Inputs, please

overbore · June 2011

I am an old hand at battery banks, marine, but need advice on my new system, please.

I have 12 Crown flooded 12v 125's wired with #1/0 cables, through a Guest marine battery switch ( "off", left, right and Both banks) to a DC fuse then to a
Xantrex 12-24 charger inverter that will be only used to charge batteries and power the refer and two freezers of about 1400 max watts / 24 hrs.

The Question: what size panels do you suggest???

10 120watt???

Many thanks, overbore

Cariboocoot · June 2011

Re: Inputs, please

Clarification: you have two separate banks of six 125 Amp hour 12 Volt batteries?

First off, six batteries in parallel is a bad idea; even with bus bars it will be difficult to keep the current flowing evenly through all.

Second, 750 Amp hours per bank is a lot. That's trying for 75 Amps of charge current, which will need a big FM80 charge controller or two smaller ones. Plus roughly 1400 Watts of panel to recharge. That's for one of the banks. If you need to charge them simultaneously ... double.

Frankly this is a situation where I'd suggest increasing the system Voltage to at least 24 and closely examining the power needs with a Kill-A-Watt and every other inventive idea to get the consumption down. Refrigeration equipment is hard on battery systems, both due to the start-up surge and the total Watt hour consumption.

overbore · June 2011

Re: Inputs, please

Cariboocoot wrote: »

Clarification: you have two separate banks of six 125 Amp hour 12 Volt batteries?

First off, six batteries in parallel is a bad idea; even with bus bars it will be difficult to keep the current flowing evenly through all.

Second, 750 Amp hours per bank is a lot. That's trying for 75 Amps of charge current, which will need a big FM80 charge controller or two smaller ones. Plus roughly 1400 Watts of panel to recharge. That's for one of the banks. If you need to charge them simultaneously ... double.

Frankly this is a situation where I'd suggest increasing the system Voltage to at least 24 and closely examining the power needs with a Kill-A-Watt and every other inventive idea to get the consumption down. Refrigeration equipment is hard on battery systems, both due to the start-up surge and the total Watt hour consumption.

I am replicating my marine experience where I agree more voltage is "more better"; however, I' m sticking with 12V because of the large market supply of 12V marine appliances and lights.

My system thus far is a Onan 7,5 Kw standby power via a manual dp-st manual switch. Since this Honda natural gas /propane powered gen set is 3,600rpm, I am running Mobil Extended performance oil as this is tornado and ice storm country. In 1998 we were ground zero for a tornado that hit our house. We lived on a generator for two weeks. I am in the process of adding another dp-dt switch to allow the addition of a emergency 5KW pmg generator powered by a 10/1 Listeroid slow speed diesel now on hand.

Since I am a retired pilot of Boeings, I have replicated their standby, emergency and battery power schemes but the solar is designed to charge the batteries from my Xantrex if the standby and generators fail or have no fuel or if the electric power costs rise significantly.

I think 30A of solar power will keep my two battery banks of six float charged but may not be enough to recharge form a 50% discharge.

What are your kind panel thoughts as I think 10 120 watt panels may suffice.

Many thanks for your kind expertise, cordiallly,
overbore

Cariboocoot · June 2011

Re: Inputs, please

On a good day 1200 Watts of panel would "max out" a 60 Amp charge controller for a 12 Volt system. That's roughly 8% of 750 Amp hours, so yes it would work in that respect. On the full 1500 Amp hours you'd only have 4% charge rate, which becomes problematic. Might keep it floating, but would be a very tough recharge especially with loads on.

But that is on a good day. The sun doesn't always shine. If you want this for bad weather back-up, that's when the sun shines least. It would probably under-perform terribly and not contribute enough to be worth the investment. To say nothing of the risk to panels in tornado weather.

Personally I wouldn't want the nightmare of trying to keep all those batteries balanced either.

I still think you should re-evaluate your emergency power needs and see just how low you can get the requirements.

The back-up generators are far more practical if you can keep fuel on hand. Diesel and propane are both easier to store, and industrial gens run slower and longer.

Frankly, solar is very impractical for emergency back-up power.

mike95490 · June 2011

Re: Inputs, please

tornado alley is not a great place for relying on PV panels as a power source. Maybe a pair of 100W panels, to keep a single engine starting battery topped off, but mounting a large array, or even storing it in a bomb shelter, a small EU2000 inverter genset converted to a couple 20# propan bottles, seems like a better idea.

overbore · June 2011

Re: Inputs, please

Cariboocoot wrote: »

On a good day 1200 Watts of panel would "max out" a 60 Amp charge controller for a 12 Volt system. That's roughly 8% of 750 Amp hours, so yes it would work in that respect. On the full 1500 Amp hours you'd only have 4% charge rate, which becomes problematic. Might keep it floating, but would be a very tough recharge especially with loads on.

But that is on a good day. The sun doesn't always shine. If you want this for bad weather back-up, that's when the sun shines least. It would probably under-perform terribly and not contribute enough to be worth the investment. To say nothing of the risk to panels in tornado weather.

Personally I wouldn't want the nightmare of trying to keep all those batteries balanced either.

I still think you should re-evaluate your emergency power needs and see just how low you can get the requirements.

The back-up generators are far more practical if you can keep fuel on hand. Diesel and propane are both easier to store, and industrial gens run slower and longer.

Frankly, solar is very impractical for emergency back-up power.

Great data and thanks, sir.!!

Inputs, please

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