Panels + Sonnen Battery = is this working ok?

[eggerda]

Hello! We just got solar panels installed + 10 kW Sonnen Battery in our home by a local installer. It turns out, this is only the 2nd Sonnen they had ever installed, and there was some confusion on their end during the installation.

They are supposed to come back and "finish it up" but it's been weeks - they say they will get to it, but so far, I'm the only one reaching out.

I've been monitoring the numbers on the Sonnen App, and the "Engage" solar panel app. And I'm comparing our grid usage BEFORE installation, and AFTER installation. Here's what I'm seeing, and I'm wondering if it's working ok?

Before installation, GRID USAGE typical weekday:

before.png

And here is a typical week day now of GRID USAGE after installation...

after.png

I guess the question becomes... we are generating ~30kW during the day (over twice what we need, and backfeeding the grid once the battery is charged back up to 100% which happens by noon). Then in the evening the battery starts to power things.

But why are we still using grid energy at night? (These images are the Edison meter readings.)

When they installed, they put 9 of the home's circuits on the new circuit breaker box - I had to choose what would be backed up in case of an outage. Does this mean these are the only circuits that will be powered by the battery at night? (i.e. we didn't put the dishwasher ,microwave ,etc on the new panel as we didn't see those as necessities)

So could this explain why we still use the grid?

I guess the main question is - are these numbers typical - is this how it is supposed to work?

I know there's been some question as to if the CT's were put in the right places, and I was told by the installer that they should have moved over more circuits to the new breaker box.

This is all new to me, but I've been learning - and I'm just curious about what some of the experienced solar users here in the group might have to say about if what I'm experiencing here is normal? (I've been working with Sonnen support, and they say on their end, after making some configurations, it seems as though things are normal and working well... but I'm just not sure.)

Thanks for any help or guidance.

I appreciate it!

Dan

[SolTex]

Dan, I'm new to this forum, and also new to solar. Our system has been in operation for about 3 months. There may be differences in how our systems are sized and connected, but it sounds like you are trying to run your system on basically the same "profile" that we use. We have our whole house backed up, so when we go on batteries everything in the house is powered. The plot below shows a typical bright sunny day with optimum solar conditions. Starting at midnight, the house is running on batteries (two 10 kW modules). When batteries reach "emergency reserve" of 30% in the early morning, the house goes on grid power. When the sun comes up and solar starts producing, system priority is as follows: first, power the house. Second, recharge the batteries. Third, sell excess back to grid. Batteries are 100% usually by noon. In the evening, as solar production tapers off, the batteries take over powering the house.

Since you have a separate breaker box for your backed up circuits, I believe, as you state, that these are the only ones that will be supported by your battery. We have production and consumption CTs on our system. The installers mis-wired our CTs initially, and our data was all screwed up. Once they corrected the wiring, it all began to make sense. Keep working with your installers until your system is working correctly. Learn all you can about how your system is controlled and monitored. If you have a net metering contract, watch the numbers shown on your electric bill to see if they agree with your data. Good luck!


Screen Shot 2022-04-10 at 5.09.48 PM.png

[SunEagle]

Dan, I'm new to this forum, and also new to solar. Our system has been in operation for about 3 months. There may be differences in how our systems are sized and connected, but it sounds like you are trying to run your system on basically the same "profile" that we use. We have our whole house backed up, so when we go on batteries everything in the house is powered. The plot below shows a typical bright sunny day with optimum solar conditions. Starting at midnight, the house is running on batteries (two 10 kW modules). When batteries reach "emergency reserve" of 30% in the early morning, the house goes on grid power. When the sun comes up and solar starts producing, system priority is as follows: first, power the house. Second, recharge the batteries. Third, sell excess back to grid. Batteries are 100% usually by noon. In the evening, as solar production tapers off, the batteries take over powering the house.

Since you have a separate breaker box for your backed up circuits, I believe, as you state, that these are the only ones that will be supported by your battery. We have production and consumption CTs on our system. The installers mis-wired our CTs initially, and our data was all screwed up. Once they corrected the wiring, it all began to make sense. Keep working with your installers until your system is working correctly. Learn all you can about how your system is controlled and monitored. If you have a net metering contract, watch the numbers shown on your electric bill to see if they agree with your data. Good luck!

That attachment is not viewable.

[Mike90250]

Why are you depleting / aging your expensive batteries at night when the elect co rates are the lowest?

Why not use the battery during the expensive hours, when there is sunlight, and if your PV panels have met all the house loads, they can recharge the batteries too.

[SolTex]

Where we live there isn't any "lowest" or "Highest" rate...just one single constant utility rate at all hours. Because our buyback agreement charges so much more for import than it pays for export, it is most advantageous for us (financially) to minimize imports. We do this by consuming the max amount of solar production possible each day. We purchased the batteries for this purpose, and they are doing the job for which they were designed. If the batteries are still holding 80% of capacity after 10 years, I will be totally satisfied.

