Parallel Off Grid Solar Inverter with Diesel Generator Output

Hi Ramesh

Thanks for your reply

I am located in lebanon where average sun hours is close to six

I understand from your e mail is that DG shall have the option of parallel operation

I will be doing this as a trial using around 25kw solar panels which is 10%of diesel generator rating. So can i set the load management module to have DG run at fixed base load say 80% and additional load will be covered by solar panels

regards

shaman abla

One could, though it would be more economical to have the solar as "duty", and the diesel as "assist".

You cannot run the way #1 suggested because I think he did not notice that the Solar panel is only 25kW against the 250 kVA DG! This will not be practical.

Follow the last comment just before this one.

The Solar panel can be fitted with an adequate Inverter that has the facility to synchronise with the DG so that your 24kW will be fully utilised whenever the sun permits. The base load will be the DG.

This is a very dangerous and incomplete answer.

Running a master con- or inverter from solar panels and letting it be the master is the recipe for disaster. Solar is not a stable enough source to feed an inverter. If you step to first charging batteries and run the inverter from there, you make a little better chance. One of my neighbours just blew up his inverters - again!!!

The way is to grid tie and see the generator as grid.

Your ratio is very safe: 1:10. In fact the only thing you need to respect is your minimal load. If this is 25 kW, the generator starts to run idle, but keeps its frequency and the solar production runs your load, assisted by the gen, when necessary.

My scenario, I run with is way different. My ratio is about the opposite, and again, with the load variation in the range of solar + generator production it works well.

25 kW panels produce in my location system about 30 Megawatthours per year. (and I can show this, since I monitor 24/7/365.25.

Remember the name to go with and work safe. And for the " specialists", please come and have a look. In case of blackout, I start a 10 kVA generator manually and adjust the load. The inverter kicks in when the conditions are good and I feed up to 25 kWatts load with it. (this is only possible with good sun on the panels)

A solar inverter as base plant?

I beg you to differ totally on this concept.

Who will make its main source an inverter????,

1. That hasn't even a stable solar exposure.

2. That has not even close a capacity compared to the demand.

These inverters are running on a dozen IGBT's, how reliable is that?

The OP is in Lebanon, we do not know what he is using the generator for and what what frequency of use. I recall working in Kiev after Tsjhernobyl collapsed and when power supply was strictly regulated too. Every day - for years.

Dear Ramesh,

I live in Bangalore. The seniors village where I live has a system where the main source is the local escom and we have a DG of 165 kva rating. Recently we installed a roof-top solar power system (TATA solar) of approx 210 kw nominal capacity (actual peak production is about 150 kw) and the Electrical Inspector asked us to provide a reverse power relay to prevent solar power 'driving' the DG set. The village load is about 75 kw.

We experience frequent tripping of the DG set due to RPR operation when Bescom is switched off and the load is met by the DG and sunshine is fierce.

What would be the consequence if we disable the RPR - will we be jeopardizing the safety of either the DG or the Solar arrays?

S M Subba Rao

You can do it and need NO synchronizer at all, given that you install a good inverter that is fit for the job.

A good inverter follows the generator and copies it output within programmable set points. A good generator keeps it frequency within these tolerances.

Search for fronius, that work good here and also on 50 Hz, one- or 3 phase units, voltages universally - all in one unit.

Yes. It could be done.

There is a garment manufacturing firm in Tirupur, South India, who have a solar panel array that is connected to a diesel generator. The generator is kept on all the time, and when the load is connected during the day when sun is shining bright, the generator is almost in idle mode, and when there is a shortfall of solar power, due to cloud, the diesel generator automatically raises its out put to match the load.

Actually solar power is rather uncertain, and reservoir of power, whether the grid or diesel is need to complement for the equipment to run at fill capacity. Diesel generator, of course has to be 'ON' all the time, and this the wear and tear will be more.

What would the fuel consumption when DG run at low power compared to its fully running condition.

If you use a grid-tie inverter, it will only output power when the DG is running (for safety reasons), and it will self synchronise to the DG output, nothing else would be necessary.

