Adding storage to my Enphase system

[GXMnow]

Just got my SCE Bill for Feb. to Mar.

The taxes and "Non Bypassable Charges" came up to about $10, but we also got a $71 CA Climate Credit. That makes my bill -$60.31 so I have a nice credit going into the warmer weather. For this billing period, I ended up net exporting 92 KWHs. That comes out to just over 3 KHWs per day on average. And my DC solar panels have been producing over 5 KWHs a day. Without the DC panels, I would have been a net importer for sure. On those cloudy days, it was the DC panels that put enough charge into the battery bank to make it through the peak rate time.

On the energy charges, they changed the rates yet again. So I have 6 entries for the time of use, 3 at the Feb. rates and 3 at the Mar. rates. My billing period ends on about the 16th of each month. The rate change is pretty small, but they didn't list the date on each charge, but comparing to my last bill it looks like the delivery charges went down a tiny bit on all 3 rates. On the generation charges, Mid Peak went down, Off Peak and Super Off Peak both went up. As long as I am getting net export credit, they keep adding it up and I am now at $37.61 in credit so far. But since I am on monthly billing, when the credit goes below zero, I pay it off. On this billing year, I did pay them $51.59 for energy in Nov. and Dec. at the end of last year with the really bad weather. By the end of the next billing month, I will have more than that in credits. With the additional DC panels, I have to decide if I want to go back to annual "True Up" or stick to the monthly payments. I just wish they would use my energy credit to pay off the taxes and such. But no, the money has to go in a big circle.

Can you guess what days we had rain and clouds?

The odd part is that the battery delays the energy import a day. On the day I don't get much solar, the house still runs on the battery, but then I need to use grid power the next day.

 

[GXMnow]

My refrigerator might not be as much of an energy pig as I thought it was.

We had a spill in the kitchen, and the clean it up fully, I had to pull the fridge out to clean under and behind it. The exhaust from the condenser fan was more than 50% blocked. Some of it was just dust that clogged up the holes, but there was also a cardboard sheet that evidently fell off the top behind the fridge. It was laying over half of the exhaust vent and deflecting the hot air back under the fridge to it's are intake. The coils were also a bit dirtier than I could tell from trying to clean it from the front.

I don't have an official number, but looking at my overnight load graph, the compressor on time appears to be 2 to 4 minutes less on each cycle now. That is a pretty big drop. At 5 am when no one is around, the run cycle dropped from 44 minutes to 40 minutes. That is 10% less energy. Just from clearing the exhaust vent and moving a piece cardboard.

The off time is still short, and it is still using more than the Energy Star label, but it's better.

The weather was horrible today, but I decided to not interfere and see how it goes. The system has been only discharging to 53.5 volts while my cut off is not until it drops to 51.0 volts. And from 53.5, decent sun has been getting it fully toped up to 57.8 volts before 3:00 PM. So today, I just looked in on it a few times to see how it has been going. With the heavy clouds today, the usual 23 KWHs from the Enphase system dipped to just 9.6 KWHs. And the 6 to 7 KWHs from the DC system dropped to just 3.03 KWHs. The battery only got back up to 56.0 volts, and the weak DC output was only able to keep it up there to 4:30 pm where it started to discharge again. So I am going into this night starting 1.7 volts low. They are predicting clouds with on and off rain all day tomorrow, and heavier rain on Tuesday as well. So I will likely throw it on to charge from grid again tonight. It will easily make it past the 9 pm high rate, but then it leave me nothing for tomorrow. And they are also giving a 90% chance of rain on Wednesday as well. Guess I will be using up some of my SCE energy credits.

And my consumption is going to be up a bit as well. My son is coming home for spring break from college. He wanted to do a brake job on his car, but that won't be fun in the rain.

 

[GXMnow]

I finally got around to signing up to take the Enphase University courses. I am at 55% complete of the first section. A lot of it is just the same old repetition with only a few things unique to Enphase tossed in. Out of all the tests so far, I did get one question wrong, and I still think I am right. It was a section about the voltage rise caused by the inverter current on the wire resistance. I even went back, watched the video again, and even went to the install manuals on the Enphase site, and the terms they use are making sure the voltage rise from the PCC "Point of Common Connection" to the furthest microinverter should be less than 2%. And it is telling me that is the wrong answer. The other choices don't make sense. I think they have an error in their answer table. One is "Across the house", and the last is "PCC to Envoy". That does not include the voltage rise in the Q cable. But I still pass with ease with just one answer marked wrong so far.

