Enphase center feeding

[DaylanDarby]

Enphase recommends center feeding (installing the junction box mid-span) to reduce Voltage Rise/Drop. I plan on 44 M215's 17,17,10 and splitting the 17's at 10 (and not splitting the 10) to match their recommendation. This will drive up my cost a little bit (slightly longer runs in the attic) and having the junction boxes hidden beneath the panels (harder to get to and having to complete the electrical before the panel installs).

Has anyone split their trunks? Did you feel it was worth it? Anybody not split their trunks and regret it?

Thanks in advance for any wisdom on this topic.

[Volusiano]

Why are you using microinverters? Do you have shading issues?

How hot is it in the summer where you live?

[DaylanDarby]

Why are you using microinverters? Do you have shading issues?

How hot is it in the summer where you live?

I initially designed for a central inverter but after doing further investigation decided that M215s were a better deal ASSUMING warranties were a valid indicator of life expectancy (meaning I'd have to replace a central after 10-15 years, but probably not the M215 over the life of the panels). If I remember correctly the material cost numbers slightly (2-5%) favored the central inverter, however A) I could not find a method to design the strings to pack a maximum (44) number of panels on the roof, B) the left/west most 4-8 panels will experience shading during the late afternoon, C) I like the idea of monitoring individual panels and D) I'll be doing the install myself and assume the M215s will be easier to install and have to pay the electrician less. The M215s were a natural fit for the 17,17,10 spacing I have available.

The average highs for July are 91 (but in years past there has been summer weeks exceeding 100).

Are there other considerations I should understand to convince me to go with the central inverter design?

[Volusiano]

I initially designed for a central inverter but after doing further investigation decided that M215s were a better deal ASSUMING warranties were a valid indicator of life expectancy (meaning I'd have to replace a central after 10-15 years, but probably not the M215 over the life of the panels). If I remember correctly the material cost numbers slightly (2-5%) favored the central inverter, however A) I could not find a method to design the strings to pack a maximum (44) number of panels on the roof, B) the left/west most 4-8 panels will experience shading during the late afternoon, C) I like the idea of monitoring individual panels and D) I'll be doing the install myself and assume the M215s will be easier to install and have to pay the electrician less. The M215s were a natural fit for the 17,17,10 spacing I have available.

The average highs for July are 91 (but in years past there has been summer weeks exceeding 100).

Are there other considerations I should understand to convince me to go with the central inverter design?

Yes, you should google up and read The Great MicroInverters Debate to understand the pros and cons of all 3 options (string vs micro vs optimizer). If you don't have shading issues, going with microinverters may give you more trouble than it's worth. The optimizer approach is a compromise where only optimizer circuitries are on the roof, but they still all feed into their own string inverter on the ground.

I've heard that Enphase 215 micros have been unreliable. The 250 are supposed to be better, but the jury is still out because it's only been around for a short time, and did you know that Enphase has dropped labor warranty on their new inverters? That tells you how little confidence they have with the reliability of their microinverter approach. You'll potentially have 44 multiple points of failure cooking day in day out on your hot rooftop in the summer. And each time there's a failure (and it won't happen all at once, that means up to 44 different times), you'll have to go up on the roof and unravel your array to get to the bad microinverter, with no labor cost covered by any warranty. With the string inverter, at least there's only 1 or 2 down on the ground where it's cooler (hopefully you put it on an east facing wall or somewhere with shade) and very easy to replace.

The SolarEdge optimizer approach at least only puts the optimizer circuitry on the hot roof, leaving their own string inverter still on the ground. And at least from what I know, SolarEdge has labor warranty included for their optimizers.

You said you're not sure how to design your configuration of 44 panels for a string inverter. Well, SMA has their own Sunny Design website for their solar design tools where you can go on there and input your panel configuration and try out different scenarios with their various sized inverters to see which inverter is best fit for your configuration. I have 44 250W panels and I use 1 Sunny Boy 7K and 1 Sunny Boy 4KTL and this works just fine for me. I can potentially add 12 more panels to these 2 inverters and still have an energy usability factor close to 100 in my case. You can get help from SMA on how to design your system with your panels' configuration on the Sunny Design website if you get stuck, too.

[DaylanDarby]

Yes, you should google up and read The Great MicroInverters Debate to understand the pros and cons of all 3 options (string vs micro vs optimizer). If you don't have shading issues, going with microinverters may give you more trouble than it's worth. The optimizer approach is a compromise where only optimizer circuitries are on the roof, but they still all feed into their own string inverter on the ground.

