In Solar Power World’s recent webinar, “How to Choose and Care for Your Solar Inverter,” J.S. Roy, VP of solar development at Beacon Power Services, discussed the two types of module power electronics, microinverters and DC optimizers, and how each affects operations and maintenance.
J.S. Roy, VP of solar development at Beacon Power Services.
Microinverters take the direct current from the back of the solar panel and convert it to alternating current. DC optimizers take DC coming from the back of the solar panels and convert it to DC at a higher voltage. For example, 30 to 35 volts DC will be converted to around 350 volts DC. That higher DC voltage will then be put into a standard or proprietary inverter, depending on the technology, allowing that particular inverter to reach those higher peaks of efficiency.
Operations and maintenance for micorinverters and DC optimizers can be thought of in three separate components: monitoring, preventive maintenance, and unscheduled maintenance. The monitoring piece pulls information from the system. Preventive maintenance is the standard schedule to verify that everything is working as expected; it can happen bi-annually, semi-annually, or annually, depending on the location. Unscheduled maintenance occurs when there’s a fault or error within the system. In this case, there’s nothing else to do but send someone out to figure out the issue and fix it.
Each solar panel of a module level power electronic displays what it’s putting out. If, for example, 29 out of 30 panels are putting out 200W, and one panel is only putting out 100W, the display tells you exactly where the fault lies. There’s no need for a weather station; simply compare each of the panels against each other.
From the monitoring point of view, the best thing to have is data, data, and more data. Most module level power electronics come with their own monitoring system and website path that helps process the data. Going through all that data gets a little challenging at times, but it does help having all that data for monitoring.
There’s little to no preventive maintenance, depending on which technology is used. The newer microinverters require no preventive maintenance because they are potted, meaning all the electronics are sealed and they can be operated with the case removed. There are no replacement parts, no fans, and no filters; there’s nothing that needs to be inspected.
With DC optimizers, on the other hand, there is still some maintenance regarding the inverter that takes the boosted DC voltage down the trunk lines and converts it to AC. Thus, the DC optimizers themselves have not maintenance (they are potted like the microinverters), but the inverter itself has fans and other parts to inspect.
Of those issues pertaining to unscheduled maintenance, a single fault has little impact on the overall system and overall system production. Every solar panel is essentially independent and will produce solar power independently. For instance, if you have a system with 100 solar panels and one of them has an issue, you’re only down 1%; it’s not a significant impact.
At the end of the day, you have to ask yourself one question: Is the ease of operation worth the added up-front cost? For some systems it makes sense; for others it doesn’t. A few years ago the cost gap between using string inverters and central inverters versus module level power was substantial. Now that cost is somewhat reduced.
Another thing to take away is how maintenance of the module level power electronics is slightly different than string or central inverters. Use the large amount of data gathered from these systems to tailor your maintenance strategy for a system that will allow you to deliver high customer service and high system output at a low cost.
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