 

[svetz]

... I think they have an error in their answer table....

You can use the "Contact Us" link to report them. Not sure they do anything with them, sound suspiciously like the ones I reported. ; -)

 

[GXMnow]

I completed the first Enphase U course. The only wrong answer on my whole thing was the one I mentioned before. I got 40 out of 40 on the final test. How much more do I need to get my installer access?

 

[svetz]

I don't know, I never really expected it. I was just taking classes I was interested in and it just showed up one day unannounced, thought it was a change everyone received. If you search back in your thread I posted a list of the classes I've taken, it should be some subset of them.

 

[GXMnow]

My 4.8 KW SilFab/Enphase panels hit a new record for March production yesterday at 28.9 KWHs. That works out to 6.02 sun hours. That is well over the estimate from the Solar Handbook online calculator. And it is actually even a bit higher because the microinverters were clipping solid at 3,900 watts for over 2 hours. That was a cool and windy day, but almost no clouds and intense sun, and the panels have been well rain washed.

You can also see that it was well over the power from last year for almost the whole day. It hit as much as 500 wats above last year. And it looks to be matching that so far today as well.

 

[GXMnow]

This is the third day in a row with the Enphase system clipping the inverters for 3 hours straight. Just topped 29 KWHs yesterday, and I think it is a little ahead today. It's already at 27.5 KWHs and I still have 90 minutes of solid sun to go.

The DC system has also been going into power curtailment because the battery is full. I am producing more power than I can use right now. I exported 15 KWHs just yesterday. The DC system has been producing about 7.4 KWHs before it drops to float charge at 4 pm.

The funny thing is, the charge controller just lost it's settings again. I think I know what might be doing it. It happened when I connected to it to check the production. The fact it produced so well, I know the settings were right before I checked it. When I went to the settings page, it hesitated a bit before it updated the display and went back to the defaults. I will forward this to the company and see if it makes any sense.

Meanwhile, here is the Enphase production and the resulting battery charge graphs. The bars are today up to 6 pm, the upper line is yesterday to line up with the battery graph.



Too bad I can't get a plot like that for the DC system with this cheap charge controller. But you can very clearly see where the DC charge just kept pushing up the voltage for nearly 3 more hours. Then it stayed in Boost, and then float and kept the voltage up all the way to 7 pm. With out low usage at this time of year, we never pulled the battery below 53 volts. So it will top up early yet again. 53 volts comes out to 3.786 volts per cell. On Li NMC cells, that is still about 73% state of charge. Pulling it up to 57.8 volts is 4.128 volts per cell or 95% charge. That is more than I want to go each day, but until I start using more power, the only way to keep this lower would be to waste power.

95% - 73% = 22% capacity used last night. So we used less than 8 KWHs overnight. Here is what SCE saw yesterday.
The Enphase system exported 15.76 KWHs back to the grid.
Here is the battery voltage to SoC chart that I use.

I really like that they show this at 0.25C rate with separate lines for charging and discharging. The 0.25C is actually a bit more current than I am normally running, so my lines would be in between those two. That means my true state of charge might be a little less while charging and a bit higher while discharging. So I am not cycling as far as this graph would suggest. Even when I run down all the way to my 51 volt cut off, I am at more than 45% remaining. If the XW-Pro inverter was running at it's maximum constant power of 6,800 watts, it would still only be 130 amps or so, and from 720 AH of battery, that is just 0.18C. The cells are rated at 3C discharge rate (2,160 AMPS!!!)

 

[GXMnow]

It has been a good week here. Even with another storm moving through, we had enough sun that I net exported every day. There was only one day where the battery did not get fully topped back up.

