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Old 12-02-2017, 15:45   #61
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Re: Illustrated Guide to Solar Installations on Boats

Quote "it is possible that the voltage could be lower if there was a heavy load, for example, the inverter was running an electric hotplate."

You are correct the only time I have seen 131 amps is when battery is above 90% SOC and I have turned on the 1200 watt 220 V AC hot water service, running off the inverter via 1 hour timer switch. I then used tp keep an eye on the current to make sure the batteries would recover to 100% before days end.

After living with the system for a couple of years, I tend not to look at charge current very often. Inverter is usually turned off at night on anchor, so will check SOC % in am, when turning inverter on and thats usually it.

You are out there to go cruising and enjoy life, not be an unpaid power monitors, so get the system to the point that it meets your electrical needs and hopefully then you can forget about it.

Either way I am pretty happy to see 131 amps when it is required. Next time I see it will take note of the voltage.
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Old 13-02-2017, 02:34   #62
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Re: Illustrated Guide to Solar Installations on Boats

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Thanks Nolex, so to confirm on my 24v system...when testing in the next few weeks I should see something below:
327 x 4 / 28.8 = 45 amps @ 24V


Yes, this is the output Sunpower measure assuming it was converted to 28.8v by a 100% efficient solar controller.

However, the measuring conditions used by Sunpower, and all the solar manufacturers, is exceptionally good. It corresponds to very bright conditions and very cold temperatures. It does not take into account the losses in the wiring or inefficiencies in the solar controller converting the roughly 60v of the panels to 28.8v (if that is the battery voltage at the time).

So in practice even in very good conditions you will see less than this. 85% to 90% (so 85% would be 0.85x327x4/28.8=38A) would be a reasonable maximum number on most days. However, if you monitor the system long enough and operate in an area with very good solar output you will see exceptional conditions. There is no need to stare at the dial. The better solar regulators will record and store the maximum results often for 30 days or more.

These exceptional conditions often occur on days with scattered cloud. With the sun behind cloud the solar panels can cool down. As the sun pops out there can be both direct sunlight and reflected sunlight from the edge of the cloud. The brightness can briefly exceed the test conditions and you will hit the "theoretical" maximum or even slightly more, which in your case would be 45A if your battery voltage is 28.8V at the time. More if the battery voltage is low (with a heavy load) and less if the battery voltage is high. Watts are independent of the voltage so are a better unit for this measurement if you solar regulator will display the output in this way.

These brief maximums are not of much significance in influencing your total output, but they demonstrate your system is working well. You will not hit these peaks if there are any suspect connections or excessive voltage drop in wiring etc.

Just a word of warning. The meters on solar controllers are often optimistic, sometimes significantly. I suspect this is deliberate, higher numbers imply the solar regulator is doing a good job. So if you want accurate numbers verify the dial with some independent check of current. A simple way is to use a clamp on multimeter or turn off all loads (make sure they are truely off, not just on standby) and compare the current input shown on the battery monitor to the result displayed on the solar regulator. Clamp on multimeters and battery monitors are not wonderfully accurate, but they don't have the consistent optimistic display that is common on solar controllers.

Once you have some idea of the error, you can make a mental allowance when reading the output shown on the solar controller.
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Old 13-02-2017, 12:21   #63
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Re: Illustrated Guide to Solar Installations on Boats

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Yes, this is the output Sunpower measure assuming it was converted to 28.8v by a 100% efficient solar controller.So in practice even in very good conditions you will see less than this. 85% to 90% (so 85% would be 0.85x327x4/28.8=38A) would be a reasonable maximum number on most days.
As partially indicated in the quote above, which I have heavily edited, some of the calculations become not just complicated, but controversial.

For many of us it is difficult to keep up, perhaps particularly for those of us, such as myself, who are still working on and attempting to count the number of angels dancing on that pin head, which is a question which arose when we were much, much younger, but remains unsolved. Hard to believe, but some think the answer is zero because angels do not dance, but I am counting anyway.
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Old 13-02-2017, 12:47   #64
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Re: Illustrated Guide to Solar Installations on Boats

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That was my impression also and when I checked the Sun power specs it shows a Max wind loading rating (above and below) of 245kg/sqm

For the engineers out there, how many MPH does that equate to per sqm?

