Solar Panel Output

JC522

Member
95
22
I'm looking for a small flexible solar panel that would output about 50ah on an average day. Is there a factor to use in converting a panel's wattage rating to approximate amp/hrs? Lacking that, what wattage panel do you have and how many ah/day does it put back in the bank?
 

Zonker

Super Anarchist
10,128
6,313
Canada
Yes. Rule of thumb - about 1/3. I.e. 150W panel = 50 A.hr/day. That assumes panel is relatively unshaded, some reasonable sun, not too short hours of daylight (winter in higher latitudes)

So not a tiny panel anyway
 

gptyk

Anarchist
781
437
California
It depends.

It depends quite a bit on latitude and prevailing weather conditions. Depends on mounting and shading. Depends on MPPT vs PWM controller, cable lengths, battery acceptance, etc...

As a almost useless, very very rough back-of-the napkin calculation, 5 hrs sun/day and 70% panel output can be used for guessing. That gives a guess of a ~150 to 180W panel to get to 50Ah/day.

Biggest panel(s) you can mount, good MPPT controller.
 

JC522

Member
95
22
Thanks. I can get a 400 watt panel (or 2x200watt) with controller for $180 to $225 on Amazon. I'd guess they are cheap "foreign made" panels, but If I buy my own better quality MPPT controller from West or Defender is there anything to be concerned about from a safety standpoint? I'm only going to use this when I'm anchored for several days, and otherwise I'll store it under a mattress.
 

steele

Super Anarchist
1,756
242
Land of the locks
Spend up to get a separate Victron or similar controller with bluetooth built in. It will protect your batteries, and the bluetooth and app works well. It is handy to help set up and montior your energy input, and it just fun to watch free electricity flow into your boat in real time.
Because of shading etc 2 panels would be better than one big one. On a sunny day one panel may be enough for your needs, and you can deply the second if overcast etc.
 

gptyk

Anarchist
781
437
California
^^^ this. 2 panels better than 1 because of shade/being on the non-sunny side.
I've got 2 200W panels and 2 Victron controllers. It is nice to be able to monitor performance (my port panel is better than my stbd). It's nice to see when float is reached and how much float time you really get per day.

Skimp on the panels, fine. Get good controllers. You'll get more power out of them and your batteries will be happier.
 

mckenzie.keith

Aspiring Anarchist
847
281
Santa Cruz
I'm looking for a small flexible solar panel that would output about 50ah on an average day. Is there a factor to use in converting a panel's wattage rating to approximate amp/hrs? Lacking that, what wattage panel do you have and how many ah/day does it put back in the bank?
There is a multiplication factor that depends on latitude, attitude and shading. For where I live that factor is 5. So a 10 A panel would put out 50 Ah on an average day. However it may be best to convert to Watts and Watt-hours in case your solar panel voltage doesn't match well with the 12 V battery. 50 Ah is 600 Wh. So maybe a 120 W panel would do for you. But again, multiplication factor varies. If you want it to work in the northern latitudes in winter, then maybe you need to use 4 or even 3. If you are going to be between the tropics of capricorn and cancer, then maybe 6 or 7 hours is your multiplier.

And just to clarify, you will NEVER get the rated power from a solar panel UNLESS you can point it directly at the sun on a clear day and keep it at 25 C while it is so-pointed (that is the condition under which rated power is guaranteed... heat lowers the maximum power it can put out). So these multipliers or 4 or 5 or 6 or 7 hours, they don't represent actual day length or anything. They are just convenient multipliers that help you estimate how much power you will get from different sized panels or arrays.
 

solosailor

Super Anarchist
4,204
902
San Francisco Bay
I'm looking for a small flexible solar panel that would output about 50ah on an average day
It won't be small.... A 110W Sunpower panel with a Victron MPPT in full sun, zero shading, outputs 7A. If it had many hours of uninterrupted sun exposure and could articulate you might hit your mark. 50A from a single panel is a lot to ask with normal shading from the rig, etc.
 

harrygee

Member
391
121
Tasmania
Solar panel ratings are subject to wild exaggeration so ignore the output, rated as watts.

