SMA inverters: Better reliability but no panel level monitoring. Good tradeoff?

[J.P.M.]

Great to learn! Can it help me get a more accurate sense of what my estimated output might be (annually?). I'm seeing discrepancies in the estimated annual output for my proposed rooftop system, even with similarly sized systems, with panels all tilted similarly and on the same 200 azimuth. PVWatts seems to be higher than Aurora. I get no shading so not sure why this difference exists.
PVWatts has "System Losses" as one of its factors and has a default of 14%. Is that a realistic estimate? Dropping that to 10% raises the output quite a bit.

I've been modeling solar thermal and later PV systems for going on a half century as more than a hobby, but less than a job.

There are a lot of models out there. I had a minor hand in creating a couple of them. PVWatts is good for preliminary design of residential PV systems. It's easy to learn, and if used correctly, produces results that are probably as realistic as any and somewhat flexible in how it can be manipulated to do stuff the designers may not have had in mind. The drawback is it doesn't do any shade analysis and a couple of other things.

I'd encourage you to get familiar with the model. Do so by reading ALL the info and help screens a couple of times before doing any inputs.

Also, and to your question, many users find a system loss parameter closer to 10 % produces model output that seems to get closer to actual long term system output than the 14 % default.

Also, unless you learn and do your own modeling, you won't be at the mercy of some peddler who has a vested interest in manipulating models (and they all can be manipulated) in ways that will cause the models to produce less close to probable long term average output. Reason: That way, they can more easily justify what's actually an oversized system.

If you really want a deep dive into PV system modeling and have some engineering background, you might want to look at something else from NREL called "SAM". It's kind of like PVWatts on steroids. It's free but not for the faint of heart.

For most folks however, PVWatts produces reliable and understandable results in a reasonable amount of time and for not much hassle that are fit for purpose without the need for an engineering degree.

Also, while you're at it, and before you spend dime one, download a free PDF of "Solar Power Your Home for Dummies". It'll fill in a lot of info spaces for you.

[solarintexas]

Another vote for a good string inverter over micros or an optimizer system. I have both, Enphase micros and an SMA string inverter. The string inverter has been more reliable, eight years of dutiful service, day after day. My Enphase micros are a bit more than a year old and have acted up twice already, leading to some production losses.
Yes, the micros will extract slightly more electricity from your panels, but they are also more expensive. A good string inverter is easily serviceable, can be installed in a specific, more protected location, etc.. Simpler and better!
personally, I don’t care about monitoring every single panel as you could with the Enphase system. Solar panels almost never outright fail. They are relatively robust. Not much to monitor there in my opinion.
I have a separate revenue-grade production/consumption monitor that I love. It enables me to read my two systems separately and cumulatively. That is all I need. The granularity of my monitor is actually much better than what Enphase offers.
For me, like for most people, solar is an investment. While I love the technology that is available in today’s quite powerful panels and the advanced inverter technology, the purpose is primarily to save me money in the long run and to reduce the load on the power grid, stabilizing it during peak load conditions. That means fewer grid incidents under such conditions.
i would go for a good string inverter system as you seem to have no shading issues.

[oregon_phil]

On 3: I can be a PITA quite well with a string inverter, but because it's a string inverter, being a PITA to vendors and mfgs. is much less necessary.

You could also ask your installer to see if they keep a spare string inverter on hand. My installer had an older SMA inverter sitting around just in case.

Most warranties have an out if they determined your system was impacted by lightning. I learned from this forum to make sure I had adequate surge protection for my inverter. I have a midnight solar surge arrestor on my inverter power line and a Siemens whole house surge protector on my main panel. This would be an easy install during solar installation.

Another thing is that current SMA inverters might have wifi omitted due to the chip shortage. There is a direct hardwired ethernet port built into the SMA comm board.

[Seltos]

You could also ask your installer to see if they keep a spare string inverter on hand. My installer had an older SMA inverter sitting around just in case.

