Grid-Tie Inverters with Batteries [RE-wrenches]

[Bill Brooks]

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William,

Back when battery-based systems were king in California, typical additional
costs were 20-25% more than without batteries for the same size system. I
agree with the other comments, that the efficiency of the stand-by power
system needs to be evaluated and justified separately from the PV system.
What you have is an inverter capable of several operating modes. If you
float the battery at night, that is a power consumption by the standby
system, not the PV system. It may be semantics, but installers and marketers
get these issues all confused and do not effectively sell the benefits and
costs of these types of systems.

Bill.

-----Original Message-----
From: William Korthof [mailto:wkorthof at earthlink.net]
Sent: Tuesday, August 17, 2004 10:50 PM
To: RE-wrenches at topica.com
Subject: RE: Grid-Tie Inverters with Batteries [RE-wrenches]

Chris

>I don't think that the additional cost of the batteries, installation
>and additional switchgear HAS to end up being $4000 to $8000 - My
>figuring works out to be more in the $2000 range,  assuming a relatively
>small battery and only a few backed-up circuits in the house.  We need
>to separate out providing some back-up power (for necessities like
>lights, tv and cold beer) from trying to powering the entire house.

The extra cost includes many components. For a typical 3-6 kW system:
-on a "maxed-out" system, the charge control+battery inverter cost is
  close to break-even versus a PV direct inverter (thanks Outback!!)
-batteries add $500-$2000
-battery enclosure adds ~$200++
-heavier cable/wire runs to the roof/yard add ~$300
-extra panels (to overcome the higher inverter loss) $1000
-ancillary circuit breakers, disconnects, boxes, cable..... (~$1300)
-design time is *at least* twice as much (for us)
-ordering, stocking, and equipment handling is far more complicated
-installation & training time is at least 50-100% greater.... if normal
  installation costs are $1/watt for basic grid-pv, 75% extra labor on
  a 4 kW system would represent an extra $3,000.
-the likelihood of inspector problems is much higher
-the warranty liability and service requirements (5 or 10 years) are
  far greater for battery systems ( x 3 ? )
-the need for more interface/customer orientation on system operation
That's an extra equipment cost of about $3,000 alone. The labor and
other "soft" costs can easily add another $3,000. So we're up to $6k.

For a bigger system, or one with more inverter capacity than PV, the
premium can easily be greater---or a larger part of total system cost.
And my hunch is that to fairly count our own labor and O/H costs,
the installation cost premium would be even more than 100%.
***snip***

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