Battery or non-battery UI? [RE-wrenches]

[Ezra Auerbach, Trace Engineering]

 Hi All,

My two cents worth follows from what Kirk has to say. There is a basic inefficiency which will always be
a penalty with Grid Tied/Battery Backup systems.  Yes I do hope that Trace or someone comes along and
makes it better than the 60-75% we see evidenced today.  I also expect that straight Grid Tie/PV will
always have an efficiency advantage.  In the end, I think that what the customer wants is defined by
their location, the reliability of their local utility, and their perceived dependence on full time
power.  Some of those folks are truly appropriated candidates for a hybrid battery based system. It's
all of our jobs to be sure that we let them know that there are efficiency trade off's to be had with
the reliability of full time power.  If we don't engender then with unreal expectations an equation
which states that "you will get about 65-70% efficiency from the inverter/batteries in Grid Tie
application, and back up power for a matter of days" is not such a bad deal.

Ezra Auerbach


"Kirk Herander, VT Solar" wrote:

> Hello Jeff,
>
> I  lean more towards battery-based UI. Once I explain to customers that they will have zero power for
> critical loads in a non-battery system
> should the power fail, most don't care about the economics or efficiency. They want critical load
> power to bridge the blackout.  They value this peace of mind more, and often bring up the "ice storm"
> of a few years ago to reinforce their own opinion. Because if you live out in the boonies, it may be
> days before power is restored after a bad winter storm, especially in a rural state such as Vermont.
>
> I don't have data to back this up, but I think that battery UI using a MPPT controller can make up a
> good bit of the efficiency losses in cool / cold (i.e. low panel temp) conditions if the controller
> is never allowed to leave bulk charge (by programming inverter sell voltage well below the bulk
> charge setting). Granted, MPPT efficiency varies from season-to-season, but it can help to justify
> battery-UI depending on application.
>
> regards, Kirk, Vt. Solar
>
> "Jeffrey Wolfe, Global Resources" wrote:
>
> > Based on the above, I have taken a very strong inititative to try to keep
> > on-grid people from buying a battery system. If they are living without
> > backup power now, I try to keep it that way. If they need backup power, I
> > look for options. (Computer UPS's are very cheap.) However, as we all know,
> > battery backup is a big selling point. (Here we are in marketing again!) So
> > we're spending time educating people. I've done the comparisons on cost.
> > For a small system, you're looking at about a 30-40% material adder, plus
> > more shipping and installation costs. (This is based upon using the new
> > Trace SL line tie inverters, versus those FETful SW's).)
> >
> > The only way you can touch a 15 year payback is with energy costs in the
> > mid teens per kWh, interest rate at 0%,  a direct grid tie batteryless
> > system, and a lot more sun than we get in Vermont. If you can make those
> > numbers work, give me a peak at them!
> >
> > Jeff
> >
> > Jeffery D. Wolfe, P.E.
> > Global Resource Options, LLP
> > A Woman-Owned Vermont Limited Liability Partnership
> > 4 Kibling Hill Road
> > P.O. Box 51
> > Strafford, VT 05072
> > 802/765-4632
> > 802/765-9983 (Fax)
> > global at sover.net
> > www.globalresourceoptions.com
> >
> > T
>
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for info contact: <michael.welch at homepower.com>
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