Re: [RE-wrenches] Interconnection with Generator

[Chris Mason]

Using PV and battery backup to reduce generator run time is a no-brainer,
and we all are familiar with that sort of stuff. But using PV to augment a
Prime Power generator is not going to work at small generator sizes for a
couple of reasons.
1) Small generators are not built to run continually.
2) Any diesel generator will wet stack and experience problems with
blow-back if ran without load. So you have to load the generator anyway.
I don't think grid tied PV can offer a serious advantage with one generator.

I recently did a design for a 4MW power plant using 5 x 800KW generators
and 400KW of PV, and using ComAp controllers and SMA Fuel Save technology.
This works because there was five generators, so the generators could be
taken offline progressively as the PV came online. Include some grid
storage and it all gets very interesting. You can model all of this in
Sunny Design 3+. Very cool software.






On Tue, Oct 28, 2014 at 7:35 PM, 
wrote:

> Hi:
>
> Xantrex did some early work on generator with inverter compatibility back
> in 2007.  AC coupling PV to generators was very new back then and we wanted
> to find the benefit of using a battery based inverter to reduce the run
> time of generators.  One system was a small 5kW off-grid house and the
> second a 90kW generator running a couple of dozen homes.  For the trial is
> set up with power monitoring for back-feed and much more.
>
> The systems are still running.  Here are a few training slides which
> summarize the results and a link to the archived study from 2007 at the
> Natural Resources Canada.
>
>
>
>
> http://www.nrcan.gc.ca/energy/publications/sciences-technology/renewable/solar-photovoltaic/6215
>
> The bullet form summary is:
>
> - The smaller the generator, the large the savings whether you grid tie to
> the generator or use a battery based inverter to reduce generator run time.
>
> - PV is not needed to get the bulk of the savings in systems using battery
> based inverters to reduce run time of small generators.
>
> JARMO
>
>
> On Oct 28, 2014 4:48 AM, "Corey Shalanski" <*cshalan...@joule-energy.com*
> > wrote:
> Wrenches,
>
> We frequently encounter residences with backup generators. The question
> that arises: how should the PV system be interconnected?
>
> I have searched the archives and found some good information about this
> subject, but nothing definitive. I have fallen into the habit of broadly
> proclaiming that the PV system *must* be interconnected on the "utility"
> side of the transfer switch - in order to prevent backfeeding into the
> generator and thereby eliminate unintentional equipment damage. Is this
> concern justified? If so, should this be an absolute rule or would it
> depend on the generator make/model?
>
> Thanks for any insights.
>
> --
> Corey Shalanski
> Joule Energy
> New Orleans, LA
>
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Re: [RE-wrenches] Interconnection with Generator

[Dave Click]

The inverter to generator ratio is entirely the designer's call and 
comes into play for large generators (for residential systems as 
mentioned in earlier replies, it's a bad idea).


Interconnecting in spot networks in dense urban areas has a similar 
issue in that the distribution system can't handle backfeed. In downtown 
Boston a few years ago I believe that the max PV that could be 
interconnected was something like 1/10 or 1/15 of the demonstrated 
MINIMUM demand for that building over the previous year-- just to make 
absolute sure that there wasn't a chance of backfeed. Other solutions 
include things like reverse power relays such that if the PV system does 
start backfeeding the system, the relay would trip the inverter offline.


Of course any time you're interconnecting on the load side, you of 
course take responsibility for anything bad that happens with the 
generator. This should lead to an extremely conservative ratio being 
used and regular monitoring to verify that the PV never comes close to 
backfeeding something it shouldn't. Also, any issues with power quality 
(real or perceived) can complicate your project substantially, thinking 
of William's recent issues with the UPS and Sunny Islands. I wonder if 
this could complicate a generator warranty, too, unless you were somehow 
able to get the manufacturer's blessing ahead of time.


Another comment I remember from an earlier Wrench conversation was that 
inverter contributions on the load side of a generator won't 
proportionally drop fuel consumption-- that is, if your generator's load 
is 500kW and your PV is putting out 250kW, you're not going to have a 
50% reduction in fuel use. So it takes some equipment-specific analysis 
to figure out what exactly your customer's savings would be.


