Wednesday, 2 January 2013

Sync diesel generator with solar grid inverters - during Islanding condition

Abstract: As mentioned in my previous blog on solar grid interactive inverters, there are various issues involved with solar grid inverter for Indian conditions. Now in this blog I will be discussing more about the issues and methods to integrate/synchronize a grid connected inverter with diesel generator during a power cut/grid failure. In states like Tamil Nadu we have power-cuts every day, so the solar rooftop owner will try to consume all the power generated from solar and reduce its dependence on diesel generators.

The inverters do not start without the reference voltage and frequency, so during this islanding condition the rooftops owners cannot use their solar power generated. The owners usually consider solar as a backup for power cuts and also consider payback by selling excess generated. Now the only solution in the market is the hybrid inverters, but these are very expensive compared to normal grid inverters. But what about installations with existing grid inverters? Most of the rooftop owners are not aware of these islanding conditions and the EPC vendors just install existing grid inverters without any alteration proposed below.

What I propose here is, the grid inverters needs to be connected to a common bus bar. In the common Bus-bar all the sources and loads are connected. During the islanding condition the DG switch ON to generate reference voltage and frequency to start up the solar grid inverters (we fool the inverters here). Once the inverter is ON the load will be supplied by both inverter and DG sets (at low RPM). Is it practically possible to synchronize a grid tie inverter with a diesel generator (DG sets) and make it work? ie. during a power failure, when grid power is not available.

I feel its possible only under the following condition's 
  • We have a stable/good quality generator which gives good stable voltage and frequency. 
  • The other condition is the generator should not sag, dip or create any surge current when the inverter turns ON. 
Lets now consider that the inverter has turned ON using the DG sets reference voltage and current. I see two possible conditions now,
  1. The load is always more than the PV generator supply
  2. Possibility that load can be less than PV generator supply
During the condition 1, i do not see any issues if everything works fine. 
But during the condition 2, the power generated from PV will be greater than the load requirements and hence there is a possibility that this current will be fed to the ac line of of the bus bar / DG sets (stator of DG sets). What will happen during this condition? We can expect a rise in AC voltage and frequency- above critical level. If this happens, this condition can trip the inverter due to over-voltage/frequency protection circuits. Now the rooftop owner cannot consume power from the solar and therefore he is forced to operate the DG sets. This condition can also damage the vital parts of the generator, here the protection of generators become very important. 

How to custom design the distribution panel board to use the solar generator during the condition 2 and also protect the DG sets? I also foresee very high requirement of a effective control system, which can handle all the above and below conditions

- Using a dump load to remove the excess power generated. 
- Effective control of loads  (To increase or decrease the load as per requirements using PLC based controls) 

I can also see that there will be no commercial benefit in running a generator just for reference voltage and current. This is because when we operate the DG sets running at lower efficiency (20-30%) or less than its rated value can consume more fuel than during rated power (ie. 85-100% efficiency). This can be solved by using a smaller DG sets (Just for the emergency load) than the required full load size, but the disadvantage is during power failure in the evenings or night.
 

67 Comments:

At 30 January 2013 at 02:16 , Blogger pankaj shende said...

How to custom design the distribution panel board to use the solar generator during the condition 2 and also protect the DG sets? I also foresee very high requirement of a effective control system, which can handle all the above and below conditions

- Using a dump load to remove the excess power generated.
- Effective control of loads (To increase or decrease the load as per requirements using PLC based controls)

Can you please elaborate these two possiblities in details.

 
At 31 January 2013 at 08:15 , Blogger CareyGlass Solar said...

We also need to consider the capacity ratio between Dicess PV currentesel Generator (DG) and PV Plant. As we all know grid is considered as unlimited bus, but DG is a finite bus. Therefore as per practical experience, PV Plant size should not exceed 50% of the DG capacity.

Excess PV power (when load is less than PV generated power)cannot flow to DG set if we put reverse protection relay between Inverter & DG set.

 
At 1 February 2013 at 03:54 , Blogger Rex said...

When the DG starts it does not start at 50Hz and it takes time to run on a constant frequency of 50HZ. The inverter should be selected in such a way that it can handle the drop and rise of frequency. As most inverters in the market are designed only to handle highs and lows of grid than DGs. I would prefer to give a delay circuit for 2mins before the syn. with the inverter.

 
At 1 February 2013 at 04:00 , Blogger giridaran srinivasan said...