I am finding that the DC coupled panels are really showing their worth when there is clouds and weak solar production. If the Enphase system is not making more than the house is using, there is no "extra" power to direct to charging the battery. But no matter how weak the solar production is, every watt the DC system produces does still go into the battery bank. On days with very good sun, the extra power form the Enphase system is well over double what the smaller DC system makes. But when solar production is down to 30% of a good day, then nearly all of the battery charging comes from the DC system. I had a couple bad days where the battery did not make it through the night, but it has made it past the 4 to 9 pm peak rate time every day, thanks to the energy from the DC system.

iPhone Weather is showing "Sunny" for 8 of the next 10 day's, and the two that are not listed as just sunny are "Windy" and "Partly Sunny". Now I just need to start using more electricity ;-)

 

[GXMnow]

April Fools Day was no joke.

28.6 KWHs produced from the SilFab/Enphase panels. The battery bank topped up to 56.7 volts at 11 am. The remaining extra energy from the Enphase system exported 17.71 KWHs back to the grid. And the DC system pulled the battery bank to 57.9 volts by 3 pm, and kept it there in float mode to almost 8 pm, pushing 6.7 KWHs from the Amazon solar panels. Had the Charge controller stayed in MPPT mode and the battery didn't top out, the 2,000 watts of DC panels should have made nearly 10 KWHs. It's a bit of a shame I am throwing away this kind of power.

If I didn't have the DC panels, it's obvious, the Enphase system made enough that I would have still exported at least 10 KWHs on this day. The XW-Pro sat idle for over 7 hours while the house just ran off of the microinverters, and the DC panels kept charging the batteries.

This is looking very good for when I start using the A/C. Too bad I am banking most of the energy credit at the "Super Off Peak" rate. But even that is up to 26 cents / KWH now. If I keep banking over 10 KWHs a day, it will go a long way to covering my A/C use this summer. And looking at the numbers from last summer, the extra power coming in from the DC system is also going to help a ton getting through the worst hot days.

 

[GXMnow]

It was COLD today. We had strong winds out of the mountains that still have a huge amount of snow up top. Temps only got to the 40's F. We did have some clouds in the morning, but then they cleared away. The Enphase system set another record.


All 16 iQ7 inverters were clipped out for 3.5 hours. How much higher would the peak have gone without clipping? And hitting 30 KWHs on just April 3rd is crazy. That is 2.8 KWHs more than last year. 6.25 sun hours of AC into my system after the inverter efficiency losses and the clipping.

The XW-Pro stopped charging before 11:30 am just as the clouds cleared, so this is going to be a huge export day. The DC system looks like it went into float by 2:30 pm and curtailed down production a lot. The 2,000 watts of DC panels topped out at only 1,704 watts. I am convinced these panels are just 90% of their ratings, making the array really just 1,800 watts. Then the watt hours match up pretty good with the Enphase inverters with real 300 watt panels. Since the panels topped up so early on this day, the DC system wat hours is actually a little low at 6.721 KWHs, but that is because they were curtailed to float during the last 3.5 hours of sunlight.

 

[400bird]

Do you have any rough idea or numbers on the kWh or between something like 3.8 volts/cell and 4.1 volts/cell? Or any other points of reference?

 

[GXMnow]

Going by this graph, I get a rough idea.


I'll use the number that are on the left side of the graph for an example. When charging, if I go from 3.75 volts to 3.95 volts, the SoC is going from about 55% to 76%. That is a 21% increase in SoC. Let's do this in Amp Hours to make it a little easier to manage. Each cell group in the Bolt batteries are 3 x 60 amp hours. Then I run 4 of those in parallel, I think you do too now. That give me 720 amp hours max. 21% of that is 151 amp hours into the batteries. At an average voltage of 3.85 volts per cell x 14 in series, that section of the graph yields 3.85 x 14 = 53.9 volts x 151 amp hour = 8,139 watt hours for that 0.2 volt increase.

Looking at my battery summary graph from yesterday, I went from a low of 54.26 volts to a high of 57.86 when it was all done charging. Going back to this graph, that is going from 3.875 per cell = about 71% SoC to 4.133 per cell = about 92% SoC. That is also a 21% increase in Amp Hours. So I put 151 amp hours in at an average voltage of 56.06 volts = 8,465 watt hours. The XW-Pro only supplied about 3.5 KWHs of that, the rest came from the DC charge controller. It reported about 6 KWHs by itself, but, the XW-Pro was actually inverting part of the time, using some of the energy. But I still think the batteries actually took more energy than this calculation suggests.

