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 resultsto 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 estimatewhat the monthly yield would be for each of these three systems. Afterall, that is the estimate that the utility is relying upon to determineyour rebate so we consider it a reasonable baseline estimate. However,the CSI calculator does not take into consideration any performanceimprovement factor for micro-inverters.
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 awhopping 28.5%. All three systems had individual months where the yield improvement exceeded that overall yield, whereas two systemsexperienced months where yield was below predictions – mostly likely due to weather impacts.
We have also included the averaged shading percentage from theCSI/Solar Pathfinder data and it is interesting to note that the highest yield improvement did not correspond to the system with the greatestdegree of shading. (However, the system with the least shading did have the smallest yield increase which would be expected.) Why would thatbe if shading is what drives the performance improvements? We believethat the difference is in the type of shading. System 2, eventhough it has the highest degree of shading, has long periods of timewhen no portion of the array is shaded at all. Thus its performanceduring those periods is comparable to what would be seen with a stringinverter, and it therefore experiences a more modest – but still robust – yield improvement.
The bottom line here is that for a relatively modest increase inprice over that of a string-inverter system, these three systems showsubstantial, real-world performance improvements thanks to usingmicro-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.