There are panels advertised as 100 watts with a maximum current output of 2 amps.

The current is easy to measure and harder to fudge.

A panel that produces 12+ amps at 14+ volts could reasonably be called a 200 watt panel.
 

mckenzie.keith

Aspiring Anarchist
847
281
Santa Cruz
They are not exaggerated at all. The outputs are guaranteed and if they cannot achieve the rated output under standard test conditions you can get your money back. However the test conditions are generally not representative of the real world. The rated power can only be obtained with 1000 W/m^2 irradiance while the panel is at 25 C. That is equivalent to aiming perfectly at the sun on a clear day while the panel is somehow maintained at 25 C (which will be difficult on a clear day, unless the panel is in a cold place).
 

DDW

Super Anarchist
6,695
1,227
And even if the panel is in a cold place. On a 10 deg day, with 1000 W/m^2, the black panel will be too hot to touch. Unless it is a 10 deg day with 50 knots of wind and the back of the panel is well ventilated.
 

JC522

Member
95
22
And even if the panel is in a cold place. On a 10 deg day, with 1000 W/m^2, the black panel will be too hot to touch. Unless it is a 10 deg day with 50 knots of wind and the back of the panel is well ventilated.
Thanks for the replys. I'll get (2) 200 watt panels and a Victron or Xantrex MPPT controller. That should be enough to give me 50ah per sunny day. The panels get too hot to touch? They aren't going to be permanently installed, but it sounds like I can't just bungee them on top of the Sunbrella dodger or bimini when in use.
 

slug zitski

Super Anarchist
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worldwide
Thanks for the replys. I'll get (2) 200 watt panels and a Victron or Xantrex MPPT controller. That should be enough to give me 50ah per sunny day. The panels get too hot to touch? They aren't going to be permanently installed, but it sounds like I can't just bungee them on top of the Sunbrella dodger or bimini when in use.
Yah ..panels get hot …air gaps are needed

this is the defect with flex panels on canvas …be alert

seems that most folks go for cheap panels and a high quality controller with properly sized copper cables

a typical way to mount ..at anchor panels…. Is hung on the lifelines , then removed and stored for sailing ..it’s a very simple , cheap effective installation

many times it’s best to mount them forward of the mast, for less shading and no interference with sun awnings

9212AC42-AAC5-4306-B5E4-0E703CD35336.jpeg
 

steele

Super Anarchist
1,756
242
Land of the locks
My 115w flexible panel has never gotten too hot to touch. I did mount it on white corplast sheet to make it a bit more sturdy, and also add some airflow/insulation below the panel. A friend used thin
wall polycarbonate sheet which is good too. This allowed him to make a stoway set up like Slug's photo since the polycarbonate is stiffer. Both are stocked at Home Depot.
As long as I am giving dubious advice, these things are handy for tying down the panels for temporary use, https://niteize.com/camjamr-cord-tightener.

Also, for cables you can make your own but I had good luck with BougeRV brand pre-made cables from Amazon. Get the 12g, not the 10g that I did; too stiff and bulky.

1669825763016.png
 

JC522

Member
95
22
OK. I can tie them between the lifeline and the coach roof handrail. I'll run the wires into the mast at the wiring inspection cover, down the mast step and into the boat. Thanks
 

slug zitski

Super Anarchist
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1,465
worldwide
OK. I can tie them between the lifeline and the coach roof handrail. I'll run the wires into the mast at the wiring inspection cover, down the mast step and into the boat. Thanks
Yah

usually the best solution is first go with the simplest solution…live with it for a while …then go to plan B or whatever to solve issues that bother you

folks that overthink things frequently produce expensive mechanical monsters
 

longy

Overlord of Anarchy
6,985
1,279
San Diego
OK. I can tie them between the lifeline and the coach roof handrail. I'll run the wires into the mast at the wiring inspection cover, down the mast step and into the boat. Thanks
This will seriously hamper your travels to the foredeck!
And, as always, try for the shortest possible wiring run to the batts. Or a large part of panel output will disappear into wiring losses.
 




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