Design Challenge (Was Sunny Island Experience?) [RE-wrenches]
Jeff Clearwater
clrwater at earthlink.net
Sat Feb 4 12:21:00 PST 2006
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Hi Good Colleagues,
Thanks for the feedback Jeff and Travis - good to hear AC coupling is
out there and being used successfully in the US!
OKAY DESIGN MINDS - Here's my design challenge - input most
appreciated! Consolation prizes available after the contest (just
kidding).
I'm designing a multi-residence off-grid system with 12 KW PV, 30 KW
(120 A) Diesel Genset, 12-15 KWs of inverter loads with about 24 KW
peak, a 100 KWH battery pack and the following long distances between
components:
Picture an equilateral triangle with roughly 600 foot sides. Point 1
is Loads, Point 2 is Generator, Point 3 is PV array site. This is
pretty close to the actual situation on the ground (as unfortunate as
that might be). Close enough for easy discussions. Power Shed has
yet to be located: Generator site is practically set in stone.
There are also some loads past the Genset side of the triangle.
In the future we will also have wind and hydro coming in from about
2000' away from the PV side of the triangle. Generator is in and
can't be moved, neither can the house complex, and the PV site is the
only one non-shaded so it's a given too.
PROPOSED SYSTEM #1: 4 Sunny Islands (2 sets of 2 stacked split
phase) in power shed located near the generator shed. This allows us
to feed the long distance array to the system at high voltage -
either high voltage DC or 240 VAC depending on where we located the
SB. It also allows us to not have a ditch and conduit along the
PV<>Power Shed side of the triangle as the PV can feed into the AC
line at the house. It also allows us to to feed Windy Boys and Hydro
Boys at high voltage in the future to any point on the system.
MAJOR DISADVANTAGE: Unfortunately the present US version of the SI
only allows 2 SIs stacked in split phase with no parallel stacking
for bigger systems. So that means we'd have two sets of the
batteries, two sets of AC, 3-wire outputs at 56 amps each instead of
of one at 120. And the load peaks would have to always be
distributed amongst the outputs to handle the peaks and overall
loads. It also means that any expansion faces the same hassle.
PROPOSED SYSTEM #2: 8 Stack of Outbacks located near the array.
MAJOR DISADVANTAGES: A 1200' line and ditching would have to be
added from gen site to array/power shed to house to feed the
inverters from the generator with major sized wire as all power would
have to be fed through inverters. - 120 Amps of 240 now having to go
1200' (over 4% drop using 750 MCM) when there are already existing
AC wire runs are from Generator to house. So all the power would
have to run around two sides of the triangle to get to the load and
the existing 600' of 3/0 Al 3 wire goes unused. . Also another AC
line would have to be run back to feed the loads that I didn't
mention that are on the other side of the generator from the house.
Getting into massive AC wire runs here just because we are limited to
the MX60s voltage for charging from the array and hence need to keep
the power shed close to the array. Future wind and hydro inputs
will work if we use a HV/LV scheme (240-600 V Alternator rectified to
48VDC at power shed) as they are closer to the array. All future PV
or other input expansion would have to come to this power shed,
however - not be able to tie in anywhere on the AC "grid" as in the
SI/SB system.
SO I SEE THIS SITUATION AS THE PERFECT ILLUSTRATION OF THE NEED AND
LIMITIATIONS IN THE INDUSTRY. I do alot of small village power
systems. AC coupling is the cat's pajamas, IF you have the european
SI!
On the SI side, the limitation of no parallel stacking is a MAJOR
problem. Kind of eliminates the whole point of AC coupling for
larger systems - the flexibility to grow systems and feed them
anywhere on the AC side with high voltage. On the Outback side no AC
coupling means that array and generator have to be close to the power
shed and all future inputs are relegated to DC (which for wind and
hydro is not too bad as you can do them high voltage AC and then
rectify and transformer down). But in many situations (not this
one) having to always come back to one point instead of being to tie
into the AC grid anywhere on the property will always be a major
limitation.
SO QUESTIONS AND POSSIBLE SOLUTIONS:
1) I could try to do a SB running into an Outback stack located near
the gen shed. But we are talking 12 KWs of PV here - with no
software talking - this could get hairy. And I'd have to run control
wire between SB and Outback for the relay.
2) Any charge controls out there that go higher voltage than the
MX60s 72 volt nominal? If I run the calcs of trying to run even the
72 volt (figure 84 volt input?) 600 feet so I can have my power shed
at my genset, we are looking at over 750mcm wire! not going there.
What we need is a 500 VDC MPPT charge control that feeds into 48!
3) I can play with locating the power shed at various places within
the triangle . . . . . but all the problems are still there - just
trading off different sets of problems for other sets.
4) According to SMA an updated version of the SI is planned -
hopefully with increased parallel stacking (and hopefully throttling
of inverters like the Outbacks). According to rumors, Outback is
looking at AC coupling. In the meantime my client is burning through
THOUSANDS of dollars of diesel running that 30 KW genset to just to
cook breakfast. The race is on. In the meantime, what do I do?!!!!!
Well if you read this far, this post should raise some discussion!
Let's be gentle on both SMA and Outback now folks! It's great we can
even be having this discussion thanks to the great innovation from
both companies!
Have at if if you will!
Thanks!
Jeff Clearwater
Village Power Design
>Hi Jeff,
>
>About 6 months ago we set up an off grid system with two SI's coupled with
>three SB3800's and about 9 kW of Sanyo HIT's spread evenly amongst the
>SB3800's. It's all set up as 120/240 with no transformers.
>
>No problems after we upgraded the software. Everything talks and gets along
>fine.
>
>Travis Creswell
>Ozark Energy Services
>
>-----Original Message-----
>From: Jeff Clearwater [mailto:clrwater at earthlink.net]
>Sent: Friday, February 03, 2006 4:37 PM
>To: RE-wrenches at topica.com
>Subject: Sunny Island Experience? [RE-wrenches]
>
>Hi Folks,
>
>Anyone running SBs into SIs with AC coupling? What's your experience been?
>
>I talked to SMA a few times about running WBs and HBs into SIs, but
>was advised that that would be smoother when SI version 2 is released
>- but they didn't know when that would be. Anyone try that yet?
>
>Apparently version 2 may have true multimastering as well - where
>you can have different SIs on different points on the AC network,
>have SBs feeding in and not have the two SIs confuse or compete with
>each other. The present SIs don't support that.
>
>Thanks in advance!
>
>Jeff C.
>Village Power Design
>--
>~~~~~~~~~~~~~
>Jeff Clearwater
>Village Power Design Associates
>Sustainable Energy & Water Solutions for Home & Village
>http://www.villagepower.com
>gosolar at villagepower.com
>
>530-470-9166
>877-SOLARVillage
>877-765-2784
>425 Nimrod St.
>Nevada City, CA 95959
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~
--
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design Associates
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com
530-470-9166
877-SOLARVillage
877-765-2784
425 Nimrod St.
Nevada City, CA 95959
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~
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