How much power do you actually get from a 100W panel!

skyflyer

skyflyer

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Not 100W, I guess, unless its set up on the surface of the planet Mercury!

So realistically, in SW of UK, typical summer day (i.e. sunny but cloudy intervals) with the panel horizontal on the deck, what sort of average output is it going to provide?

Supplementary question. If the panel has a couple of lines and halyards running across each corner, what sort of loss does that cause? I can go for a smaller panel to fill the unshaded space or a larger one but lose a couple of corners. Dont want to waste money if the larger one ends up producing no more power!

Thanks
 
I've a basic cheap 100W panel and I do seem to get pretty close to 100W in good conditions. Bear in mind that power is V times I so if you use a basic controller as I do you lose out between the panel voltage and the charging voltage it outputs.

I've had over 5A in summer, so I don't complain about that. If I wanted more I'd get another panel or a better controller. Other times when I've checked the output I've had 4A in March sunshine. 1A in summer torrential rain (it was so dark and overcast I expected less) and I still seem to be able to get around 1A in winter in the middle of the day even when fairly overcast.

Locations for this: Ireland, NI, Irish Sea, SW Scotland.
 
Ah thats good news thanks. We are pretty frugal with 'normal' electric and do enough motoring to keep the batteries topped up for that, but i wanted to add a panel to offset the drain from the fridge. The good news of course is that the fridge is most often needed when it is sunny! I dont expect a panel (given the restraints I have on space) to be able to run it on its own but it will keep the battery drain down
 
What does your fridge draw? Mine takes 3A about 50% of the time, so well within the capabilities of a 100W panel in summer.
 
I've got a 100w panel, and during the summer I can pretty much sit on the hook indefinitely with the fridge running 24/7 and just led lights at night (and maybe the telly on a bit).
 
This website is very useful when trying to estimate Ah/day which is much more useful than knowing the max. likely output in mid. summer.

http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php

The site uses kWh but the easiest workaround is to just enter 100 for your panel. It's 100kW but just use the output but read as W not kW. Easy enough to convert to approx. Ah/day.

N.B. This is the max. you are likely to get with panels flat on deck and no shading.

Average Ah/day in any given month for a boat on S. Coast of UK with 100W panel flat on deck
Jan 4.2
Feb 8.4
Mar 17.4
Apr 26.8
May 30.9
Jun 34.1
Jul 32.4
Aug 26.1
Sep 19.6
Oct 10.9
Nov 5.7
Dec 3.3

Cheaper regulator, poor location etc. all reduce the actual output but it's good to know the max. you can expect. I've found my own real life figures are usually quite close to those predicted.

I hope that's of some interest.
 
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Gladys said:
I upgraded to 2x100W panels into an MPPT controller at end if November and in the 6 ish weeks since, the meter tells me the panels have output 1.84kW hours.
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A rough calculation from that gives about 44Wh per day, or roughly 5.5W over a nominal 8 hour day.

Are you sure about the decimal point or units you've quoted?
 
I have 2 x 50W panels. According to the controller, the maximum they have ever produced is 5.1A. Generally I reckon on 2A on a sunny day and 4A on a very, very sunny day.
 
Gladys said:
I upgraded to 2x100W panels into an MPPT controller at end if November and in the 6 ish weeks since, the meter tells me the panels have output 1.84kW hours.
Click to expand...

Interesting, about 50% of predicted output from a completely unshaded installation flat on deck (assuming S. Coast).

At least it's not 200% of the estimate. Are your panels shaded part of the time?

lpdsn said:
A rough calculation from that gives about 44Wh per day, or roughly 5.5W over a nominal 8 hour day.

Are you sure about the decimal point or units you've quoted?
Click to expand...

Certainly not out by a factor of ten and well within normal range I'd expect for Dec./Jan.
 
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you lot are very optimistic!

having a corner or two slightly blocked or a shadow across a couple of cells may render the panel useless. Many examples, you can search in youtube.
Discussing the issue with a guy here that does this for a living, I've heard all sorts of obscure stories about why panels didn't produce what they should.

for the record I installed 2X300W panels and a victron mppt 100/30 controller on a 24V system. Best I've seen during August was 16point something Amps@24V which is some serious power. However, it's on a hard top with nothing masking it now. When I first fitted it, I had an oddly shaped radar support and I was loosing some serious power in the afternoon (casting shadow on a few cells. Now modified it and only have the VHF antenna to worry about. Mast shadows are a no-no, booms the same!

cheers

V.

