Hi Steve,
Since the solar panel generates all sorts of voltages depneding on conditions, it's easier to use the watt rating.
I think that John is pretty close on the math, he wants to replace 960Wh in three days and he's got an 85W panel. Let's assume 65W of boosted output towards the batteries after all losses. That's just under 5 hours at 65W average (may be higher at noon, lower at other times). Let's look at a Sun Hours per day map
http://www.wholesalesolar.com/Information-SolarFolder/SunHoursUSMap.html
and an explanation of what "peak sun hours" means
http://pvcdrom.pveducation.org/SUNLIGHT/AVG.HTM
We can see that zone 3 should easily deliver the 320Wh of 24V charging per day, more in the summer and less in the winter. If the whole system turns out to be more efficient than my 65W guesstimate, the math works out even better. But if the boat is in Zone 5 (4.2 SH/d) on the map, the system will need an average output of 77W to meet the 320Wh demand.
Of course, panel position and tilt have an effect on the total output along with plenty of other factors, that's why I used 65W instead of 85W to try to even out the stuff that will become more obvious once the installation is complete.
The hardest part of vetting ideas that are tossed out to this group is all of the stuff that isn't mentioned. That's why I try to be conservative with the figures that I use. People rarely complain if a system or project performance exceeds their expectations, but missing one's performance numbers can be very dissapointing indeed.
Fair winds,
Eric
Marina del Rey, CA
PS BTW, I met a fellow group member this weekend. I want to clarify that my "Fair winds" is just a closing or farewell phrase. I am not a marine or EV/EB professional, just an active hobbyist.
--- In electricboats@yahoogroups.com, "Steve" <sstuller@...> wrote:
>
> To replace 40 amp-hrs at 24 volts (960 watt-hours) your charge booster would need 80 amp-hrs at 12 volts (960 watt-hours) plus efficiency losses from your solar panels. Thanks. Steve S.
>
> --- In electricboats@yahoogroups.com, "John" <johnpomer@> wrote:
> >
> > — Solar Panel and "Charge Booster" for a Capri 22 —
> >
> > I just placed the order for a solar panel and charge controller for my boat — about $600.
> > I ordered 85W Solarland (Kyocera KC85T Replacement) solar panel from eMarine and a "charge booster" GVB24-8 from Genasun LLC in Cambridge MA....
> >
> > DESIGN PARAMETERS:
> > • to be able to replace 40 amp-hours in normally 3 days (85 watt panel should do this
> > most every time)
> >
> > • minimize the area and placement of the solar panel and not have it interfere with normal sailing
> >
> > • keep the cost "reasonable"....
> >
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