Outback grid tie ineffciency [RE-wrenches]

Christopher Freitas --- OutBack Power cfreitas at outbackpower.com
Mon Jul 23 14:27:39 PDT 2007


Carl - your two messages came through fine to me - I did not check the
on-line site but am responding to your posting as an individual email.  

The OutBack GTFX turns off during the night and only uses power to keep
the internal AC transfer switch closed and the computer board powered.
This should be about 6 watts or so.  This nighttime power is drawn
completely from the battery - so there should be no reversing of the KWH
meter during the night. The morning production of the PV array should
replenish these nighttime losses before the inverter starts up each
morning.  The MX60 will count this power production in the morning even
though the inverter is not yet running.  

The efficiency of the entire grid-tie with battery system depends upon
several factors - it can be affected severely by the programming of the
inverter (i.e. set points) and by the size and type of battery you are
using.  

With proper programming (i.e. the defaults usually) and a small set of
sealed AGM batteries (100AH @ 48VDC) we have seen AC output KWH
performance exceed 90% of the DC KWH produced by the array - but your
setup may be different. Non-sealed batteries without the temp comp
sensor could result in much higher losses in warmer temperatures for
example.   

Also - the 24VDC OutBack system's performance is lower - I have not
personally measured how much different for a grid-tie system - but I
suspect that 5% less AC KWH compared to a 48VDC system's performance is
possible.  

One note on the MX60 is that the KWH meter is an estimate (accuracy is
in the 3% or so range).  We have been showing the new FLEXnet DC product
at all the shows which is much more accurate of a measuring device - it
is able to show not only how much the PV array produced (both AH and
KWH) but also gives the amount that went into and out of the battery as
well (again both in AH and KWH).  This is ideal for understanding where
the power is going in a system like this.  

Let me know a little more detail (size of the battery, type of battery
and any set points which have been changed) and I will give you a more
detailed response.  

Also - are you using a HUB and a MATE on the system as well?  

Christopher Freitas

OutBack Power Systems, Inc. 
cfreitas at outbackpower.com
www.outbackpower.com






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