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Synchronizing Five DG SET with One (2.5MW) PV Plant

Updated: Apr 10, 2020

Hello there, this is Mohammed Yakub Ansari, I am the owner of this business and the creator of this site, its very simple to create website on Wix.com.


During begging of 2019, I got a mail form a Saudi Arabia based company named Desert technology. They have an upcoming project of 2.5 MW On-Grid Solar power plants in Jeddah, Saudi Arabia. They never disclosed the name of their client and type of factory where this plant will be installed. So, we have no idea about the type of load they have. But they (Client of Desert Technology) are running their whole factory on 5 nos. of 1025 kVA (820kW) DG SET, because there is no Gird Power available there.


Since it is a normal practice in Saudi, because the price of diesel is lower than drinkable water there.

Following details of PV Plant and site were provided by them:

  1. 16x100kW SMA Make on Grid Inverters

  2. plus, 8x50kW ABB Make on Grid Inverters

  3. 2.5MW of Solar panels (name of make was never disclosed)

  4. Location of Plant Jeddah, Saudi Arabia

  5. Rating of DG SET 820kW (1025kVA) Cummins Make

  6. Switching ON & OFF for the DG SETs is manual.

Refer below Diagram for your better understating



And they ask us to help them to design the same and tell them, what is the possible way to run this PV Plant (2.5 MW) successfully.

For this type of DG + PV plants there are two possible ways, by which PV Plant can damage DG SET.


a) If, PV Output Power > Load Connected,

Then excess power of PV plant will be feedback to DG SET, this will either trip the main incoming breaker from DG SET to Load or in some case burnout the coil of Alternator of DG SET.


b) If, Load - PV Output Power < 30% Rating of DG SET

Then DG SETS will continuously be running on 30% or on less loading and it isn’t advisable. Because running DG SET at high idle with little or no load reduces the heat in the cylinder, allowing unburned fuel and oil deposits to leak through the exhaust slip joints.


To design PV Plant with DG SET we need to keep it in mind two things:

  1. DG SET should be minimum 30% loaded.

  2. Plus, there should be no surplus power generated by PV Plant.

Special Note: If we satisfied “condition 1”, as mentioned above “condition 2” will be satisfied too.

To do so, we need to control the output of the solar inverters as per the factory load. And for the same we use our ZED Advance controller (to get the pricing and tech spec of ZED Advance click here).


Since all DG SETs are in synch with each other there are five possible way of their working. And with each possible way there are five different conditions of 30% minimum loading on DG SET.

  1. All Five DG Sets are running i.e, 30% of 1025 kVA x 5

  2. Four DG Sets are running i.e, 30% of 1025 kVA x 4

  3. Three DG Sets are running i.e, 30% of 1025 kVA x 3

  4. Two DG Sets are running i.e, 30% of 1025 kVA x 2

  5. One DG Sets is running i.e, 30% of 1025 kVA x 1

As you can see in below reference single line diagram, all DG SETs, Outgoing feeders and Incoming from PV Plant are connected on same busbar.



We can’t use one Multi-function meter to measure the total load on DG SET. So, we have to measure load on each DG SET incomer by using CT’s and multi-function meters. And take this information (load) to ZED Controller via LAN Cable. And further connect all the On-grid inverters to ZED Controller with LAN cable, refer below single line diagram.



Location of Current transformers is very important we have to put them between DG SETs and their respective incoming breakers.


During commissioning of ZED Advance, we set the sharing point at 30% and named each MFM input as M1, M2, M3, M4 and M5. These inputs are nothing but load shared by each DG SET.

Also, we input rating of DG SET in our controller and named them DG#1, DG#2, DG#3, DG#4 & DG#5 now let take all five conditions.


1) All Five DG Sets are running

Total input (or total Load) = M1+ M2+M3 +M4 +M5

ZED Controller Estimated 30% of (DG#1+ DG#2+ DG#3+ DG#4+ DG#5) and Make sure the Power output from solar inverters shall not exceed from {(M1+ M2+M3 +M4 +M5) - 30% of (DG#1+ DG#2+ DG#3+ DG#4+ DG#5)}


2) Four DG Sets are running

Total input (or total Load) = M1+ M2+M3 +M4

ZED Controller Estimated 30% of (DG#1+ DG#2+ DG#3+ DG#4) and Make sure the Power output from solar inverters shall not exceed from {(M1+ M2+M3 +M4) - 30% of (DG#1+ DG#2+ DG#3+ DG#4)}


3) Three DG Sets are running

Total input (or total Load) = M1+ M2+M3

ZED Controller Estimated 30% of (DG#1+ DG#2+ DG#3) and Make sure the Power output from solar inverters shall not exceed from {(M1+ M2+M3) - 30% of (DG#1+ DG#2+ DG#3+ DG#4+ DG#5)}


4) Two DG Sets are running

Total input (or total Load) = M1+ M2

ZED Controller Estimated 30% of (DG#1+ DG#2) and Make sure the Power output from solar inverters shall not exceed from {(M1+ M2) - 30% of (DG#1+ DG#2)}


5) One DG Set is running

Total input = M1

ZED Controller Estimated 30% of (DG#1) and Make sure the Power output from solar inverters shall not exceed from {(M1) - 30% of (DG#1)}


Now let’s take condition no.1 from above and assume that total load is equal to Pload.

i.e, M1+ M2+ M3+ M4+ M5 = Pload.


And Combine rating of connected DG SETs is equal to DGkW.

i.e, DG#1+ DG#2+ DG#3+ DG#4+ DG#5 = DGkW.


Also let Output Power from Inverter#1 + Inverter#2 + … + Inverter#24 is equal to PVout


So If, PVout > Pload - 30% of DGkW.

Then ZED Controller will ramp down Output power of all inverters to match below equation.

PVout = Pload - 30% of DGkW.


And If, PVout ≤ Pload - 30% of DGkW .

Then ZED Controller won’t do any change in output power of any inverter.


Also If, Pload ≤ 30% of DGkW .

Then ZED Controller will switch off (via control signals over LAN Cable) all inverters. And there will be no power generation by any PV Inverter.


And when Pload become > 30% of DGkW, (this can be achieve by switching off one or more DG SET)

ZED Advance will switch ON inverters but keep PVout ≤ Pload - 30% of DGkW.


Accordingly, we can design PV+DG Set Hybrid system with any numbers of DG SETs with any size of PV Plant.


ZED Advance controller also provides remote monitoring of PV Plant in conjunction with DG SET, so you don’t any separate remote monitoring for your project. You can check the running time as well as load shared by each DG SET for full day (even in night).

“Desert technology accepts our proposal but due to some unknown reason deal is still pending to close. I am still pursuing this project and they (Desert Energy) said that they will close the same by March 2020.”

They are many other benefits of ZED Controller too, it has 2 DO (digital outputs) and 2 DI (digital inputs) which can be increased up to 8 DI and 8 DO by using multiplexer. And we can use these signals to automatically switch ON or OFF DG SETS as per the load requirement.


If you have any question regarding ZED Advance, leave a comment below

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