I don't know where you shop mate but take a look at the real world.
Solar Panel Output
- Thread starter JC522
- Start date
mckenzie.keith
Aspiring Anarchist
Yes. Maybe in a place with clear cold winters. Nowhere that I would like to visit with a boat will it be possible to keep the panel at 25 C with 1000 W/m^2 incoming. But I would not say there is no such place on earth. Maybe somewhere on the eastern side of the rocky mountains somewhere there is a solar panel that sees full direct sunlight without getting hotter than 25 C.
mckenzie.keith
Aspiring Anarchist
Virtually all solar panels sold for installation on roofs or in solar farms have guarantees that they will meet their rated power UNDER THE TEST CONDITIONS I MENTIONED. They also have guarantees that the power production will only decrease by a certain amount over time. Nowadays there are temperature coeficients given for Vmp and Imp so you can calculate power at other temperatures. The panels will meet these specs. Count on it.
Most places that cold aren't that sunny. I have a 4.5KW rated array on the house. On a cold but sunny winter morning it starts out at 25 deg F (-4 C) and I can get 4.8KW out. That lasts about 1/2 an hour before it begins to drop even as the sun gets higher. By 11 it will be down to 2.5WK with air temp barely changed. So sure there is probably someplace cold enough and sunny enough to practically meet "standard conditions". Nowhere I've been though.
- Thread starter
- #26
I don't see a problem. I can put both panels on one side or just step up to the coach roof to go forward. The panels are only out there while I'm at anchor. If I use a reasonable wire gauge (offhand maybe 14 gauge), the 20 foot run shouldn't be an issue.
slug zitski
Banned
- Banned
- #27
Always think about shading
I’ve seen small at anchor panels on the bow pulpit , looks like the ideal location
SCARECROW
Super Anarchist
Make the wires as short as possible and a lot thicker than you'd normally spec for the current and keep the MPPT as close to the panel as practical. The MPPT algorithm uses the panel output voltage as a data point and any voltage drop between the panel and MPPT will effect the efficiency. Normal wire sizing for DC boat system usually result in a voltage drop of around 2%.
El Borracho
Meaty Coloso
True about the wire size, but the typical MPPT tracking algorithms are insensitive to the absolute panel voltage. Like tuning a radio by ear. It’s better that way because the designer doesn’t know the panel or wiring characteristics.
mckenzie.keith
Aspiring Anarchist
14 awg wire is about 2.5 mOhms per foot. You can look this up in a table online. If you have 20 feet that is 20 x 2 x 2.5 = 100 mOhm total round trip wire resistance.
If you run 10 amps through 100 mOhms, that is 10 Watts of loss (P = I^2 x R).
I am not sure if 10 Amps is accurate. It depends on which panels you use. If the current is 5 Amps, that is only 2.5 Watts of loss in 14 AWG wire. I don't think I would want to lose 10 Watts of solar panel power in my wiring. But 2.5 Watts seems OK.
Anyway, 20 feet will likely be no problem if you just use the same wire diameter as what comes out of the panels (or go one size up).
Somehow I think that moving panels and panels on lifelines are eventually going to cause a problem.
I have three semi-rigid panels screwed to the deck on the centerline of my cabin top. They do the job. May through August there is enough solar that I don't recharge with engine. I usually run the engine for ten minutes a day to heat shower water and I tend to move every 2-3 days which means another ten minutes of engine while anchoring etc. No sharp corners, no moving parts, nothing to trip over, nothing hanging off of lifelines and it's good enough.
I have three semi-rigid panels screwed to the deck on the centerline of my cabin top. They do the job. May through August there is enough solar that I don't recharge with engine. I usually run the engine for ten minutes a day to heat shower water and I tend to move every 2-3 days which means another ten minutes of engine while anchoring etc. No sharp corners, no moving parts, nothing to trip over, nothing hanging off of lifelines and it's good enough.
El Borracho
Meaty Coloso
Yes, a liberating philosophy for the enlightened pleasure boater. Put panels wherever they can be unobtrusive while working well enough. Relax. Run the machinery if necessary. Simplify.
gptyk
Anarchist
I'd say put the controllers as close to the batteries as possible. The higher Vmp from the panels reduces loss between panel and controller and a more accurate voltage sense on the batteries helps the charge algorithm.
