Enphase M215 vs M250

What is the right size Micro-Inverter?

The M215 will handle a panel up to around 275W, and even then the inverter isn’t stretched or over-worked, it will just clip some of the output on those few occasions where the panel is performing at its peak output.

In our experience (and backed up by our monitoring of customer’s production data), we have found that a system using, say 265W panels, achieves more generation and yield with an M215 micro-inverter than with an M250 microinverter. This may sound counter-intuitive, however, the reason is the increase is achieved by having a better panel to inverter ratio – where in a perfect world, the panel output should be in excess of the inverter output.

This notion is also confirmed by data and analysis from Enphase. Enphase state that it isn’t until the DC to AC ratio increases beyond 140% (more than 300W!) that losses begin to exceed additional gains:

“annual losses to inverter saturation increased geometrically with module size, and at a certain point, the marginal losses would begin to exceed the marginal gains. This crossover typically occurs above 140 per cent DC-to-AC ratio.”

“Through real-world testing, Enphase has shown that when using larger modules on the M215 Micro Inverter, annual output losses are less than 0.5% on panels up to 275W

“Overall, annual losses to inverter saturation were insignificant. In 90% of the scenarios using the M215 Microinverter, including all scenarios with module nameplate ratings below 275W, annual losses were less than 0.5 %. Conversely, increasing module size [compared to microinverter size] resulted in significant gains in annual production, even while inverter size remained unchanged.

“…applying high power solar modules to microinverters leads to greater lifetime performance, lower installed cost per watt, and ultimately, the highest return on investment for the end-customer.”

Conclusion

For microinverter systems, we recommend using the M215 inverter for panels up to 275Ws as the increased yield deliver greater benefits from the solar system. For panels from 275Ws up to 340W, we recommend the M250 Micro Inverter. The main high-efficiency panels on the market at the moment are the LG NeOn2 range.

Additional Reading

http://www2.enphase.com/global/files/Enphase_White_Paper_Module_Rightsizing.pdf