Maximizing Residential Solar Panel System Performance


microinverter

We recently attended the Intersolar North America conference in San Francisco and spent some time talking with installers, distributors, and manufacturers about ways to maximize system performance for residential solar energy installations.

When it comes to shading, residential solar installations tend to be more affected than utility scale or commercial scale installations.  Whether it’s a tree branch, bird droppings, dirt, or a Frisbee, once a panel is partially covered its performance drops dramatically.  With a traditional solar installation once the performance of one panel drops, the rest of the panels are brought down to its level.  It’s a very real example of a chain only being as strong as its weakest link.

However, as we learned during our prior interview with eIQ Energy, there are several new approaches to ensuring that the rest of the solar array continues to perform at its maximum ability even if one or several of the panels are shaded.

Lets look at the example of having five 100 watt panels with one performing at 50% of it’s capacity due to shading.  In a traditional installation all 5 panels would be bought down to 50% of capacity which would mean 5 panels x 50watts = 250 watts.  However, using a microinverter or a parallel boost technology only the one shaded panel would be impacted.  So you’d have 4 panels x 100 watts + 1 panel x 50 watts = 450 watts.  Huge increase over the 250 watt outcome.  (I realize 100 watt panels are not typically used for residential installations, but they do make for easy math in examples)

I’ve now heard of three ways to get this same effect (450 watts rather than 250):
Enphase’s microinverters, eIQ’s parallel vBoost, and Tigo Energy’s Module Maximizer.  From the conversations we had, this is my understanding of the pros and cons of each.  I’m sure there are additional pros and cons or each approach, but I wanted to get the conversation started with these:

Microinverter
Tigo Energy Module Maximizer
eIQ Parallel vBoost
Pro
  • Maximize output per panel
  • Should last longer than traditional inverters, possibly even as long as the panels
  • Installers are only dealing with AC current
  • Ok if you to mismatch and/or add panels in the future
  • Maximizes output per panel
  • Very simple device – no real electronics to fail
  • Comes with great online monitoring capabilities
  • Maximize output per panel
  • Gives design flexibility
  • Can mismatch panels
  • Helps central inverter last longer
Con
  • Puts complex electronics on the roof under the panels where it is less accessible (vs at ground level in a main inverter)
  • Relies on a central inverter which may still need to be replaced after 10-15 years.
  • Relies on a central inverter which may still need to be replaced after 10-15 years.

At the end of the day all 3 options help maximize the system performance which is the goal.  I believe all also now offer good monitoring options.  However, what we don’t know is how each will perform over the life of an installation.  Initial tests look good, but until a micro-inverter is on a roof for 25 years we won’t know how they perform over that timeframe.  Similarly, we won’t know if eIQ’s parallel vboost really does help a central inverter last longer until they’ve been in use for 15 or 20 years.

Installers, are you selling any of the three I listed, and if so, which do you prefer and why?  And which have you had the most success with?  Additional pros & cons?  Or, are there other approaches you’re using to ensure maximum system performance?

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