Earth Notes: Even More Enphase AC Battery Home Storage (2021-10-28)

Updated 2023-12-29.
And then there were four! #storage #grid #selfConsumption
That escalated quickly! Doubled AC-coupled storage again 2021-10-28 to ~5kWh/1kW when I took up the offer of two second-hand units: reuse rocks!


Having doubled up just last month I thought that that would be it.

But then EcoPartners offered me two second-hand AC Batteries for circa half price. They have done approximately 500 and 370 cycles, which is in between the 892 and 29 cycles of the current two. Still probably more life than the house itself, given the impending redevelopment...

2021-10-28: Physically Fit

The installer came again by estate car, with a junior, and had plumbed in the two new devices electrically in an hour.

It will require someone back at EcoPartners HQ to configure them to attach to the rest of the system for control, so they are just twiddling their thumbs tonight after installation.

This installation is "for science" in the sense that I'm pretty sure that this is larger than optimal, especially in winter, but I want to see if that is evident from the stats.

This brings the AC-coupled storage to ~5kWh/1kW. Off-grid storage is ~1kWh. The total is about one days' consumption.

I asked the installers to leave the Envoy firmware at version D5.0.34, so that I retain access to the production.json live stats.

As of noon the next day the two new batteries had not yet been configured to talk to my system. There was some spill to grid that could have been avoided. This has to go to Enphase for resolution, which may take another 24h+.

2021-11-01: In Sync

I called EcoPartners this morning to chase, and when I looked at 14:40Z the display now indicates all four AC Batteries.

Here are the log entries around the sync up (note the percentFull step):

20211101T14:08Z consumption.readingTime 1635775682 17.866 143.703 production.wNow 125.837 storage.percentFull 56 storage.wNow -400 storage.readingTime 1635775472 storage.whNow 1389
20211101T14:13Z consumption.readingTime 1635775981 4.475 179.149 production.wNow 174.674 storage.percentFull 28 storage.wNow -80 storage.readingTime 1635775976 storage.whNow 1389

Also, implicitly, I haven't lost access to the data API, because the Envoy firmware revision is still at D5.0.34.

It looks as if the two 'new' batteries arrived nearly empty, which is fine.

Interestingly the 'new' batteries are currently showing as zero charge cycles (and at the moment 5%/6% full). One seems to be the same part number as my original battery (800-00560-r03) and the other as my September device (800-00930-r03).

There may have been about 800Wh of energy that was spilled to grid but could have been absorbed, before everything connected up... But no use crying over spilt Joules?

The new units did not pick up any significant charge and are now empty again, leaving the other two to cover loads. That limits load cover to ~500W.

Tomorrow is forecast for "sunny intervals", so all units should get a workout.

2021-11-02: Soaking

Here is the log entry for which PV generation is being soaked up in excess of the capability of one or two AC Batteries (823W):

20211102T10:43Z consumption.readingTime 1635849782 9.45 1315.8 production.wNow 1306.35 storage.percentFull 1 storage.wNow -155 storage.readingTime 1635848978 storage.whNow 50
20211102T10:48Z consumption.readingTime 1635850082 -2.923 1134.649 production.wNow 1137.572 storage.percentFull 5 storage.wNow -823 storage.readingTime 1635849878 storage.whNow 248

Today I added a meter for this grid-coupled storage under that for the off-grid storage (at 16:12Z):

  • 100% usable off-grid charge (100%/1320Wh).
  • 81% grid-coupled charge (81%/4005Wh).
  • Total electrical storage: 5325Wh.

Almost nothing was spilled to grid today. All working as intended!

Enphase AC battery x4 graph
Chart of 4 x AC Batteries in operation; grid and battery flows shown. Virtually no spill to grid.

2021-11-16: Vampire Power

At the batteries are reported as drawing 15W. This figure varies a bit but would suggest about 400Wh/d of waste heat on idle batteries when (as yesterday) there is so little generation that there is nothing for them to do.

This is not totally a shock, given that previous estimates suggested that one or two packs were likely optimal in some regards.

Maybe it would be better in winter time to have the batteries inside the heated envelope to get a little free heating and keep them warmer too. But the potential fire risk militates against that.

As counterpoint, it is good to see ~50% of load being carried when cooking (and the batteries are not empty), and almost all generation being captured.

2021-12-26: Underused So Far

As of (nearly) sunset today the new units have only reported 7 full cycles!

2022-01-20: Cold Protection?

Enphase discharge stop cold weather evening 20220120
Discharging apparently abruptly stopped with temperatures not far above 0°C.

As of 9pm air temperature probably a couple of degrees above freezing and it seems as if the Enphase AC Batteries may be refusing to fully discharge because of the cold, ie they are drawing power while not empty (298Wh) and there is demand in the house.

Or, given that reported capacity dropped to zero at about 10pm abruptly without discharge being shown, is it a reporting issue?

2022-08-05: Aspiration

For 16WW with 5.29kWp of PV, typical utility/LCOE ratios imply storage of ~2.6kW/10.6kWh vs the ~1kW/5kWh actually installed.

Given our usage patterns, and if space and money were not a big issue(!), I could expand our system to nine ACB units so as to cover a 2kW typical dishwasher or washing machine load in full plus background loads. That would be ~2.4kW/10.8kWh, so not far from that utility norm.

The kettle (or simultaneous use of multiple loads such as oven and hob) would still break through to importing from the grid.


See stats from the second battery, including September (intramonth) and October (intermonth) profile comparisons.

Profile last year vs this: November

Copying over the data and running the script for 2020-11 and 2021-11. In 2020 there was only one AC Battery, for 2021-11 there were four.

% svn cp img/PV/load-profile/202110/ img/PV/load-profile/202111/
% vi img/PV/load-profile/202111/
% cp data/16WWHiRes/Enphase/adhoc/net_energy_202{0,1}11.csv.gz ~/tmp/
% sh img/PV/load-profile/202111/
November 2020 weekday profile with 1x AC Battery November 2021 weekday profile with 4x AC Battery
Weekday profile in November for 2020 (1x AC Battery) vs 2021 (4x AC Battery). There were only 2x AC Battery active until the afternoon of 2021-11-01, allowing ~0.8kWh of exports until then. Note that this is all in UTC. (Click on each graph to expand.)

This extra battery power and capacity seems to have had two effects:

Note that daily generation is basically always below daily demand in November, so loads are not carried much or at all overnight. And the extra AC Batteries are imposing an extra vampire load.

Note also that this November unlike last, the central heating was on for most of the month. This may account for the small spike in demand at 7pm as the heating comes on, and the boiler power up having been held off since 4pm.

The source data is from November 2020's and November 2021's Enphase monthly net energy reports.

Results have been captured of a run of the script (with a copy of the script as run). This includes weekday, weekend and all filters.

2022-12-05: Shoulder Payoff

Looking at the Enphase battery discharge stats by month, it seems that having 'excess' capacity that cannot usually be fully charged/emptied in a day pays off best in spring/autumn shoulder months.

In particular, March, September and October since the capacity increase to ~5kWh 2021-09 seem to show big discharge increases. These presumably reflect lowered grid flows and increased self-consumption.

2023-12-29: Shoulder Peaks

I have just seen again that there are now peaks of battery discharge/use in Mar and Oct shoulder months, ie twice yearly, since AC Battery expansion and heat battery installation. This might deserve some sonification!