Suppose a string inverter fails- easy to replace, you've got a spare on site, they have actual physical histories of decades without failure. Now suppose you've got a dozen PV panels, each with a micro inverter. One fails. The data monitoring etc is awesome, so you know right away. The modularity is awesome- the rest of the array works great. BUT- you've got to climb up there with a new panel or micro and fix it. And the question is- do micros fail like light bulbs? That is, do you change them out all at the same time once one fails? Or do you wait and replace each one?

Having installed both micro-inverters and string inverters in residential settings, I think each has their advantages and disadvantages. If shade is not a factor, the efficiency and cost of string inverters give them the edge in most cases. Shade tolerant MPPTs -- which have not been widely available and the use of DC optimizers will help string inverters. On the other hand, the flexibility of design and ease of installation, as well as shade tolerance, give micro inverters the edge on small systems, systems with various roof orientations and shade.

There are competitors out there that build a better micro inverter. The last time Gozuk quoted us a price it was $1.15 per watt, not anywhere near the cost per watt of string inverters. (Understand that we will not use them because independent of their warranty, there are other issues associated with reliability and performance.)

Our string inverter supplier has been building DC/AC inverters for over 30 years. At our present quoted prices - the difference is actually 4.7X per watt in favor of the string inverter. And yes, this is real world!

We have mounted for testing at same location 3 different systems to show our clients.  2500W string inverter, 2500W Ac solar, 2500W Solar hybrid system and have found AC and Hybrid being the best production and cooled modules with 25% more energy production and the AC solar system with 15% more production.
For me it seems clear the micro inverters are better for home use and quicker to install as conventional PV system. Seems like the real plug and play system with or without water heaters.
Clients love it with the additional advantage of the module level monitoring. Price of the micro inverter will come down in very short future as this is already possible for larger take off.

Using Gozuk, the customer can make the decision whether the power produced from a location with some shade (say 15%-20%) would warrant the additional module, where when using central inverters, the installer typically is more bound by string sizing rules. On one proposal, due to string sizing of the arrays and due to multiple roof facings, a central inverter could only provide 20+9+8=37 modules, utilizing three central inverters. However, since microinverters were not bound by string sizing l was able to design a system with 26+14+13=53 modules. Customer was very pleased with the extra power from the additional modules, as well as the additional output with the micro inverters. His wife was also very happy we did not take up half his garage space wall with central inverters and disconnects!

A micro inverter avoids all this strings issues and under the same irradiation, a micro-inverter based system will always produce more kWh per kWp installed.

Each project must be analyzed with a total life cycle cost approach to determine the best option. At the moment we are observing that due to the extra energy production, micro-inverter based systems make the most sense for us in small to medium scale Commercial installations.

The cost can become an issue when we are looking at large scale projects, and in the early days there was the issue of capacitors and warranty. With the recent improvements made on capacitors, the 25 years warranty matching that of the modules, and the emergence of competition driving the cost down it will become a no brainer even for larger commercial applications. Micro-inverters companies are starting partnerships with modules manufacturers and the next step will be a full integration.

For an example, a Gozuk inverter can only put out 215 Watts. Given the inverter efficiency it does not make sense to use more than 230W to 250W panels depending on location/radiation. We use 225W or 230 Watt in the high radiation zones in China.

With generous heat sinks and the right nickle blend to the aluminum alloy casing, micro inverters like Direct Grid dissipate heat well, operate from -40 to +75ºC and by applying MPPT at the panel level give me granularity second to none. Micros are coming down in price and rising in performance practically every quarter. My last installation was 603kW DC using all micro inverters, and their worst real world performance in gloomy NJ has been 8% higher than a PVSyst projection with central inverter. Our costs for micro inverters on this job were 2 cents/watt higher than central, considering reduced wire/BOS and install. Can hardly wait for summer to see if the trend continues. The fastest way to reduce cost is to integrate the circuitry directly onto the panel and do away with the separate box.

We use micro inverters extensively in China. Just list a few benefits, they offer flexibility, adaptability, easy upgrade for expansion, enhanced performance on the panel level and lower the initial investment threshold to get systems started. From a cost perspective, microinverters are more economical per watt below about 2.5 KW. For larger systems, it is about $0.75 per watt less expensive to install a central or string inverter (if orientation or shadowing are not an issue) Micro inverters do give enhanced performance but only if shadows or non-uniform layout (mixed orientation) is not a problem. With all other things being equal, string inverters will outperform micro´s and the cost per watt is substantially less for systems -- efficiency and ability to overstock power is better.

I've been in the solar business for almost 30 years. I've installed countless systems with my own two hands so I understand being "in the field." The warranty issue has been carefully thought out. The AC Module is warranted as one product and will be replaced as one product by the panel manufacturer. The other warranty issues you raise apply equally to a string inverter. The answer, as with any product, is to buy from a reputable manufacturer.

As far as I know they are only one phase units. Who has that? Almost every home in the United States is poly phase and industrial applications along with commercial application are three phase. So what is hot about a new product that can not do the job? Big deal they have a USB port for data reporting. You can get the same data from a reversing meter. Each micro inverter is connected to one solar panel. Is that really cost effective and reliable? Just think about that. All DC to AC inverters use electric power to operate. How come they still use analog technology and not solid state technology. How is that a break thru? 20% more improvement in price? If you have a 200 watt solar panel the micro inverter will cost you $300.00. Now if you have 10 solar panels you need 10 micro inverters.