I think I want to draw a line between the two on this graph. The internal resistance of our packs are so low, I don't think the voltage swings that much from 0.25C going in to coming out while at the same SoC. But it is still the best reference I have found. And when I used to charge my packs at just a constant current, I was able to clearly see that knee bend at the 55% SoC point.
You can see how the voltage starts to climb faster at about 52 volts. 52 / 14 = 3.71 volts per cell. Just over 50% on that SoC graph, where the lines curve upward. That was charging at 23 amps into 360 amp hours of cells ( 0.064C rate ). So probably closer to 56% SoC. That was before I got the second bank of cells connected.

 

[GXMnow]

It is almost midnight, so I have a full day of data. Let's see what it shows for the discharge energy.
The voltage at the beginning of the day started at 56.27 volts. Then it discharged down to 54.20 volts. Charged up to 57.88 volts, and then discharged back down to 56.

The XW-Pro reports to have charged just 3.7 KWHs into the battery. It stops charging at just 56.7 volts.
The BougeRV charge controller pushed 6.562 KWHs into the battery. That kept charging up to 58 volts, but only shows as 57.88 in the XW-Pro.


The XW-Pro energy comparison plot shows something interesting.
I grabbed this at 11:30 so the bars for 11 PM are only half what they will be for the whole day. But the real important thing here is how little the XW is now charging into my battery. In the 8 am hour, it only pushed 256 watt hours, then in the 9 am hour 1.4 KWHs, then 1.9 KWHs at 10, and finally, just 63 watt hours after 11 am. Add those up and we get 3,619 watt hours. Very close to the 3.7 KWHs it reported in the energy page.

Ad in the 6,562 from the DC panels and the total charge put in today is up to 10,181 watt hours. Now let's look at how much it inverted back out of the batteries. I will just add the 24 numbers in the calculator. I came up with 8,961 watt hours pulled from the battery. This looks like fairly poor battery efficiency, but I don't think it is near as bad as the number look. 8961 / 10,181 = 0.88 or 88% return. But the battery voltage is ending the day a little higher, and I think the BougeRV controller over reports it's output watt hours a bit. And the XW-Pro also under reports the DC current. Take all that into account and I think the battery efficiency is a bit better, maybe 95% as a guess.

I am going to look at the discharge energy from 1 am to 7 am today and see if it lines up with the NMC battery curves. This is 6 hours of fairly steady power draw. The voltage started at 55.99 at 1 am. That is 3.9993 volts per cell. On the chart, that looks like 86% SoC estimating between the lines. At 7 am, the voltage was down to 54.32 volts, or 3.88 per cell. Using the same chart, estimating between the lines, this is an SoC of about 71% SoC. So going by that, it looks like the system used about 15% of the battery capacity in that time. The battery bank is rated at 720 amp hours at a nominal voltage of 14 x 3.7 = 51.8 volts x 720 = 37.296 KWHs x 0.15 = 5,594.4 watt hours used in 6 hours.

In those same 6 hours, the XW-Pro says it only pulled 3,631 watt hours from the battery. That is only 65% of the energy I expected from the SoC voltage curve. So something is certainly off there. Again, I KNOW the XW-Pro always under reports DC current and power. But it is only off maybe 5% or so, this drop is huge. I think a big part of it may be the voltage readings also have an offset.

Here is a solid example of the DC current error. This is a screen shot right now as it is inverting, with no solar to mess things up, it's midnight.

The "Grid" and "Load" power is all coming from the batteries. This is showing in Watts, so it should all be taking power factor in account. It is outputting 657 wats to the backup loads panel and also outputting another 103 watts back to my main panel. That works out to 760 watts out of the inverter block. But it is only drawing 703 watts from the batteries. And Schneider only rates the inverting mode at 96% efficient. So obviously this is wrong. If the output readings are correct, and they do seem vey close, that 760 watts should be taking 760 / 0.96 = 791.667 watts from the battery bank. Hmmmm, it is only reporting 88.8% of the power from the batteries than it should be showing.

Let's scale up the DC power out by this error and see how it looks. 3,631 watt hours / 0.888 = 4,088.96 watt hours from the battery. Divide that by the discharge power estimate of 5,594.4 = 73% of the SoC voltage estimate. It's closer, but still not where it should be.

I may need to put a smart shunt on this thing to get some real data and see where the errors are.

 

[GXMnow]

Today is going to be a good test.

