Yep, you're being optimistic.
Solar installationa on buildings are different than ones on boats. On a building, the panels are optimally mounted at an angle equal to the lattitude and squared to a southern exposure (in the northern hemisphere). This angled mounting gives you the best average exposure over the course of the year. Even mounted as such, panels rarely achieve there rating for more than a few minutes on the best day, if at all, leading to the accumulated 4 to 5 hours of rated power over 11 to 13 hours of sunlight.
Now mount the panels on a boat. Which way should they be angled? The most convenient is flat or in 2 banks slightly banked away from the centerline of the boat. If going with the latter style, if the boat happens to be headed in the right direction, half the bank might only be 5 to 30 degrees away from optimal and the other side of the boat is noticably worse. Turn the boat and the solar collection will drop. Alternatively, mounted flat, the best they will do will be at noon on the summer solstice where they will only be 15 degrees from optimal, I randomly picked the Chesapeake for the location, farther north will be worse.
I know that you're reading the other posts on the board and both Mike and Myles have discussed the actual output that they have gotten from their panels mounted on their boats. You can also check with boaters in your marina to find out how much power they get from their panels while underway.
That said, you might find a day where everything falls into place and you get a current of more that 50% of your panels' ratings, but I wouldn't count on it. You're also suggesting a panel footprint larger than the boat that it is mounted to. Most boats aren't perfect rectangles.
Since there are a number of people here that aren't very familiar with most of the concepts that are being tossed around., I'm just trying to set some realistic expectations. Let's say that someone actually acts on your suggestion, purchases and installs the listed off-grid solar system expecting 3000W of drive during normal daylight hours. Once the boat is operating they find that they see 1200W regularly and 1800W rarely. How do you think that they will feel? Alternatively, if they were expecting only 1500W from the same setup, how will they feel if they ever see 1800W coming in on the meter?
Jim, you're one of the experts around here. I feel that all of us long time members owe it to the novices to discuss what we know about electric boats, both the good and the bad. Setting unrealistic expectations doesn't do anybody any good.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@...> wrote:
>
> Hi Eric,
> The rule of thumb I've been using is 4 to 5 hours of the peak rated output per day in mid-lattitudes. That's averaged over the whole day of course. Sunpower's 315W panel has about the best ratings of any I've seen at 18W per square ft. My assumption was 14x40 or 560 sq. ft. Times 18= 10,080W. Times 5 = 50.4KWH per day. I realize my math is rough and I'm probably being optimistic, but unless I'm missing something big that's a significant amount of power.
> Check out "NREL" for the solar calculations.
> Jim McMillan
>
>
>
>
> > > >
> > > > --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> > > > >
>
> > > > > as working example of how one can less dependent on fossil fuels onboard. Given the reported performance of other fixed installation solar panels, getting 50% the rated capacity seems to be about as good as it gets. So, on a good day (in the middle of the day) you might be able to get about 1500W (2hp) going towards your batteries/drive system.
> > > > >
> > > > > Just some extra considerations....
> > > > >
> > > > > Fair winds,
> > > > > Eric
> > > > > Marina del Rey, CA
> > > > >
>
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