I want to add solar panel(s?) to my boat. I don't
anticipate spending more than one to three nights out
at a time. My immediate needs will be to keep house
and starter batteries topped off. The only electronics
I have are cabin lights, water and bilge pumps, nav
lights, and starter. My 6 HP Merc does have a small
alternator (6 amp I think). I think I could get by
with a single 10-watt panel. Should I just go ahead
and order the $175 solar panel kit from GB or is there
a good reason to be looking at something different?
The 30-watt panel from GB is $500, quite a jump up in
price. I am not sure if I should bite the bullet and
get the bigger panel first, I do plan on slowly adding
more stuff later but it seems like overkill now.
I have seen 11-watt flexible panels on sale for about
$125. Is anybody out there using flexible panels? How
well do they work vs. the fixed hard panels? Is the
flexibility gained by moving the panel around worth
the hassle of have a loose panel and wires to worry
about? What exactly is included in the GB kit?
Any advice welcome.
Thanks,
WB
16 Feb 2002
I have two panels, one mounted to each side of the pop-top. I guess they
must be the 10 watt variety, don't know for sure. They were on the boat when
I got it and I have never really checked to see what the specs on them were.
I have never charged my batteries (2) in the summer. We haven't overnighted
much, but we did stay on the boat three nights in a row while we were at KY
Lake and used the cabin lights every night, also charged the cell phone and
radio/portable light batteries, ran the water pump, etc. with no problem.
We don't have a charging coil or electric start on our motor. To keep things
simple, maybe just let the motor charge it's own battery and have the solar
panel(s) charge the house batteries.
That 30 watt panel is BIG. I think I would like to see a cleaner way of
wiring it than the coiled cord (it was on the pop-top) I saw at the boat
show. Seems like sooner or later something would get caught in this and bust
it. Just my opinion though.
Rik
16 Feb 2002
I've got a 32w Unisolar flexible panel. It's wired to a plug in the cockpit
that goes thru a charge controller. When the bimini is opened, I mount it
to the top of the bimini with the cord wrapped around the bimini poles on
the way down to the plug. When the bimini is closed (I have rear struts on
the bimini to support it when it's closed), I bungee it to the bimini frame.
I can also just unplug it and stow it when it's not needed. The panel does
a fine job keeping the Lifeline 4D house battery at peak charge. I wouldn't
use a panel this big without a charge controller, though
Brian Jernigan
16 Feb 2002
I have both, two 10 watts and the 30 watt on the pop-top,
IIRC the rule of thumb is panel rating in watts times .25 equal avenge
amp/hour a day, so 20 watts worth will put in 25 amp/hours over 5 days, that
about a quarter charge on the batteries(one 115 amphour). So you most likely
wants 2, That is also why GB went to two(partial experience). The mounting
kit has the spacers that hold the panels off the fiberglass, the air under
them keeps them cool(they run poorly hot).
The flexable ones can be a pain, best place to mount them it to leave them
on the seats/lazzerret hatch when not using the boat.
MJM
18 Feb 2002
I’m off to check the blocking diodes on my two solar panels, hopefully this weekend. Check
me on this. Can I read the voltage with no load on the solar panels and the battery not
connected? Should the voltage be 13 or so volts? Resistance across the blocking diode
should be low in one directions and nearly infinity with the multimeter leads reversed?
Stan suggested that I check the panels and diodes because the batteries are not recharging
to full capacity in one week. Michelle and I do use the house bank (two batteries) a lot
when we sail. Maybe there is just not enough charging capacity to top them off after
every weekend’s use. Just top the batteries off with a charger every couple of months???
Comments welcome.
Al/Michelle
S/V Mishka
15 Mar 2002
The open circuit voltage (battery disconnected)of the solar panels under full sun should be at
least 13.6 volts and may be as high as 15 volts or so depending on the panel. To test the
diodes you must disconnect the circuit and test with an ohm meter across the diode leads,
NOT the positive-negative panel leads. The diode will only be on one leg of the circuit. If
the diodes are OK there will be very low resistance in one direction. When the leads are
reversed there will be very high resistance.
