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Old 02-06-2024, 12:46 AM   #1
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Default How much solar should you get from 300W worth of panels of the Roof?

How much solar should you get from 300W worth of panels of the roof?

I am thinking that 300W is the theoretical max, but that would require it being tilting and pointed directly at the sun whereas on the top of a Mercedes sprinter van, they are flat and don't have the right angle for maximum sun.

So realistically, how much power should you be getting on a sunny day and without shade?
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Old 02-06-2024, 12:59 AM   #2
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How much solar should you get from 300W worth of panels of the roof?

I am thinking that 300W is the theoretical max, but that would require it being tilting and pointed directly at the sun whereas on the top of a Mercedes sprinter van, they are flat and don't have the right angle for maximum sun.

So realistically, how much power should you be getting on a sunny day and without shade?

In normal good sun conditions we get about 100ah per day into AGM 12v batteries with and MPPT Blue Sky controller and 17.7v power point 18% efficient panels horizontal on the roof wired in parallel.
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Old 02-06-2024, 03:34 AM   #3
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In normal good sun conditions we get about 100ah per day into AGM 12v batteries with and MPPT Blue Sky controller and 17.7v power point 18% efficient panels horizontal on the roof wired in parallel.

The 17.7V PowerPoint is the cut-off volts for your solar charger on a 12V battery?
Is that a setting you can edit with your blue sky controller?

The AGM 12V batteries are for the living area of your RV or to start the engine?

In my RV there is the engine battery for the Diesel engine and separate lithium battery for the inside which are separate.

So how many solar panel are on the roof? Is it a single 100 watt panel?

Do you measure on the ah per day vs the peak watts?

I think my system may be incorrectly wired. I am supposed to have a 300 watts of solar on the roof, but I only get a small fraction of that even with peak sun. Like maybe 60 watts vs around the 300 watts it supposes to have.

Also, my battery shows from the renogy solar controller as 100% even when the batteries monitoring system shows it down below 88%

When you say " 18% efficient panels" do you mean that you have a 100 watt panel, and you get 18 watts on average?

Like 18% of 100 watts, or is that 18% of possible sun energy.

This is my first solar panel setup, so I am still figuring out the lingo.

Thanks.
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Old 02-06-2024, 08:34 AM   #4
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It depends on your location, angle, and shading. On a sunny day with no shade, you might get around 70-80% of the rated power, so roughly 210-240W.
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Old 02-06-2024, 10:20 AM   #5
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The 17.7V PowerPoint is the cut-off volts for your solar charger on a 12V battery?
Is that a setting you can edit with your blue sky controller?

The AGM 12V batteries are for the living area of your RV or to start the engine?

In my RV there is the engine battery for the Diesel engine and separate lithium battery for the inside which are separate.

So how many solar panel are on the roof? Is it a single 100 watt panel?

Do you measure on the ah per day vs the peak watts?

I think my system may be incorrectly wired. I am supposed to have a 300 watts of solar on the roof, but I only get a small fraction of that even with peak sun. Like maybe 60 watts vs around the 300 watts it supposes to have.

Also, my battery shows from the renogy solar controller as 100% even when the batteries monitoring system shows it down below 88%

When you say " 18% efficient panels" do you mean that you have a 100 watt panel, and you get 18 watts on average?

Like 18% of 100 watts, or is that 18% of possible sun energy.

This is my first solar panel setup, so I am still figuring out the lingo.

Thanks.

The AGM batteries were the coach batteries we had until last fall.


We have 3 100watt rated panels.


Peak watts can be an interesting reference of performance but net power per day is what really counts in the real world.


Panels are rated for their output. The efficiency tells you what % of the actual solar energy hitting the panel gets converted to electrical power.


Most solar controllers don't really seem to have a clue about whether or not the batteries are actually full, IMO. Make sure you battery monitor is setup correctly to judge full batteries and believe it over the solar controller.
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Old 02-06-2024, 06:53 PM   #6
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I have similar setup to Booster, 3 100W monocrystalline high efficiency panels, MPPT Morningstar controller, AGM batteries. In sunny day by midmorning to midday my batteries are full. About 100Ah/day in good days, no shade, mostly west coast.
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Old 02-06-2024, 08:15 PM   #7
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I have 190 watts (advertised) from two panels. In theory, I should get about 15 amps charging my house batteries, but I don't remember ever seeing much more than 10 amps (so 130 watts or so). That's about 70% of the advertised production. The panels are flat, and that would be full sun in parts of the year where the sun is the highest. I don't really have a way of scientifically measuring the amount of shade, but when it's cloudy or shady, obviously you can get a lot less, down to almost negligible.
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Old 02-07-2024, 07:52 PM   #8
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I have 190 watts (advertised) from two panels. In theory, I should get about 15 amps charging my house batteries, but I don't remember ever seeing much more than 10 amps (so 130 watts or so). That's about 70% of the advertised production. The panels are flat, and that would be full sun in parts of the year where the sun is the highest. I don't really have a way of scientifically measuring the amount of shade, but when it's cloudy or shady, obviously you can get a lot less, down to almost negligible.
I have 300 watts advertised. So 70% would be 210 watts. When I'm in full sun, it shows like 60-70 watts. App is showing a max of 140 watts however I have never seen it.

140 watts would be 70% of 200 watts. So maybe one of my solar panels was not wired correctly.

This helps support my theory.