I think the key question in Luthar's case ....Was it the panels that failed, or the attachments to the boat?

My own Bimini is made of stainless pipe (not tube) with 12 flanged attachments to the integral steel...
No flex or harmonics in high winds.

Perhaps this is not an issue if attached properly.


I don't know the MPH, but sent this to an Aeronautical Engineer who I believe will give us an answer.
I suck at math
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Old 13-02-2017, 12:59   #65
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Re: Illustrated Guide to Solar Installations on Boats

He wasn't there so help me nug this out.
first 245 KG = 539 lbs
1 sq meter = 1550 sq in
Now if I do the math right 1550 div by 539 = 2.87
So the panels will burst if a load of 2.87 lbs per sq. in is placed on them, correct?

Here is my problem, it seems that 100 mph is .17 PSI, and that can't be correct can it?
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Old 13-02-2017, 13:05   #66
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Re: Illustrated Guide to Solar Installations on Boats

I think I got that backwards and the panels will only hold .348 PSI, if so then the panels will hold 205 MPH of wind velocity.
Now surely what gets them though is the shaking or flexing from gusts? But that correlates with what I saw from the tornado, I don't think wind got any of the panels, they didn't seem blown out
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Old 13-02-2017, 13:52   #67
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Re: Illustrated Guide to Solar Installations on Boats

I believe it is not quiet as simple as just wind pressure against the panel, unless panel is at 90 degrees to a constant wind pressure. If the wind is flowing over a panel that has any angle to the wind then you will develop higher and lower pressures on the panels faces creating lift or down force. The same reason planes fly and race cars stay connected to the road while cornering.

As to shaking it's self to bits in strong winds, that could be down to vortex shedding or aeroelastic flutter, the reason that your halyards can make so much noise shaking in wind at night or what brought the Tacoma Narrows bridge down.

The calculations are probably way beyond the average solar panel installation, in complexity and cost and in reality not warranted.
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Old 13-02-2017, 14:05   #68
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Re: Illustrated Guide to Solar Installations on Boats

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I believe it is not quiet as simple as just wind pressure against the panel, unless panel is at 90 degrees to a constant wind pressure. If the wind is flowing over a panel that has any angle to the wind then you will develop higher and lower pressures on the panels faces creating lift or down force. The same reason planes fly and race cars stay connected to the road while cornering.

As to shaking it's self to bits in strong winds, that could be down to vortex shedding or aeroelastic flutter, the reason that your halyards can make so much noise shaking in wind at night or what brought the Tacoma Narrows bridge down.

The calculations are probably way beyond the average solar panel installation, in complexity and cost and in reality not warranted.
Totally out of the box but related to this is my experience weathering Hurricane Ike in Houston. After the event we saw large fir trees had been twisted apart with characteristic radial splintering due to the vertical difference in the wind speeds. Not only that but in the Downtown business area many large office towers had lost windows. Oddly, at first, the windows were not lost from the windward sides but from the "sheltered" lee sides. It took a while and a cold beer before we figured this out. As there was virtually no glass in the offices but all over the street it was clear all the leeward windows had been blown out. The answer was "trailing edge" vortices sucking the windows out by reducing the air pressure drastically.

As I said a little out of the box and on a tangent but I hope this helps people think differently about how strong winds can act in unusual ways on a structure.

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Old 13-02-2017, 14:23   #69
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Re: Illustrated Guide to Solar Installations on Boats

Kas1611, my understanding is that the reason for the windows blowing out in a sealed building is that the storms Lower Pressure outside creates enough pressure difference from the higher pressure inside to create that vacumn force.

Typhoon perpetration notes tell homeowners to open windows on the Lee side of the house to equalise the pressure.

