Solar Panel Output

[AndyEss]

Originally Posted by CapnCrunch

My question wasn't how much power I will use or need, but rather how much OUTPUT I could reasonably expect from this panel under optimal conditions. My uncertainty stems from the fact that it is a 32v panel charging a 12v system.

You probably went off the rails with the other poster when you capitalized "output".
It's usually assumed in text communication that you are yelling when you put words in caps.
Few people like to be yelled at when they are trying to help.

[a64pilot]

The thing is, in my opinion we are all Stoopid for rating things and referring to amps.
Cause amps are not a constant, the amount of power an amp is is relative to its voltage, and even if you stick to “12 volts” that is somewhere between 10.5 and 15 volts.
Case in point, 1 amp at 120 volts is equal to 10 amps at 12 volts.
But 100 Watts, is 100 Watts, period, no matter what the voltage.

Thank God Solar panels are rated in Watts, or you would never make any sense of them, the marketing guys would have a field day.

[CapnCrunch]

Originally Posted by AndyEss

You probably went off the rails with the other poster when you capitalized "output".
It's usually assumed in text communication that you are yelling when you put words in caps.
Few people like to be yelled at when they are trying to help.

DOH! (Intentional yelling there LOL) I had forgotten that bit of netiquette! I was merely trying to emphasize the word. I'll use clunky old html in the future. Thanx for pointing that out and my apologies to Sailorboy1 for unintentionally yelling.

[StuM]

Originally Posted by CapnCrunch

My question wasn't how much power I will use or need, but rather how much OUTPUT I could reasonably expect from this panel under optimal conditions. My uncertainty stems from the fact that it is a 32v panel charging a 12v system.

MMPT controller will handle the dfference between panel and system voltage. So the good old 30% or 4-5 hours full sun equivalent rules of thumb still apply.

[StuM]

Originally Posted by CapnCrunch

I wasnt disputing Sailorboy and certainly had no intention of pissing him off. I guess I muddied the waters by including the battery info. What I was really looking for (and maybe didnt express the question succinctly enough) was whether there is a "formula" that says that -under optimal conditions - a 305w panel with a Vmp of 32.7v and Imp of 9A charging a 12v system through a controller like mine should output (charge) at a rate of "X" A to the batteries. Or is the question stated correctly?

Charge rate will vary throughout the day. What's more important is the number of Watt hours you will get in a day. Max change rate into a 12V battery bank if your batteries can take it and you have no concurrent house loads will be about 20 Amps. Total Ah generated by the 305W panel per day , if your batteries and house loads can use it, should be about 100Ah on a good day.

[Suijin]

Originally Posted by sailorboy1

I get 90-120ah from my 290w panel on a good day. It depends on the clouds and whether I get any shading from the mast. So if yours is 305w you will get about the same.

This really is what Crunch wants and needs to know. We all live and die by amp hours and when it comes down to brass tacks this is the figure that we hold up against out energy budget.

But it’s a starting point. How and where the panel is installed, the latitude, weather etc all impact what you’ll get. I have two 170 watt panels and each of them have peaked in June when the boat was heeling perfectly on a cloudless day at 172/3 watts. On a cloudy day output can border on insignificant. And I’ve seen everything in between.

Me? I put on as much as I could fit, and bought sunpower cells and two controllers. Would love to have more. Put as much on as you can fit unless you’re clearly headed over your needs.

[Nicholson58]

Volts X amps = watts.

Your MPPT charge controller will convert whatever the panels deliver into the proper volts for your selected battery type and charge profile. Calculate theoretical amps

Amps = watts divided by volts

Your charge controller display, if you have one, should tell you what’s going on. It may even tally amp - hours for you.

Click on the image to see the display. Here is my Tri Star panel showing output volts, input watts, output amps, battery temperature. I can change the display to show amp hours and many other bits of data I don’t care about.