Exepcted solar output in norther winters?

[sailingharry]

On our new-to-us Saga 43, we have 4 Solbian 90W solar panels. This past summer (we bought the boat in July), I was not feeling very good about charging sources (Alternator, Solar, Wind, and Watt & Sea), but our only measurement tool is Link 2000 that tells total current. To make matters worse, all those terminate under the quarter berth, making it a nuisance to get in there.


So, this winter, I have bought several individual ammeters. Cheap Hall Effect ammeters, probably not terribly accurate but useful indicators. https://www.amazon.com/gp/product/B07STHDKSH
I've hooked them up, and am starting to get information even though we aren't using the boat. We are on shore power, but I can pull the battery down significantly by running a space heater on the inverter.


So here's my question. There are 4 Solbian 90W panels, going through individual Genasun MPPT controllers. We live in Annapolis, latitude 39N. I was on the boat on Dec 22, one day after the shortest day of the year. It was 1PM, an hour after noon. My solar was putting out about 5A, evenly distributed across all 4 panels. A naive newbie would say "well, 4 90W panels is 360W, at 15V is 25A, you have a problem." I'm not so sure! Is 5A about all I can expect from a 360W array with the sun so far south this time of year, an hour after noon? I did look at the sun, and it surely isn't overhead! Math says it is 50 degrees lower than it is on June 21.



Thanks for thoughts.


Harry

[tkeithlu]

Ratings on solar panels assume everything just right - 0 degrees latitude, panels square to sun at noon on clear day, etc., such that they are more use in comparing panels than predicting output. You have a bunch of real-life factors involved, such as latitude, angle of panels, orientation of boat, shadows, fog, etc., all of which will have minus signbs in front of them.

So, I would set out with the new ammeters to chart amperage vs. time of day under realistic test conditions. Feed the output into a low battery briefly at various times, and mark poinst on the graph. On another day, some conditions will be different. Chart that day, noting the conditions. Pretty soon you'll be able to predict what your panels will do for you by estimating your immediate conditions relative to your chart.

It's fun and rewarding to understand your boat at that level.

[sailingharry]

Originally Posted by tkeithlu

It's fun and rewarding to understand your boat at that level.

I am a mechanical engineer... some people would say it's "really wierd" to understand your boat that way... LOL It's a gift... right?

[Pete7]

Originally Posted by sailingharry

Is 5A about all I can expect from a 360W array with the sun so far south this time of year, an hour after noon?

Harry, we managed 36w (3A) in a brief period of mid day sunshine last week from 150w of solar and we are 50N. Looking at the history there have been days of virtually nothing during heavy cloud and rain. We are currently making 11w with a 50% light cloud cover.

So we rely on shore power during the winter. However, during the summer we make great gains with lower temperatures and long days.

Pete

[GordMay]

The intensity of insolation received, at any given latitude, can be found using Lambert’s Cosine Law.

Direct solar radiation on various slopes from 0 to 60 degrees
➥ https://www.fs.fed.us/pnw/pubs/pnw_rp142.pdf

NOAA Solar Position Calculator
➥ https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html
Or ➥ https://www.esrl.noaa.gov/gmd/grad/solcalc/

[tkeithlu]

Quote: I am a mechanical engineer... some people would say it's "really wierd" to understand your boat that way... LOL It's a gift... right?
___________

You got me on the wierd part, Harry. I nearly became a mechanical engineer - switched out half way through my junior year after a totally unprovoked beating by Electrical Engineering 101. Guess I still have wierd tendenices. Know I do. I Enjoy it.

[thomm225]

So you are at 39N and I am at about 36N. I took a sun site a couple days ago with my beginner sextant and the sun at noon was at 30 degrees. (it's higher angle of the day)

That's pretty low and it will be lower up there where you are.

Around June 21st the sun here will be at about 77 degrees and will be scorching hot on a Northerly sail but our solar will be working great. Mine usually stays in Float for my entire 20 mile sail across the lower bay to Kiptopeke.

Sometimes when I get to the boat at 3pm or so my system has drop out of Float (to about 13.2 volts) and is in bulk charge mode again from the one 65 watt panel I have lying flat.

