Battery vs no Battery grid tie systems - efficiency[RE-wrenches]

[Warren Lauzon]

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Interesting that there is so much difference in the two systems between the 
SW and FX. I know that the older SW were not all that good at selling back, 
due mainly to the way that it picked the sellback voltage vs battery 
voltage.

Supposedly the SWP than the SW is better, but it is hard to get real info on 
these type systems.


----- Original Message ----- 
From: "John Berdner" <jberdner at sma-america.com>
To: <RE-wrenches at topica.com>
Sent: Monday, April 18, 2005 12:00 PM
Subject: Re: Battery vs no Battery grid tie systems - 
efficiency[RE-wrenches]


Wrenches:

We do not have data for the SWP but we do have data for the FX and old
SW w/.GTI.
As you correctly noted the net energy production (generation minus
standby / battery charging losses) does vary quite a bit.
Depends on variables like battery type, battery size, battery age,
inverter charging algorithm, and inverter efficiency.

That being said we have a couple data points compared straight grid tie
with a Sunny Boy 2500U.
- SW with GTI in Sacramento - 50 to 60% of straight grid tie.
- FX in Grass Valley about 93 to 95% of straight grid tie (MX-60 and
100 Ahr/48 Vdc concord battery bank)
(Christoper F. Please chime in here if needed)
- We have recently launched the Sunny Island and are monitoring it at
the Sacramento site.
I will provide data as it becomes available.

Best Regards,

John Berdner


Does anyone have any real world information on the overall system
efficiency of a battery based grid tie system, with backup (such as
using Xantrex SWP inverters), vs straight grid tie, such as the SMA
inverters?

My calculations show that there "should be" about 25% less total
conversion efficiency from panel to grid with a battery based system,
but those are based on some assumptions that might not be correct, such
as how much the battery efficiency etc affects the overall system, and
how the inverter determines when the batteries are fully charged.

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