Roof-mounted micro inverter VS wall-mounted string inverter
A failure of a roof-mounted micro inverter requires a much larger effort to replace, compared with a wall-mounted string inverter. I expect the cost differential in labor to replace a roof-mounted micro inverter vs. a wall-mounted inverter would be substantial. This may factor into the overall system availability if a homeowner opts to not replace a single failed micro inverter right away.
I have also heard the opposite case to hold true for certain (primarily government) installs where the budget to purchase the PV system is available, but the budget for O&M down the road is zero. In this case, it is expected that the system output degrades gradually over time with individual component failures, versus a complete system failure should a central inverter fail with no budget for repairs.
I do find this installer's claims of having failures on 100% of their installed microinverter systems to be hard to believe. This seems like an outlier to me, not in line with anecdotal evidence that I am hearing from other installers. However, I'm not an expert in reliability, so I'm not going to get into it.
I would like to point out that evidence does exist for performance improvement under shaded conditions, be it from nearby trees or adjacent chimneys. A rule of thumb that I've seen from a number of simulations and real-life conditions is that per-panel MPPT solutions tend to recover 20%-30% of the losses due to shading, relative to a string inverter with single MPPT channel. For instance, I'm seeing 4-5% more power on an annual basis from a PV system that was measured to have 20% annual shade loss using a SunEye imaging device.
I'd also like to point out that ways exist for string inverters to reduce the impact of shade as well, including utilizing multiple MPPT channels or stringing panels in a single long string vs. parallel strings, where possible.
I have also heard the opposite case to hold true for certain (primarily government) installs where the budget to purchase the PV system is available, but the budget for O&M down the road is zero. In this case, it is expected that the system output degrades gradually over time with individual component failures, versus a complete system failure should a central inverter fail with no budget for repairs.
I do find this installer's claims of having failures on 100% of their installed microinverter systems to be hard to believe. This seems like an outlier to me, not in line with anecdotal evidence that I am hearing from other installers. However, I'm not an expert in reliability, so I'm not going to get into it.
I would like to point out that evidence does exist for performance improvement under shaded conditions, be it from nearby trees or adjacent chimneys. A rule of thumb that I've seen from a number of simulations and real-life conditions is that per-panel MPPT solutions tend to recover 20%-30% of the losses due to shading, relative to a string inverter with single MPPT channel. For instance, I'm seeing 4-5% more power on an annual basis from a PV system that was measured to have 20% annual shade loss using a SunEye imaging device.
I'd also like to point out that ways exist for string inverters to reduce the impact of shade as well, including utilizing multiple MPPT channels or stringing panels in a single long string vs. parallel strings, where possible.
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