Tags: performance data

06/26/11

  08:10:00 am, by Jim Jenal - Founder & CEO   , 400 words  
Categories: All About Solar Power, Solar Economics, Residential Solar

Micro-inverters: Are They Worth the Cost?

Last June we reported some preliminary performance data for three of our installed systems that use Enphase Micro-Inverters to try and answer the question, Do Micro-Inverters Really Make a Difference?  That continues to be a popular post so we wanted to update our results to show you a full year’s worth of data - and the answer is still YES!

We started with the output data from the CSI calculator to estimate what the monthly yield would be for each of these three systems. After all, that is the estimate that the utility is relying upon to determine your rebate so we consider it a reasonable baseline estimate. However, the CSI calculator does not take into consideration any performance improvement factor for micro-inverters.

Year's worth of Enphase micro-inverter performance data for three Run on Sun solar power systems

We then took the daily output for each system - easily available thanks to the Enphase Enlighten website - and compared monthly totals to the CSI predictions.  The results are summarized in the table above.  All together, the three systems experienced a combined yield of 15.6% above the CSI predictions.  The individual systems ranged from an annual increase of 5.1% to a whopping 28.5%.  All three systems had individual months where the yield improvement exceeded that overall yield, whereas two systems experienced months where yield was below predictions - mostly likely due to weather impacts.

We have also included the averaged shading percentage from the CSI/Solar Pathfinder data and it is interesting to note that the highest yield improvement did not correspond to the system with the greatest degree of shading.  (However, the system with the least shading did have the smallest yield increase which would be expected.)  Why would that be if shading is what drives the performance improvements?  We believe that the difference is in the type of shading.  System 2, even though it has the highest degree of shading, has long periods of time when no portion of the array is shaded at all.  Thus its performance during those periods is comparable to what would be seen with a string inverter, and it therefore experiences a more modest - but still robust - yield improvement.

The bottom line here is that for a relatively modest increase in price over that of a string-inverter system, these three systems show substantial, real-world performance improvements thanks to using micro-inverters.  When we do a solar evaluation at your home, we will be able to let you know which type of system makes the most sense for your site.

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

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