[foggysail]

Dan, I'm new to this forum, and also new to solar. Our system has been in operation for about 3 months. There may be differences in how our systems are sized and connected, but it sounds like you are trying to run your system on basically the same "profile" that we use. We have our whole house backed up, so when we go on batteries everything in the house is powered. The plot below shows a typical bright sunny day with optimum solar conditions. Starting at midnight, the house is running on batteries (two 10 kW modules). When batteries reach "emergency reserve" of 30% in the early morning, the house goes on grid power. When the sun comes up and solar starts producing, system priority is as follows: first, power the house. Second, recharge the batteries. Third, sell excess back to grid. Batteries are 100% usually by noon. In the evening, as solar production tapers off, the batteries take over powering the house.

Since you have a separate breaker box for your backed up circuits, I believe, as you state, that these are the only ones that will be supported by your battery. We have production and consumption CTs on our system. The installers mis-wired our CTs initially, and our data was all screwed up. Once they corrected the wiring, it all began to make sense. Keep working with your installers until your system is working correctly. Learn all you can about how your system is controlled and monitored. If you have a net metering contract, watch the numbers shown on your electric bill to see if they agree with your data. Good luck!


Screen Shot 2022-04-10 at 5.09.48 PM.png

I have signed a contract for a 10.4KW system scheduled for a September install and have some concerns about the Enphase IQ8 plus inverter that it will use. Your performance graph shows what I am concerned about. It looks like there is power clipping done by the inverter. Which Enphase inverter are you using?

Thx

[SolTex]

It looks like there is power clipping done by the inverter. Which Enphase inverter are you using?

Yes, where the power graph flattens out is definitely clipping. This is due to the DC/AC ratio purposely designed into my system. I used LG 380W panels and IQ7+ inverters. The IQ7+ has a max AC output of 295W. Dividing the panel DC (nominal) output of 380 by the inverter AC output of 295 yields a ratio of 1.29 to 1. This is called the ILR (Inverter Loading Ratio). In most cases, it is advantageous to keep this ratio around 1.25 to 1. Doing so results in optimum performance over a wide range of solar irradiance conditions. On an annual basis, a system that clips during good solar production days will exhibit superior performance on less optimum days. See the discussion linked below for more info:

https://help.helioscope.com/article/248-understanding-dc-ac-ratio

[Ampster]

......... This is called the ILR (Inverter Loading Ratio). In most cases, it is advantageous to keep this ratio around 1.25 to 1. Doing so results in solar production days will exhibit superior performance on less optimum days. .....

The clipped power is an obvious loss to the casual observer. What is hard for them to understand is the higher performance on other days. Your explanation was even better than the system designer who designed a system for me at 1.5 to 1. It performed well.

[peakbagger]

Yes, where the power graph flattens out is definitely clipping. This is due to the DC/AC ratio purposely designed into my system. I used LG 380W panels and IQ7+ inverters. The IQ7+ has a max AC output of 295W. Dividing the panel DC (nominal) output of 380 by the inverter AC output of 295 yields a ratio of 1.29 to 1. This is called the ILR (Inverter Loading Ratio). In most cases, it is advantageous to keep this ratio around 1.25 to 1. Doing so results in optimum performance over a wide range of solar irradiance conditions. . See the discussion linked below for more info:

https://help.helioscope.com/article/248-understanding-dc-ac-ratio

I looked at that link and nowhere does it appear to back up the contention that "On an annual basis, a system that clips during good solar production days will exhibit superior performance on less optimum days". Obviously there is initial capital cost reduction in installing undersized inverters and in consumer markets where there is no summer/winter rate or a yearly non reset net metering there may be reasons to install lower inverter capacity than panel capacity but its specific to the location and tariff structure. I am also of the personal opinion that electronics tend to last longer when loaded less than 100%.

In my case in a northern climate with 4 to 5 months of snow, a combination of cold daytime temps and increased insolation from snow on the ground especially with my adjustable vertical tilt 2 KW pole array leads to clipping of my 2 KW string inverter on many sunny days. Many net metering tariffs I have heard of have an involuntary true up that usually occurs in the early part of the year (Jan to March are typical). On that true up date the excess generation hours being revert to zero or are paid out in market rate power sale. In this case winter production is important as the homeowner is not carrying a surplus to ride through low production months.

I will agree that there is small impact from inverter efficiency over a range of inputs. The inverter has a certain internal operating power that is best spread out over a higher power load but in most cases the curves I have seen is that that peak efficiency is somewhere in the 90% loaded range with some drop off as the inverter approaches 100%. I speculate that the loss is the need for cooling fans at higher loads (obviously not an issue with microinverters).

[SolTex]

I looked at that link and nowhere does it appear to back up the contention that "On an annual basis, a system that clips during good solar production days will exhibit superior performance on less optimum days". I am also of the personal opinion that electronics tend to last longer when loaded less than 100%.

I will agree that there is small impact from inverter efficiency over a range of inputs. The inverter has a certain internal operating power that is best spread out over a higher power load but in most cases the curves I have seen is that that peak efficiency is somewhere in the 90% loaded range with some drop off as the inverter approaches 100%. I speculate that the loss is the need for cooling fans at higher loads (obviously not an issue with microinverters).