Most warranties have an out if they determined your system was impacted by lightning. I learned from this forum to make sure I had adequate surge protection for my inverter. I have a midnight solar surge arrestor on my inverter power line and a Siemens whole house surge protector on my main panel. This would be an easy install during solar installation.

Another thing is that current SMA inverters might have wifi omitted due to the chip shortage. There is a direct hardwired ethernet port built into the SMA comm board.

All excellent suggestions. Whole house surge protector? Need to dig into that too it seems.

But as for sending an ethernet line over from my router, that prospect doesn't excite me. The router is indoors and the Sunny Boy would be outside for starters. (Or should I put it in the garage far from the meter?). Perhaps I should ask my installer to verify if the inverter will omit WiFi before installing. I had not heard that this was an issue with Sunny Boy inverters now being shipped.

[Seltos]

I've been modeling solar thermal and later PV systems for going on a half century as more than a hobby, but less than a job.

Most impressive! You should offer a consulting service so that lay homeowners shopping for solar can secure an unbiased estimate for a proposed solar system's projected annual production.

[azdave]

Cons:
1. No panel level monitoring.
2. Ten year warranty (vs 12 for SolarEdge or 25 for Enphase).

I'll make it simple for you.

Panel-level monitoring and long warranties are both highly over-rated "benefits" (but great marketing tools for salesman).

Don't count on anyone but you to monitor your system performance. Watch your strings and not individual panels and you'll be fine.

[J.P.M.]

Most impressive! You should offer a consulting service so that lay homeowners shopping for solar can secure an unbiased estimate for a proposed solar system's projected annual production.

Opinions vary. There's about 150+ homeowners with PV on their property in my HOA that some would say have had a tool in their neighborhood to maybe counter some of the more egregious B.S. from the solar conmen. Others think differently, sometimes in quite energetic and emphatic ways.

In any case, I've got more time than money, more money than brains and starting to run short on all three just now.

On another front, what do you think I've been up to for at least some of 14,177 posts over close to 9 years around here ? Before retirement a number of years ago, I got ~ $200/hr, w/ a 4 hr. minimum for my services as a P.E. in a different arena. Consider yourself the beneficiary of some pro bono largess in the form of free advice.

Besides, that service is already provided by NREL in various ways, much better than I could hope to match in either quantity or depth, PVWatts being just one of them. Most of the problem with that source (NREL) is most people are short on ambition and self determination to get off their mentally and physically slothful dead asses and help themselves.

Anyway, and only as a personal opinion, beyond a few initial shoves and points in the right direction to get someone started, I'm not too big on what I see as enabling behavior that never has an end, or dealing with people who think and behave as though they're entitled to be spoon fed stuff they can get on their own.

But all that's off topic. Back to Seltos' question(s).

Take what you want of the above. Scrap the rest.

[oregon_phil]

All excellent suggestions. Whole house surge protector? Need to dig into that too it seems.

But as for sending an ethernet line over from my router, that prospect doesn't excite me. The router is indoors and the Sunny Boy would be outside for starters. (Or should I put it in the garage far from the meter?). Perhaps I should ask my installer to verify if the inverter will omit WiFi before installing. I had not heard that this was an issue with Sunny Boy inverters now being shipped.

Search SMA america's website for: "Temporary discontinuation of the Wi-Fi function: successful commissioning via Ethernet interface".

[Seltos]

1) In any case, I've got more time than money, more money than brains and starting to run short on all three just now.

2) Consider yourself the beneficiary of some pro bono largess in the form of free advice.

3) Besides, that service is already provided by NREL in various ways, much better than I could hope to match in either quantity or depth, PVWatts being just one of them. Most of the problem with that source (NREL) is most people are short on ambition and self determination to get off their mentally and physically slothful dead asses and help themselves.

4) Anyway, and only as a personal opinion, beyond a few initial shoves and points in the right direction to get someone started, I'm not too big on what I see as enabling behavior that never has an end, or dealing with people who think and behave as though they're entitled to be spoon fed stuff they can get on their own.

