We’ve been fans of micro-inverters for awhile, especially after a frustrating winter last year in which we lost more than 200 kWh of production due to snow on our roof-mounted 5.59 kW home solar system here in Aurora, Colo.
While we wouldn’t have gotten all 200 kWh we lost as a result of our snow + central inverter set-up, it’s pretty clear we wouldn’t have lost as many kWh with a microinverter based system.
Results from a study recently released by Enphase Energy – the biggest player in the microinverter market – underscore the potential production advantage of microinverters over a central inverter based system, though, as far as we can tell, the study didn’t specifically look at snow and snow melting issues. (Hint to Enphase: Do a study that looks specifically at snow issues!)
Slow melting snow really hurt the production of our central-inverter solar system. Here, you can see several panels are completely free of snow, but several are not. Unfortunately, with a central inverter, string-based system, it is the lowest producing panels that dicate production. This is a problem microinverters allow you to avoid.
According to Enphase, the results show that Enphase installations on average outperform PVWatts by eight percent, with a majority of sites outperforming PVWatts by 10 percent or more.
A review of similar published PVWatts studies, such as the 2009 study authored by Gostein, et al., indicates that solar installations using traditional central inverters actually underperform PVWatts estimates by 8 percent on average.
When considered together, these results indicate that Enphase Microinverters can potentially improve the performance of solar installations by up to 16 percent on average.
The study examined energy production data from over 143 Enphase systems installed by Real Goods Solar, Solar Universe and Astrum Solar in California and across the Eastern U.S. This data was compared to performance forecasts generated by the National Renewable Energy Lab’s (NREL) PVWatts calculator, based on geographic location, system design factors and product specifications for each installation.
Yes, microinverter based systems might cost more than central inverter systems – although, one expert solar installer we contacted told us that in many cases there is little to no total cost difference. However, they’re clearly more efficient and yield more production
And, again, there’s the snow melting factor – or, really, in our case, the glacially slow snow-melting issue, thanks to our shallow roof pitch of 19 degrees. We so wish we had micro-inverters every time it snows and we wait, and wait, and wait for the snow to melt off that one last panel that’s severely reducing the production of an entire 13-panel string.