2014-09-25 15:43:48 -0500
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Prospective from a designer/installer/service technician/consultant
String inverter- you'd better have a great monitoring service/company that will have their best interest in mind - hence a PPA or a lease. This is of course if the solar access is perfect. Otherwise, string inverters aren't really scalable. Shading is really tricky and not for the best. Performance is great, but warranties aren't quite there. Future expansion is very limited
Micro-inverters - While I've had my brushes with a few manufacturers, Enphase seems to have the best platform (IT). When a failure occurs, the failure is isolated to a single point of failure as opposed to string inverters. Their responsiveness to service and RMA units is great. They've proven to hold up their end and for a service contractor, it's a great deal! They keep us busy and for the end user- the production is all there. Future expansion is easy and highly expandable but has it's limits in regards to circuit ampacity overload and interconnection, i.e- you may need to add space for a new circuit in your service panel, this could mean a service upgrade.
Optimizers - This seems to be a favorable choice amongst designers and estimators. It's certainly a more affordable way to sell top notch performance. Module level monitoring is KEY! My only concern is that if/when a single optimizer fails, will that bring down an entire string? I haven't witnessed this first hand, but that's a good thing. They don't fail to often due to the fewer amount of electrical components within the casing. Future expansion is somewhat limited, but if designed properly, you could add up to 5-6 panels without having to add an extra inverter and upgrading the main service panel.
Choosing the right inverter technology to fit your needs is just as important as choosing an engine for a car. It drives your needs and those needs need to be reliably fulfilled. It's the single most important decision in a system's design.