1) You crack me up. I might have to steal that line as I just retired too.

2) I do, in spades

3) Hopefully, I'm not TOO short on ambition here. I've been using PVWatts with a 10% system losses figure, and also a 14% figure. One big kahuna solar contractor in town uses Aurora, and their numbers are sufficiently different from PVWatts, especially when using a 5% tilt. (They seem to match up when flat). So my curiosity is aroused. You mentioned earlier that NREL had a more complicated free system called SAM, but it was "not for the feint of heart". So in the hopes that SAM will be the tie breaker between Aurora and PVWatts, just five minutes ago, I was inspired to watch this YouTube video about it:

https://youtu.be/ba5NcqlANZQ

Maybe I can tackle it. Can't hurt to try. I don't want to overbuild because the ROI drops a lot obviously when that happens. But we'll have to switch to a 4pm-9pm Time of Use billing plan from the current seasonal one, so I need an offset. The highest usage of my last 3 years was about 9.9 KwH (other two, on either side, was around 8.8kWh), so if I go with the highest year, and allow a 120% offset for the higher early evening billing rates, I'm aiming for a 12000 kWh system. Or 11,500 kWh at the low end could be OK too. Reasonable target?

4) I can't disagree with your opinion here whatsoever.

[Ampster]

.......

But as for sending an ethernet line over from my router, that prospect doesn't excite me. The router is indoors and the Sunny Boy would be outside for starters. (Or should I put it in the garage far from the meter?).

If the Sunny Boy is exterior rated I would expect that the Ethernet connection is inside the cabinet. I find hard wired connections more reliable for critical devices. I consider monitoring my GT inverters and hybrid inverter critical devices. You can verify with your installer if it is waterproof.

[J.P.M.]

1) You crack me up. I might have to steal that line as I just retired too.

2) I do, in spades

3) Hopefully, I'm not TOO short on ambition here. I've been using PVWatts with a 10% system losses figure, and also a 14% figure. One big kahuna solar contractor in town uses Aurora, and their numbers are sufficiently different from PVWatts, especially when using a 5% tilt. (They seem to match up when flat). So my curiosity is aroused. You mentioned earlier that NREL had a more complicated free system called SAM, but it was "not for the feint of heart". So in the hopes that SAM will be the tie breaker between Aurora and PVWatts, just five minutes ago, I was inspired to watch this YouTube video about it:

https://youtu.be/ba5NcqlANZQ

Maybe I can tackle it. Can't hurt to try. I don't want to overbuild because the ROI drops a lot obviously when that happens. But we'll have to switch to a 4pm-9pm Time of Use billing plan from the current seasonal one, so I need an offset. The highest usage of my last 3 years was about 9.9 KwH (other two, on either side, was around 8.8kWh), so if I go with the highest year, and allow a 120% offset for the higher early evening billing rates, I'm aiming for a 12000 kWh system. Or 11,500 kWh at the low end could be OK too. Reasonable target?

4) I can't disagree with your opinion here whatsoever.

1.) Call it yours. Just speak kindly of me when I'm gone.

2.) Just take what's offered here for nothing and remember (perhaps somewhat cynically) you get what you pay for or less. No one is vetting the stuff around here, including my mental spoor, in any seriously consistent way. Caveat Lector.

3.) I don't doubt you're more ambitious than others, but if I were you, I'd stick w/PVWatts for now. SAM is pretty powerful, but unless you have need or want of it, PVWatts will give you more than you'll probably need without the time, toil and frustration learning SAM will entail.

BTW, given the same inputs, and provided the application isn't too off the wall, SAM and PVWatts will produce pretty much the same outputs. A lot of the subroutines and modules are the same. "PVWatts on steroids". Besides, both are free, and have a bunch of folks at NREL justifying their jobs by keeping them up to date and pretty much debugged. They've also not got anything to peddle or favor from a commercial standpoint.

