons are networked to the battery temp and voltage widget and then to my smart phone. So I can see at a glance what is happening and adjust all the settings from the phone.

Barden are just up the road from me and I use them for items at work. However, for the boat I prefer to shop around. Unless you can afford the Solara semi flexible panels that can take foot traffic. Ours came second hand at lasted perhaps 10 years with the dog sitting on it. Couldn't afford to replace it with like for like when it eventually failed. We used velco to attach it to the deck and provide an air gap. Lifted once a year to clean underneath. Cheaper flexible panels fitted in place of the Solara have failed in short order, so given up on them.

 

[PaulRainbow]

Proximity to the panels also keeps the leads short and avoids unnecessary voltage drop.

This is incorrect. Proximity to the batteries is more important than proximity to the panels.

 

[Kelpie]

The jury seems in favour of rigid panels which is fine for a gantry where it is out of harms way but if it is to go on a coach roof where inevitably it will get fenders and warps dropped on it if not intentionally trodden on, are the semiflexible ones more robust? some are sold as having self repairing surfaces for minor knocks and as scratch resistant. Do the rigid ones suffer from the glass shattering?

Rigid are pretty tough, but if you jumped in the middle of one you'd probably break it. I wouldn't want to make a habit of walking on any type of panel. Ideally put them somewhere that they will not be walked on. Chances are they will get less shade that way, too.

The jury also seems in favour of MMTP controllers but the ones sold by recognized marine electrical suppliers like mastervolt and victron are a lot more than generic e bay offering: do you get more functionality or reliability in the marine environment?

You'll find the letters 'MPPT' written on very cheap eBay charge controllers, but it is meaningless. They will be PWM or even simple voltage cutoff types. Nothing wrong with either of these, but you can't reach full efficiency with them.
A genuine MPPT controller from ePever or Victron will cost a lot more but for a large array would be worth it.

In general is it best to go via chandlers as providing marine equipment, specialist suppliers like Barden or cheapest off the internet?

I've had success with the cheapest eBay rigid panels and PWM controller. You'll see the exact same stuff sold by the like of Photonic Universe for a big markup. As you get more expensive and specialist, it becomes worth buying from a proper supplier.

How about mounting; I have read that an air-gap is better than being directly fixed to the deck?

Yes, you want to keep the panels cool if you possibly can. But don't sweat about squeezing every last watt out of the the system unless you actually need it.

I am looking at something in the 50 to 100 watt range to go one the aft cabin coach roof of a centre cockpit ketch as a top up to batteries rather than as a main supply for live aboards.

Can't you fit it on the hatch garage? 50w is pretty small, I've got that size of panel on the hatch of a 33ft boat.
I recently added a 100w panel on the guardwires. I really like it, it hangs vertical like a dodger most of the time, but I can swing it up to catch the sun and it's actually quite satisfying to keep adjusting the angle throughout the day if I need the power.

 

[David Tom]

We can choose solar panels in 3 steps:

1. Determine solar panel efficiency and compare to the industry average of 16-18%
2. Check solar panel manufacturer warranties against an industry average of 10-25 years
3. Compare the cost to relative efficiency – efficiency is important, but the most efficient panels aren’t always the best value

 

[Graham376]

The jury also seems in favour of MMTP controllers but the ones sold by recognized marine electrical suppliers like mastervolt and victron are a lot more than generic e bay offering: do you get more functionality or reliability in the marine environment?

In general is it best to go via chandlers as providing marine equipment, specialist suppliers like Barden or cheapest off the internet?

I am looking at something in the 50 to 100 watt range to go one the aft cabin coach roof of a centre cockpit ketch as a top up to batteries rather than as a main supply for live aboards.

I've had a generic Chinese (supposed MPPT) and compared to later fitted Victron, it was pretty poor. Go for one which can be programmed to suit battery type, many cheap ones just have fixed charging regime.

Chandlers providing "marine" equipment? I often see brass seacocks and many items which are far cheaper in caravan/motorhome shops, hardware stores or on-line.

When UK based and mainly weekend sailing, a 25w semi flexible panel on the aft coach roof was large enough to charge 220AH during the week but it didn't last long. Fit rigid and as large as there's space for.

 

[affinite]

Just a follow-up to my original post re PV panel choice.
Covid Regs permitting, Im flying to Greece in a couple of weeks and plan to fit my new solar panel.

I was going to buy a 350W SunPower Max2 but having checked again I'm not so sure ...

The cost of a 350W Sunpower Max2 is €325 however the same supplier can do a 380W Amerisolar panel for €195

Both claim around 20% efficiency and the physical footprint is similar.
Both are suitable size for my gantry but the Sunpower panel is 3kg heavier and 30W less max power

I know that SunPower are regarded as the premium brand and Amerisolar is actually manufactured in PRC but I'm now seriously considering the cheaper panel
I cant see a good reason to pay 65% more more the "premium" brand but Id welcome comments and opinions

(BTW - I've thought about this a lot and have decided to fit 1 large, rigid panel on a shade-free stern gantry so I dont really want to reopen the debate about multiple panels again )