Thread Tools Search this Thread Display Modes
Old 10-19-2019, 09:08 PM   #1
Senior Member
SeaBreeze's Avatar
City: Va Beach
Country: USA
Vessel Name: SeaShell
Vessel Model: 1974 Marine Trader 34 Sedan
Join Date: Aug 2018
Posts: 168
Solar Panel Output

How many amps should two 120 watt solar panels put out on a sunny day in mid-October in the mid-Atlantic area?

SeaBreeze is offline   Reply With Quote
Old 10-19-2019, 09:21 PM   #2
oscar's Avatar
City: Bethlehem, PA
Country: United States
Vessel Name: Lady Kay V
Vessel Model: Don't know yet.....
Join Date: Oct 2015
Posts: 509
Average sunlight/day 7 hours in Asheville NC in October. So, 120x2x7= 1680W/12= 140Ah for the day.... Or, 120x2/12= 20A/hr * 7 hours is 140Ah

HOWEVER.... what quality panels, how old, what efficiency, how clean, how well oriented? In other words how many of those 120W it says on the box do you actually get?

So the real answer is: "No way to tell from here". Anywhere from 10-20/hr so 70-140Ah/day is my guess.....

Currently boatless but looking. Avatar is my first boat....Holland, 1965 ish.....
oscar is offline   Reply With Quote
Old 10-19-2019, 09:41 PM   #3
Comodave's Avatar
City: Au Gres, MI
Country: US
Vessel Name: Never Say Never
Vessel Model: President 41 DC
Join Date: Jul 2015
Posts: 5,771
Well you asked about amps not amp hours so 120 watts of solar panels should put out 10 amps if they have good exposure. P=IxE so I= P/E or amps = watts/volts.
Boat Nut:
If you are one there is no explanation necessary.
If you aren’t one, there is no explanation possible.
Comodave is online now   Reply With Quote
Old 10-20-2019, 09:57 AM   #4
Group9's Avatar
City: Bay Saint Louis, Mississippi, (or where the anchor drops)
Country: USA
Vessel Model: 1973 42 Bertram MY
Join Date: Sep 2013
Posts: 829
We had two 140 watt panels on our last boat. I think I calculated maximum theoretical amps at around 26. The most we ever saw was one day with the sun directly overhead and that was 22.5 amps. Usually we were happy to get 14 to 16 amps. But, they would be putting out 2 amps when the sun was barely up.

This was in Florida and the Bahamas.
"It's the tides. They can work for you, and they work against you. And, confidentially, I've had this problem with the tides before." Captain Ron
Group9 is offline   Reply With Quote
Old 10-20-2019, 10:21 AM   #5
djmarchand's Avatar
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 4,836
Presuming that the panels are mounted horizontal on the roof or similar:

In mid October in Virginia Beach the sun never gets perpendicular to the surface of the panel, maybe 30 degrees at best. And then before and after that peak output it is less than 30 degrees, probably 60 degrees at 9:00 in the morning or 3:00 in the afternoon.

One rule of thumb is that a horizontal panel will put out 40% of its rated wattage in amp hours on a sunny day in the summer months in a moderate latitudes. Your panel doesn't meet those latter two criteria of course.

So maybe use 25% or 60 amp hours as a SWAG.

djmarchand is online now   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 06:40 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012