Your concept is only for when you connect the solar inverter to the generator.

The original poster has already solved the transition from a failing grid, where the generator kicks in.

The inverter does not care whether its has its pilot signal from a DG set or a grid, which is actually pretty similar. In case the transition is not smooth, the grid tie inverter will take a 5 minutes break and will only kick in when the conditions, i.e. frequency, voltage, shape of sinus and duty cycle are within the working set points of the inverter.

The inverter is the easiest part. Once installed, you will hardly notice there is one, except on your reduced power bill.

And yes, a grid tie inverter of the latest generations is a device, that only works, when voltage is present and in range to modify the received power from the solar panels - it conditions the amplitude - AMPLIFIES (Andy?) when not high enough and reduces (ATTENUATES) when too high. (this is a common system used when the solar array RMS equivalent voltage is higher than the grid)

This DC voltage is chopped - at multiple times the frequency of the grid - (e.g. 16.000 Hz)

That many times the available voltage is superposed onto the grid or whatever sinus by a typical 0.3 - 0.7 volts.

I have posted oscilloscope pictures of this before in earlier posts.

Re: Parallel Off Grid Solar Inverter with Diesel Generator Output Again building on the comment of dvmdsc, If I may make so bold as to paint a broader picture, by now most participants will realise the grid connect inverter must have an already existing grid, and that the original question as to whether the OP can use a standard grid connect inverter to add 25kW of Solar to his 250kW gen set is yes, no synchroniser is required, the Solar input will reduce the power output from the diesel genset in exactly the same way as a negative load and the diesel will compensate as usual, but more questions arose in the discussion, about changing the status of the grid control etc. and of course in my life as a system designer the question always arises "but that means the diesel has to run 24/7" and for normal power requirements it does, not a fully satisfactory solution as the load, eg. after midnight, may be negligible yet the generator still thumps away, wearing poorly as it is not under enough load and still consuming expensive oil products. Therefore the ideal is to have one of the 'female' Inverters I mentioned in my post 8, these run on batteries, create a grid, can tolerate other inputs on their grid and indeed will maintain their grid even when the grid voltage rises, - as is the case if the other contributors to that grid are putting in more than the total load, in which case the inverter charges it's batteries, only turning off when the batteries are full. Should one want the Inverter to stay on then either those other inputs need to be switched off, (easily done, usually) or the extra load dumped, the inverter itself will control that as you have programmed it. So now you have a secure grid that will run 24/7 with no problem with tiny load, you can add as many extra grid connect Inverters as you wish, one system I have is with Solar and Wind, the wind can be too prolific at certain times but wind droughts can be longer, - in that situation the Solar goes onto the country (National, or Regional, etc.) grid, as there is a grid feed payment, the Wind is not allowed by the local retail authority so just supplies the local grid, and should the load exceed the wind supplied batteries so they start to go down, the Inverter switches the Solar grid connect Inverter to it's local grid until the batteries are full, - a back-up generator can be turned on, again simply connected to the local grid, in cases where there is neither wind nor sun for a considerable time. As you can see, with that system you can add as much Solar, Wind or any other AC source to the local grid, (- which could also be connected to a national grid if the national monopsony allowed) as you like. This sort of system is perhaps an overkill for single house stand-alones but has a great future for more complex systems, particularly if needed to connect to other big or small grids or electrical sources, and also if the national grid is of poor quality.

Thanks for your comments. can you send me specification of your inverter and price

Regards

shaman abla

Re: Parallel Off Grid Solar Inverter with Diesel Generator Output Hi Shaman, this is probably more properly a conversation we should have on the person to person CR4 channel, the biggest Inverter can do 20kW per phase, Costs $60,000; Cheers, Geoff.

20kW per phase: If this is producing a 3 phase output from a DC input (or even AC theoretically), then the total power is 34.6 kW (20 x Sqrt(3) = 34.6...). It is not 20 x 3 = 60 kW (if this is what you are suggesting (?) ).

This must be quite hefty and sophisticated , Special Inverter to cost $60,000 ! Also, I am sure that there must be bigger units than 20 kW.