We have had 2 very bad days of poor solar production due to heavy clouds. I was going to cheat a bit and force a bit of charging from grid power, but I decided to wait it out and se how it goes since production has ben toping up the battery by 1 am on clear days. The first day, the battery discharged down to 53.8 volts, and even with the poor sun, it did still get it up to the 57.6 volts where the XW-Pro stops charging, and the DC pushed it up to 56.9 volts, a full volt below where the DC would go into float.

Yesterday, April 13, 2023 the solar production was way worse. On the 1th, the Enphase system made 26.3 KWHs, then on the 12th, just 13.4 KWHs. But then on the 13th, just 10.6 KWHs. I did chicken out and kicked on the charge at just 7 amps at 7:30 am. This caused the system to take about 40 wat hours of Grid power before the sun finally hit enough PV output to zero the grid again. But that didn't hold for long. From 9 am to 3 pm, the Enphase PV solar was only making more than the house usage in short spikes. The XW-Pro charge rate kept dropping to the minimum 7 amps with only a few spikes where the sun would peak between the clouds. This did cause the system to use a bit more grid power, but only at the lowest "Super Off Peak" rate. With the XW-Pro barely charging, and everything the DC system could do in these conditions, it only got the battery up to 56.5 volts. It was already inverter from battery before 3 pm. But I decided to just let it go. By midnight, it was still running on battery power, but the battery was down to 53.7 volts.

Overnight, running the house base load, including the furnace blower most of the cold night, the voltage dropped all the way to 51.1 volts. The inverter would shut down at 51.0 volts. That is just over 3.64 volts per cell. That should be about 50% SoC. The BougeRV SoC showed just 28%, but I think it is using just a voltage chart based on Lead Acid cells. At 8:30 am, the sun came out and the XW-Pro was able to go into charge mode by 8:50 am. so it never ran the battery to my shut off point, but it got very close. Had I not done the little grid charge yesterday, it may have shut off this morning. but now the real test begins.

The forecast is still calling today "Partly Cloudy" with some chance of rain later. Will the system recover enough to make it through another night? My furnace kicked on again right as clouds moved over, so the XW stopped charging for a bit, but the DC was still pushing a little. It is just 9:20 am as I type this. The XW-Pro has only managed to take 532 watt hours from the Enphase system to put into the batteries, while the DC system has done 450 watt hours. Not too bad for less than half the PV watts of panel. But at the same time, the Enphase panels are also powering all of the loads in the house.

The XW-Pro actually just went back to inverting to cover running the furnace as the Enphase system is not covering the house load. But it is only pulling 1.8 amps from the batteries, while the DC system is pushing 5 amps to the batteries, so it is still technically getting a net charge into the batteries.

 

[400bird]

Wow, big difference in the weather down there.

I turned off the AC charging through the XW. My DC panels have been doing all the recharging and recovering overnight energy usage.
Yesterday, the charge controller entered CV at noon. We're heading the same direction today. It is 10:30 and the SOC is already back up to 94%

 

[GXMnow]

The clouds are spotty here today. The sky is starting to clear a bit and the battery is now hitting 52.5 volts already. The iPhone weather App is saying it will be mostly sunny by noon. I am curious to see if it can fully recharge from just 51.5 volts to my full 57.8 volts today. By the numbers, that would require over 14 KWHs of charge power, beyond what the house is using. The BougeRV charge controller is now showing 33% SoC, up from the 28% low that it hit this morning.

Each time a cloud moves over, the XW-Pro is dropping to the 5% charge rate still, and I am using a tiny bit of grid power. At this point 10:45 am, the XW has only managed to charge 1.4 KWHs into the batteries. The DC panels have pushed 1.03 KWHs. To top up the battery, it will take 6 times this much energy before sunset today.

 

[GXMnow]

The clouds that were predicted to clear yesterday, never quite cleared. But enough sun poked through that the XW charging did reach the 56.7 volt set point by a little after 2 pm. It was helped a lot by the DC panels. And the DC system kept pushing al it could from the spotty clouds, managing to pull the voltage up a bit more to 57 volts even by sunset. Here is the battery summary graph.

