Earth Notes: Yet More Enphase AC Battery Home Storage (2025-04-17)

Just The One

I last doubled up 2021-10-28.

This time I was offered between one more (£1000 all-in) and three more (£2250). Both offers are reasonably competitive against new storage solutions, though with lower power output per kWh than a new system would provide.

In part because Enphase still refuses to restore the local stats access that it broke by doing an unauthorised firmware update against my wishes, I am only taking one unit.

Why consider more at all, given that by some measures the first ACB unit on its own was 'optimal'? Quadrupling battery capacity in late 2021 only roughly doubled battery throughput, ie flows kept away from the grid.

(In 2024 total energy ('charge') accepted by the ACBs was 929kWh, which makes for a round-trip loss of ~25%, for the ACBs themselves.)

The motivating change is the installation of our heat pump, and seeing how well it worked in February and March (ie shoulder months) alongside the storage to minimise imports. Eg on cold nights pipe-freeze protection runs entirely from the battery.

Various self-consumption tweaks such as setting an input power limit on the heat pump (which will mainly apply to DHW), and then raising the Enphase maximum power (to 1.3kWp) should help.

Also, it should be a little easier to run appliances such as the dishwasher more from local energy when the sun is not fully out.

To fully cover large loads such as the kettle would require ~12 ACB units, for which I have neither space nor appetite! This addition is about improving self-consumption especially in shoulder months, so a small reduction in grid imports from typical ~2kW loads such as dishwasher, washing machine and oven. Covering those fully, assuming no other/simultaneous household loads, would be ~8 ACB units.

The new 6kWh energy capacity covers a day's non-heating electricity use. For about half the year, DHW should almost entirely be provided by PV diversion. And there is no need for space heat even longer than that. Thus it is about the maximum energy capacity that makes sense without changing to a time of use (ToU) tariff and working the battery much harder, eg filling it with cheap energy in the night in winter. For that a full winter day's consumption including the heat pump (15kWh+) capacity would be more sensible. But not for this house, I think!

An extra ~100Wh/d quiescent consumption in winter for the extra ACB unit seems acceptable.

The Bill

£1000 for the single unit all in, including installation. VAT is currently zero for batteries such as this.

{"eddi":[{"deviceClass":"EDDI","sno":0,"dat":"22-04-2025","tim":"01:47:51","ect
p1":0,"ectp2":24,"ectp3":17,"ectt1":"Internal Load","ectt2":"Grid","ectt3":"Mon
itor","bsm":0,"bst":0,"div":0,"frq":50.02,"gen":0,"grd":22,"pha":1,"pri":1,"sta
":1,"tz":0,"vol":2384,"che":0,"isVHubEnabled":false,"hpri":1,"hno":1,"ht1":"Tan
k 1","ht2":"Tank 2","r1a":0,"r2a":0,"rbc":0,"tp1":127,"tp2":127,"batteryDischar
geEnabled":false,"g100LockoutState":"NONE","cmt":254,"fwv":"3200S5.427","newApp
Available":false,"newBootloaderAvailable":false,"productCode":"3200"}]}
{"eddi":[{"deviceClass":"EDDI","sno":0,"dat":"22-04-2025","tim":"01:57:51","ect
p1":0,"ectp2":26,"ectp3":14,"ectt1":"Internal Load","ectt2":"Grid","ectt3":"Mon
itor","bsm":0,"bst":0,"div":0,"frq":49.96,"gen":0,"grd":18,"pha":1,"pri":1,"sta
":1,"tz":0,"vol":2388,"che":0,"isVHubEnabled":false,"hpri":1,"hno":1,"ht1":"Tan
k 1","ht2":"Tank 2","r1a":0,"r2a":0,"rbc":0,"tp1":127,"tp2":127,"batteryDischar
geEnabled":false,"g100LockoutState":"NONE","cmt":254,"fwv":"3200S5.427","newApp
Available":false,"newBootloaderAvailable":false,"productCode":"3200"}]}

Date/Time,Energy Produced (Wh),Energy Consumed (Wh),Exported to Grid (Wh),Imported from Grid (Wh),Stored in batteries (Wh),Discharged from batteries (Wh)
...
2025-04-22 02:45:00 +0100,0,32,0,2,0,30
2025-04-22 03:00:00 +0100,0,33,0,3,0,30