Analysis of Enphase Microinverter Failure Rates

I recently conducted an interview with Enphase, which you can watch here:

In that video, a failure rate of 0.05% was mentioned. This failure rate was also quoted back in 2021 by their CEO here.

The question is: What does that mean in reality? This is especially relevant for someone looking into purchasing an Enphase microinverter solution who wants to understand the financial implications of any unit failures over a 25-year lifetime.

My Analysis

So, I thought I'd enlist ChatGPT to help me turn that figure into something more realistic. I started by giving it this prompt:

“A unit has an expected lifetime of 25 years and a known average failure rate of 0.05% every year. What is the probability of a 10-unit system not failing over 25 years?”

This gave an answer of 88.25%. That means after 25 years, there's only around a 1 in 10 chance that you'll experience a failure - that's pretty good odds if you ask me! Remember that's after a whole 25 years of operation...

And of course, if a unit were to fail duirng that time, you'll only lose a small percentage of your overall generation - and only if you choose not to get the failed unit replaced.

But actually, there's more to it. Enphase said the failure rate is not uniform, with the chance of failure being higher in the first 2 years due to infant mortality. Because of this, their reimbursement policy is designed to cover such early failures. So, we could maybe skew the calculation slightly, like so:

“What if the chance of unit failure was far greater in the first two years than the remaining 23 years - say 5 times greater? Assuming the system was still working perfectly at the end of 2 years, what is the chance that it will still be working perfectly at the end of 25 years?”

The answer this time was 92.78%. What that means to me is that if all the units are still working after 2 years, then the chance of you getting any kind of failure then on is only about 1 in a 14 - pretty good odds!

My Conclusion

So, if it were me, I would simply get an agreement from the installer that they will pay for any unit failures in the first 2 years only, then I can relax... :-)