Thanks.
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Old 02-07-2024, 11:45 PM   #9
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I have 300 watts advertised. So 70% would be 210 watts. When I'm in full sun, it shows like 60-70 watts. App is showing a max of 140 watts however I have never seen it.

140 watts would be 70% of 200 watts. So maybe one of my solar panels was not wired correctly.

This helps support my theory.

Thanks.
The state of charge in your batteries also impacts how much solar you will see on the controller. Do you have AGM or Lithium batteries?
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Old 02-08-2024, 12:30 AM   #10
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The state of charge in your batteries also impacts how much solar you will see on the controller. Do you have AGM or Lithium batteries?
I have Lithium batteries being charged by the solar.

How low do the batteries have to get in order to get a decent reading from the solar charger?

Thanks.
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Old 02-08-2024, 12:47 AM   #11
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I have Lithium batteries being charged by the solar.

How low do the batteries have to get in order to get a decent reading from the solar charger?

Thanks.

If they are down to 13.2v or lower they should take the max amount they can, which will be way more than your solar can do.


What voltage are you seeing from the solar when charging. If it is low you won't charge fast and it might be stuck in float.
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Old 02-08-2024, 04:44 AM   #12
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If you only get 60-70W from 300W of solar panels that are not shaded even by a bit, then something is not right.

If, on the other hand you have 2 or 3 panels wired in series and one of them has some shade (like from an A/C hump), then it could be just that.

I think ideally you'd see about 80% with a high quality panels lit up fully in a good angle.
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Old 02-08-2024, 04:58 PM   #13
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If this is your layout you could be prone do have shade on your panels, partial shade on one panel will likely kill a panel output, as stated in previous post, in certain Sun position you could be killing two of them, one by AC and one by the antenna. My 3 panels are away from any roof gadgets potentially shading them.
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Old 02-08-2024, 05:27 PM   #14
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It is worth noting that quality current-generation panels have built-in bypass diodes that effectively partition the panel into different zones, such that a shadow on one zone does not affect the output of other zones. This greatly mitigates the "small shadow" problem. For this reason, it is important to distinguish newer panels from older ones when discussing shadow issues.

Also, my understanding is that external bypass diodes can also be installed on each panel in a series circuit, in order to make the panels independent of each other.
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Old 02-08-2024, 06:48 PM   #15
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It is worth noting that quality current-generation panels have built-in bypass diodes that effectively partition the panel into different zones, such that a shadow on one zone does not affect the output of other zones. This greatly mitigates the "small shadow" problem. For this reason, it is important to distinguish newer panels from older ones when discussing shadow issues.

Also, my understanding is that external bypass diodes can also be installed on each panel in a series circuit, in order to make the panels independent of each other.

Even our decade old panels have the bypass diodes in them. They work but seem to add some inefficiency themselves probably from their internal resistance that drops voltage. 100 watt panels the have two zones.




Still better than nothing, though.
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Old 02-08-2024, 06:50 PM   #16
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It is worth noting that quality current-generation panels have built-in bypass diodes that effectively partition the panel into different zones, such that a shadow on one zone does not affect the output of other zones. This greatly mitigates the "small shadow" problem. For this reason, it is important to distinguish newer panels from older ones when discussing shadow issues.

Also, my understanding is that external bypass diodes can also be installed on each panel in a series circuit, in order to make the panels independent of each other.
Agree, but each string of cells with associated bypass diode needs to provide minimum charge voltage. Difficult to guess home many strings each panel has on the OP van but I wouldn’t be surprise if just two, so shade on even one cell of a string will only allow ˝ panel to work.
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Old 02-10-2024, 06:37 AM   #17
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Agree, but each string of cells with associated bypass diode needs to provide minimum charge voltage. Difficult to guess home many strings each panel has on the OP van but I wouldn’t be surprise if just two, so shade on even one cell of a string will only allow ˝ panel to work.
It's a 2024 GrechRV Strata-ion. There are constantly changing suppliers for different parts, so it's hard to know which brand components you are getting.
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Old 02-10-2024, 06:40 AM   #18
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If this is your layout you could be prone do have shade on your panels, partial shade on one panel will likely kill a panel output, as stated in previous post, in certain Sun position you could be killing two of them, one by AC and one by the antenna. My 3 panels are away from any roof gadgets potentially shading them.

I think that is my configuration. That matches what the manual shows but I might have to fly my drone over the van to get an actual look at how it works.
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Old 02-10-2024, 06:34 PM   #19
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Pending on the design of your panels you could be prone to low output pending on Sun location. Info which can help:
1. You could have 1 or 2 or 3 strings in each panel
2. One PV cell can generate 0.5-0.6V
3. One string needs about 16 V so about 28 - 32 cells
4. One cell shaded in the string will kill that string

If shading is indeed your issue with panel performance one way to help to eliminate it would be raising your panels by 1-2 inches to reduce shading from the awning, antenna, AC, and front vent.

This is good video with explanation.


Working on my roof layout I eliminate shading from my in close and open position. Had a little more room than your van and no AC.
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Old 02-10-2024, 07:20 PM   #20
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I have always dreamed of implementing a "pointing" system by mounting the panel on four liner actuators. You see folks putting hinges on one side and actuators on the other. But, I am picturing using four actuators that lie flat under the panel and attached to the corners. The panel would be only attached to the actuators, so it could point in any direction. The geometry would be complex and probably only practical for 10-20 degrees or so off horizontal. Not sure if that is enough to make much difference.
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