Hello Rex,

Thanks for your inputs and your interest in this article. I guess most of the GT inverters in the market start only when the grid frequency and voltage is stable at least for 1-5min (checked with Inverter manufacturers). So i see no problem in this. Latest high quality diesel generators in the market has the capability to work exactly like Grid, so i see no issues with the DG sets too.

 
At 1 February 2013 at 04:18 , Blogger giridaran srinivasan said...

Hello CareyGlass Solar,

Thanks for your inputs. Yes you are right regarding the reverse current relays, these are very useful in finding the reverse current entering the stator part of the generator. I have been continuously working on this topic since my post on Jan 2nd (almost a month now), i have a updated paper on this topic which has been sent for publishing (this includes the concept of reverse current relays).

I will share my finished article here once it is published in the magazine. Thanks again for you useful comments and your interest.

Regards,
Giridaran Srinivasan

 
At 26 February 2013 at 11:30 , Blogger lucifer said...

Giridharan,
I am working on a similar system in India in mumbai ..can't give out company name on a blog ...can you get in touch with me at apuravonline@gmail.com

Thanks

Apurav

 
At 6 May 2013 at 05:53 , Blogger Tony Robbins said...

A diesel generator is the combination of a diesel engine with an electrical generator to generate electric energy. Diesel generators are mostly used without connection to the power grid or even as a standby power-supply in case of grid failure. Small portable diesel generators range from about 1kVA to 10kVA, while the larger industrial generators can range from 8kVA - 30kVA for homes, small shops & offices up to 2000kVA used for large office complexes, factories. Sizes up to about 5 MW are used for small power stations and these may use from one to 20 units. These generators are widely used not only for emergency power, but also many have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators.

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At 11 May 2013 at 16:58 , Anonymous Anonymous said...

Solar installations are expensive because they are mainly an asset at this day in age with the broken economy, though it is very worth it. Once the panels are paid off within a couple of years, you have a free energy producing home. diesel generator for sale.

 
At 19 May 2013 at 02:41 , Blogger amu said...

Amit Sakariya from Navkalp groups hear i give u asuggestion to replace the generator with installation off solar hybrid system..our system is contineously 24 hours working in gujrat state 2kva off grid plant...it reduce your capital investment in generator & life time relise with diesel..

 
At 19 May 2013 at 02:42 , Blogger amu said...

WWW.navkalpgroups.com plz visit the site

 
At 5 June 2013 at 05:56 , Blogger Tony Robbins said...

A diesel generator is the combination of a diesel engine with an electrical generator to generate electric energy. Diesel generators are mostly used without connection to the power grid or even as a standby power-supply in case of grid failure. Small portable diesel generators range from about 1kVA to 10kVA, while the larger industrial generators can range from 8kVA - 30kVA for homes, small shops & offices up to 2000kVA used for large office complexes, factories. Sizes up to about 5 MW are used for small power stations and these may use from one to 20 units. These generators are widely used not only for emergency power, but also many have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators.

 
At 16 June 2013 at 22:04 , Blogger Violet Jessy said...

Nice one about diesel generators!

 
At 19 June 2013 at 21:18 , Blogger Raj Mohan said...

what will happen if we put reverse power relay?. Weather it will shut down DG or it will not allow the reverse power to DG?

 
At 22 August 2013 at 01:51 , Blogger suki lee said...

i like your post its very informative. keep sahring more.
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At 27 August 2013 at 10:10 , Blogger sparik said...

Can someone help me to note the limitations of the Grid tie system synchronisation with Diesel Genset power ? My points are..
1. Sizing point of view what is best one ? 1:1:1 or 1/2:1:1 OR1:1/2:1 OR 1:1/2:1/2 FOR PV:DIESEL:LOAD ????
2. Which is the most economical method for controlling the most efficient ratio of DG:PV ?
3. What is the protections required other than Reverse Power protection relay between PV Inverter and DG ?
4. How the Fuel saver controller can help to save the diesel as claimed by few reputed companies when the DG Sets are operating below its most efficient operating point?
5. What is the minimum size of PV Diesel Hybrid system be efficient and benefitial? i mean, can we go for small domestic DG set or it is benefitial at Industrial applications with bigger DG sets?
-sunilparik@gmail.com
Please reply.

 
At 28 August 2013 at 22:45 , Blogger giridaran srinivasan said...