PS. needless to say that my data are for Greek summer, no cloud for weeks, not overcast summer days...
 
Real World East Coast figure. 2x100w on an arch at the rear and 2x30w panels on the coachroof. The coachroof panels contribute little, due to shading, the 100w panels don't suffer from shading. During the Summer around 1kwh per day. This time of the year, not much, between 60wh and 120wh, but that figure is skewed because the mains charger is also on.
 
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vas said:
having a corner or two slightly blocked or a shadow across a couple of cells may render the panel useless.
Click to expand...

I've done tests. To get a significant reduction you need a hard shadow (umbra, not penumbra) across the whole of one of the wafers in a panel. If like many bigger panels you have two parallel strings of wafers them you need a hard shadow over one wafer in each. Soft shadows cut the output a bit but don't block it. In reality it's quite difficult to get the hard shadow required. Just make visitors don't leave a cushion on the panels.
 
PaulRainbow said:
Real World East Coast figure. . . . 2x30w panels on the coachroof. The coachroof panels contribute little, due to shading,
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JumbleDuck said:
I've done tests. To get a significant reduction you need a hard shadow (umbra, not penumbra) across the whole of one of the wafers in a panel. If like many bigger panels you have two parallel strings of wafers them you need a hard shadow over one wafer in each. Soft shadows cut the output a bit but don't block it. In reality it's quite difficult to get the hard shadow required. Just make visitors don't leave a cushion on the panels.
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I'm struggling to reconcile these two suggestions.
- JumbleDuck, are you suggesting that shadows such as from mast and boom are unlikely to render a coachroof panel a bit pointless?
- PaulR, are you suggesting your coachroof panels are a bit of a waste time, due to shading, or just significantly outshone by the other panels with are not only unshaded, but also 3.3 times larger?
 
skyflyer said:
Mines a bit ancient so 4.5A but once cold usually runs only about 40% of the time I think
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Just remember your fridge will still draw the same amps at night. So unless your battery bank is big enough to carry your fridge through the night, with anything else that could be switched, 100W is marginal to keep fridge running 24/7.

That's my experience on west coast Scotland.
Donald
 
LittleSister said:
I'm struggling to reconcile these two suggestions.
- JumbleDuck, are you suggesting that shadows such as from mast and boom are unlikely to render a coachroof panel a bit pointless?
- PaulR, are you suggesting your coachroof panels are a bit of a waste time, due to shading, or just significantly outshone by the other panels with are not only unshaded, but also 3.3 times larger?
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I think JD was talking about shading from the likes of a line or two, which i'd agree isn't going to cause significant losses.

My coachroof panels suffer shading to some degree for much of the day, either from the sprayhood, the boom or the mast. I wouldn't say they are a waste of time, but the yield from them is much less than it would be without the shading.
 
skyflyer said:
Not 100W, I guess, unless its set up on the surface of the planet Mercury!

So realistically, in SW of UK, typical summer day (i.e. sunny but cloudy intervals) with the panel horizontal on the deck, what sort of average output is it going to provide?

Supplementary question. If the panel has a couple of lines and halyards running across each corner, what sort of loss does that cause? I can go for a smaller panel to fill the unshaded space or a larger one but lose a couple of corners. Dont want to waste money if the larger one ends up producing no more power!

Thanks
Click to expand...

Lets simplify things a bit: basically Watts= Amps X Volts -so your100w panel is nominally 8.3 amps at peak. This is unlikely to be achieved. If you fit a good MPPT controller you may get 7 to 8 amps in near ideal conditions.

I am in Singapore right now - basically on the equator (well 60 miles North). The boat is living on a mooring with no shore-power at all. When the sun is directly overhead and there is no cloud or haze I get just over 13 amps form 2x 100W panels with an Mppt controller. I fitted this controller 2 months ago to replace a damaged older PWM one.The panels are the same and I have noticed my peak output is up by over 40% with the MPPT while my daily average is up by over 50%. The solar is now keeping my batteries topped up while running the fridge all day and night, using the 12v fans to keep cool, the LED cabin lights and anchor light.

I've turned the windgenny off (it was noisy anyway). On passage we still need extra power from the Windgenny or Alternator every few days to keep up with the consumption of the Autopilot, Radar and Navigation instruments etc.
 
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