net metered system question [RE-wrenches]

[sunwise at cheqnet.net]

William Miller wrote:
> 
It is regarding the problem of inefficiencies of the
> battery connected SW inverters when used for grid interite.  As I
> understand it (and please correct me if I am wrong), the biggest cause of
> inefficiencies is that AC loads connected to the SW output draw the
> batteries down overnight and the SW charges them from the grid.  The
> biggest power consumption is when the inverter initializes a bulk charge.
> Is this correct so far?  

Hey William -- I don't believe the inverter powers ac loads at night
unless power was lost to AC1.  No bulk charge is triggered.  The problem
is simply that the inverter foats the battery at the float voltage
setting all night using grid power to do so.  It is essentially a
battery charger that is running all night holding a fully charged
battery up at float voltage while home loads are powered from the grid. 
It might not sound like much but it really can add up. 

> Why not treat the output of the SW as one might treat a generator AC feed,
> that is, run it through a transfer switch.  Normally, the AC output of the
> SW inverter(s) goes nowhere (transfer switch switched to utility)..
> Therefore, the batteries never deplete enough at night to trigger bulk
> mode.

Again, the loads depleting the battery is not really the issue.  The one
fix that does seem to work pretty well (thee "work-a-round) is to
automatically disconnect AC1 at night (on PV, not Wind systems).  AC1 is
reconnect automatically when battery voltage is back up to snuff the
next day.  Though the equipment to do this is very inexpensive, it only
works well on systems that do not have lots of large loads on the
Trace's dedicated loads panel.

Kurt Nelson

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