Hello Sunil,

Nice to see you here. Please refer my latest blog on DG here. It will answer most of your questions.

Regards,
Giridaran Srinivasan

 
At 21 October 2013 at 05:46 , Blogger YB Suresh said...

Very well written story. It will be beneficial to anybody who employs it, including me. Keep doing what you are doing – looking forward to more posts.
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At 13 December 2013 at 03:18 , Blogger Arun Sharma said...

dieselpower.in are produces very good way for customers across the country have risen too. We can do so without fear or business can run smoothly. Without electricity cuts. The prosecution has now been outside the country abroad. Due to the imports and exports of raw materials abroad. Metal Works the way these cold, cold metal cabinets, metal Acoustic Enclosures Cold, Cold Metal Fabrication, Causes control Panel Boards, Kanak considered part of fabrication generator.


 
At 3 January 2014 at 07:49 , Blogger Naveen Murali said...

Nice post about Solar Inverter. We are also manufacturers and Suppliers of Solar Inverter in India.

 
At 5 March 2014 at 05:17 , Blogger vignesh iyer said...

hi, giridhar.. we have the same problem whenever we combine the solar with DG.. its frequecy gets varied when the solar generates its output.. is there is any synchronising relay for merge the both DG & solar generated voltages to get the output.. if it is possible means pls suggest the type & capacity of the relay.. our solar power should be 100KW & DG is 200KW..

 
At 8 March 2014 at 04:13 , Blogger giridaran srinivasan said...

Hello Vignesh,

Thanks for your comments. I can see that the PV penetration is almost 50% of the DG capacity, so there can be some issues like you mentioned. Please get in touch with me directly for the solution.

Thanks.
Giridaran Srinivasan
+91-98847 27147

 
At 9 April 2014 at 07:56 , Blogger Naveen Murali said...

Nice post about Solar Inverter. We are also Manufacturers and Suppliers of Solar Inverter in Bangalore, India.

 
At 9 April 2014 at 23:16 , Blogger Sushant Jain said...

Dear Giridaran

Thanks for the article. It strengthen my belief that I can run my PV system on DG. I am doing a new setup at my unit in Gurgaon, Haryana of 6KW rooftop PV. And I am putting the new technology i.e. microinverters along with the panels (At least new for me). And I hope that once the mains is out and DG is ON, the panels would still give output. I have a 32.5KVA DG set and now with so many AC's, it becomes insufficient to support the load. Instead of upgrading the DG set and going the wrong way, I am hoping to use solar. Hope my plans work out.

Any suggestions?

Regards

Sushant

 
At 20 April 2014 at 00:02 , Blogger Ramesh Pakala said...

In scenario 2 ,you need to cut SPV Generation to reallu utilise the Solar o/p. the DG shall be on no load.
or have a referencing inverter with battery back up facility and altogether do away with DG.

 
At 9 May 2014 at 05:42 , Blogger Naveen Murali said...

It is one of the useful information blog. The SolarInverter helps us to fulfill the needs of home appliances as well as for professionals to save money and eco friendly. And we are the best manufacturer and Exporter of solar inverter in India.

 
At 9 May 2014 at 05:43 , Blogger Naveen Murali said...

It is one of the useful information blog. The SolarInverter helps us to fulfill the needs of home appliances as well as for professionals to save money and eco friendly. And we are the best manufacturer and Exporter of qpcsolarinverter solar inverter in India.

 
At 29 August 2014 at 01:52 , Blogger KNS PRABHAKAR said...

Good morning every one.
one of our installation,5okw grid tied system installed but we r also facing same problem.If load exceeds its generation no problem but it is under the solar generation at generator synchronizing with solar.At he time the balance power definitely reverse flow to generator(160kva).we r heared that the generator capacity is 3 times greater than the reverse power there is no problem on that time.I am sure this information is works r not.so,please help me in this case.my email id is kns07207@gmail.com,9961029272

 
At 5 September 2014 at 22:57 , Blogger Niroj said...

Fine post on Solar Power Generator. Explore more about Solar Power Generator

 
At 21 April 2015 at 06:30 , Blogger Adpower.ae said...

Thanks for the post, I will look forward to see more posts from your blog and and also about
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At 6 May 2015 at 03:25 , Blogger Perfect Sales said...

Thanks for sharing very nice post
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At 28 May 2015 at 02:34 , Blogger Power One said...