DKC



On 2014/10/28 12:35, Phil Forest wrote:

Interconnecting the inverter output to the utility side of the transfer switch 
is not necessarily an absolute rule. A knowledgeable solar EE told me a few 
years back, that interconnection can be made on the load side if the inverter 
kW output is small compared to the generator kW, that large kW generators can 
produce clean AC power allowing the inverter to operate and to operate without 
risk of burning out the generator.  I don't remember what the inverter to 
generator ratio needs to be, or if other criteria needs to be met.
Never tried it, we always connect to the utility side.

Phil Forest
South Mountain Company


On Oct 28, 2014, at 10:48 AM, Corey Shalanski  
wrote:

Wrenches,

We frequently encounter residences with backup generators. The question that 
arises: how should the PV system be interconnected?

I have searched the archives and found some good information about this subject, but 
nothing definitive. I have fallen into the habit of broadly proclaiming that the PV 
system *must* be interconnected on the "utility" side of the transfer switch - 
in order to prevent backfeeding into the generator and thereby eliminate unintentional 
equipment damage. Is this concern justified? If so, should this be an absolute rule or 
would it depend on the generator make/model?

Thanks for any insights.

--
Corey Shalanski
Joule Energy
New Orleans, LA
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Re: [RE-wrenches] Interconnection with Generator

[Chris Mason]

We run into this a lot in the Caribbean. Our general rule is that it
depends on the load. If it is a constant commercial load and the PV is
about half of the load, no issue. But for residential and where PV exceeds
the lowest load, we prefer to be on the utility side of the ATS or use a
contactor on the PV combiner held in by the utility power.

On Tue, Oct 28, 2014 at 10:48 AM, Corey Shalanski <
cshalan...@joule-energy.com> wrote:

> Wrenches,
>
> We frequently encounter residences with backup generators. The question
> that arises: how should the PV system be interconnected?
>
> I have searched the archives and found some good information about this
> subject, but nothing definitive. I have fallen into the habit of broadly
> proclaiming that the PV system *must* be interconnected on the "utility"
> side of the transfer switch - in order to prevent backfeeding into the
> generator and thereby eliminate unintentional equipment damage. Is this
> concern justified? If so, should this be an absolute rule or would it
> depend on the generator make/model?
>
> Thanks for any insights.
>
> --
> Corey Shalanski
> Joule Energy
> New Orleans, LA
>
> ___
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>


-- 
Chris Mason
NABCEP Certified Solar PV Installer™
Solar Design Engineer
Generac Generators Industrial technician

www.cometsolar.com 
264.235.5670
869.662.5670
Skype: netconcepts
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Re: [RE-wrenches] Interconnection with Generator

[Phil Forest]

Interconnecting the inverter output to the utility side of the transfer switch 
is not necessarily an absolute rule. A knowledgeable solar EE told me a few 
years back, that interconnection can be made on the load side if the inverter 
kW output is small compared to the generator kW, that large kW generators can 
produce clean AC power allowing the inverter to operate and to operate without 
risk of burning out the generator.  I don't remember what the inverter to 
generator ratio needs to be, or if other criteria needs to be met. 
Never tried it, we always connect to the utility side. 

Phil Forest
South Mountain Company

> On Oct 28, 2014, at 10:48 AM, Corey Shalanski  
> wrote:
> 
> Wrenches,
> 
> We frequently encounter residences with backup generators. The question that 
> arises: how should the PV system be interconnected?
> 
> I have searched the archives and found some good information about this 
> subject, but nothing definitive. I have fallen into the habit of broadly 
> proclaiming that the PV system *must* be interconnected on the "utility" side 
> of the transfer switch - in order to prevent backfeeding into the generator 
> and thereby eliminate unintentional equipment damage. Is this concern 
> justified? If so, should this be an absolute rule or would it depend on the 
> generator make/model?
> 
> Thanks for any insights.
> 
> --
> Corey Shalanski
> Joule Energy
> New Orleans, LA
> ___
> List sponsored by Redwood Alliance
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> List Address: RE-wrenches@lists.re-wrenches.org
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Re: [RE-wrenches] Interconnection with Generator

[Daniel Young]

We also go to the utility side as a rule. 

