Thursday, November 13, 2014

Enphase and SolarEdge

The most popular microinverter and the most popular DC optimizer butt heads a lot in the current solar market.  Both are panel-level MPP trackers that maximize individual panel yield.  Both make the array more resistant to shading and panel mismatch.  And both are fully compliant with the latest Rapid Shutdown requirements for solar systems.

So, what should you use, savvy solar installer?

I can't speak for financials personally, but from a pure technical standpoint I know what I would put on my roof, and it's all AC baby!  Enphase would be my choice for a residential system, and I base that decision on ease of install, system reliability, and annual energy production.

Installing Enphase means mounting microinverters to your solar racking system and running AC trunk cable to a junction box where it transitions into a raceway.  The trunk cable is outdoor rated and extremely robust, and comes included with every Enphase system.  Solaredge's procedure is similar, but there is one tradeoff.  While they don't run an AC trunk cable at the array, they still have to use a junction box to transition into a raceway.  Additionally, a SolarEdge system has to use a string inverter to manage the optimizers and create AC power, since they only do a DC-DC power conversion.  Without a string inverter to mount, Enphase has a clear advantage over SolarEdge on ease of install in residential systems.

System reliability is hard to compare without having long-term hands-on experience with both systems.  When you are mounting a small power electronics box under each panel for each system, it's a wash, and each system features a 25 year warranty.  However, there is one key difference between Enphase and Solaredge that makes Enphase more reliable, and that is the single point of failure in the SolarEdge string inverter that is required on every system.  Enphase doesn't have a single failure point in it's system, but with SolarEdge if the inverter fails the entire system goes down.  Additionally, the SolarEdge string inverter only has a 12 year warranty, which points to it failing more often than microinverters or optimizers.

Annual energy production is the easiest thing to compare, especially if actual site data is available. Thankfully, we have such data in a study by PV Evolution Labs, a 3rd party testing agency in California.  The study concludes that Enphase systems produced at least 2.4% more energy on a kWH per installed kWP basis.  To confirm their results, I created a PVSyst simulation to compare the two systems (available upon request).  The difference in production between the two systems? 2.4%!  In searching for alternative test data, I found an older test by SolarEdge that compared it to SMA and Enphase under shaded conditions, but the results mainly focus on how SolarEdge outperforms SMA, not Enphase which is almost identical in their results.

I'm doing my homework and I keep coming up with Enphase microinverters as the superior panel-level MPPT solution, especially for residential systems.  The SolarEdge system is not without its benefits, but it's single failure point and added labor on string inverter installation make Enphase the optimal choice.