And, if the unit you are talking about is 20kW , 3Ph , then the 20kW is the overall power meaning that per phase it will be 11.5 kW (this is a 3phase output) to give a 20 kW rating. Example:

at 220 V , 3 phase, supply, and rated 20kW, ==> Amps = 20000/(220 x 1.73 x 0.8) = 65.7 A. If 400 V and same then 36.8 A { 0.8 = Load Power factor as standard, and phase to neutral = 127 V).

Actually it is three single phase inverters, one for each phase, linked, drawing from the same DC supply. - 120 volts DC. Plans are underway to build larger units.

LookFar, you are looking too far.

The person raised question is asking of the Grid use of Solar and DG Set and you are writing on Inverters designed for Grid.

The person needs a simple solution - to use 20kW PV panel with 250kVA DG Set.

Simpler and cost effective solution for him is to Fix Solar PV as Base Unit - Generating 20kW peak or whatever it can depending upon the sun light and DG synchronised with it and take the balance load.

Inexpensive and proven microprocessor based modules for operation, supervision, protection and LOAD MANAGEMENT of DG Sets are readily available in the market.

The Gentleman who has put the question on net is from Lebanon and in Lebanon SERK is one such packager of DG Set who can assist him with suitable DG Set.

The basic requirements were already explained to Gentleman- pl see my earlier comments (Comment #1).

Let us not confuse him.

Sorry if my words hurt you - mine is only a request to not to confuse the asker.

Regards,

Ramesh

GA

Ramesh, This is interesting but some questions come to mind:

-You have a solar panel producing DC power to a frequency inverter that produces AC voltage and current to an private grid.

-You get a DG to run and synchronise to the grid. So far so good.

-now the solar panel output drops drastically due sudden or gradual loss of insolation.

--> the DG takes over completely and becomes the leading power supplier!

---> What happens when the Sun shines again and the Solar panel comes back to life? I think that the control circuitry must be really elaborate and not so simple to be able to re-establish the leader (solar panel) ...? This scenario will repeat many times during the day.

On the other hand, if the system works in reverse, with the DG leading, there are equipment designed for that and they work perfectly everywhere in Europe and elsewhere, supplying solar power from hotovoltaic panels, to the grid as and when there is sufficient insolation. This scenario is workable with a DG supplied grid in so far as the DG is well fitted with an adequate governor.

Thought that also some years ago. There is a difference between 50 Hz and 60 Hz apparatus. Check the working specs please.

I have a 200 kg 50 Hz unit sitting here, not working for that reason. It isn't even worth returning it, due to the shipping costs.

Just for pick up.

LUKE, FOR PURPOSE OF CLARITY I HAVE EXPRESSED MY OPINION AGAINST YOUR TEXT. HOPE IT WILL BE FINE WITH YOU. MY COMMENTS ARE IN CAPITAL AND BOLD LETTERS.

-You have a solar panel producing DC power to a frequency inverter that produces ACvoltage and current to an private grid. THIS IS FINE

-You get a DG to run and synchronise to the grid. So far so good. FINE

-now the solar panel output drops drastically due sudden or gradual loss of insolation. BETWEEN OUTPUT OF PV PANEL AND INVERTER THERE IS BLOCKING DIODE. BEFORE BLOCKING DIODE INSTALL DC UNDERVOLTAGE RELAY TO CUT OFF INVERTER WHEN VOLTAGE IS BELOW PRESET VALUE SAFE FOR TRANSFER OF POWER TO LOAD.

--> the DG takes over completely and becomes the leading power supplier! ONCE PV PANEL IS CUT OFF, DG WILL OPERATE IN ISLAND MODE WHICH IS FINE.

---> What happens when the Sun shines again and the Solar panel comes back to life?I think that the control circuitry must be really elaborate and not so simple to be able to re-establish the leader (solar panel) ...? This scenario will repeat many times during the day. THE LAYOUT & LOGIC OF THE COMPLETE SET UP SHOULD BE:

1. POWER GENERATING BUS IN TWO BUS SECTIONS WITH BUS SECTION POWER CONTACTOR (20KW RATING AC1 DUTY), TWO INCOMERS ONE FOR PV PANEL (SAY ON LH BUS) AND DG INCOMER ON RH BUS SECTION.

