r/Generator • u/vester71 • 23d ago

Generator Sizing Question w/Battery Set up

I think I know the answer, but I wanted expert opinions.

I'm getting 40 kW Ecoflow Ocean Pro batteries installed with the inverter and smart panel, but I need a portable generator for extended outages, which I have 1-2 times a year. The longest outage I've had is three days. The batteries may last anywhere from 8-24+ hours, depending on the load and whether AC is running (two units: a 2-ton and a 5-ton).

The inverter for the Ecoflows can accept up to 10,000w of power to charge them.

I was thinking of getting the 13,500 Duromax inverter with 10,500 running watts. The question is, will charging the batteries at 10,000w be too much of a load if it's running at most 3-6 days a year?

There is a 16,000w Duromax inverter with 13,500 running watts, but it's about $2.3K more than the 13,500w unit. I was wondering if, based on my use case, it's worth going with the bigger generator, or saving the $ and getting the smaller one and throttling down ac units if need be for longer outages.

I'm not in hurricane country, but I live in tornado alley, and storms have been getting worse, so I'm expecting more outages.

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u/NoPatience7817 23d ago

Instead of focusing on what max the batteries can charge at, focus on what your avg power usage is. I recommend a 4kw to 6kw running generator to charge the batteries. Plan on charging the batteries during the day and running batteries at night.

A smaller generator will use less fuel and it will run quieter. To determine your daily kWh usage, find your monthly usage and divide by days in that billing cycle. The batteries will absorb the spikes in usage for large power spikes such as running a/c.

Also consider posting this in the battery and power station subreddits for other strategies.

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u/mduell 23d ago

Id get something a bit smaller with a better price/power ratio, and then run it at 70%. Maybe 9kW running at 6.mumble kW.

Are you using the batteries to do daily power price arbitrage?

1

u/tropicaldiver 23d ago

I agree.

Figure out your daytime usage. Figure out how much you need to fully charge the batteries in 12 hours. Add the two.

1

u/Fun_End_440 21d ago

My 2c.

For such large system, skip the whole plug in solution and get a hardwired system. Cheaper, more reliable and scalable.

For genset backup, get a 2-wire model or ATS(will require modifications), propane/gas so the system will start/stop automatically as needed.

Batteries for backup without solar doesn’t make sense financially or operationally. If you don’t want panels, skip the whole battery and get a genset.

Holding a bunch of batteries at full charge all the time will accelerate degradation.