Grid-Tie Inverters with Batteries [RE-wrenches]

[William Korthof]

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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%.

>I know that many of the PV inverter manufacturers are working hard to
>reduce the cost of including back-up capability to a PV system AND have
>already improved the performance significantly.  My measurements in the
>field on real side-by-side systems has shown that under ideal conditions
>the grid-tie with battery system can produce 90 to 95% of the

I can certainly grant (and appreciate!) the efficiency and effective
work Outback has done to improve the performance and $$$ for
solar+battery systems.

I do advocate solar-UPS systems as a superior option versus
back-up generators for customer who really want emergency
power (about 10% of our installations include batteries), but
major issues remain... We're just one among many hundreds
of solar installers in this industry...but in our mostly urban
market, I think our company *has to* focus on the grid-tie-only
configuration.

/wk

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