Grid-Tie Inverters with Batteries [RE-wrenches]

[Allan Sindelar]

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----- Original Message ----- 
From: "Joel Davidson" <joeldavidson at earthlink.net>
Wrenches,

<Wrenches,

The Home Power folks have been looking at this dialogue and think that there
may be a good article about grid-tie battery and batteryless PV systems. The
questions about payback resulted in a pretty interesting article so I trust
their judgment. Truth is customers ask almost daily about battery versus
batteryless. So here's a few more questions. Thanks in advance for your
answers.>

What percentage of the time is the grid down in a typical U.S. city, suburb,
and country location?
I dunno, Joel.

What about grid down time in your locale?
I live off-grid, so my info is second-hand from our customers. Very little
in the Santa Fe area, it seems--that is, it's not a presenting issue as a
primary reason for inquiring about an RE system. Occasionally someone at the
end of a rural line expresses concerns about outages, but not very often. We
have one good customer (definitely not a nut!) who wanted security against
major grid failure, so we put in 3.6 kW of PV and a 10 kW generator on a
sealed battery-based system in town with major house rewiring. But few
customers have $60K to invest in a serious system like that.

What percentage of your grid-tied PV installations are battery? batteryless?
New Mexico currently has no state incentives, so our GT customers' primary
motivation is green, not economic. Also, in spite of this, we have installed
the most GT systems in the state, I believe. But that's only 17 systems
since
1997, both battery and b'less, for a total of 44+ kW. Note too that I am
only
including systems with a net metering agreement with a utility as GT
systems--we also have at least one battery-based system with grid backup.
Until 2001 it was all battery-based SW stuff. We installed our first b'less
system on 9/11/01. Since then only three systems have had battery storage.

How important is backup to your urban, suburban, rural users?
See above. Most of our rural users are off-grid.

What is the financial and efficiency cost of adding backup? Are your
customers aware of these costs?
We resolve battery/batteryless questions very early in the lead
development-educational process. My first two questions at an initial
meeting are "Where'd you get our name?" and "What's your primary
motivation?" I listen carefully to motivation. Only if "power during an
outage" is given as primary do I discuss batteries. Most people would prefer
a no-maintenance system. I explain why the system shuts down during an
outage, even if the sun is shining, and customers accept that explanation
(lineman safety/UL requirements) as reasonable.

How often do your batteryless PV system customers regret not having battery
backup?
Hasn't happened yet. We have used Sunnyboys exclusively for our b'less
systems, and I have explained to a couple of customers that in a year or two
the Sunny Island will be available to add to their system if they want
backup later.

How often do your grid-tie battery PV system customers regret not going
batteryless?
Hasn't happened yet. My message here is be clean and clear in communicating
with the customer; offer straightforward answers about what to expect;
under-promise and over-deliver. Our customers seldom have or express regrets
to us.

What other important things come to mind when you and your customers talk
about battery versus batteryless PV?
When I encourage b'less to a green-motivated customer, I point out that
while the system shuts down during an outage (and why), that's no different
than it was before the system was installed. Since most customers here
didn't come to us with "power during outages" as a primary motivation, it
becomes a non-issue for them.

Until recently, if a customer wanted GT with batteries, we encouraged them
to wait, as better technology was on its way than the current SW/GTI
hardware. Now that better choices are available, some aspects of our
approach may change. I think the biggest issue is dealing with site-specific
issues: how difficult is it to add a critical-loads subpanel and move some
existing circuits over to the new panel? I think our approach will not
change in a major way--we just have better solutions now when a customer
indicates that backup is of primary concern.

Allan at Positive Energy

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