I think the wind forces on a typical yacht solar panels is Lift and harmonics on the fasteners.

But for the panels to actually break from direct pressure, still trying to translate the max load rating of 245kg/m2 to wind speed?
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Old 13-02-2017, 15:12   #70
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Re: Illustrated Guide to Solar Installations on Boats

Pelagic,

I thought that too but it doesn't explain why there were no (or very few) windows out on the windward side. If the hurricane reduced air pressure enough to suck out windows it would happen equally. Ike took air pressure down into the low 900mbs from memory.
The theory we came up with was the trailing edge vortices reduced the air pressure further thereby sucking the leeward windows out from their frames while the pressure of the winds against the windward side pressed them into the frames.
Now I'm a Geologist not an Aeronautical Engineer, Meteorologist or Fluid Dynamicist so I could never claim this theory is correct but it did fit with the observed damage at the time.
I shared it to help show that wind damage can occur on the leeward side as much as on the windward.

Cheers and cold beers

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Old 13-02-2017, 22:32   #71
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Re: Illustrated Guide to Solar Installations on Boats

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Pelagic,

I thought that too but it doesn't explain why there were no (or very few) windows out on the windward side. If the hurricane reduced air pressure enough to suck out windows it would happen equally. Ike took air pressure down into the low 900mbs from memory.
The theory we came up with was the trailing edge vortices reduced the air pressure further thereby sucking the leeward windows out from their frames while the pressure of the winds against the windward side pressed them into the frames.
Now I'm a Geologist not an Aeronautical Engineer, Meteorologist or Fluid Dynamicist so I could never claim this theory is correct but it did fit with the observed damage at the time.
I shared it to help show that wind damage can occur on the leeward side as much as on the windward.

Cheers and cold beers

Keiron
Without the math attack, you postulate that everything is equal. But if one area is even slightly weaker than the other it goes first, and the entire dynamic changes after it blows out.
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Old 14-02-2017, 05:57   #72
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Re: Illustrated Guide to Solar Installations on Boats

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But for the panels to actually break from direct pressure, still trying to translate the max load rating of 245kg/m2 to wind speed?
I was incorrect about the 205 MPH, reason is the pressure increase is not linear, the correct answer from the Engineer is below.

Using 2.2 lb per kg & 1550 sq.in. per sq. meter, a 245 kg/sqm pressure loading works out to ~ .348 psi = ~50 psf dynamic pressure, which in turn would result from a 205 ft/sec or 140 m/h wind velocity (assuming a flat plate with a CD = 1).


Now realize this is for the panel being 90 degrees to the wind, a very unlikely event. I doubt many mounted on boats are ever broken by wind force alone, I think other forces are at play. Like possibly flutter, I can see flutter breaking them, or of course flying debris
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Old 14-02-2017, 12:43   #73
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Re: Illustrated Guide to Solar Installations on Boats

Fantastic a64..Please thank your friend

Strike one more concern off the list....
......Flutter....what I called harmonics
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Old 14-02-2017, 13:12   #74
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Re: Illustrated Guide to Solar Installations on Boats

Flutter gives me the absolute willies, this video scares me every time I see it.


A very good friend of mine, Dr Ralph Kimberlin during certification flight tests of the Aero Commander 112, the tail got into flutter, and underwent explosive disassembly in like 1.5 sec. Ralph got out, the other Engineer didn't. The other Engineer was the flutter DER who had signed off the aircraft as being safe and was told if you say its' safe, well get in it and fly the test with Ralph.
Not much of a write up, I'm sure the NTSB has a better one
https://aviation-safety.net/wikibase/wiki.php?id=2731
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Old 14-02-2017, 13:25   #75
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Re: Illustrated Guide to Solar Installations on Boats

Helicopter ground resonance, this is a harmonic vibration, the frame rate of the camera makes it look odd as you don't see the rotors turning right



Point being of course that if the panels got into a harmonic resonance freq, I can see how it would bust them.
You should be able to put a spolier on the top surface that would stop that though
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