Why So Many Voltage Variations

BearWolanBearWolan Registered Users Posts: 4

I'd like to cut my GRID power consumption to near neutral or even give back some for compensation. But one thing that has struck me as confusing is the variance in system voltages 24V/48V wind, some off grid 12V/24V, while on grid are going up to 1000V DC Fronius (with most in 400V-600V DC input range SMA, OUTback) with a solar array. 

Why so much of a spread? Is it to force incompatibility between off grid solar, even wind and on grid systems? Or is it more of an economics thing with cable sizes and costs? Do the high voltage systems actually do a DC-DC conversion back down with a buck converter to increase usable household current before inverting. Can you go grid and still reserve a small battery bank for backup if the grid is disrupted? Or is a backup generator the cheaper way to go?

I was hoping to find a system that would provide an inverter that could run off of many variations of green sources and even provide a backup from battery or a generator option for when there are disruptions on the grid. I can only predict that this will increase with the growth of metropolitan areas. And even the utilities say that they switch power around to limit the disruption for any one group to less than an hour if they can, while killing power in a perfectly clean area. 

Is there one vendor that is plug and play with a variety of sources more than the others?


  • mike95490mike95490 Solar Expert Posts: 8,073 ✭✭✭✭✭
    edited November 2015 #2
    Backup generator is the way to go, until you have weeks of power cuts.  
    Generator  $1,000, Fuel @ 1/2 gal hr x 16 hrs day  x 4 weeks  $900, and live nearly normally
    Batteries  (8, 6v batt, 400ah) $3,200  Charge controller  $700   Solar install, 3Kw @ $4watt  $12,000  6Kw Inverter $3,000
    and you replace the batteries every 5 years.

    The Grid Tie inverters produce 240VAC power, and benefit from a wide 300 - 600V input range.  Battery systems, per code, max out at 48V and as the difference from output - input voltage increases, efficiency falls.

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • oil pan 4oil pan 4 Solar Expert Posts: 759 ✭✭✭✭
    edited November 2015 #3

    Or do what I did, get the $1,000 generator for the big stuff and night time, then add some solar to run the tiny loads. Actually my generator is a 7kw, $900 unit that I bought for $100 because it was broken and I fixed it for $20 in parts. I wasn't able to get off so easily with my solar power system.

    For generating off grid power $1,000 got me two 80 watt solar panels, a kisae 900w pure sine inverter, 15 amp Morningstar Mppt and a 100ah group 31 AGM battery. And really all I can expect that to do is run the refrigerator while the sun is up, or power very tiny loads at night. I could have gotten more for less money or the same for a lot less if I went with the cheapest of everything, but I didn't do that.

    As far as the voltage variations go, high voltage DC is just cheaper to run. Say you tried to make a 5kw grid tie system using 200ish watt 12 volt panels, you would need to run each + and - wire 12 or 10 gauge, from about 25 panels to the inverter or a terminal block. Or you just series them all up and run 300 to 400 volts DC on one 12 gauge wire to the inverter.

    But then if one panel or wire or connection goes bad you lose everything. Where as in a parallel or series parallel set up you would only lose one panel or a section of panels. So there are advantages and disadvantages to both.

    With a smallish off gird system lets say you run 48 volts, and to get 48 volt you series up 4 really big 300 watt "12 volt panels". Lets say these are the only 4 panels you have. Then one of them quits working. Or a one of your batteries you have in series dies. Now what?

    On paper, in a perfect world where everything always works perfectly just seriesing the panels up for max voltage is always the clear winner.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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