Saturday, June 23, 2012

Solar Data!!! What does Solar on a Boat Really Produce?

Ahh, love it…

Today Kristi must have been bored, as she kindly rearranged the FHSUs (Forward Horizontal Storage Units  aka V-Berths) clearing access into the starboard cabinet.  As a result I could pull out a Keyspan USB <--> RS-232 adapter and connect up the TriStar MPPT data logging software.  And guess what, they had already configured it from the factory to capture some good stuff!!!

Daily AH produced via 480W of panels
Here is a graph of daily Ah’s produced starting from when we fired up the panels (May 25th being the 1st Full day), and yup you can see those first couple of days were productive ones!  Looking at the data closer I again notice a correlation between very low output days and when we motored, but not symmetrically.  All the ‘really low’ days (100Ahs or less) were days we motored.  However there are also some days we motored where the output did not drop real low..  No real answer for that.   Finally  I would ‘guess’ the days in the 120-160 range were likely rainy days, but I did not mark the calendar so cannot say with certainty.

This is where monthly averages come into play!  And the controller was pre-configured to capture total Ah’s produced from 1st power-on.   4,462 Ah’s were delivered over a 29 day period.  Or an average of 153Ah’s per day.  (A more ‘correct’ measurement is the KWh’s produced, which is 59KWh total, or a bit over 2KW’s per day.  Seeing as Boaters seem to like Ah’s will stick with that for now.)

OK, this is real results for two 240w panels oriented largely ‘flat’ here in the PNW.    How does this compare and what does it mean?  4,462Ah comes to around 45 hours of generator time we did not need.  And in fact, we have only used the generator twice after installing the panels – both times to support Laundry.

My modeling had indicated 61KWh (or 4,583Ah) for the month of June.   Looks like I hit it within 3%.

Side note:  The TriStar has optical isolation on the RS-232 port which is self-powered via the external RS-232 connection (they steal power from DTR and/ or RTS).  I had good results using a Keyspan 19HS adapter, but when I tried another no-name one things would not work.  Not only does there need to be a connection on DTR and/or RTS, but it must be sufficient 'voltage' to power to optical isolation.  Many lower-cost RS-232 dongles may have the signal, but skimp on the voltage - trying to get by with just 5v from the USB connection.  I have always had good luck with the Keyspan 19HS, it is kind of the golden-standard of the industry.

See a bit more here:
     or here:

This will be interesting to see how things progresses over the summer.  I will add a ‘Solar Ah produced’ row to the month ‘Costs’ summary.  Keep an eye there!

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