Sunday, April 14, 2013

Solarized At Last

New Bern, NC

Finally, after all these years we have an adequate and functional solar panel installation. Why not earlier you may ask. 

We had a 50 watt panel that came with Tarwathie.  It supplied about 30% of our use.  (We also have 220 amp-hours of batteries.  Most cruising boats carry 400 amp-hours or more.)

Equalization (also call desulfating) is the process of raising battery voltage to 15.2 volts (or higher) for two hours.   That causes the built-up of sulfates on the battery plates to dissolve.  It is a kind of rejuvenation.  For the past 8 years we had no way to to that; not via the solar ppanel (50 watts is not enough), nor through the shore power controller (our 25 amp controller does not have an equalization function.)  That has been expensive. More than once we were forced to buy new batteries when the old ones were only one year old because of sulfation.

For years, I've been agonizing about how and where to mount more panels, or a bigger panel.  The answer is there is no possible place on Tarwathie for more or bigger permanently mounted panels.  Period.  It was only after I abandoned that idea in favor of panels that we can mount temporarily and then stow below when under way, that I moved past that mental block.

Down in Miami this year, I bought two 80 watt panels from Sun Electric.  Only $110 each, a great price.   My friend Bob was with me.  As Bob and I stared at the charge controllers for sale, Bob mentioned that he had one that he didn't use, and that he would give it to me.  Great!  The salesman at Sun confirmed that with a small amount of panels and with low voltage, that a more expensive MPPT controller would not be justified.

With 1x50 and 2x80 I have 210 watts total capacity.   I had previously calculated that 120 watts was sufficient to meet our needs most days.   The limiting case is when we are at Champlain at 45 degrees north latitude.  All other things being equal, one needs 50% more panels at 45 degres thanb at 25 degrees.  So I now have 210/120 or 75% excess capacity.  That won't go to waste, it will help me on cloudy or partly cloudy days.

This summer we will be away from the boat for 5 months.  The panels will allow us to keep the fridge on while we are gone.  Our fridge runs for years with no maintenance when it is cold, but if we allow it to get warm, the collant leaks out in just a few days.  If that happens, we have to hire a refrigeration guy to use his vacuum pump to purge the air and then recharge it.  I plan to lash the panels between the boom gallows and the stern pulpit to (hopefully) withstand strong summer storms.

I decided to mount the panels hanging off the lifelines on the starboard side when in Marathon.  That keeps them pointing south almost all the time because the wind blows from the East or Northeast almost all the time.   On Champlain we will be putting the panel up and down frequently.  I plan to put them on top of the mainsail/boom.   You can see that arrangement below.  In either case, if severe thunderstorms approach, we'll take them down.

Note two panels on top of the mainsail, and one high above the stern.
The wiring arrangement has to be flexible because of the shifting mountings.  I need to be able to unplug the panels when stored below.  My solution was to run 14 feet of 12 gauge wire from each of the 80 watt panels, to the type of plug one used to connect trailer taillights.   14 guage wire runs to the original 50 watt panel.  All three come together where the thru-hull penetration is for the wires. You see that in the picture below.

Unfortunately, the Xantex C40 controller that Bob gave me failed to work.  I suspect that corrosion got to it in the years that he didn't use it.  Thanks anyhow Bob.   I actually only need a 15 amp controller, not 40.  However I already had the mounting screws done and the wires trimmed for exactly the arrangement of the C40.  I found that I could buy a C40 on Ebay for about the same price as a C15 retail, so I did.  You see a picture of it below.

The controller is connected to the thru-hull by 7 feet of #12 wire, and connected to the batteries by 1.5 feet of #8 wire.  I had enough #8 to run the 7 feet to the thru-hull, but that wire was too fat for the rubber thru-hull bushing.  Here is my voltage drop calculation for the installation.  The power loss in the wiring is 0.87 watts.

Today was the first full-scale trial.  It was a complete success.  We ran 12 hours with no shore power yesterday.  This morning, we were down 17 amp hours. the solar panels kicked in and by 11:00 we were at 100%.   Then I initiated equalization,  the charging current surges to 10.2 amps and the voltage up to 15.2.   Then the controller backed off the current to 6.5-7 amps for two hours holding a constant 15.2 volts.  Perfect.   That is the first time in 8 years I have been able to equalize batteries on board.

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