Round house [RE-wrenches]

Jeffrey Wolfe, Global Resources global at sover.net
Thu Oct 11 18:48:24 PDT 2001


William, while I do not have field experience with this, I have analyzed 
similar situations, and come to the same conclusions. Facing panels south 
isn't so important, but having very similar orientations on all panels tied 
to one MPPT device is. An option (that I have NOT thoroughly thought 
through...) would be to use an SW, with the smallest permitted battery bank 
(minimal battery drain losses), and then use multiple Solar Boosts to 
divide the array. Look at the costs, it might be less expensive, and allow 
you to really break the array down as far as you need to.

Keep us posted.

Jeff
Jeffery D. Wolfe, P.E.
Global Resource Options, LLP
A Woman-Owned Limited Liability Partnership
Trace Certified Dealer - Charter Member
Bergey Windpower Certified Dealer
4 Kibling Hill Road
P.O. Box 51
Strafford, Vermont 05072
800-374-4494 Toll Free
802-765-4632 Phone
802-765-9983 Fax
global at sover.net
http://www.GlobalResourceOptions.com


On Thursday, October 11, 2001 10:29 PM, William Miller 
[SMTP:wrmiller at slonet.org] wrote:
> Colleagues:
>
> I have a unique design challenge on my desk right now.  I'd like to
> describe it and solicit any input any of you may have.
>
> I have a potential grid tie client with a 12 sided, passive solar house.
> He designed and built it himself and it is quite nice.  He wants to 
install
> a grid tie system that will supply 100% of his power needs.  He has a 
large
> lot, but it is heavily forested and there are no ground areas that are 
not
> shaded.  His roof is large (the home has a radius of 40 plus feet), but 
is
> has many skylights and has some shading.
>
> I determined where we could shoehorn 36 panels onto the roof in areas 
with
> minimum shading.  These panels will by necessity be facing various
> directions, from 75 through 275 degrees true, in 30 degree increments.
>
> I performed an analysis on each group of panels.  I also analyzed the 
same
> number of panels facing due south.  The panels arranged around his roof
> will produce 93% of the power that the control group will.  This is great
> news.
>
> The supplier raised a point that has to do with the MPPT circuitry in the
> available grid tie inverters.  The MPPT values for a given panel change
> drastically if the orientation changes significantly in a given moment.
> Therefore, the panels facing 75 degrees will have different power point
> values than the panels facing 275 degrees.  Will this cause a problem 
with
> the MPPT electronics on a Sunny Boy or an ST inverter?  I suspect it 
will.
>
> One work-around would be to provide 2 or 3 inverters and wire them to
> similarly oriented panels.  This, by the way, is much more easily done 
with
> the ST series inverters as they require only 4 12 volt modules in a 
string.
>  This is indeed the advantage of the ST 4 module string wiring, a point I
> have been meaning to make since a recent posting to Wrenches asking about
> the lower voltage strings.  I might also add that the ST inverters have 
the
> metering, ground fault interrupter and input and output breakers built 
in.
>
> Please let me know if any of you have any experience with any scenarios
> such as the one described here.
>
> Thanks.
>
> William Miller
>
> __________________________________________________________________
> William Miller
> SLO Communications: Communications and Power Systems Consulting
> PO Box 50, Santa Margarita, CA 93453
> Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
> email: wrmiller at slonet.org
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