Very interesting post Coop! Thanks for sharing it! It is always a joy to learn something that I didn't know. I have you to thank for teaching me something new, and I appreciate it very much. :-)

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At 9 July 2015 at 01:45 , Blogger Bimal Luthra said...

Dear Sushant

I am planning to put up a 1 MW solar plant on rooftop. Would like to speak with you and take benefit of your experience.

Thanks

Bimal 9811157677

 
At 6 September 2015 at 23:04 , Blogger Raghvendra Singh said...

Which company is making the interface device (PLC based controls) for dump load. If our total load (including Dump Load) load is less than PV Generation then how we can reduced our diesel consumption of DG. Can you brief us regarding to dump load (This Imaginary or real Load). I think connection of this PLC interface device will be on communication port of Grid- Tie PCU.

Regards,
Raghvendra
9990152055
raghvendra606@gmail.com

 
At 21 October 2015 at 09:24 , Blogger vj said...

Hi Mr. Raghavendra, dump loads (eg. heating loads) are generally employed in the electric grid of islands where to maintain the efficiency of the diesel generator under the light load conditions (as explained by Mr. Giridharan in the article that DG sets cannot be run on lesser loading conditions) are intentionally added into the grid. These dump loads are only switched on under this condition and not during the normal loading operation of the DG sets.
Hope I have answered part of your query.

 
At 27 October 2015 at 05:20 , Blogger Unknown said...

Dear Friends,
Actually we are installed two numbers of 8KW system at same site in Hyderabad. One system is for common load, and another system is for 4th floor load. Presently we don't have that much load on common system(<2KVA) on day time, we are planning to synchronize this system with DG set(capacity: 30KVA) in the site. Is it ok to connect the system like above? If it is ok, can you please tell me how to synchronize the above system with DG set.

 
At 6 December 2015 at 12:45 , Blogger Quickthorn said...

Sync diesel generator with solar grid inverters - during Islanding condition ... isolargenerator.blogspot.com

 
At 30 December 2015 at 03:43 , Blogger Unknown said...

hello giridaran , I want to know the reason behind the installation of DG set of 50% capacity in PV connected on grid installation.

 
At 14 March 2016 at 00:44 , Blogger John Carter said...

Nice stuff dear. I like it diesel generator maintenance & diesel generator hire

 
At 19 April 2016 at 00:30 , Blogger AjAy NkuMaR said...

it is a good post i have this info and can train on the aspects

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At 20 July 2016 at 00:28 , Blogger Nodsmil Sescar said...

Hi sir I've been studying reverse power relay for a long time for Grid Tie inverter application I'm looking forward for your released article
Thanks!

Engr. Nodsmil Sescar
nodsmil@gmail.com

 
At 9 November 2016 at 03:31 , Blogger John Carter said...

Nice stuff dear. I like it load bank hire & generator maintenance

 
At 22 November 2016 at 01:15 , Blogger Giridaran Srinivasan said...

This comment has been removed by the author.

 
At 21 April 2017 at 20:55 , Blogger patil vc said...

We have found out the solution sir, we have 250 KVA DG set and 100 Kwp solar plant. What we did when load is less than 80KVA, we can shutdown inverter. WE HAVE under current sensor at load which will sense current below 100A, if load Current is Less Than 100A the inverter will shut down.If load more than 100A both DG GT will work together.

 
At 27 April 2017 at 09:53 , Blogger GuptaPS said...

Raw RPPR will shut down solar plant in case of power flow to DG set.

More important aspect: under no circumstance should the power get exported to grid... hence custom design of the Distribution Panel should primarily take this into consideration.

 
At 27 April 2017 at 10:11 , Blogger GuptaPS said...

Dear VC Patil, We use RPPR which trips the Solar plant MCCB in case of reverse power flow. Your scheme seems to be quite good and workable, but how do you shut the inverters? Is it thru' a PLC panel? Please share the details on guptaps at hotmail dot com

 
At 7 May 2017 at 21:09 , Blogger patil vc said...

Through relay which is connected series with inverter,

 
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Nice and useful information about solar inverters. I really liked it.
Good work.



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Dear Sir,

We have Solar DG Set Hybrid solution in DEIF, please visit our website link http://www.deif.com/hybrid, we have around 70 sites in india for reference which is live and running. PLC has its own draw back any minor changes at site requires an PLC enginer to visit site with our system it is scale able, easy to commission at site since our system interface has been achieved by most of the inverter.

 
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