If I pull out my 20 watt panel and aim it at the sun, my system will soon go to absorption and charge up to about 14.6 volts then drop back into Float within 10 minues or so

Btw, was it clear or cloudy?

[sailingharry]

Thomm, I have been doing that math too. It's staggering to realize the sun is only 30 degrees above the horizon. That's why it's so damn cold!


It was a clear day, but because the sun doesn't come up very far, it was shining through the tops of the trees.

[sailingharry]

Pete, your real-world numbers are very helpful. I think I will forget about this problem until the spring! Thanks a bunch.

[ikanode]

The USA government has a helpful solar site. It's targeted at homeowners but it will work for you. <https://pvwatts.nrel.gov> The form asks for KW but I checked and it accepts 0.36 KW. It asks for panel angle and location and generates a monthly chart of output.

[Dartanyon]

Here in Seattle at 48N, on the 23 DEC at noon, I happen to be doing the same experiment! Our 505W of horizontally mounted panels were peaking at 91W in about as much sunshine as we get in the winter, there were a few whispy clouds but primarily sunshine. The batteries were a touch below 80% and would have certainly accepted as much as we could have thrown at them.

[peter loveridge]

I have 3 x 75 watt panels, in Shelburne, NS (43 40N) If you are getting 5A in mid winter, you are doing well, I don't usually get more than 7A in midsummer

[wrwakefield]

Harry,

I'm spending this winter at the dock at 56°N. Attached is a screenshot I just took showing representative outputs over the last 30 days from of one of 3 solar panels onboard- all facing south and tilted ~30°. They each have a dedicated Victron SmartSolar MPPT controller- which is the source of the screenshot.

Basically, no real useful gain this time of year despite the daylight period averaging ~7 hours long...

Summer up here is a different story. [The 102kWh figure in the bottom of the screenshot is the accumulative total for this single 135W panel for 2019. The other two panels (165W each) accumulated 105kWh each.]

If you are interested in more details about mid and high latitude solar power potential, I wrote a detailed blog post last year that ties back to another CF thread.

In case any of this is useful.

Cheers! Bill

[Don Lobo]

I have lived on solar for 25 years, most recently in a house with 720 W on the roof. This is in southern Baja, near Los Cabos, and in winter when the sun is not so high in the sky, if it’s a cloudy day I get almost no charging. To get through the day and have a little light at night, I leave the inverter off all day long and make do without power so then in the evening I can have a few hours of light.

Alternatively, on a sunny day I can run big power tools all day And still have plenty of power in the evening, even around the winter solstice. I have always wanted a wind generator because usually when it’s cloudy there’s wind. Ive noticed that many sailboats now have two wind generators off the back corners... that seems an extremely smart set up. The other option would be a small 1000 or 2000 W generator, preferably by Honda, that will top off the batteries on those cloudy winter days where you’re getting almost no charge. From my experience, a cloudy day offer such a tiny charge the batteries that at the end of the day they might not be any higher than at the beginning of the day, and that’s if you had kept the inverter off all day long. A well designed solar system with wind and generator back up is a great way to go and by reducing consumption on cloudy days and two back up sources of power will get you through anything, I would think. I plan to live on a boat someday soon and that is my strategy, I have high confidence in the system and my ability to be flexible.

another great option for Light if you don’t want to use your solar batteries, is to use a Few Lucie Solar camping lights. You can find them on Amazon or other sites, I prefer the ones that are frosted because the light is more diffuse and pleasant. They have their own tiny solar panel and battery and will give several hours of nice light each evening. Not so sure how well they might charge on a cloudy day, probably not a full charge but may be enough to get you through the hard times

Solar camping lights. You can find them on Amazon or other sites, I prefer the ones that are frosted because the light is more diffuse and pleasant. They have their own tiny solar panel and battery and will give several hours of nice light each evening. Not so sure how well they might charge on a cloudy day, probably not a full charge but may be enough to get you through the hard times

Cheers!!

[sailingharry]

Bill, I'll go look up your other thread. Our first big test of the boat systems will be 2021 when we do "the down east loop" including PEI, Newfoundland, etc. Definitely high latitude solar!