Ac-coupled Systems

From HeatSpring.com PV Boot Camp Discussion Board

Q:

Sean:

This is a great class and thank you! Your lecture suggested that ac coupled systems are becoming more commonplace. It seems this requires finding the right balance of energy storage to feeding the grid over the life of the array and other components, noting that batteries (maybe hydrogen?) will become more cost effective over the next 20 years. How should one plan for sizing battery systems and infrastructure needs in a market that is changing so quickly?

Also, will we have the chance to get more into system design? I am a newbie, and look forward to getting into the meat of these systems.

Again, thank you for a great course.

A:

Ac-coupled systems are becoming more common, however they are still no where near as cost effective as a plain grid-tied (Interactive) inverter. It is my opinion that ac-coupled systems will become more common as people are adding batteries to the system.

For example, the ac-coupled extra inverter that you have to buy for a SMA ac-coupled system is called a Sunny Island and that inverter is around $4000 in the US. It also needs a transformer (autoformer) if you only buy one to make the 120Vac inverter work at 120/240Vac. That autoformer costs about $1,500. Then you need to buy batteries and some other things. I have asked SMA a few times if they are going to come out with a 120/240Vac Sunny Island and am still waiting for a good answer. In other countries, they do not need to make split-phase power (120/240).

It is interesting how Tesla is connecting their batteries to the system. From what I have seen at this early stage, they are making the connection on the dc side of the inverter with SolarEdge systems.This would not be an example of ac-coupling.

Thanks,

Sean White

From HeatSpring.com PV Boot Camp Discussion Board