net metered system question [RE-wrenches]
Todd Cory, Bald Mtn. Solar
toddcory at jps.net
Wed Mar 7 07:17:50 PST 2001
William Miller wrote:
> 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.
Actually most grid intertied systems (without TOU meters) do NOT cycle the
batteries. The wasteful (700 watt hours/day) one hell of a huge phantom load is
from the SW running all the time... continuously floating the batteries AND
it's constant idle current.
The idea is to encourage trace to give the SW enough "brains" to see when there
is nothing to sell back, and shut itself off (silent mode) until needed again
when it would wisely go back into sell mode again... that is why it has been
called "silent sell". Both modes provide for grid outage backups, which is why
people have batteries.
> 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
Normally the output of a grid intertied SW goes to house loads... having a
transfer switch on the output would negate the reason for having a battery
based system which provides for grid outage backups. The SW's internal
"transfer switch" shifts SW output loads to the grid when it is active and
backs up these same loads up from the batteries/inverter during grid outages.
Hope this helps...
Todd
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