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Micro Inverters vs String Inverter vs Power Optimizing

asked 2014-07-18 17:50:13 -0500

ereeder gravatar image

updated 2014-07-19 18:03:39 -0500

It appears that Micro Inverters have significant advantages over a single String Inverter. The only Micro Inverter disadvantages I've heard are cost and perhaps some lost efficiency due to voltage drops for "large" systems (whatever large means).

I'm curious why the Power Purchase Agreement folks I've spoken to have proposed String Inverters?

I'm thinking of an outright purchase of my system and to me it seems like Micro Inverters have the advantage.

An additional comment. I just got a recommendation from an installer for Solaredge inverters. He said that their power optimization capabilities and lower cost make them much more attractive than micro inverters. There is an that article addresses the issues but I can't post the link, so search for "To Microinvert or To Power-Optimize, That Is the Solar Question", but I don't know who to believe.

FWIW - I'm looking at a 9.7 kw system.

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answered 2014-07-22 16:11:27 -0500

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updated 2014-07-22 16:11:27 -0500

john gravatar image

Hi, great questions! Some PPA providers do offer micro-inverters. Micro-inverters are more expensive and have less of a long-term track record, so for some investors in PPA financing, this poses a risk and makes these projects less "bankable." From my perspective, panel-level power management is optimal as it helps to mitigate the impacts of shade from trees or other structures, but also from clouds. Panel-level power management would include both micro-inverters and the optimizers your refer to. The power optimizers have some of the benefits of micro-inverters without the added cost, making them more scalable financially for a system of the size you are considering. Every installer will have different pricing, so it's hard to make a blanket statement. Since there is not much in the way of 3rd party testing, I would review the websites for each product, consider the price differences and make a call. At the end of the day, the production difference will be a few percentage points, so hopefully not hugely material in the long run. I think you will happy with either option!

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answered 2014-09-16 22:05:42 -0500

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updated 2014-09-16 22:05:42 -0500

Power optimizers and micro-inverters are great because you can usually view power production from every panel and if there is a problem with a panel, you can easily see and identify which panel needs maintenance.

As an installer, I like running AC romex (flexible multi-wire cable) which is allowed in a house with micro-inverters, much better than running metal conduit which is required for DC systems.

With Solar Edge optimizers, you can have a larger number of panels per string and can often run one set of three wires because the voltage is higher (Solar Edge sets the optimizers at 350 volts) and the amps are lower, rather than running five wires from two strings. Basically, you save on work and wire with their system.

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answered 2014-09-25 15:43:48 -0500

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updated 2014-09-25 15:43:48 -0500

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.

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answered 2014-12-12 14:32:44 -0500

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updated 2014-12-12 14:32:44 -0500

We have been installing micro-inverters for some time now. We believe it is the best technology and not only brings better output & Warranty it is also safer. The most common question I've heard is that there are multiple points of failure with micro-inverters. This is true but a single point of failure and only a 10 year warranty on your string inverter should give you pause. Who is going to pay for the replacement and labor in year 15. Add the optimizers and now you have a single point of failure coupled with multiple points of failure. Adding more components doesn't seem to be the answer to me. Installers like the optimizers because they give the appearance of micro-inverters at a lower price point. If you want the best system and a warranty that matches your panels - choose EnPhase (25 years) for your project. We've been installing them since 2009/2010.

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Asked: 2014-07-18 17:50:13 -0500

Seen: 2,035 times

Last updated: Sep 09 '16