Design Challenge (Was Sunny Island Experience?) [RE-wrenches]
William Korthof
wkorthof at earthlink.net
Sun Feb 5 11:57:57 PST 2006
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A thought here... is the generator capable of self-synchronizing its
output? If it can sync to the inverters' output, here's a configuration
that might cut the wire cost and complexity...
Solar array on grid-tie inverters located at corner A of triangle
(A connected to B with (3) 3/0 aluminum sets or single 500 MCM set)
Houses/loads, and battery Inverters on corner B of triangle
(B connected to C with (3) 3/0 aluminum sets or single 500 MCM set)
Generator connected on corner C of triangle
All power components are coupled through a common 240Vac AC bus...
-Use grid tie inverters for all of the PV output. Use a battery voltage
monitor to shut off SMA inverters (staged relays) on high batt voltage.
-Operate the generator by two signal inputs: (1) operate it when battery
voltage drops below a determined threshold (2) operate it when load on
the battery inverters exceeds a determined threshold (say, 40A for 15
seconds measured by a load monitoring sensor).
With this method, any grid tie inverter output (PV production) would
automatically displace demand on the battery inverter output, increasing
the capacity to handle peak loads during daytime hours. Power flows run
the shortest possible distance and at reasonably convenient voltage.
Average load voltage drop for PV to load is under 1%, leaving room for
2-3x expansion
Voltage drop Generator to load = 2.5% @120A, or 1.8% @more typical 20kW.
The loads past the generator spot should have acceptable voltage drop in
all cases so long as the feeder from generator to them is sized ~1% drop
Have customer try to run loads during PV output hours and they should be
able nearly avoid use of the generator for peak load demands.
Maybe I'll think about this some more...
/wk
Jeff Clearwater wrote:
> 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
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~
>
>
>
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