4.) Opinions are like noses: Everyone has their own and most of them smell most of the time.

[Seltos]

If the Sunny Boy is exterior rated I would expect that the Ethernet connection is inside the cabinet. I find hard wired connections more reliable for critical devices. I consider monitoring my GT inverters and hybrid inverter critical devices. You can verify with your installer if it is waterproof.

For sure they are more reliable. But my router is inside the house. How do I get an ethernet cable from where the router is back to the exterior of the house where the panel is. It probably means putting holes in walls (leading to marital tensions, LOL) and doing a lot of cord fishing besides. I can run ethernet out the window I suppose to commission it if necessary. But I do wonder if all the Sunny Boys now shipping have this "no WiFi temporarily" issue.

[Ampster]

For sure they are more reliable. But my router is inside the house. How do I get an ethernet cable from where the router is back to the exterior of the house where the panel is. It probably means putting holes in walls (leading to marital tensions, LOL) and doing a lot of cord fishing besides..........

Marital tensions? The WAF (Wife Acceptance Factor) over rides any rational risk management reasons. My wife always complains about the WIFI speed so I tell her that the time in the attic is to make the WFI faster. It is partly true because I have distributed some WIFI nodes around our property. .LOL

[nomadh]

Been thinking about the electronics under a solar panel.
They have it pretty good compared to the electronics under your car hood. Those can go from below zero to over 150 degrees within an hour, then back down to below zero, depending on the season/location, in addition they are subjected to vibrations and shocks that the solar electronics do not experience.

Hopefully the solar engineers have studied the best practices that the auto engineers use to have long lived electronics in hostile environments.

That is a very very good point.

[Calsun]

I installed my system in 2012 and two weeks ago the dual MPPT inverter failed. Fortunately I had purposely chosen the top installer in the area and a top brand of inverter (Sunpower). Both are still in business and providing after sale support. My panels have a 25 year output warranty and this is not excessive as many panels produced in the 1970's are still providing more than 90% of their rated output.

I paid for an extension of the inverter warranty that was 10 years to get 20 year coverage. This is something everyone should do as average inverter life is 5-7 years. I was lucky to get 10 years from my Sunpower inverter but it still failed and I am glad it will be replaced under warranty (I pay the labor to install the new electronics but that is trivial). Glad I went with Sunpower and not one of the smaller companies for the inverter.

At the time a dual string inverter was uncommon but it allowed me to use two strings of panels with different output voltages. I have 5 panels mounted horizontally at a 10 degree angle and 6 panels mounted vertically at a 20 degree angle. They are on racks built for this design to maximize the annual output from the array. This is also a good approach with a roof where the panels will not all get the same amount of sunlight during the day.

California state has a calculator that allows you to easily determine the best angle for the panels at your latitude to maximize output in the summer or for a calendar year. This optimum angle is not likely to be the same as the pitch of the roof of the house.

I did not go with the panels that each have their own microinverter as that would add 11 more points of failure. There are no real advantages to this approach for a residential system in actual use.

I did find that companies would produce panels for the residential market and other panels, with high output, for the commercial market. I went with a solar system company that did both residential and commercial installations and this enabled me to specify higher output commercial panels for my house.

Solar panel output depends in part on the ambient air temperature and the output declines when the temperature rises. It helps to elevate the panels off the roof to allow airflow behind the panels.

A neighbor had a company install the panels on his house and they located them where half the array is in shade during the day. There was room to have them out of the shade zone and 10 feet further away from the mains for the house but the installers could not be bothered and the homeowner foolishly trusted them to get it right.

Panel installations usually entail putting holes in the roof which can later result in water in the attic and walls. I had my system installed by a company that is also an established roofing company and they put on a few roof before installing the panels. Any problems and there would be no finger pointing as to who was at fault. I was told it could cost up to $3,000 to remove the panels for a roofing job and put them back into place over the new roof. Something to consider if your roof is at the end of its life.