2. THE SYNCHRONISING SHALL BE ALWAYS ON BUS SECTION CONTACTOR.

3. DEAD BUS SYNCHRONISING FUNCTION OF THE SYNC RELAY SHALL BE DEFEATED.

4. AS AND WHEN SYNCHRONISING RELAY FINDS THAT VOLTAGE AT LH SECTION IS AVAILABLE - IT SYNCHRONISES DG SET WITH PV PANEL.

5. WHENEVER THE DC SUPERVISION RELAY CUTS OFF THE SOLAR PV PANEL/ INVERTER - IT ALSO CUTS OFF THE BUS SECTION CONTACTOR.

6. TO SAVE SOLAR PV FROM SUDDEN OVERLOAD - THE BUS SECTION CONTACTOR SHALL CUT OFF IN DG SET TRIPS ON FAULT OR THE FREQUENCY OF DG SET (OR BUS IS BELOW PRESET LIMIT) OR df/dt OPERATES.

On the other hand, if the system works in reverse, with the DG leading, there areequipment designed for that and they work perfectly everywhere in Europe andelsewhere, supplying solar power from Photovoltaic panels, to the grid as and when there is sufficient insolation. This scenario is workable with a DG supplied grid in so far as the DG is well fitted with an adequate governor.

MOMENT STEP 4 ABOVE COMPLETES, A SIMPLE GOVERNOR OF DG SET WILL TAKE CARE AUTOMATICALLY AND ENSURE BALANCE LOAD ON DG SET. EXAMPLE:

- BEFORE SOLAR PV PANEL CAME IN SERVICE, ASSUME THE LOAD ON DG SET WAS 200KW.

- ASSUME THAT SOLAR PV IS ABLE TO GENERATE 8KW EARLY IN THE MORNING.

- MOMENT THE TWO SYNCHRONISE SOLAR PV SHARES 8KW LOAD.

- DG SET WILL SEE A LOAD OF 192KW, THUS ITS SPEED WILL TEND TO INCREASE AND GOVERNOR WILL AUTOMATICALLY BRING IT TOSYNCHRONOUS SPEED.

- AS THE DAY PROGRESSES, SLOWLY AS THE SOLAR PV WILL START AUTOMATICALLY SHARING MORE AMD MORE OF LOAD AND DG WILLAUTOMATICALLY START LOOSING LOAD (THIS DOES NOT NEED ANY COMMAND TO GOVERNOR - THIS IS INHERENT PROPERTY OF GOVERNOR).

- VICE VERSA WILL HAPPEN AS EFFICIENCY OF PV PANEL DROPS IN THE EVENING.

AT THE MOST WHILE SELECTING INVERTER - HE HAS TO CHECK ITS SPECIFICATIONS THAT IT HAS BETTER VOLTAGE REGULATION THAN THEGENERATOR AND AVR OF GENERATOR HAS TO BE SET AT 3% DROOP (MINIMUM). ALSO BETTER IF THE REGULATION OF GOVERNOR CAN BE MODULATED BY EXTERNAL MOTORIZED POTENTIOMETER OR BY DIGITAL IMPULSE - SO THAT SUPERVISION OF MODULE CAN SEND REQUIRED ADJUSTMENT COMMAND TO INVERTER IN CASE OF SHARING ISSUE.

Best regards,

Ramesh

The best is to install grid-tie inverter. The DG will act the grid. The DG most to have good speed and voltage regulation (electronic governor). You need also reverse power protection on the DG.

Dear shaman abla,

paralleling is not a simple operation, though modern electronics have improved the situation dramatically.

You give me an impression that you are new in this field, so be very careful as if an error occurs, vast currents can flow, in worst cases alternators can be torn from their beds and thrown about like a huge child's toy. What happens to your solar inverter would not be nice, cheap or safe!!!

