ST & DR vd. SW [RE-wrenches]

[Phil Undercuffler]

A few more lashes at that dead pony....
    We all know that when batteries are in a system, the pv runs at below
their MPP.  Remove the batteries from a gridtie system, and it is possible
to use three high volt panels (such as BP85) to produce nominal 48v.
    So, lets ignore all the inefficiencies of the SW & PS inverters in
gridtie for a moment.  The "dual inverter" system can provide nearly the
same watts to the grid with three panels as the "gridtie with battery"
system provides with four panels.
    Then add the cost savings previously calculated by Travis, even
adjusting to a sinewave output inverter.
    Finally, add the inefficiencies of the SW & PS inverters, and the math
tells me to keep the systems separate.
    If the client's primary concern is power outages, then the solar will do
little to aid them in a winter storm.  If their primary concern is being
green, then our design should maximize efficiency.

----- Original Message, (edited) -----
From: Travis Creswell, Ozark Solar <ozsolar at ipa.net>
To: <RE-wrenches at topica.com>
Sent: Friday, October 20, 2000 12:25 PM
Subject: ST & DR vd. SW [RE-wrenches]


> What I did was to prove that you could produce more usable/sellable kWh's
> with the same array for less money.
> If I was to install a DR and a ST I would make no effort to ever charge
the
> batteries from the solar.  The batteries are not there to be charged from
solar, they are there to back up
> the critical loads in the house for a day or so.  99% of the power outages
> in the US are less than a few hours.  > No matter what you do to a SW you
cannot produce as many kWh's a ST (or any
> battery less inverter).  The batteries pull the array off its power point
> and you still are floating the batteries with the solar or other RE
source.
> I agree with Kurt that we just might be asking for two much from one piece
> of hardware.
>
> Travis


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