what size system can i install, i have been asked to install a 54 panel system

[stubo300]

i have been asked to install a 54 panel system which equals 9.72kw on 3 phases so 18 panels on each phase,

i did the 4 day pv course, but i cant remember how large a system the mcs will cover me for, am i ok to install a 9.72kw system or is that to large for them.

 

[mmccx]

You are accredited to install any size system under MCS. The problem you will encounter however will be with a possible G 59 installation. Under current regs you are allowed to install up to 16 amps per phase (so its generally limited to 4kWp, max ac out put of 3.6kW from inverter). However you are technically allowed to install up to 48 amps on an installation but only if you have a 3 phase electrical system. You can do this by spreading the 48 amps generated by the system across all 3 phases giving you 16 amps per phase and keeping within G83. This can be achieved by using a 3 phase inverter or by installing 3 or more smaller inverters (1 or more per phase, note that the max ac output combined for each inverter on a phase cannot by greater than 16 amps, otherwise G59...)

Incidentally 42 Romag SMT6(60P)235Wp modules will give you 9.87kWp witch can be connected to 1 x Fronius IG plus 100 3 phase (3 strings of 14) inverter would be perfect for you.

 

[TJLinks]

Can you install more than 16A on a single phase supply? A client has asked for 8Kwp on his roof, he only has a 100A single phase incomer. Any advice would be apreciated Thanks

 

[mmccx]

Yes you can but this would be a G59 install. The DNO would need to be contacted, a fesibillity study would need to be carried out on the electrical supply by the DNO at a cost, a G59 protection relay would be required which are very costly and there is also a connection to the grid fee. You would better off installing a 4kWp system for a domestic client.

 

[DomB]

Just on the max size of the array for 16A - is that not 16A x 240V = 3840W, i.e. 3.84kWp out of the inverter?

Or do we do 16A x 230v = 3.68kWp?

 

[TedM]

The G83 limit is 16A at 230V.

 

[DomB]

Thanks TedM.

So the upper limit before advising the DNO & going onto G59 is actually 16A x 230v = 3680 Wp or 3.68 kWp. I guess most people seem to be referring to the 4kWp of the highest rate Feed in Tariff, but that's a bit of a red herring there.

 

[stubo300]

real good reply thanks allot for that

 

[mmccx]

kWp refers to the array size and has nothing to do with the max ac output of the inverter

 

[mmccx]

Thanks TedM.

So the upper limit before advising the DNO & going onto G59 is actually 16A x 230v = 3680 Wp or 3.68 kWp. I guess most people seem to be referring to the 4kWp of the highest rate Feed in Tariff, but that's a bit of a red herring there.

No g59 refers to the out put of the inverter so it's 3.68kW ac output! Not 3.68kWp kWp refers to the array size and decides which fit bracket the system falls into

 

[DomB]

kWp refers to the array size and has nothing to do with the max ac output of the inverter

That's somewhat freaked me out. Doesn't the kWp define the inverter size and therefore the max AC output?

 

[DomB]

So here's the info straight from a DNO:

[FONT=&quot]"Calculation of the size of the SSEG[/FONT][FONT=&quot]
[/FONT]
· [FONT=&quot]Add the total rating of all of the solar panels. Call this SP_Rating.[/FONT]


· [FONT=&quot]Identify the efficiency of the inverter. Some inverters have charts showing how the efficiency varies with the DC Input Voltage, and other factors, and some just state an 'Average Efficiency'. Call this Inverter_Efficiency.[/FONT]


· [FONT=&quot]Multiply the two figures (i.e. SP_Rating x Inverter_Efficiency). Call this Output_1.[/FONT]


· [FONT=&quot]Compare Output_1 with the maximum rated output of the Inverter. Take the smaller figure. This is the SSEG output which should be reported.[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]Consider the following worked example:[/FONT]
[FONT=&quot]7 solar panels rated at 235 Watts each, with a Sunny Boy 1200, (rated at 1200 Watts)[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]7 x 235 = 1645 Watts (SP_Rating)[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]Inverter Efficiency = 92% (Inverter_Efficiency).[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]SP_Rating x Inverter_Efficiency = Output_1.[/FONT]
[FONT=&quot]
[/FONT]
[FONT=&quot]1645 x 92% = 1513.4 Watts (Output_1)[/FONT]
[FONT=&quot]
Compare Output_1 (1513.4 Watts) with the rated output of the Sunny Boy 1200 (1200 Watts), and take the smaller figure, which is 1200 Watts

[/FONT][FONT=&quot]If you are considering an installation which is between 3.68 and 4kW, then you will need to Apply for permission to connect this generation[/FONT][FONT=&quot]"

So that final figure is what they are saying should not go above 3.68kW. I guess we can work backwards from that to suss out the largest array possible for a given efficiency of inverter.
[/FONT]

 

[SolarCity]

DomB, what DNO is that?

 

[mmccx]

but we are only ever going to be generating the max ac output in kW (which is the rating of the inverter) From this we can apply ohm's law to calculate the max output in amps for that inverter. Surely that is the figure we need to keep below 16amps per phase.

using you SB1200 example

kW rating of inverter is 1200W.

apply ohms law and A=1200/230

which is 5.217A max output from the inverter

 

[SolarCity]

3840kWp array with Fronius IG TL 3,6 inverter.

As the Fronius inverter has maximum AC output of 3680w, this is 16A.

We have applied to the DNO for this installation and they are holding us up. (Central Networks by the way) Maybe we should just go ahead and install it?

Seems like each DNO have their own rules. JulianC has said it before and I think he is totally right - If the max output of the inverter is 16A, what business is it of the DNO how many panels you have on the roof?

It seems reasonable to expect that the 16A threshold should apply to the inverter and NOT the array power.