Pv Commercial 4.8Mw Site

[dsa1000]

Hi guys, 

Struggling with voltdrop in a commercial pv installation, some of the cables for some of the runs will be crazy over-sized to compensate the 1% VD.  Im answering my own question however without going to HV and then dropping to LV locally I cannot see another alternative way? From origin to the furthest away inverter will be in excessive of  250 meters.

I was planning in coming off the LV side of the transformers as these are located locally and straight into air circuit breaker switch panel with sub mains to each area. 

Also im afraid the g59 relay, any recommendation on a company to supply and program, if im honest looks pretty easy to be honest....however what do you guys use to prove to DNO its working, the manuals say connect ot a appropriate test source to simulate conditions....... eh? 

My DC runs, does anyone take in to consideration grouping within there DC calculations for load as this will affect string sizing. All DC runs will be on tray or basket. 

Anyone specialise in pv design as im pretty sure im almost there.

Cheers

 

[steptoe]

there are a couple of guys on here that deal with G59 PV,

I'm sure they will help you out when they see this.

 

[binky]

ok,

1 / the 1% VD is to prevent high grid voltage causing inverters to hit top limit and trip out eg national grid at 250V inverter does not have enough head room to work, though many inverters can be reprogrammed to cope. With your own grid connection to DNO this is unlikely to happen, so 3% is probably fine.

2/ every solar farm I've worked on has several 11kV substations around the park, which connect back to incoming point and DNO sub-station. Inverters are normally in banks close to substation, so you end up with long DC runs rather than AC runs, not convinced this is ideal situation, but then I haven't crunched the numbers. i ceratinly think it is unsafe looking to the future. Most farms actually use lots of 20kW inverters rather than big central units - more MPPTs is more efficient.

 

[dsa1000]

ok,

1 / the 1% VD is to prevent high grid voltage causing inverters to hit top limit and trip out eg national grid at 250V inverter does not have enough head room to work, though many inverters can be reprogrammed to cope. With your own grid connection to DNO this is unlikely to happen, so 3% is probably fine.

2/ every solar farm I've worked on has several 11kV substations around the park, which connect back to incoming point and DNO sub-station. Inverters are normally in banks close to substation, so you end up with long DC runs rather than AC runs, not convinced this is ideal situation, but then I haven't crunched the numbers. i ceratinly think it is unsafe looking to the future. Most farms actually use lots of 20kW inverters rather than big central units - more MPPTs is more efficient.

Many thanks for the reply, yes there is existing 11kv substations yet the sub mains  for local boards is still about 250 meters due to size of the arrays and roof spaces available. 

I have crunched the numbers and yes its all varying from 8.5kw - 30kw inverters, all couple hundred of them!  I called ABB (power one) and they dont recommend a volt drop of less than 1% from origen to inverter connections, a fewe cable cals later and im running 95mm 4c for 30amps of power in some of the long runs. Think job just went over budget already.... 

 

[Sidewinder]

ok,

1 / the 1% VD is to prevent high grid voltage causing inverters to hit top limit and trip out eg national grid at 250V inverter does not have enough head room to work, though many inverters can be reprogrammed to cope. With your own grid connection to DNO this is unlikely to happen, so 3% is probably fine.

2/ every solar farm I've worked on has several 11kV substations around the park, which connect back to incoming point and DNO sub-station. Inverters are normally in banks close to substation, so you end up with long DC runs rather than AC runs, not convinced this is ideal situation, but then I haven't crunched the numbers. i ceratinly think it is unsafe looking to the future. Most farms actually use lots of 20kW inverters rather than big central units - more MPPTs is more efficient.

Many thanks for the reply, yes there is existing 11kv substations yet the sub mains  for local boards is still about 250 meters due to size of the arrays and roof spaces available. 

I have crunched the numbers and yes its all varying from 8.5kw - 30kw inverters, all couple hundred of them!  I called ABB (power one) and they dont recommend a volt drop of less than 1% from origen to inverter connections, a fewe cable cals later and im running 95mm 4c for 30amps of power in some of the long runs. Think job just went over budget already....

Another client who has no idea of what is required then?...

 

[dsa1000]

Another client who has no idea of what is required then?...

the client is not involved in design or installation. 

 

[Sidewinder]

So how can it go over budget then?

 

[dsa1000]

So how can it go over budget then?

because above my pay grade it has been allocated a budget PC cost. 

 

[Sidewinder]

Ohh, ok , someone else mucked up then, once again, nothing new!

Obviously, not your fault, but, people apportioning costs to jobs, against which they have no idea, thus, no competence, thus, they should not be getting involved.

I got palmed one over to me today to sort out.

Going to go well over budget because the specifier had no electrical competence what so ever, had another two weeks ago, people who are incompetent making assumptions, and you know what assumptions make ass u (&amp m (e) ptions...

 

[dsa1000]

yup i feel your pain,      its typical oh look there is a spare 400amp 3phase isolator there, no problem we can just go and add 2mw to this roof now...... then it lands on my desk months later to make it happen

 

[Sidewinder]

Ahh, no pain here,

Consultant!

So, I just get more money to sort out the muck up.

Kerching!

 

[dsa1000]

maybe you should give me youre details for future projects

 

[Sidewinder]

Hmm, not a solar consultant, but, it's still electricity...

 

[kerching]

Ahh, no pain here,

Consultant!

So, I just get more money to sort out the muck up.

Kerching!

Luckily i rebranded to. " kerching "

Otherwise i may have assumed you were calling me in!

 

[Sidewinder]

Luckily i rebranded to. " kerching "

Otherwise i may have assumed you were calling me in!

I know, hence, the upper case K!

 

[binky]

the electrical calcs don't vary apart from the volt drop. Don't forget the inverters output balanced 3 phase so neutral size is not an issue, which helps reduce cable sizes. you could also spec the swa as the earthing saving a core.

might be worth getting a software package like pv-Sol, or just throw problem at inverter manufacturers for answers, if you are buying a shed load of inverters, they should be keen to help.

DC grouping is less of a problem, you would really need to talk to cable manufacturers, but insualtion is much higher spec than normal cables, so can tolerate higher running temperatures. 6mm features strongly on most sites I've seen for the longer runs.

with the substations do make sure good ventialtion is built into design, ie good vents in roof. The ones I've worked on have amazed me by not melting - lovelly and warm in winter, open doors and walk away for 30 mins in summer to bring down to tolerable. Data cabinets so hot I almost burn't my hand ffs. Don't need fans just good natural airflow by convection, vents at low level and vents in roof.

 

[Sidewinder]

the electrical calcs don't vary apart from the volt drop. Don't forget the inverters output balanced 3 phase so neutral size is not an issue, which helps reduce cable sizes. you could also spec the swa as the earthing saving a core.

might be worth getting a software package like pv-Sol, or just throw problem at inverter manufacturers for answers, if you are buying a shed load of inverters, they should be keen to help.

DC grouping is less of a problem, you would really need to talk to cable manufacturers, but insualtion is much higher spec than normal cables, so can tolerate higher running temperatures. 6mm features strongly on most sites I've seen for the longer runs.

with the substations do make sure good ventialtion is built into design, ie good vents in roof. The ones I've worked on have amazed me by not melting - lovelly and warm in winter, open doors and walk away for 30 mins in summer to bring down to tolerable. Data cabinets so hot I almost burn't my hand ffs. Don't need fans just good natural airflow by convection, vents at low level and vents in roof.

So basically good competent engineering design for the application then binky!

 

[binky]

yep!

but it does get a little scary just due to scale / worrying its different to normal electrics