This week I was writing a company profile for SolarBridge that will be included in the Cleantech edition of the 2012 VDC “Fast Forward-Insights for Leaders” series of reports. SolarBridge is a start-up company that makes microinverters for solar panels. Microinverters are a very interesting product and can enable solar panel installations in places that would have marginal or negative ROI otherwise. As a result, they will likely increase the market for residential solar panels.
What are Inverters?: Before we begin, it is worth taking a quick look at what an inverter (micro or otherwise) does. A solar panel outputs a DC voltage. To be able to use the power generated by the solar panel installation at the residence and/or output it to the grid, it needs to be converted to a set AC voltage. This means that the output from the solar installation is the correct frequency (50 or 60Hz.), and is in phase (i.e. synchronization) with the grid. This conversion process is performed by the inverter.
What are the Challenges?: Many embedded and/or residential sites that could potentially be used for solar panels have problems in that shadows from trees or rooftop items fall across the panels during the day. When a centralized (single) inverter is used in an installation, any shadows or obstructions on a single panel will reduce the effective output from all of the panels. This is not unlike having a bad battery mixed in with good ones in a flashlight. Because of this problem, the efficiency of the entire installation is based on the lowest common denominator from each of the individual panels and that often makes the site economically unsuitable.
What is the Main Benefit?: If microinverters are installed on each solar panel they become independent from each other. This is to say that each panel in the installation drives the grid at the maximum efficiency it is capable of at a particular moment given sunlight and shadows/obstructions. This is the main benefit derived from microinverters as they make many residential sites viable for solar panel installations.
Other Benefits: There are other benefits to microinverters in that all of the solar installation’s power wiring and connections are standard AC voltage and current. This makes installation much less complex. With centralized inverters, there are high voltage DC connections and wiring that require specialized components and installation expertise. Lastly, if a centralized inverter fails, the entire installation goes down whereas a microinverter only takes a single panel down.
Potential Microinverter Problems: VDC believes that there are a few potential issues that can interfere with widespread market adoption of microinverters. The major ones are as follows:
Reliability: A centralized inverter is often installed indoors, near the main electrical panel where a microinverter is located on the solar panel. This means that the microinverter typically is located in a much more severe environment. Obviously, the microinverter companies such as SolarBridge, Enphase Energy, and Power-One have taken this in account with their designs that eliminate components such as electrolytic capacitors and in some cases, are offering 25-year warranties. The question that remains is whether the company in question would be in business to support this kind of warranty. This problem would be addressed if a large conglomerate such as ABB, Emerson, GE, or Siemens stepped in and acquired the microinverter supplier.
*Panel Supplier Issues: VDC believes that there can be some business and technical issues for a panel supplier that chooses to sell panels with the microinverter integrated to the panel in the factory. The optimal time to integrate the microinverter is likely before the final assembly. Unfortunately this may interfere with the final test process where the finished panel is typically flashed with a calibrated light source to have its output measured. As a microinverter may not be capable of responding quickly, it can interfere with or, at a minimum, complicate this process. From a business perspective, supplying both integrated and standard solar panels will increase channel inventory. For these reasons, VDC believes many panel suppliers will look for field installation module/kit solutions.
Safety: VDC believes that one of the biggest features with solar panels with integrated microinverters is their less complicated installation. Unfortunately, this feature could enable situations especially in the residential market where consumers and/or less qualified service people install them incorrectly. If, for example, multiple panels were plugged into electrical outlets, they would pretty much work by powering up the house circuits and reducing power supplied from the grid. Unfortunately, if there were a power outage or a service situation where power is supposed to be off, the incorrectly installed/configured solar panels might create unsafe conditions in the house or even on power lines in the street. This could leave solar panel and/or microinverter suppliers exposed to lawsuits. This problem would be less likely to be seen in the embedded market.
In conclusion, VDC believes that microinverters will be a very important part of cleantech as they will enable solar panel installations in less than perfect locations. In general, the benefits greatly outweigh the problems and, as these microinverters prove their reliability claims, they will win increased acceptance in the market.
*Note: Special thanks to persons at Spire Solar who provided guidance and insight to VDC with respect to solar panel manufacturing processes and microinverters in general.