Load Balance Planning

Mangas
Mangas Solar Expert Posts: 547 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
I learned something this week during inclement weather. I'm not an electical engineer so this may be obvious to many of you. But, for those of you having limited skills as I do this may help you if planning a system.

When it's overcast, I am more aware of voltage levels in our two battery banks (32 Trojan L16s' each - bank total 64). I noticed the other day that during extended inclement, darker days voltage levels on one bank of batteries consistently runs about 2 volts or, less lower than the other bank. I didn't think much of it.

When we built the ranch house, we split the primary A/C feed loads into two 100 amp A/C breaker boxes based on rough power usage calcs to assure some redundancy i.e. one HVAC handler and A/C compressor on each panel. Turns out, in reality one air handler runs quite a bit more than the other given it is located near the garage and servicing more square feet than the other air handler. The result is house A/C power usage is slightly higher in one zone than the other, especially with added appliances post construction which weren't planned.

The engineers asked me which set of inverters usually auto starts the genny when the batteries need a little boost. Yep, same set, same battery bank. After they chastised me a little for not being more observant they are going to increase charging to the weaker bank and reduce the stronger one to balance each bank's volatge levels consistent with the actual power utilization in the house.

I didn't realize how much of an impact running say 1.5 to 2 volts lower in one bank than the other has on genny run time, maintenance and fuel usage.
Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
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Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #2
    Re: Load Balance Planning

    I have four inverters, two SW+5548 and two SW4048. The two 5548plus units run primarily the HVAC or other 240v heavy loads.

    Having two independent banks almost always will create a delima with unequal discharging between two banks.

    I have all four inverters fed from common 1100 A-H battery bank.

    When charging on generator, above the 85% SOC the efficiency is poor and taking this hit twice for two independent banks uses more fuel.
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  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    #3
    Re: Load Balance Planning

    I know RC, I've got four inverters too but chose the split set up. Nothing wrong with the way we did it but, I just wasn't paying enough attention to what was really going on between the banks to balance it right in the first place.

    As you correctly point out the imbalance can chew up unnecessary generator time, particuarly during the winter months.

    Learned another lesson.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
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