[RE-wrenches] grid tie sync with big stiff genny?

[Darryl Thayer]

HI All
This system is very large and is out of my experience range.  BUT I have seamlessly integrated a 40 HP motor and a grid/generator/solar tie.  We also do a related lab experiment in my solar class.  Voltages may make these methods prohibitive in your case prohibitive in your case.  This is a little bit outside of the box so read carefully.

Your load is mostly motors, probably with a much much smaller need for 120/208 lighting and plug loads (perhaps less than one percent).

Motors and particular pumps for a water system are on speed drives for reasons of control and energy savings.  These speed drives have DC busses that operate from AC power sources and drive AC motors.  

DC coupled solar gen set
The DC from the solar array can be feed directly into a VFD "speed drive's" DC buss.  In our lab experiment the students connect the solar array directly into a 10 hp VFD, and 3 phase motors are driven from the speed drive.  The array voltage must be in range of the allowed VFD bus voltage, the speed drive will stop drawing AC as the array provides all the power, current, and share current as the array power drops.  The problem is of course you do not have MPPT on the array.  The second approach is to use an inverter from the Array and boost the voltage above 10% or so above the AC voltage of the AC mains and rectify the this to power the DC bus of the VFD.  Caution the non-linier load of the rectifier may overload the inverter.  

I have done the first suggestion, but not the second.  
DT   


--- On Thu, 3/12/09, Drake Chamberlin <drake.chamberlin at redwoodalliance.org> wrote:

> From: Drake Chamberlin <drake.chamberlin at redwoodalliance.org>
> Subject: Re: [RE-wrenches] grid tie sync with big stiff genny?
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Thursday, March 12, 2009, 9:40 PM
> This should be possible.  I have discussed what it might
> take to set 
> up a system like that in the Gambia, with wind generators. 
> It would 
> take a control system with differential current sensors and
> other 
> features.  The UL 1741 specifications would probably need
> to be 
> opened up on multiple direct grid tie inverters. There
> would be a 
> practical limit on the percentage of feed to the generator
> mini grid.
> 
> This being said, I've not received much encouragement
> with this 
> idea.  There are a lot of factors to consider.
> 
> 
> At 09:35 AM 3/11/2009, you wrote:
> 
> >Undoubtably many of us are getting interesting project
> requests as 
> >folks want to sprinkle magic stimulus dust on things to
> make solar 
> >panels grow...
> >
> >
> >
> >We have a project with a huge electrical load, pumping
> water for a 
> >medium sized city.  They want solar... great.  Easy.
> >
> >
> >
> >They had a power outage and kept running with 2.6 MW of
> diesel 
> >generators.  They are interested in solar's ability
> to do 
> >"backup".  I don't think that many
> batteries will fit in my pickup 
> >truck, and I hate working with 300/0 wire.
> >
> >
> >
> >QUESTION:  (and maybe its an easy one and the SMA guys
> will say, 
> >sure, we did that in Greece).  Is it viable to set up a
> micro-grid 
> >in this scenario and run an island-mode, with available
> solar 
> >reducing the genny plant demand?  Should I just say
> "forget it" or, 
> >at this MW scale, would the switchgear and effort be
> practical?
> >
> >
> >
> >Thanks.
> >
> >For a brighter energy future,
> >
> >Geoff Greenfield
> >President
> >Third Sun Solar & Wind Power Ltd.
> >340 West State Street, Unit 25
> >Athens, OH 45701
> >
> >740.597.3111     Fax 740.597.1548
> >www.Third-Sun.com
> >
> >Clean Energy - Expertly Installed
> >
> >
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> Drake Chamberlin
> Athens Electric
> OH License 44810
> CO License 3773
> 740-448-7328
> 740-856-9648  
> 
> 
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