Need a transformer upgrade?

[Photon_Farmer]

A friend has a 150 kva pad mount transformer at his commercial facility. They are considering installing a 188 kW AC, 150 kW DC solar array. Their average hourly demand is 19-22 kW across the last month and last 12 months respectively. It's a retail store without a lot of loads that peak higher than that, with the possible exception of their AC.

Would they need to replace their transformer with a larger kva unit? If they decided to go with a smaller array, at what DC power output could they stick with their current transformer?

 

[ggunn]

A friend has a 150 kva pad mount transformer at his commercial facility. They are considering installing a 188 kW AC, 150 kW DC solar array. Their average hourly demand is 19-22 kW across the last month and last 12 months respectively. It's a retail store without a lot of loads that peak higher than that, with the possible exception of their AC.

Would they need to replace their transformer with a larger kva unit? If they decided to go with a smaller array, at what DC power output could they stick with their current transformer?

I would not install a PV system on a service with a smaller (kVA) utility transformer than the total inverter AC kW rating, and the utility will almost certainly say the same; they may even require it to be smaller by some percentage (some do). The amount of DC attached to the inverter is irrelevant.

 

[winnie]

Why would you install a system with larger AC than DC rating?

 

[electrofelon]

Why would you install a system with larger AC than DC rating?

I was going to question the op whether he mixed those numbers up, it doesn't really make sense. He could certainly have excessive inverter capacity for one reason or another, in which case some people might use the totality of the inverter AC output ratings as the AC rating. In any case, assuming this is a utility transformer you are talking about it is up to the power company.

 

[pv_n00b]

The inverter AC rating has to be less than or equal to the service rating. You can't assume there will always be loads consuming power and preventing it from being exported.

 

[ggunn]

Why would you install a system with larger AC than DC rating?

Leaving room for expansion on the DC side? Limited inverter availability?