Solar Guppy Discussion Forum :: Surrette battery efficiency : All Things Hardware For Solar Installations

I was wondering why all residential off grid systems are kind of lower voltage. I know gridtie run high volt systems. But kind of curious by batteries do not. I mean connecting batteries together to make a 120volt bank would be easy,

Obviously you would need an inverter handling this charge.
Maybe Solar Guppy can chime in as he has a good knowledge of the practical design of the internals.

I would imagine that it is not a problem with inverters as gridtie have high dc voltage values.

That leads me to believe it is a battery problem??? Just the amount of batteries need to tie them together or an actual problem with battery banks as voltage increase.

Author:	niel [ Sat Jun 14, 2008 12:26 am GMT EthGMT ]
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animatt wrote: I was wondering why all residential off grid systems are kind of lower voltage. I know gridtie run high volt systems. But kind of curious by batteries do not. I mean connecting batteries together to make a 120volt bank would be easy, Obviously you would need an inverter handling this charge. Maybe Solar Guppy can chime in as he has a good knowledge of the practical design of the internals. I would imagine that it is not a problem with inverters as gridtie have high dc voltage values. That leads me to believe it is a battery problem??? Just the amount of batteries need to tie them together or an actual problem with battery banks as voltage increase. i'm not quite sure where you are going here. now in theory a 120v battery system would pose smaller wires to be needed and it would nearly equal amps dc in to amps ac out plus inverter needs, but then you are locked into buying batteries 10 at a time. another problem is that the controllers are not made for this range of voltages needed to charge such a large voltage battery bank. all this is not worthwhile to somebody with just a few pvs, but may have some theoretical advantage only in the largest of systems. also note that 12v/24v is common to use as some items can bypass the need for higher losses from inverted ac by running direct from the 12v/24v battery bank. now there may be miscomunication or misnomers going on here, but i'm not seeing the problem let alone a battery problem. can you elaborate more specificly what leads you to believe there is a battery problem.

Author:	Solar Guppy [ Sat Jun 14, 2008 10:03 am GMT EthGMT ]
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Its all about NEC regulations, battery banks larger than 48VDC get into some VERY hard to implement safefty requirements, so all the manufactures stay at or below 48VDC ( nominal ) to stay clear of the regulations A Hi-Voltage DC battery bank is very lethal ...

Author:	niel [ Sun Jun 15, 2008 2:39 am GMT EthGMT ]
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forgot about that one sg and i believe the cutoff is supposed to be 50v. that is a sticky area when using a 48v system imho as voltages are typically going to be about 54.8v on a fully charged and rested 48v battery bank. individual inspectors may vary on this opinion if it falls under hi voltage or not. most would agree 48v nominal to mean 4 seriesed 12v batteries and not throw in the technicalities. i guess it depends on whether the inspector is not very bright or if he wants to be a jerk about things. come to think of it i'm sure insurance companies would pull this type of a boner even if the inspector passed it. you are quite right about its lethalness as ac being alternating may allow you to let go whereas dc can cause and hold a muscle contraction more readily.

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