Sol-Ark 12/15k vs EG4 18kPv Efficiency as Backup Only ESS

[johhen]

I'm looking at California approved ESS for battery backup only, and trying to decide between a few systems.


SGIP Approved Equipment

My decisionmaking sheet

The thing that is standing out to me is the listed battery capacity, vs the SGIP list's battery capacity. If you look in my decisionmaking sheet, I have a reduced number of combinations I'm interested in, and their AC Output in kWh, vs their battery storage in kWh

For HomeGrid Stack'd + SolArk, their 9.6kWh batteries produce 9.25kWh of AC output. 96%.

For EG4 PowerProESS, the 14.3kWh of battery produces 11.097kWh of AC output. 77%.

That's wild to me. If you look at other rows with EG4 batteries, they are all around 77%. There is a SolArk15k + 6 EG4-LL's at 77%. And an EG4 18kPv + 3 EG4-LL's at 77%. Looking at the other rows without calculating, they all seem around that.

Any speculation as to why? Misconfigured batteries? Improper testing?

 

[johhen]

We can keep the comparison a it cleaner, looking at the Battery tab. Compare the Stack'd 9.6kWh DC to their rated 9.6kWh DC to the EG4 11.44kWh out of 14.3kWh.

Measurement/calibration issue? Is it a true capacity issue? Is it an inefficiency issue.

 

[Quattrohead]

Looks to me like they are using full plate capacity for everything except the EG4 batteries, these seem to be listed at 80% of rated capacity.
Also the rated output of the 18k is 12kw not 11kw.

 

[olivinelife]

Homegrid Stackd 9.6 kWh is 200 Ah while Powerpro is 280 Ah. That's basically the summary of it. Although using Ah "doesn't make sense", Ah is better for comparing batteries because the voltage changes w/ usage pattern, temperature etc so energy content is dependent on how you measure it.

 

[johhen]

Okay - normalizing all the kWh DC capacities to 48V * amp-hours, EG4 doesn't look _as bad_. It appears EG4 calculate kWh based on a 51V nominal, whereas many others are using 48V, and some 50V. But it still isn't great. The normalized vs SGIP certified DC kWh is 85% for EG4, and the same for AC kWh is 82% (makes sense here, its an efficiency loss on top of the battery capacity).

For the WallMount, its 11.44 SGIP vs 13.44 (280aH*48V).

 

[olivinelife]

I think you are overthinking this. The SGIP test procedure is opaque and makes things more confusing. Ignoring solar, the only two components are the battery and inverter. For the battery, if they are both 48V 16S LFP batteries then you can compare Ah capacity. For the inverter, 18kpv or Sol-Ark 15k will have very similar efficiencies as well. Expect ~90-95% efficiency converting battery energy to grid AC energy.