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Hello, I'm new to the forum but I have been following older threads for a month or two to help figure out what to install in my Sacramento (actually Sierra foothills, about 35 miles east of Sac) 2 story all-electric home. I read with considerable interest a lengthy thread comparing SunPower to SolarWorld in a San Diego application which was very helpful; however my main concern is a different one than was addressed there.
The heart of my query has to do with the shade and/or multiple roof plane management capacities of the SMA Sunnyboy TL string inverter and its "multiple MPP trackers and OptiTrac Global Peak" software, which the SMA spec sheet on this product line claims will "mitigate the effect of shade and allow for installation at challenging sites." Typically these are exactly the areas of greatest weakness for string inverter-based systems.
My house is on a hillside sloping to the east, with several different roof segments that slope at different pitches and in different directions; nowhere is the roof flat. One very large roof segment slopes mainly to the south (a little to the east) and 2 smaller segments slope mainly to the east (a little to the north). These segments are at right angles to one another. It gets hot in the summer here, with many days in the 90s and 10 - 15 days over 100 in recent years.
My roof gets direct sunlight all day long, and cloudy, overcast days are rather rare here, even before the long drought set in. However there is a 4-foot chimney on the outside edge of the big south roof that casts a shadow in a 180 degree arc throughout the day, like a big, thick, sundial pointer; I estimate that its shadow will sweep across perhaps 5-7% of the south-facing panel array, moving continually, and of course not affecting the east facing section. Other than that, there is no shading but of course the east-facing smaller sections do not receive full, direct sun in the afternoon to the same extent as the big south facing section.
I have 2 bids that I like, and the cost of each is virtually identical, with a difference of only a few hundred dollars:
1) 16 Sunpower 327 panels generating 5.23 kW with an SMA Sunnyboy 5000TL string inverter;
2) 20 SolarWorld 280 panels generating 5.6 kW with EnPhase 250 microinverters.
I need help figuring out which way to go. Here are some factors I am already weighing:
Microinverters are more efficient and are generally quite strongly preferred in applications with more than one roof plane and any significant shading, but the SunPower 327 panel does not yet have a compatible microinverter for pairing instead of the string inverter, although optimizers such as Solar Edge and Tigo can be added.
The EnPhase product is the market leader and warrantied for 25 years (as are both the SunPower and SolarWorld panels, with linear guarantees), and will combine satisfactorily with the SolarWorld 280. (I have followed discussions of whether or not the EnPhase 250 restricts the output of a SW280 panel in any significant way, and suspect that, based on what I have read, it will not; but am open to hearing divergent views based on my particular circumstances).
However it remains to be seen how this technology stands the test of time in high temperature environments, which I consider mine to be. The SolarWorld panels are slightly larger than the SunPower (40x65 vs. 41x61, I believe) and 20 of them would eat up twice the rooftop real estate on the east side of the house (with 8 panels vs. 4 of the Sunpower), but they will be effectively invisible from below so that is a very minor issue.
The SolarWorld panel is rated at 16+%, which is not especially high, although it is considered sturdy and reliable, while the SunPower is rated at 20%. Both products are warrantied to retain efficiency very well over their projected 25 year lifespan. The SunPower is known and accepted to be more or less the "gold standard" in the residential PV market and as such may hold resale value better than less well known and lower rated products that in practical terms may perform about the same.
The SunPower output may be reduced as a result of using a single string converter in my 2-plane environment with some, but very little, shading; although adding power optimizers such as the Solar Edge product is too expensive an option for me.
The question I cannot answer but hope someone here can address is how well the current line of SMA string converters including this Sunnyboy 5000TL that has been proposed for me, actually perform at optimizing string efficiency, given that they deal with inputs of 1 - 3 strings as basic units, rather than each modular panel as can be done with microinverters.
If the east-facing cluster of say 4 SunPower 327s is on one string, and the large south-facing array of 12 Sunpower 327s is split into 2 strings of 6 panels each, can the SMA TL inverter compete at all evenly with the actual efficiency of a 20-panel SolarWorld array coupled with EnPhase 250 microinverters in my specific situation? Would the actual throughput vary much in this scenario? Would there be other considerations I haven't mentioned (given that the costs of the 2 systems as described are equivalent)?
Unless there would be a significant difference between the performance of the two systems, I am inclined to go with SunPower/SMA even though that would violate the single-plane/no shading rule of string inverters. But if the penalty in lost efficiency would be too great, then it would be a mistake and I should go with SolarWorld/EnPhase, it seems to me.
