Inverters and grid connection sync

[revjames]

Hi there

Still on my 2391-20 project. I am trying to work out how best to connect 3 PV arrays to the system. I have gone for the grid connected rather than standalone option. As it is a 3 phase supply I am assuming it will be better (probably more efficient too) to invert the DC from the PVs into 3 phase with a 3 phase inverter. The question is how does it synchronise with the 3 phase supply in the board and how does the system know to draw the free power instead of the mains?

Still confused and awaiting some well informed friendly advice. bad day explode

James:coat

 

[Andy™]

looks like no-one here knows the answer

 

[revjames]

Hmmm maybe I'll have to post it on Screwfix..............

 

[Lurch]

Hmmm maybe I'll have to post it on Screwfix..............

So you keep saying.

TBH, it's not something I'd know OTTOMH, as is the same with others I'd imagine. If I researched it all and had all the manuals and info etc... I'm sure I'd be able to fit the kit. You have all that, so the info must be in there somewhere.

 

[revjames]

I have spent hours on the internet trawling through sites. I have to show 'using manufacturers data' how I would connect it all up. Its the 3 phase that confuses me. I am assuming I could get a single 3# inverter and hook up the DC Bus to the PVs its just how does it know how to synch with the supply etc etc.....

I'll keep looking..........

I was only kidding about the SF forum, its just it was mentioned a few times in the rather long winded thread about the 1 head 2 cables etc etc.....

 

[Lurch]

Can you get 3 phase inverters for PV arrays? If so then surely it's just a case of connecting it up as per instructions, the detailed workings of the internals are not of any great concern as far as the outcome of this project is concerned?

 

[revjames]

Perhaps I'm going into too much detail. to me it would make sense as its a 3# installation to have the solar power being put into all 3#

If I cant find what I'm looking for I will treat all 3 PVs on the roof as individual sources going to their own inverter and feeding back to L1 L2 L3 in the main CCU.

 

[karlb]

by having a 3 phase inverter for pv arrays it simply makes it easier to install at the distribution board. the max pouwer output by the pv system is spread accross each phase equally. (its easier to have 1 3 phase inverter rather than 3 single phase inverters, saves money too!)

check out the fronius website or sunnyboy websites for info on the dc inveters they produce and for the data sheets.

ive just started working for a pv installation compnay so its all quite new to me, but i can tell you some infomation of what i have learned so far

also in you question you mention you have 3 arrays? are you sure you dont have 3 modules and more than one module makes up an array.

each module will be connected to eachother to form a string, you can then have multiple strings connected to the inverter.

 

[revjames]

by having a 3 phase inverter for pv arrays it simply makes it easier to install at the distribution board. the max pouwer output by the pv system is spread accross each phase equally. (its easier to have 1 3 phase inverter rather than 3 single phase inverters, saves money too!)check out the fronius website or sunnyboy websites for info on the dc inveters they produce and for the data sheets.

ive just started working for a pv installation compnay so its all quite new to me, but i can tell you some infomation of what i have learned so far

also in you question you mention you have 3 arrays? are you sure you dont have 3 modules and more than one module makes up an array.

each module will be connected to eachother to form a string, you can then have multiple strings connected to the inverter.

Thanks Karl just the sort of info I need. I'll check that site out. as for arrays, I'm probably just trying to sound clever and failing! all I know is there are 3 large panels shown on the tiled roof of the Community centre which have no actual values given for Wp (whats that mean? ) or voltage or anything. For the purposes of my assignment I can put an assumption in that they are XWp each and produce Xvolts - these figures can be whatever we need to get the right inverter. I guess we need to produce 230V DC to make 230VAC although some types use lower voltages and transformers.

 

[karlb]

Wp means Watts peak, basically the rating of a pv system is usually in kwp. So if a system is 4kwp that means it will generate 4 kw per hour during peak conditions (i.e on a nice sunny no clouds day) any other time and it will generate just a fraction of this power output.

im not sure i can post links yet but if you type into google fronius dc inverters and then download there configuaration tool, it will basically tell you you will need x inverter(s) for x modules and it will produce x power in kwp.

The Configuration Tool

.

 

[revjames]

Thanks Karl, I have checked the site and downloaded a data sheet. I can basically make it suit the inverter so will spec the PVs to the inverter spec. Its all theoretical. I just have to show the whole installation set up from the PVs down to the grid connection.

 

[karlb]

heres a little explanation

pv > dc isolator (2 pole) > dc inverter > ac isolator (next to dist board) > mcb in distboard

it might be a good idea to include a kwh meter between the ac isolator and dist board so the customer can see what power is being produced by the pv array.

on a side not it might be good to mention that if there is a power cut on the main supply then the dc inverter automatically switches off to stop any voltage and current being fed back into the grid, the last thing you want to be doing is working on a over head power line during a power cut but it still being live because of the microgeneration

 

[revjames]

Thanks. Part B of the question asks for a summary of the requirements of BS7671 so will write a couple of paragraphs and include the bit about the inverter shutting down in the event of a mains failure. Its a bit ironic really. pay