While your batteries are disconnected from the panel, take a voltage reading to determine
approximate state of charge. A fully charged battery will show around 12.9 to 13 .2 volts
if it is in good condition. 80% charge is around 12.6-12.7 volts. 50% is around 12.2 volts.
Fully discharged is 10.5 volts. Check each battery separately. If they show below 80%, it is
not likely that a solar panel would bring them back to full charge as they do not provide
enough current to break down the lead sulfate on the plates. Long term sulfate buildup from
undercharging is the biggest cause of lost capacity and premature battery failure. To get
the batteries back to a fully charged state requires charging currents of at least 15% minimum
of the amp hour rating of the battery. 20%-30% is better. Charge each battery separately and
monitor electrolyte levels closely and add distilled water as required, a heavily sulfated
battery will use some water before it is returned to a healthy state and may take a
surprisingly long time to charge due to high internal resistance. My group 27 70ah battery
required 36 hours on a 6 amp two stage automotive charger after sitting all winter last year.
It was fully charged when stored. The battery is fully charged when it will hold an open
circuit voltage of at least 12.9 volts after being off the charger for a couple of hours.
When first taken off the charger, the voltage should be about 13.2 volts. If a battery
will not maintain a 12.9v full charge, it has lost capacity due to sulfation and plate
erosion. If it will not maintain at least 12.6 volts, it is near the end of its life
expectancy. There are new devices on the market that help condition and maintain battery
health when connected into the charging circuit. They generate a frequency pulse in the
3.2mHz range which is the resonant frequency of lead sulfate crystals. This causes them
to break down faster and at lower current levels, restoring the plates to healthy condition.
if you are using your batteries a lot when sailing, I would put them on a 10-15 amp shore
charger overnight at least once a month. The solar panels will help maintain charge between
times, but won't be up to the task alone.
Razz
16 Mar 2002
I would suggest you either get a hydrometer or use a very accurate digital volt meter to
determine the state of charge of your house batteries. Make this measurement at the end of
your weekend sail. Then, knowing the size of your battery bank, calculate the number of
amp-hours required to recharge the battery bank. Compare that recharge requirement with
the capacity of your solar cells. Solar cells are rated under perfect conditions: i.e.
noon day sun, clear - cloudless weather conditions, antiseptically clean solar panels
oriented perfectly with the sun, etc. Under real life conditions, it is quite usual to
actually obtain about 50% of the rated capacity of the solar cells. So, if your measured
weekly recharge requirements are more than about 50% of the rated capacity of your solar
cells, then your solar cell bank is too small for your electrical requirements. This would
be my 1st step as it would be true even if there is nothing wrong with the batteries, solar
cells, or blocking diodes.
If your blocking diodes are bad, then your house batteries would very likely be completely
discharged when you return after a week. Since this is not happening, the blocking diodes
are, in all probability, OK.
Roger Pihlaja
S/V Dynamic Equilibrium
16 Mar 2002
I’m sorry to be so long in reporting my solar panel test results. My multimeter showed about
18 volts across the positive and negative leads in the noon sun in Tampa, FL on a really
bright day. Both panels (cells) showed the same results (without a load). When the
multimeter was placed inline with positive lead and connected to the battery (as an
ammeter), it showed just off scale (300 ma.) I’m guessing about 400 ma. This was also
true for both panels (cells) and battery setups.
Of course, now I had to fiddle with the adjustment on the battery condition meter. It
indicates over 100% battery state and about 15 volts on the batteries. The battery state
meter was installed by GB. Any suggestions on how to adjust the accuracy of the meter
would be appreciated. Maybe zero’d without any connections???
Thanks all for your suggestions. It appears that I just needed a good charge on my
batteries.
Fair winds,
Al/Michelle
s/v Mishka
31 Mar 2002