I've heard that Enphase 215 micros have been unreliable. The 250 are supposed to be better, but the jury is still out because it's only been around for a short time, and did you know that Enphase has dropped labor warranty on their new inverters? That tells you how little confidence they have with the reliability of their microinverter approach. You'll potentially have 44 multiple points of failure cooking day in day out on your hot rooftop in the summer. And each time there's a failure (and it won't happen all at once, that means up to 44 different times), you'll have to go up on the roof and unravel your array to get to the bad microinverter, with no labor cost covered by any warranty. With the string inverter, at least there's only 1 or 2 down on the ground where it's cooler (hopefully you put it on an east facing wall or somewhere with shade) and very easy to replace.

The SolarEdge optimizer approach at least only puts the optimizer circuitry on the hot roof, leaving their own string inverter still on the ground. And at least from what I know, SolarEdge has labor warranty included for their optimizers.

You said you're not sure how to design your configuration of 44 panels for a string inverter. Well, SMA has their own Sunny Design website for their solar design tools where you can go on there and input your panel configuration and try out different scenarios with their various sized inverters to see which inverter is best fit for your configuration. I have 44 250W panels and I use 1 Sunny Boy 7K and 1 Sunny Boy 4KTL and this works just fine for me. I can potentially add 12 more panels to these 2 inverters and still have an energy usability factor close to 100 in my case. You can get help from SMA on how to design your system with your panels' configuration on the Sunny Design website if you get stuck, too.

Thanks Volusiano. I revisited the SMA website (it still had my plans) and saw where I gave up in frustration: I was trying to cram all 44 panels into a single inverter. I was able to mimic your selections (with my preferred 245W panels) and got the design to work. For anybody that reads this: It is okay to design to multiple inverters! I'm still worried about my shading issues (left/west 4-8 panels), so I'll also study the SolarEdge solution.

[Volusiano]

Thanks Volusiano. I revisited the SMA website (it still had my plans) and saw where I gave up in frustration: I was trying to cram all 44 panels into a single inverter. I was able to mimic your selections (with my preferred 245W panels) and got the design to work. For anybody that reads this: It is okay to design to multiple inverters! I'm still worried about my shading issues (left/west 4-8 panels), so I'll also study the SolarEdge solution.

If you are going to go with the SMA option, pay attention to the minimum DC and startup voltage. The 4000TL-US has a lower min/start DC voltage compared to the 4000-US, while the 7000-US has a lower min/start voltage compared to the 7000TL-US.

Generally, while a TL is more desirable because it's a newer and transformer-less design, a lower startup voltage is also desirable because that means that your inverter will be turned on sooner if the startup voltage is lower, hence producing for a little longer in the day.

The 4000TL-US is a no-brainer choice over the 4000-US because it's TL, has the lower startup voltage (125Vmin/150Vstartup on TL compared to 250Vmin/285Vstartup on 4000-US), and also has the SPS feature (secure power supply).

The choice between the 7000TL-US vs 7000-US is a little tougher. The TL is nice, but it has a higher min/startup of 345Vmin/360Vstartup compared to the 7K-US of 250Vmin/300Vstartup. My installer went with the 7000-US for me, partly because the 7000TL-US wasn't available in the US at the time, but also because it has a lower min/startup voltage.

[silversaver]

If you are going to go with the SMA option, pay attention to the minimum DC and startup voltage. The 4000TL-US has a lower min/start DC voltage compared to the 4000-US, while the 7000-US has a lower min/start voltage compared to the 7000TL-US.

Generally, while a TL is more desirable because it's a newer and transformer-less design, a lower startup voltage is also desirable because that means that your inverter will be turned on sooner if the startup voltage is lower, hence producing for a little longer in the day.

The 4000TL-US is a no-brainer choice over the 4000-US because it's TL, has the lower startup voltage (125Vmin/150Vstartup on TL compared to 250Vmin/285Vstartup on 4000-US), and also has the SPS feature (secure power supply).

The choice between the 7000TL-US vs 7000-US is a little tougher. The TL is nice, but it has a higher min/startup of 345Vmin/360Vstartup compared to the 7K-US of 250Vmin/300Vstartup. My installer went with the 7000-US for me, partly because the 7000TL-US wasn't available in the US at the time, but also because it has a lower min/startup voltage.

Yes, you get good and bad side of each. TL will yield better efficiency than the US model but with higher min voltage required to start up the inverter. Because of min voltage required, not many installers favor of the 6000 to 12000 TL model, they are harder to design the arrays of it requirements. I remember in the early morning looking at my 6000TL-US trying to start up, you can heard the sound of internal (jumper or switch) turn on. You might lost few hundred Watts in that short period of time, but you generated more power during solar production. The TL runs much cooler