I personally cannot see a good and practical method of tying the two together that is worth while, though I am fully prepared to be completely wrong in this matter....

If your solar was say able to produce a similar load to to the diesel and the diesel was set to vary its output to suit the vagaries of the sun/solar, and its oad requirements, it could work, but it (the diesel) cannot be (should not be) set to take a fixed load only.......if the Sun gets covered by a cloud, what would take up and supply the load at the correct voltage and frequency?

I personally would just say, forget it.....I look to see if the cost and the possible problems are worth having for the savings in Diesel fuel etc..

Have a great day.

Lookfar, please clarify, you said

"Grid connect inverters have no circuitry to create AC from DC, they must have AC already...."

but look at the specs on one of the Grid Connect Inverters from the brand recommended by dvmdsc above:

http://www.fronius.com/cps/rde/xchg/SID-A2DD7B50-18D8FD2A/fronius_usa/hs.xsl/2714_1453.htm

to me it is clearly DC input 2500w maximum, AC output 2000w maximum, efficiency up to 95%.

what dont I undestand here? isnt that a true inverter?

No Capybara, I am familiar, (although not good friends, - old goons joke) with Fronius, they are just ordinary old grid connect "Inverters", they only work when connected to the grid, - not because of safety issues such as Islanding etc, but because they can't work if there is no grid to provide the AC they can then amplify. The specs aren't wrong, just misleading if you don't know they need the grid to provide the AC. Cheers, Geoff.

I personally believe that you are using the wrong word(s), substitute "synchronize" with "amplify" and your comments make better (but FAR from perfect) sense......

This demonstrates to me that you do not REALLY understand what you are talking about, or you have no idea how to put it into words that another HB can make sense of......

Sorry, but that is what I get from your comments. It appears that I am not alone either....

You need to look farther.......

Hi Andy, neither do they actually synchronise, the voltage is tweaked to be app. half a volt higher so that there is current flow, this is in fact a bone of contention with some grid operators. Just consider, you can now buy a 1.5kW grid connect Inverter for app. $300; - tested and approved, - does that sound like a stand alone Inverter price? I don't understand your criticism, what do you think happens in a straight grid connect Inverter receiving variable high voltage DC? PS, what is an HB? G

You do not know the whole science of paralleling AC systems, you are talking only about a single part of it......

As I have mentioned already on this blog, there can be massive forces that can seriously damage any of the components involved, to such an extent that an alternator plus its prime mover, can be thrown many feet, taking the base with it, possibly crushing to death anyone nearby.

Correct settings of the following are required before paralleling:-

1) Frequency must be slightly higher on the offline system.

2) Voltage must be sightly higher on the offline system.

3) No phase difference at the time of switching the offline system online and parallel.

As I said before, you need to "LOOKFAR-ther".....I did not mean it just as a joke. I mean it seriously, you do not understand the problems of paralleling without causing possible damage to life and limb.

Just leave it alone and do not bring half hearted knowledge where it at best only makes you look laughable, or at worst it could cause serious injury or death to a CR4 member who wrongly believes you know what you are talking about.....

I am sure that neither of these are attractive to you.....

Furthermore, if I see any further inaccurate comments on this subject by you, I will make a formal complaint to Admin..

CR4 relies on the integrity and knowledge to help anyone here, it does not want dangerously flawed information.....have you understood?

It is obvious to anyone qualified in this area that you are not......

Hi Andy, I still do not understand where you are coming from here, please recall that I am doing this stuff, not theorising about it, - yes admittedly I have not undergone an Engineers training at university, (although have done some relevant courses but I have no degree) however my university is the university of Life, surely the best teacher for an enquiring mind? By all means contact Admin, my approach is not traditional, if Admin requires strictly traditional, I will no doubt be excluded, but I don't get that feel from my previous discussions on this forum. I respect your opinions, I feel you should justify them, not threaten or bluster about machinery thrown sideways without explaining just what happened there, - you must know.. or you wouldn't quote it, and then how that applies to this particular discussion? Cheers, Geoff Thomas

I am not alone here in questioning your understanding of paralleling, did you answer them too? I never noticed you say anything......I can point out the posts for you if you missed them...