We have only one exception. A 60kW Solectria inverter is tied into a
building system that is supported by a 1 MW generator. It's a university
heating plant where it was clearly shown the base load was far larger than
the 60kw solar PV system, even when the plant was at "idle". The facility
had a building management system with historical 15min usage data to support
this.

Unless you have hard data that your solar inverter will never ever meet the
buildings real-time demand, tie into the grid side. This is best practice to
the best of my knowledge.

With Regards,

Daniel Young, 
NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90
NABCEP Certified Solar Heating InstallerTM: Cert #SH031409-13
 

-Original Message-
From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On
Behalf Of Aaron Mandelkorn
Sent: Tuesday, October 28, 2014 11:20 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Interconnection with Generator

I always connect to the utility side of the transfer switch. Since the
transfer switch is a listed electrical enclosure it is the best option I
have used. 

Aaron

Aaron Mandelkorn
Owner/Solar Specialist
Renewable Energy Outfitters
719-221-5249
970-596-3744
www.reosolar.com
reoso...@gmail.com


> On Oct 28, 2014, at 8:48 AM, Corey Shalanski 
wrote:
> 
> Wrenches,
> 
> We frequently encounter residences with backup generators. The question
that arises: how should the PV system be interconnected?
> 
> I have searched the archives and found some good information about this
subject, but nothing definitive. I have fallen into the habit of broadly
proclaiming that the PV system *must* be interconnected on the "utility"
side of the transfer switch - in order to prevent backfeeding into the
generator and thereby eliminate unintentional equipment damage. Is this
concern justified? If so, should this be an absolute rule or would it depend
on the generator make/model?
> 
> Thanks for any insights.
> 
> --
> Corey Shalanski
> Joule Energy
> New Orleans, LA
> ___
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Re: [RE-wrenches] Interconnection with Generator

[Aaron Mandelkorn]

I always connect to the utility side of the transfer switch. Since the transfer 
switch is a listed electrical enclosure it is the best option I have used. 

Aaron

Aaron Mandelkorn
Owner/Solar Specialist
Renewable Energy Outfitters
719-221-5249
970-596-3744
www.reosolar.com
reoso...@gmail.com


> On Oct 28, 2014, at 8:48 AM, Corey Shalanski  
> wrote:
> 
> Wrenches,
> 
> We frequently encounter residences with backup generators. The question that 
> arises: how should the PV system be interconnected?
> 
> I have searched the archives and found some good information about this 
> subject, but nothing definitive. I have fallen into the habit of broadly 
> proclaiming that the PV system *must* be interconnected on the "utility" side 
> of the transfer switch - in order to prevent backfeeding into the generator 
> and thereby eliminate unintentional equipment damage. Is this concern 
> justified? If so, should this be an absolute rule or would it depend on the 
> generator make/model?
> 
> Thanks for any insights.
> 
> --
> Corey Shalanski
> Joule Energy
> New Orleans, LA
> ___
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Re: [RE-wrenches] Interconnection with Generator

[Jerry Shafer]

We make it a rule simple and safe. We have 3 to 500 k gen-sets and its all
the same
On Oct 28, 2014 4:48 AM, "Corey Shalanski" 
wrote:

> Wrenches,
>
> We frequently encounter residences with backup generators. The question
> that arises: how should the PV system be interconnected?
>
> I have searched the archives and found some good information about this
> subject, but nothing definitive. I have fallen into the habit of broadly
> proclaiming that the PV system *must* be interconnected on the "utility"
> side of the transfer switch - in order to prevent backfeeding into the
> generator and thereby eliminate unintentional equipment damage. Is this
> concern justified? If so, should this be an absolute rule or would it
> depend on the generator make/model?
>
> Thanks for any insights.
>
> --
> Corey Shalanski
> Joule Energy
> New Orleans, LA
>
> ___
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