R 22

Rhodes 22


Solar Panels

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.


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.

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.

18 Feb 2002

Iím 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 weekendís use. Just top the batteries off with a charger every couple of months???

Comments welcome.

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.

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

Iím 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.) Iím 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 zeroíd without any connections???

Thanks all for your suggestions. It appears that I just needed a good charge on my batteries.

Fair winds,

s/v Mishka
31 Mar 2002

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