99.9kW system - loooong AC cable run - Please help!

[Brince]

Its a 3 phase 99.9kw pv system, 3 x Tripower 17000TL inverters.

Distance from the inverters to the consumer unit is 160m!

Two options I can think of, the second im not too sure about...

First is to have a 4 core SWA cable (3 phases + neutral) buried underground all the way to the CU, but according to my software, to keep power loss uner 1%, it would have to be 95mm squared cable, and will cost over £4,500!!!

I am trying to avoid this enormous cost, any suggestions?

The other thing ive thought about is to connect the AC to a nearer power outlet, not necessarily all the way to the CU... is that possible? advisable? any precaustions ?

Thanks

 

[Worcester]

You'll need more than three 17000TL's for that - you'll need 6

Your sizing is correct, price seems reasonable to me

After all his 100K system is costing a little more than that isn't it!

You need to connect it up to where the power is used... the CU?

Don't make false economies, after all he's getting a few £k per year in FiT

 

[Brince]

Sorry, the system is 49.9 kw not 99.9!! mixed it up with another...

So you would say that 95 square millimeter cable is the way to go...

Thanks Worcester

 

[Worcester]

With only 50 kWp and allowance of 3% on the voltage drop (it is allowed sometimes, and I would suggest putting the meter at the inverter end of tha cable ) You could get away with 50mm2 that will still carry the current OK, and assuming 16mm tails from end of large cable to inverter(s) no longer than 10m, and 6mm2 for the DC cables, at 50mm2 (4 core SWA copper) your total losses should be in the order of 2%

So 50mm2 should be Ok

What did you use for your sizing?

 

[Brince]

I used Sunny Design.

My main concern is that if a cable that causes too much voltage drop is used, the voltage may end up being lower or equal to the grid voltage and so the customers consumption may not draw from the PV system first. As this is a dairy farm and electrical consumption is very high, i need to make sure this doesnt happen...

have you dealt with this before?

 

[Worcester]

The Inverter should pump up it's output OK to cope with the losses, what it 'sees' is the loss figure where it's connected, not the consumer end figure, the problem comes if you have a high input voltage with high losses, the inverter will trip out with overvoltage, otherwise it wants to rise enough to pump out. (hence putting the meter at the inverter end, yoiu get 'paid' for the losses as well) same current, voltage loss, say generates 100kWh in a day that will be used at the consumer end as 98kWh (at 2% losses) which is what the user won't import, he gets paid for the 100kWh generated though.

From what I remember the G59/2 settings on the 17000TL have an overvoltage setting of 264.5V
Correction Stage 1 is 253 V, test results 250.7
Stage 2 264.5 test results 262.2

So the figure that matters is 250.7 Volts

 

[BruceB]

3 x 17 = 51 which is over the 50kW limit and presumably not where you want to be in tariff terms, or are you doing it before the August(?) deadline.
There are significant design issues in this installation with its size and being around cattle.
Your description at #5 of how you thought it works raises enough concerns to gently suggest you find someone used to doing this sort of installation.
Regards
Bruce

 

[Worcester]

@BruceB if he's going over 50kWp it won't be an MCS install either!

It's the same as the 3.68kW / 4kWp calculations (or even 'overpowing' on a west facing "4kWp" system) so there is no reason why 3 x 17000TL's can't be used on a post 1st August 50kWp installation.

Everyone has to do their first job of this size sometime, and it's good that people ask here rather than guess.

 

[BruceB]

Yes it's good people ask, but I sometimes worry about the level of knowledge that some questions demonstrate. I did wonder whether to just wind my neck in, but I was concerned that the descriptions of voltages around the system (not yours!) showed a complete misunderstanding of how these things work. As you say you could use 3x 17000TL for a 50kW installation, but assuming you are not going to software tweak the inverters to limit their output that would mean the output was limited by the kWp of the panels, which would mean the inverters were being driven very inefficiently.
Regards
Bruce

 

[Brince]

Thank you Bruce, but the modules total up to 49,980, and thats even beofre multiplying by inverter efficiency, which if taken to be 98% would leave 48,980 as the declared output of the system, so easily within the 50kw FIT category.

 

[BruceB]

OK I'll wind my neck in now!

 

[Brince]

"sometimes worry about the level of knowledge that some questions demonstrate" - People like you shouldnt be on "forums", they should be on a stand up comedy show where only you get to speak....

Seems you have forgotten that one day, your "level of knowledge" was in need of other people's help.... or were you born that way?

Anyways thanks for your patience and help Worcester!

 

[BruceB]

I am sorry I have offended you. I do try to help people on here and I have learnt a lot from it.

Hang around a bit longer and I am sure you will see some questions asked that surprise you.

 

[JD6400]

"sometimes worry about the level of knowledge that some questions demonstrate" - People like you shouldnt be on "forums", they should be on a stand up comedy show where only you get to speak....

Seems you have forgotten that one day, your "level of knowledge" was in need of other people's help.... or were you born that way?

I must addmit Bruce there was a tint of being a wee bit condescending in one of your posts .
But you are well out of order for your comment's brince , the man had already as good as apologised and in the long run was only giving possible company saving advice for free , which you would not get from most of the snakes in this industry even when paying a good sum of money for it !!!
I for one respect all of the help and advice given by your self Bruce and others and would sincerely hope this will not be putting you off from helping others in the future .

Many Thanks as always !

Dave

 

[Brince]

sniff... sniff... someone fishing in muddy waters.... oh dear...

Not offended Bruce, but if I knew the answers I wouldnt I come here, so it is in no way constructive to point to my admitted ignorance. We all have to learn before we know.