Looking to set up a 48 Volt system

System
System Posts: 2,511 admin
in General Solar Power Topics #1
I realize this thread is a year old but it is along same line as information I am in search of. I have one of these Alphagen 5kw DC 48V 96 amp units that I am wanting to use to setup an off grid cabin. Want to charge a 48V bank and use a 48V inverter to supply AC power. Hoping someone can give me some insight or point me in the right direction in terms of battery bank, controlling the generator charging output/startup etc. Generator output is spec'd at 52V... is that high enough voltage to charge a 48V bank?
Have this generator and a 48V Inverter... looking to get insight as to the best way to complete the system in between.
Thanks,
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Looking to set up a 48 Volt system

    Welcome to the forum.

    Yes I moved your post: you get your own personal thread! :D

    As for your questions ...

    First off, 52 Volts is not enough to charge a 48 Volt system. The charging Voltage would need to be around 57. But it could be used to charge a 24 Volt system.

    So here's the drill: loads. Always determine your loads when designing an off-grid system. You'll need to know three things: 1). Your peak maximum Watts; 2). Your daily Watt hour requirements; 3). The type of loads you expect to run. It makes quite a difference to the plan: it will give you the info you need to select the inverter and size the battery bank.

    I see you already have a 48 Volt inverter. Then generator could do much of the Bulk charging, but it would not be able to bring it up to the Absorb stage and hold it there. Equalization would be out of the question. Someone is bound to suggest using a DC to DC converter to up the Voltage, but I don't believe that is practical.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: Looking to set up a 48 Volt system

    Can you dial up the generator output either by speeding it up a few RPM or changing the exciter? I confess I don't really know how large DC generators regulate their voltage.

    tony
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  • blackswan555
    blackswan555 Solar Expert Posts: 246 ✭✭
    #4
    Re: Looking to set up a 48 Volt system

    Should not be difficult to dial up the voltage, You may even be able to use a "smart" voltage regulator, but on a search I found this http://www.alpha.com/Media/Documents/Bellingham_SolarWindHybridPower%20case%20study_2pg.pdf may be worth a call to them ?

    Tim
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: Looking to set up a 48 Volt system using DC generator

    Thanks for the kind comments.

    If I am set up so that my primary generation is via a 5kw DC gen I am confused why I should spend too much time estimating (guessing) my daily consumption. Even if the gen runs at 25% duty that is still 30kw hours per day (ignoring system losses) which we would have to work hard to waste power to get that kind of consumption. Am I missing something and being naive in my thinking? My thought is that as long as my inverter will meet the peak consumption and generator will far our produce average consumption then it should be fine.

    I will have to do some research and examine the unit to see if I can find a way to dial up the output voltage. I assume then what I am looking for is 57V open circuit volts? Do you figure I need a controller or a more simple voltage switch that would turn the charge generator on at a certain voltage and off at another.

    At some point I do plan to supplement the charging with wind/hydro/solar, but at this point it is just a every other weekend place so overall average consumption is pretty minimal.

    Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Looking to set up a 48 Volt system

    Well for one thing generators are actually more efficient when running loaded 50% or more of their capacity. Even then they burn fuel, whereas solar doesn't. Ideally an off-grid system runs on solar as much as possible, with the generator fired up only when absolutely necessary.

    And if you want to size an inverter properly knowing how much power it has to provide is key. Bigger inverters have bigger stand-by power demands. It's all about striking the right balance that works for your particular install. It can be tricky, and it certainly makes your head swim at times! :p
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: Looking to set up a 48 Volt system
    Cariboocoot wrote: »
    And if you want to size an inverter properly knowing how much power it has to provide is key. Bigger inverters have bigger stand-by power demands. It's all about striking the right balance that works for your particular install. It can be tricky, and it certainly makes your head swim at times! :p
    That's the truth! It's frustrating when someone approaches me with a request for a quote for an off-grid or battery backup installation and I ask him what his electrical needs will be, and he responds only with the size of the house. Like the square footage of the building is all I need to know.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Looking to set up a 48 Volt system

    tell him it's $1000/sq ft.:p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Looking to set up a 48 Volt system

    One of the other reasons we are asking about your power usage is that is it not very easy or cost effective to scale a solar PV system by much more than 2x larger in size without practically redesigning the system and replacing major components (i.e., going from 12 to 24 to 48 volt battery bank, new inverter, charger, batteries, etc.).

    If you want to start with a smaller system and know that you may need a major upgrade later. Or, if you start with a larger system the is more than you need now with plans to use more power in the future.

    In the end, solar PV systems are horrendously expensive (relatively speaking), and we are just trying to understand your loads.

    Very roughly (just to set an expectation for budgetary planning), a solar PV system costs around $10-$20 per watt of solar panel installed...

    A 5kW inverter system (assuming it matches your generator capacity) + batteries + panels is quite large... It would not be out of the range of a 2kW solar array and batteries costing you $10-$20,000 or more... Large for a Cabin.

    Generally for a "cabin" most people would probably estimate a 1-2kW AC genset (like a Honda eu1000i/eu2000i) which would use 1/4 the fuel of the DC genset you are looking at. With the price of fuel in the US scheduled to hit $4-$5 per gallon here in the near future (and include delivery charges/costs for a remote cabin)--A large "inexpensive" genset is no "cheap" because of excessive fuel costs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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