Thursday, August 23, 2012

Solar Power

One of the nicest things about living on a sailboat is that it is (or at least has the possibility of being) a very self-sufficient lifestyle.  Although we tap into the city's electricity grid and freshwater supply while at the dock, Sea Gem can go for weeks without using either.  We can make our own water with our watermaker, and we can make our own electricity with our diesel generator, engine alternators, and solar panels.

Our ability to operate off the grid is primarily limited by our fuel supply: although substantial (almost 400 gallons), it is not endless.  And at 4 to 5 dollars a gallon, it is awfully expensive to rely on diesel fuel for our energy needs.  Our generator, for example, burns about three quarters of a gallon an hour, and it must be running in order to run our A/C or our electric stove.  Even without A/C (which is not so necessary when in a breezy anchorage), we need to run the generator a few hours a day to top off the batteries, cook, etc., and that starts to add up quickly.

Solar energy, of course, is limitless and free.  The more we can rely on our solar panels, the less fuel we need to burn, and the longer (and less expensively) we can stay off the grid.  Unfortunately, the solar system that came with Sea Gem barely made a dent in our energy needs.

Sea Gem's prior owners installed four large rectangular solar panels and two half-size panels on the top of our hard bimini (cockpit roof), where they receive fairly direct sunlight:

Two of Sea Gem's Four Full-Size Panels
The panels came connected to a solar charge controller mounted at the navigation station, and the controller is connected to the battery bank.  During periods of peak sunlight, the controller would register between four and five amps DC.  And, of course, we only get four or five hours of peak sunlight per day.  That is enough to run our fans or small instruments (i.e. not radar) while sailing, but it is not even close to enough to keep our food cold, use the microwave, make water, and so on.

Five amps works out to only about 65 watts of power being generated by the panels, and based on the size and number of panels, that is a very, very small number.  Panels rarely put out more than 75% of their rated capacity (due to imperfect angles, air quality, clouds, etc.), but even accounting for those inefficiencies puts the maximum possible total output of the panels at only 85 watts or so, and modern panels of the same size would be rated at around 300 watts.  And so I assumed that the panels were either very old and inefficient or very old and no longer working completely.  Because we'd like to increase our ability to be self sufficient, replacing our solar system has always been in our long-term upgrade plans.  New panels, unfortunately, are expensive, and because the controller that came with Sea Gem was limited to 15 amps, we would need a new, larger controller as well.  Because complicated, expensive upgrades are the easiest to defer, we settled for our measly five amps for our first year aboard Sea Gem.

Out of curiosity, I recently decided to remove one of the solar panels to find the model number and determine whether the panels are so old that they were always inefficient, or if they are so old that they became inefficient with time.  To my surprise, the panels are together rated at over 250 watts--far more than the 65 watts they were putting out, and a drop in performance of that degree is much more than one would expect after the 15 or 20 years that have passed since they were installed.  A drop in output of about 10% of the rated output every ten years is more typical, and so I would expect to see a maximum of about 150 watts produced by the panels (250W x 80% x 75%), which works out to 11.5 amps at 13 volts--more than double what we were getting.

And so I suspected that the charge controller was the culprit.  Because a charge controller is less expensive to replace than the panels, and because we will need a new, larger charge controller at some point anyway, I figured that upgrading the controller was a worthwhile investment.  Fortunately, birthday money came from Krissy's parents at just the right time, and I ordered a new 30-amp digital solar charge controller, the Samlex SCC-30AB.  (I did well for my birthday this year.)

Here it is, neatly installed at the navigation station:

Samlex SCC-30AB
The results?  I saw readings of nearly 140 watts--more than double the output of the exact same panels with the old controller, and that was with clouds in the sky and before the sun was at its zenith.  Although that output is still not enough to permit us to rely solely on the panels, it makes a real dent in our total usage and reduces the amount of time we will need to run our generator while at anchor.  Once we add enough panels to produce close to the 30-amp capacity of the controller, and maybe a wind generator as well, we should be in a position where we can rely on renewable energy for the bulk of our day-to-day energy usage, and that will be a nice feeling indeed.


  1. hi. thats an amazing post. loved your ideas. do keep up posting more such inspiring posts.

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  2. Amazing post! It makes me smile when someone concerned how beneficial to use solar energy especially when you use in your own home. Right! Keep it up...

  3. It is true that some of the advantages of solar energy are that it is limitless and free. And this is why some people nowadays are considering solar power as an alternative source of power. Good to know that you’ve fixed the problem with your solar panel controller. How much energy does the solar panel generate? I hope you already got the wind generator. That would definitely boost the energy efficiency of your boat. Like solar energy, wind energy is a renewable and clean source of energy.

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