Alright, time to crunch some numbers:
Let’s get the stabilizer numbers out of the way, it’s a V-Guard VGMW 500 Plus Mainline Stabilizer, rated for 15A.
Efficiency for the last ~8 hours has been 14.80 ÷ 15.03 = >98%. Pretty happy with that.
I wish i knew why it was bringing down a perfectly fine 230V to 210V.
I’ll revisit this calculation after a week or a month.
And now the actual charge efficiency numbers!
So that’s been 14.80 kWh into the inverter - 12.96kWh out of the inverter + 4.25 kWH offset from before
Which is 6.09kWh, that’s total energy taken up by the inverter to run and to charge the battery.
We need to take out the inverter’s running load for the last 8 hours, that’s 1108W - 1043W × 8 = 520Wh.
Actual charge/discharge (round trip) efficiency would then be 4.65 ÷ (6.09-0.52) = 83%.
We’re putting in 5.57kWh to get 4.65kWh out of the battery.
I think… that’s not completely horrible.
But now let’s add the inverter’s consumption/losses and see what we get for total system roundtrip efficiency.
That’s actual power out from the inverter ÷ actual power used in charging the battery.
For that we’ll need to figure out how long it took for the battery to reach 100% SOC.
Let’s say that’s 7 hours, so the inverter consumed 7h × 65W = 455Wh
And now the calculation is 4.25 ÷ (5.57+0.45) = 70%
That’s definitely less impressive but it’s good to know.
How much energy does the inverter use every day, if we have no power outages?
65W x 24h = 1560Wh or 1.5 units or Rs 15 per day or Rs 450 per month.
That, i think, is perfectly reasonable.
And at 70% efficiency, for every 1kWh I use from the battery, I consume 1 ÷ 70% = 1.42kWh from the electricity board, or 42% per more, which is probably inline with most other inverters.
In other words, if my load is 1kW, which it currently is, then every hour of a power outage is costing Rs 4.2 extra over my regular bill.
Time to bring our favourite chatbot in to the conversation and ask for a TLDR:
- Battery + conversion efficiency (excluding idle): ~83%
- True system round-trip efficiency (including idle): ~70%
- Standby energy cost: ~1.5 units/day (~₹450/month)
Fair price to pay for uninterruptible power, woo.
Okay, but what if i say this entire testing is flawed?
As in the numbers are worse than they actually are?
It’s because I completely forgot I have a parallel 7Ah lead acid battery bank attached:
Theoretically, this means there’s a potential for the numbers to be better, but that’s for another day when the battery is permanently set up.
Please let me know if you see any glaring/non-glaring issues.
Hopefully my 10th-grade maths worked out okay here.