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Try Doing That with a String Inverter!

08/27/13

  12:48:00 pm, by Jim Jenal - Founder & CEO   , 552 words  
Categories: Residential Solar, Ranting

Try Doing That with a String Inverter!

There is a vigorous debate among solar installers about the relative merits of microinverters, such as those made by Enphase Energy, versus those of string inverters, such as those made by SMA. We can’t claim that we have resolved that debate once and for all, but our experience this past week reaffirms our confidence in the microinverter choice.

Almost exactly a year ago we did a residential installation at a seriously shaded site.  We explained in detail to the homeowners about the reduced yield that any solar power system would provide given just how much shading they had, but they were still eager to press forward.  The shading mandated that we use microinverters, and they were excited to see how their system would perform using the Enlighten monitoring system.

In addition to the shading, there was another limitation - a 150 Amp service meant that we couldn’t install as big a system as they needed.  However, they were about to embark on a six-month renovation of the home and as part of that they were going to upgrade the service.  We decided to build the first half of the system right away and include the additional infrastructure that would be needed for the later addition - down to the standoffs on the roof.

Here’s how the install looked a year ago:

First phase of project completeAs you can see from the photo, there really is substantial shading present - and you can also see our Unirac standoffs waiting for Phase II.  Sitting on top of those Enphase M215’s are LG 250 Watt solar modules - our preferred product at that time.

Fast-forward to this past week.  We are still using M215’s but LG has moved up the curve and the new modules for the second phase of this project are 280 Watts each.  The homeowner wanted the higher power modules incorporated into the existing system, and they wanted them installed not on the open bottom row, but wherever they would be able to get the greatest amount of sun to maximize their return on investment.

The first great advantage of having microinverters on this project then was the ability to combine significantly different power modules into the same array.  But the second goal - placing the new modules in the ideal locations - was one that we could only solve with confidence thanks to the Enphase Enlighten data.  Indeed, all we had to do was go to the monitoring page for this site and request the display of lifetime energy.  Here’s how that looked:

lifetime energyNow isn’t that interesting?  There is a huge difference going from the NW corner down to the SE.  Overall, taking the top row along with the three west-most modules from the second row seemed like our best plan.

Here is how the expanded array looked after we completed the install:

expanded arrayPretty easy to see where the new panels were installed - they are the bright shiny ones!  (The break in the bottom row is to avoid the utility service mast.)

Here is how the new system performed yesterday (after the old panels were cleaned!):

yesterday's energy yieldOur higher power modules are installed in the optimal locations, thanks to the ability to mix and match modules in the array, combined with the ability to know at the module level where are our best performing slots in the array.

Trying doing that with a string inverter!

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Jim Jenal is the Founder & CEO of Run on Sun, Pasadena's premier installer and integrator of top-of-the-line solar power installations.
Run on Sun also offers solar consulting services, working with consumers, utilities, and municipalities to help them make solar power affordable and reliable.

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