Battery type for 20kva

PatrickPatrick Registered Users Posts: 3
i am designing a PV-diesel hybrid system for a building of 20KVA . The idea is to reduce diesel consumption to the lowest minimum. In other words,the system will run less on generator and more on solar. Please what type of battery would you recommend?


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery type for 20kva

    Welcome to the forum.

    What exactly do you mean by "20kVA system"?
    In battery terms there has to be a system Voltage and an Amp hour requirement. If this is 20kW hours per day, that's one thing. If it's a 20kW array, that's another. The battery bank should be sized according to the daily Watt hour requirement, and the array & generator sized to recharge that.
  • PatrickPatrick Registered Users Posts: 3
    Re: Battery type for 20kva

    @cariboocoot thank you for the correction. The building has a capacity of 20KW hour per day. i will like to know the type,size and model of batteries. Required to run the building efficiently.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Battery type for 20kva

    more importantly where are you? and what is the panel output ?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery type for 20kva

    A proper and well thought out design requires much more info. Your energy consumption is 20 kwh per day. What are your peak loads? How long do you expect your batteries to power the building when there is no solar gain? Is this system completely off grid? Do you already have the generator? Do you already have inverters and charge controllers? Have you already committed to a particular system voltage? Do you already have the array?
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery type for 20kva

    20 kW hours per day is substantial for off-grid, but not impossible.
    You are definitely looking at a 48 Volt system. It will require approximately 463 Amp hours to achieve this, depending on actual usage and inverter efficiency. That means an absolute minimum of 926 Amp hour battery (that at 50% DOD). If you want to limit DOD to 25% you'll need at least double that.

    There's a couple of ways you could go here. One is with forklift/industrial batteries. One example would be to use two of these in series for 1000 Amp hours @ 48 Volts (cost about $9,235). They also have an 1875 Amp hour version for about $7,200.

    Another way is with 2 Volt cells like this: You'd need 24 of them and it would run the bill up to around $17,280. There are versions up to 2550 Amp hours.

    Were it me, I'd choose the forklift batteries if at all possible. They're a pain to handle because they're big and heavy, but they'll take deeper discharge. They also cost a lot less, but can be more difficult to set charging parameters for.

    You'll probably want to source them locally, as shipping is hugely expensive too (for any kind of battery).

    For charging this much battery you're looking at a need for at least a 6.2 kW array. But to replace 20kW hours AC per day you're looking at as much as 10kW, depending on your location. Try the PVWatts program to run some simulations for your location and see what you get.

    Using "typical" numbers I see 10kW array to recharge 1600 Amp hours of 48 Volt battery running a DOD around 30% to be a minimum for your 20kW hours per day load demands.
  • BB.BB. Super Moderators, Administrators Posts: 31,614 admin
    Re: Battery type for 20kva

    I am guessing Johannesburg, South Africa?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PatrickPatrick Registered Users Posts: 3
    design consideration

    The energy consumption for the building is 2.9KWh. Average amount of sunlight is 5hours.
    The building is completely off-grid but has a generator set in cases of non-sunlight days.
    Please what are the specification of solar panels, batteries(sealed), and inverter will i need to power the system for 6hours a day.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: design consideration

    Right away we have a problem. "2.9kW hours" is a fixed amount of energy. Do you mean it averages 2.9 kW and you want to supply that much for 6 hours? That would be 17.4kW hours.

    The type of loads will make a difference too, as things that have start-up surges (like motors) need to be taken into account. Air conditioning, refrigeration, water pumps - all heavy power users with big start-up surges. Otherwise, based on the above assumption, you need an inverter of 3kW or more to handle 2.9kW average loads. Besides that we need to know the AC Voltage and frequency requirement (230VAC @ 50Hz, 240VAC @ 60Hz, 120VAC @ 60Hz).

    Sealed batteries? I can see why you'd want them if they have to be within "living quarters". Know in advance that they are much more expensive for the equivalent power over unsealed ones. On a 48 Volt system you'd need approximately 1700 Amp hours to get that 17.4kW hours of power.

    With 5 hours of equivalent good sun you are looking at approximately an 8kW array to provide the AC demands noted above.
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