You should be happy with me, I am spending my time, putting into print exactly what you are doing wrong, the others here just ignore such posts....or send emails to each other about it, but let you the author carry on with his faulty thinking......which do you prefer?

You really either cannot write a proper logical explanation, fully covering the subject correctly, or you don't understand it as I personally believe....but it could be either!!

Does it matter?

Yes it does, as you appear to labour under an error of thought (or three!)and many of the rest here simply ignore you......

I am trying to prevent your lack of understanding possibly involve other members, even less up to speed than you are, in possible danger and cost....but if you prefer to carry on as you are, I can easily completely ignore you, as most of the rest already are....your choice!

A further point that you should REALLY take to heart, is if you write a page (I believe the previous post of yours was written in one HUGE paragraph) on CR4 with almost no punctuation, you can reckon that basically almost nobody will read beyond the first couple of lines, if that.....some will even complain!

I only complain if it was something interesting to read, which was also why I didn't....

Lets see:-

a) if you take to task any other "non-believer" in your knowledge

b) you prefer ALL the rest of us to ignore your further posts....

My personal bet is that you will probably ignore most if not all of the points I have (tried to at least) made in several recent posts.....we will see won't we?

But I will not be bothering any further in wasting my personal time and trouble here with you, just to say that I personally have paralleled big RN alternators many times, totally manually (no other method was available to us 50 years ago), well before automatic systems were available in the RN, so byeeeeee.

You get a full and deep understanding of the problem when so learning, believe me!!! I did have a picture of a ship where a complete set made a partial, unplanned exit, out of the side of a ship when wrongly paralleled, out of phase!! Sadly, I have no idea where it is today....

Hi Andy, I hope I have answered stuff through my several replies, - if you think I have missed an important point please tell me which one, - I respect your opinion, but can not answer vague allusions, nor do I care that others who do not understand me tell you but not me, - please respect that I am still a working man, only 64 years old and very busy with doing such things as paralleling, designing battery banks to last, getting the best value for my customers with all that is available all over the world. I value your comments, as our personal communications in the past indicate, but need specific problems/disagreements/items to answer, - my life is very exercised in problem solving, please share the problems you think I claim to have solved but that you think I have not solved so I can answer. In regards to my long windedness, I am too old to like the American "Sound Bite" stuff one gets all the time, - mostly misses the point anyway, and is a tool of politicians. I appreciate that you spend the time to read my stuff, sorry, I have no time for the folk who have no time to read it, obviously they don't need to. Cheers, Geoff.

Thank you all for your comments

I am studying your comments and will decide what to do after that

Best Regards to all

shaman abla

Yes you can do it without batteries. You can use a Grid type inverter, which works on excitation frequency of grid.

Here in this case, your DG Set will work as a grid. Inverter will take reference from DG Set and excite at that frequency, operating in parallel with DG Set.

Caution the above system will not work without DG Set - this shall be fine with you as your inverter only 25 kW compared to 200 kW DG set. That also means that in case DG Set trips

Moreover it is safe for the inverter as any shock reactive load (block load due to starting of any motor or AC compressor) will be taken by the DG Set and inverter wont be damaged.

Basic operation will be that your solar will automatically take load to its full generating capacity at any instant and balance load will be automatically taken by DG Set.

For grid type inverter you do not require any synchronizer or sync. relay or load sharing relay.

But you should install reverse power relay and UV coil in MCCB in output of Generator so that in case engine trips on loss of lube oil pressure, and due to some problem in MCCB, fuel is cut off but MCCB fails to trip - the UV connected in series via NC contact of Rev Power Relay will protect the Engine from further damage.

For a 200 kw Engine at 90% efficiency of alternator one the engine is rolling it would require approx 11kW of power and can be easily rolled by the 25kW Solar. Set your RP Realy at 8 kw or below and 20 to 30 Sec.

Hope above shall help you

Regards

Ramesh