Looking for some guidance here please. I have two Grid tied inverters (on separate sites) from the same supplier in China (See attachment for Product name and manufacturer) - (5KW and 2.8KW Single Phase). Have had them producing power for the last 8 years - absolutely magnificent. I would now like to move them both to a new site where they would both be connected together on the same single phase mains producing now 7.8 KW (obviously each with their own string of panels). I don't know what the implications will be! The manual implies that they can be connected in parallel (See attachment diagram from manual) - but the manual shows them also being connected via RS485 - But for reporting purposes only, not for any sort of syncing? So the questions are 1) Can Grid tied inverters be connected in parallel, 2) What if they are different sizes, 3) Why do some Inverter manufacturers say that their warranty will be lost if units are connected in parallel, 4) Why do some manufacturers specify the max number of parallel inverters allowed? Many thanks

Inverter Brand.pdf Inverter Parallel.pdf

Just my 2c. Could be wrong. In principle a Grid-Tied inverter must synchronise with the grid at 230V (or whatever the grid Voltage, frequency and phase is in that moment), in other words, each inverter is almost by definition operating in parallel with the grid, and to each other.

The fact that you connect them by a communication cable has nothing to do with the way it's connected. But why are you limited in terms of using them in in parallel? My best guess/understanding is that it lies in how grid-tie works, taking its lead from the grid, and then injecting power at a marginally higher Voltage than the grid, to sink into the nearest loads. Best guess is that if you have two inverters in close proximity trying to each supply the house in tandem with the grid, that they would begin to interfere with the Voltage signal each other takes as being the "drumbeat" from the grid.

Still doesn't explain why micro-inverters work well in close proximity to each other. Again, just a guess.

Edited July 8, 20233 yr by GreenFields

I doubt that the utility would be impressed by 7.8 kW of grid tied solar on one phase.

Otherwise, as above, it should work, though they may push the voltage of your grid connection so high that you have problems with appliances popping, and the inverters limiting their export to stay under the voltage limit.

16 hours ago, TonyW said:

Looking for some guidance here please. I have two Grid tied inverters (on separate sites) from the same supplier in China (See attachment for Product name and manufacturer) - (5KW and 2.8KW Single Phase). Have had them producing power for the last 8 years - absolutely magnificent. I would now like to move them both to a new site where they would both be connected together on the same single phase mains producing now 7.8 KW (obviously each with their own string of panels). I don't know what the implications will be! The manual implies that they can be connected in parallel (See attachment diagram from manual) - but the manual shows them also being connected via RS485 - But for reporting purposes only, not for any sort of syncing? So the questions are 1) Can Grid tied inverters be connected in parallel, 2) What if they are different sizes, 3) Why do some Inverter manufacturers say that their warranty will be lost if units are connected in parallel, 4) Why do some manufacturers specify the max number of parallel inverters allowed? Many thanks

Inverter Brand.pdf 263.08 kB · 4 downloads Inverter Parallel.pdf 282.97 kB · 2 downloads

I think I can add some info. 

No problem on adding to the same phase as I am doing with 2 small units. 

Each will up the voltage but the supply authority would not allow it. 

Have 2 units on 1 phase to me would have the same affect as 2 Sunsynks on the same phase as 2 units in a complex or the same street. Surely there are a lot of Sunsynks on the same phase and point of supply in larger complexes. 

As far as I know it can be a problem if too many are connected on the supply phase for the supply authority. Once it hits the higher level of the grid code they will switch off. AFAIK our local grid code has a upper value of 260V. 

If the munic supplies at 250V it will not take too many grid tieds to move the voltage to this point. In such a case one would hope the munic is willing to drop the voltage via a tap or 2 on the transformer feeding the affected installations for all 3 phases. 

The above is partially based on an area I know of where the munic voltage went quite high during peak PV production. This area had a voltage rising to close to 260V during the 11h30 to 12h30 time slot. Lower before and after. 

Lastly if you look at the specs for branded grid ties without battery they do allow up to 6 or 7. Sunsynks can also be used in parallel and who knows when they are all exporting at the same time and perhaps on the same munic phase. 

Lastly by exceeding regulations can mean that the munic can enforce a lower export for even all installations with hybrids having a negative affect on all consumers. Too high export will cause the network to become unstable and more equipment will need to be installed. 

Rather limit the number of panels per inverter to remain within regulations or what the munic allows. May be not a problem now but could become a problem at the rate of new PV systems installed. 

See Aus special requirement for the control of inverters if I have it right. Please correct me if I have it wrong. 

Edited July 8, 20233 yr by Scorp007
Added DRM pic for Australia

Wow - Thanks Guys - I am a solar enthusiast and the understanding that I am gaining here is invaluable. I would imagine then where inverters are designed to work in parallel, they are equipped to keep reassessing what the base municipal voltage is and therefore what additional voltage they can increase to without running up voltage too high!

51 minutes ago, TonyW said:

Wow - Thanks Guys - I am a solar enthusiast and the understanding that I am gaining here is invaluable. I would imagine then where inverters are designed to work in parallel, they are equipped to keep reassessing what the base municipal voltage is and therefore what additional voltage they can increase to without running up voltage too high!

Each inverter will just synch with whatever the AC supply input is. Each inverter will just up their own generated voltage in order for the install to use it's own power 1st before drawing from the grid. 

It will be a function of the number of grid tieds connected on a phase at any given time. Also as a cloud comes over all the inverters will produce less and installs will all start drawing from the grid. It remain good practise to remain within the 4.6kw as I think the max is in the CoCT. 

Also illegal to export to grid without approved system. 

Edited July 8, 20233 yr by Scorp007