I've made the Salish Sea to Puerto Vallarta
trip (2000 nautical miles or so) three times on boats with solar panels
as their primary energy source. The power output of the panels varies wildly as conditions change and as you move south. So I'd say- there is NO single
easy or accurate answer to your question.
We have had four 125 watt solar
panels since early 2000. Used them extensively in Salish Sea 2005-2010 and two trips from Tacoma to San Diego
on to the Sea of Cortez
. Also used them in San Diego
2000 thru 2004. I have spent a great deal of time monitoring the performance of our solar system.
-Clouds - the slightest cloud shadow kills solar output
-Angle of sun relative to mast
and backstay (shadows!)
-Location of panels relative to sails
-Type of sail in use
-Rolling of boat
at sea significantly changes angle of solar incidence
-dust buildup on the panels
For example - flying the spinnaker
early in the day shadows the front of the panels for several hours when sailing SSE off the Oregon
Using the big overlapping drifter late in the afternoon when sailing WSW off the California
coast shadows the panels.
Sailing SE along the Washington
coast with a 5' quartering swell from the NW and 4' wind
waves from the west makes the boat roll 20 degrees side to side and pitch
10 degrees up and down. The mid-July solar output (two 125 watt panels) in bright sunshine would oscillate from 14 amps @ 13.5V to 2 amps in synch with the rolling of the boat. The sails
were not shadowing the panels but the panels angle of incidence to the sun was changing by over 45 degrees. And the mast/backstay was shadowing the panels as the boat moved about.
The good news is that, at least in our case, the panels made so much power that we never bothered to deploy our Ferris Towed generator
. The solar panels always kept the batteries at almost full charge. Our underway energy consumption
is about 100 amp hours / day and the panels easily made that.
My brother had a Tartan 42 with two 125 watt panels that we also used in the Salish Sea, Puget Sound
to Puerto Vallarta
, and a year in Western Mexico
. The boat had less electronic and electrical
stuff that our boat but he still used 75 - 80 amp hours / day while at sea. His solar panels kept the batteries fully charged.