Thanks in advance for any insights.
Bob
The heart of my query has to do with the shade and/or multiple roof plane management capacities of the SMA Sunnyboy TL string inverter and its "multiple MPP trackers and OptiTrac Global Peak" software, which the SMA spec sheet on this product line claims will "mitigate the effect of shade and allow for installation at challenging sites." Typically these are exactly the areas of greatest weakness for string inverter-based systems.
My house is on a hillside sloping to the east, with several different roof segments that slope at different pitches and in different directions; nowhere is the roof flat. One very large roof segment slopes mainly to the south (a little to the east) and 2 smaller segments slope mainly to the east (a little to the north). These segments are at right angles to one another. It gets hot in the summer here, with many days in the 90s and 10 - 15 days over 100 in recent years.
My roof gets direct sunlight all day long, and cloudy, overcast days are rather rare here, even before the long drought set in. However there is a 4-foot chimney on the outside edge of the big south roof that casts a shadow in a 180 degree arc throughout the day, like a big, thick, sundial pointer; I estimate that its shadow will sweep across perhaps 5-7% of the south-facing panel array, moving continually, and of course not affecting the east facing section. Other than that, there is no shading but of course the east-facing smaller sections do not receive full, direct sun in the afternoon to the same extent as the big south facing section.
I have 2 bids that I like, and the cost of each is virtually identical, with a difference of only a few hundred dollars:
1) 16 Sunpower 327 panels generating 5.23 kW with an SMA Sunnyboy 5000TL string inverter;
2) 20 SolarWorld 280 panels generating 5.6 kW with EnPhase 250 microinverters.
I need help figuring out which way to go. Here are some factors I am already weighing:
Microinverters are more efficient and are generally quite strongly preferred in applications with more than one roof plane and any significant shading, but the SunPower 327 panel does not yet have a compatible microinverter for pairing instead of the string inverter, although optimizers such as Solar Edge and Tigo can be added.
The EnPhase product is the market leader and warrantied for 25 years (as are both the SunPower and SolarWorld panels, with linear guarantees), and will combine satisfactorily with the SolarWorld 280. (I have followed discussions of whether or not the EnPhase 250 restricts the output of a SW280 panel in any significant way, and suspect that, based on what I have read, it will not; but am open to hearing divergent views based on my particular circumstances).
However it remains to be seen how this technology stands the test of time in high temperature environments, which I consider mine to be. The SolarWorld panels are slightly larger than the SunPower (40x65 vs. 41x61, I believe) and 20 of them would eat up twice the rooftop real estate on the east side of the house (with 8 panels vs. 4 of the Sunpower), but they will be effectively invisible from below so that is a very minor issue.
The SolarWorld panel is rated at 16+%, which is not especially high, although it is considered sturdy and reliable, while the SunPower is rated at 20%. Both products are warrantied to retain efficiency very well over their projected 25 year lifespan. The SunPower is known and accepted to be more or less the "gold standard" in the residential PV market and as such may hold resale value better than less well known and lower rated products that in practical terms may perform about the same.
The SunPower output may be reduced as a result of using a single string converter in my 2-plane environment with some, but very little, shading; although adding power optimizers such as the Solar Edge product is too expensive an option for me.
The question I cannot answer but hope someone here can address is how well the current line of SMA string converters including this Sunnyboy 5000TL that has been proposed for me, actually perform at optimizing string efficiency, given that they deal with inputs of 1 - 3 strings as basic units, rather than each modular panel as can be done with microinverters.
If the east-facing cluster of say 4 SunPower 327s is on one string, and the large south-facing array of 12 Sunpower 327s is split into 2 strings of 6 panels each, can the SMA TL inverter compete at all evenly with the actual efficiency of a 20-panel SolarWorld array coupled with EnPhase 250 microinverters in my specific situation? Would the actual throughput vary much in this scenario? Would there be other considerations I haven't mentioned (given that the costs of the 2 systems as described are equivalent)?
Unless there would be a significant difference between the performance of the two systems, I am inclined to go with SunPower/SMA even though that would violate the single-plane/no shading rule of string inverters. But if the penalty in lost efficiency would be too great, then it would be a mistake and I should go with SolarWorld/EnPhase, it seems to me.
Thanks in advance for any insights.
Bob
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