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Old 20-03-2019, 17:04   #1
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How much am I getting ripped off for my solar panels?

Hi all,

Very quick question:

I bought 2 x 150W solar panels. (Flexible)

They are rated at 23-25% efficiency.

What Watt power should I expect from them on average?

I appreciate it depends on angle of sun, position etc but just looking for an indication.

Thanks,
Lawrence
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Old 20-03-2019, 17:05   #2
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How much am I getting ripped off for my solar panels?

Based on my experience Iíd say if you see 200W, you should be pleased.
That is a peak power, not sustained.
I donít think I have ever seen more than 750W from my 1000W of panels
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Old 20-03-2019, 17:34   #3
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Re: How much am I getting ripped off for my solar panels?

Ah ok, makes me feel a bit better. I peak about 150/160W and I am currently in the Caribbean so lots of sun. So is that pretty standard?
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Old 20-03-2019, 17:37   #4
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Re: How much am I getting ripped off for my solar panels?

Quote:
Originally Posted by lawrence_craig View Post

I bought 2 x 150W solar panels. (Flexible)
they are rated at 23-25% efficiency.

What Watt power should I expect from them on average?

Efficicncy is pretty good.

In addition to panel location in relationship to the sun. The type of controller will make radical differences PWM vs MPPT. What are your measured voltage and current when in full sun?

What is the ratings on the panel Vmp, Imp and Pmax?

Under full sun with correct sun angle I would expect close to 300 watts.
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Old 20-03-2019, 17:40   #5
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Re: How much am I getting ripped off for my solar panels?

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Efficicncy is pretty good.



In addition to panel location in relationship to the sun. The type of controller will make radical differences PWM vs MPPT. What are your measured voltage and current when in full sun?



What is the ratings on the panel Vmp, Imp and Pmax?



Under full sun with correct sun angle I would expect close to 300 watts.


I have an MPPT controller. Measured peak voltage is about 15V, 10A.

Thatís the thing, Iím getting nowhere close to 300W. I have never seen above 200W. But I have only had during winter in the Caribbean.
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Old 20-03-2019, 17:52   #6
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Re: How much am I getting ripped off for my solar panels?

Off tangent but can you advise what brand of flexible solar panels you have bought. 23 to 25% efficiency is the highest I have heard. Can you copy the data sheet please and post


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Old 20-03-2019, 17:54   #7
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Re: How much am I getting ripped off for my solar panels?

Quote:
Originally Posted by lawrence_craig View Post
I have an MPPT controller. Measured peak voltage is about 15V, 10A.

That’s the thing, I’m getting nowhere close to 300W. I have never seen above 200W. But I have only had during winter in the Caribbean.
Just to clarify, efficiency, in this discussion, is meaningless. If the panels are rated at 150 Watt each then that's their rating and the only impact of efficiency is in defining the physical dimensions of the panels themselves. So a 30% efficient 150 watt panel will have a smaller surface area than a 25% efficient panel. But both should "theoretically" produce 150 watts in the same "perfect" conditions.

As to total output in reality, like A64, I'd like to see over 200 watts on that combination. My system consists of two banks of 380 watts and I reguarly see 360 watts from each bank in the middle of the day for about 2/3rds of the year, as the boat swings around in the wind (the rear pair are shaded by the aft stay so things have to be perfect for them to put out full power, the forward pair are un-shaded if I pull the boom to the side)

To test the panel output you do need to do a few things.

1. You need to know that the battery bank can ACCEPT the full 300 watts. There's no point testing with the battery bank full, the regulators will simply reduce the output of the panels to maintain float. In the case of my boat, when it is totally shut down with no load, that means the front panel combo put out 0 watts and the rear panels produce about 7 watts. If I want to test my system all I have to do is run the coffee machine which sucks around 1400 - 1800 watts. The panels can then put out their full potential without restriction.

2. You need to angle the panels so that they are perpendicular to the sun in BOTH axes. That's not easy and will probably involve dismounting the panels.

3. The sun needs to be at least reasonably close to equinox in your location. In practice, here in South Australia, I found in testing that I could get full output from good panels as much as three months either side of the local equinox, which surprised me, but I wasn't complaining. I don't know how low the sun is in the Caribbean in winter so I can't comment there, but it probably is not helping.

4. And, of course, as you probably know, there has to be absolutely NO shading on the panels at all. Regardless of the marketing crap that came with the panels.
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Old 20-03-2019, 17:55   #8
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Re: How much am I getting ripped off for my solar panels?

"Average" is a difficult concept given that they will produce 0 watts at night


The more relevant question is how many Watt hours per day to plan on. A common rule of thumb for un-shaded horizontal panels is around 4-5 "equivalent sun hours".



So with 300W of panels, you could plan on 1200-1500 Watt hours per day (say 100 Amp hours @ 12V)
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Old 20-03-2019, 17:55   #9
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Re: How much am I getting ripped off for my solar panels?

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Off tangent but can you advise what brand of flexible solar panels you have bought. 23 to 25% efficiency is the highest I have heard.





Greg H


And even the slightest bit of shade or shadow, or dirt on the panel, will greatly reduce output.
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Old 20-03-2019, 18:02   #10
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Re: How much am I getting ripped off for my solar panels?

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Originally Posted by lawrence_craig View Post
I have an MPPT controller. Measured peak voltage is about 15V, 10A.

Thatís the thing, Iím getting nowhere close to 300W. I have never seen above 200W. But I have only had during winter in the Caribbean.
Just read this again... 15 volts peak seems pretty high to me, if that is on the battery side. Off the top of my head I can't think of a battery chemistry that likes that kind of charging voltage.

What sort of batteries do you have?
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Old 20-03-2019, 18:04   #11
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Re: How much am I getting ripped off for my solar panels?

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And even the slightest bit of shade or shadow, or dirt on the panel, will greatly reduce output.
Tell me about it. Tested the panel output using my coffee machine trick a month or two back, that's odd... the rear pair of panels are down to 280 Watts.

What gives?

Climb up and have a look...

Oh, THAT's where I left that shifting spanner. (Doesn't shift so well any more.)
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Old 20-03-2019, 18:32   #12
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Re: How much am I getting ripped off for my solar panels?

Bear in mind that the panel’s temperature will have an effect on output as well - they perform poorly when hot - breathing space beneath them is important. Some guys use double walled polycarbonate sheet under them to get that cooling flow, spacers on the mounts, etc.

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Old 20-03-2019, 18:36   #13
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Re: How much am I getting ripped off for my solar panels?

See the attachedClick image for larger version

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Today was an average day, 2 days ago was a very good day.
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Old 20-03-2019, 18:40   #14
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Re: How much am I getting ripped off for my solar panels?

Quote:
Originally Posted by ohgary View Post
Efficicncy is pretty good.



Under full sun with correct sun angle I would expect close to 300 watts.



Which is almost never, much less an average. I assume you are giving these figures theoretically rather than based on real life experience! Best case scenarios only lead to false expectations.
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Old 20-03-2019, 18:50   #15
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Re: How much am I getting ripped off for my solar panels?

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Which is almost never, much less an average. I assume you are giving these figures theoretically rather than based on real life experience! Best case scenarios only lead to false expectations.
Sorry, I know that response was not to my post, but I have to disagree or at least clarify for the OP. I do regularly extract 360 watts from my 380 watt banks. Sure, only at the middle of the day, but it is possible, and indeed should be expected.

A properly functioning and well installed system should reach its peak theoretical output at least briefly. But as StuM notes, you then need to take that figure and apply it as a 4 to 5 hour day.
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