Getting it back up to 58 volts would have taken about 15 KWHs, the XW managed to charge about 8.9 KWHs. The DC system managed to do 7.1 so the total claims to be 16 KWHs. So either the battery was a bit further discharged (Doubt it), the battery has a bit more than rated capacity (not likely) or the charge power was over stated a bit on the XW and/or Bouge charge controller (my guess). In any case, this was a very good result. even with the clouds, it managed to recover well from the previous 2 days of heavy cloud cover and rain. My grid power usage over the last 4 days only hit 580 watt hours on 1 day, and I exported nearly 20 KWHs total from the other 3 days. Production yesterday was still just 70% of what it was last year 20.3 KWHs vs 29.1 KWHs. But that was enough to get me back topped up (almost) and it even exported 5 KWHs. Obviously, if I let the XW charge up higher, it would have certainly topped it out.

 

[svetz]

How much capacity fade are you seeing per year?

 

[GXMnow]

How much capacity fade are you seeing per year?

On the SilFab/Enphase system... The maximum output on any given day has been able to match and even exceed the production from the first year. They are just coming up on 4 years old this July.

The batteries... Hard to tell. I do not think there is any measurable loss in capacity yet. Half the cells were new and cycling 40% daily for almost 2.5 years. They went online in Aug. 2020. The other half of the cells were in a car, but it appears to have been totaled on it's first or second full charge. Those have been cycling for just about a year and a half now. They went online in Sept. 2021

I have never done a full cycle capacity test. I guess I could top them up on Solar, then tell the XW-Pro to export 2,000 watts until the BMS shuts it down, but that would look odd on my electric bill. If the batterie really do meet their rated capacity, it would take 18 hours to fully discharge at 2,000 watts. I call it 36 KWHs based on the LG ratings on the bricks. But the cells are rated at 60 amp hours each. So in theory, the full capacity is really 720 AH x 51.8 volts = 37.296 KWHs. So that is 3.6% more than they say.

The JK-BMS on the older bank is counting the cycles. But it only increments after the full capacity has been cycled. So two 50% cycles will count as one cycle. I checked it right now, it has been operating for 2 years and 277 days. So 1,007 days or about 2.75 years. In that time, it has only counted 219 full cycles. So each daily cycle is averaging just an 11% cycle. That does seem a bit low. But I will bet that has to do with it not resetting th SoC counter for the last 5 months. But I would expect it to still count the amp hours in and out.

When I took screen shot of the BMS just now, the old bank was charging at 32.7 amps 56.11 volts = 1734 watts. But this is only half of the battery bank. The XW is cranking out 2,600 watts, and the DC solar is putting out almost 1,500 watts. That is over 4,000 watts going to the batteries. The new bank with the parallel pair of BMS units does have a little lower resistance, so it is probably pulling 2,000 watts, but it's not a "smart" BMS, so I can't see it without going out with my clamp meter. But this basically proves the charge power is being over reported a bit.

Overall I trust the LG cell ratings, and I don't think there has been any measurable capacity loss yet.

I think my newer battery cabinet is actually a bit more capacity. They are Gen 2.2 cell instead of the Vista 2.1 cells in the older cabinet. The cells may actually be 65 amp hour instead of 60 amp hour. But in the Chevy Bolt, they still left the same capacity and range ratings while not cycling the cells as far. That would also help explain why the new bank is always showing over 5% more current going in or out.

Here is the BMS screen shot on the old bank.

The cells 10 and 11 are on either side of the jumper cable between the 10S bring and the 4S brick. So when it is charging at 32 amps, there is a small voltage rise compared to the very short bus bars between all of the other cells. I added a second but smaller cable, to reduce this voltage error, and as you see it is now only 4 millivolts. I set the balance function to ignore less than 8 millivolts. Cell 14 reading a little high is also probably due to the location of the balance lead to the output post. Every other cell is at either 4.007 or 4.008 volts. That is excellent balance. The Cells are just at 17C but the protection MOSFETs are at 21C with the current flowing through them.

As I am about to send this, the XW has stopped charging with the batteries at 56.7 volts now. It only pushed 4.8 KWHs. The DC has already pushed 3.48 KWHs as well. So it took 9.3 KWHs to bring the battery bank from 53.3 volts to 56.7 volts. That is just under 26% of the rated capacity. By the voltage chart, that is from 65% to 88% or a 23% SoC increase. That is pretty close.