I agree that the source I quoted does not back up my claim of "superior performance...". I just grabbed it from a number of "DC/AC ratio" links I have tucked away. I will include another link below that is a better discussion about the performance benefits (and drawbacks) of a system that regularly exhibits clipping. I am not a expert on solar system design, so I am not qualified to argue for or against a higher than one-to-one DC/AC ratio. I have just read a lot of tech papers on the subject, and they seem to back up my assertion: over sizing the array size in relation to inverter size (up to a point) will benefit performance on an annualized basis.

I also only have personal experience with micro inverters. Enphase is very clear in their tech documents that running their inverters at 100% output rating will in no way damage them or shorten their life. This may not be true for other brands and types of inverters. As you say, micro inverters and fan-cooled string inverters are not the same. One must always follow the manufacturer recommendations when employing any sophisticated electrical component. If they say "This inverter works best at 90% loaded range" then that's how it should be operated.

https://new.abb.com/docs/librariespr...vrsn=80a7614_4

[J.P.M.]

I looked at that link and nowhere does it appear to back up the contention that "On an annual basis, a system that clips during good solar production days will exhibit superior performance on less optimum days". Obviously there is initial capital cost reduction in installing undersized inverters and in consumer markets where there is no summer/winter rate or a yearly non reset net metering there may be reasons to install lower inverter capacity than panel capacity but its specific to the location and tariff structure. I am also of the personal opinion that electronics tend to last longer when loaded less than 100%.

In my case in a northern climate with 4 to 5 months of snow, a combination of cold daytime temps and increased insolation from snow on the ground especially with my adjustable vertical tilt 2 KW pole array leads to clipping of my 2 KW string inverter on many sunny days. Many net metering tariffs I have heard of have an involuntary true up that usually occurs in the early part of the year (Jan to March are typical). On that true up date the excess generation hours being revert to zero or are paid out in market rate power sale. In this case winter production is important as the homeowner is not carrying a surplus to ride through low production months.

I will agree that there is small impact from inverter efficiency over a range of inputs. The inverter has a certain internal operating power that is best spread out over a higher power load but in most cases the curves I have seen is that that peak efficiency is somewhere in the 90% loaded range with some drop off as the inverter approaches 100%. I speculate that the loss is the need for cooling fans at higher loads (obviously not an issue with microinverters).

I too read the link and agree with Peakbagger's observations and comments. I can find nothing in the link nor do I believe undersizing an inverter, will improve system performance.
The question becomes: What is the correct inverter system size and type that maximizes system performance consistent with the idea of maximizing system cost effectiveness ?

My other computer is down just now, but from memory I can write that under clear skies and for about 2 hrs. or so on either side of solar noon for a good part of the year, (6+ months or so) my array will generate somewhere between 0.83 and 0.89 of the inverter's capacity, most often at the higher end of that range. The array size is 5.232 kW. The chosen string inverter is 5 kW and clips at 5.032 kW. During initial design phase ~ 9 yrs. ago, I remember doing an analysis of a 5 kW vs. a 4 kW inverter using design data and inverter specs. I seem to remember an ~ $200 differential inverter initial cost. Numbers not handy at this point due to the other computer being down, but I clearly remember that a spreadsheet of hourly modeled system output and the cost of the lost generation quickly showed me that the loss of annual system revenue from that much clipping per year was close to the differential inverter cost, and that the LCOE cost over a 12 year analysis made choosing a smaller inverter a poorer choice by about $800 or so total life cycle cost difference. The larger inverter became a no brainer at that point.

Flat topped output curves mean lost output, most likely from clipping. Whether or not the value of that lost output (which won't be made up by non existent or very small inverter efficiency improvements from undersizing an inverter) is a question for system process economics.

I believe my system is quite well designed. An analogy to undersizing the inverter might be: Why put crappy tires on a well designed sports car ?

[Ampster]

...
In my case in a northern climate with 4 to 5 months of snow, a combination of cold daytime temps and increased insolation from snow on the ground especially with my adjustable vertical tilt 2 KW pole array leads to clipping of my 2 KW string inverter on many sunny days. ..........

From a practical perspective, adding more panels to an inverter is less expensive than a variable tilt system on a roof. Since most systems are roof mounted, higher DC to AC ratios are an economical way to get the optimal benefits of variable tilt without having to go on the roof to change the tilt.
Solar Farms just over panel because that is less expensive that tracking systems for them to get optimal return on their investment and from the footprint of land.

[SolTex]

An analogy to undersizing the inverter might be: Why put crappy tires on a well designed sports car ?

An analogy to oversizing the inverter might be: Why pay for a sports car designed to run 100 mph if you will never drive it over 80-90 mph?

[SolTex]

For the string inverter proponents, here is the SolarEdge view on the subject of "DC oversizing".

https://www.solaredge.com/sites/default/files/inverter_dc_oversizing_guide.pdf

[Ampster]

...... here is the SolarEdge view on the subject of "DC oversizing".
.....,.

Yes, they do allow DC to AC ratios up to 1.55 to 1 on their newer HDWave inverters.