Inside AC Block Architecture: A Technical Walkthrough of Utility-Scale BESS Design

The rapid deployment of utility-scale battery energy storage systems (BESS) demands a comprehensive understanding of system architecture, electrical engineering principles, and operational considerations. In this excerpt from the Foundations of BESS course, industry expert Drew Lebowitz examines the critical design elements of a 50MW/200MWh installation using an instructional scale model.

Tune into the first part of his BESS model tour in the video below to learn more about modular AC block architecture to create scalable storage solutions. To catch the full tour and so much more, enroll in the Foundations of BESS course.

Welcome to a tour of a scale model of a utility-scale battery energy storage plant. If we take a look here, we’ve got a 50 MW, 200 MWh utility-scale plant. It’s comprised of several different components, and we’re going to walk through them one by one.  

If we take a look at this side of the site, we’ve got all of our energy storage containers. You’ll see that there’s several containers arranged in a repeating unit. The repeating unit is known as an AC block. 

We take a look at this AC block. It’s made up of four energy storage containers, and in this case, each of these has 5 MWh of energy storage. If it is a 4-hour system, which this one is, that means that each of these blocks is able to output 5 MW for 4 hours, giving us a full storage for each AC block of 20 MWh. 

In the center between each of these four, we have a single skid that has both a PCS (or bi-directional inverter), along with a medium voltage transformer. 

Typical voltages for a system like this would be 1000 to 1500 volts DC on the battery side,  somewhere between 400 and 800 volts AC coming out of the inverter, and usually somewhere between 20 and 30 kilovolts on the medium voltage transformer.  

The range on the DC side is because at 1000 volts, that would be when the system is closest to 0% state of charge/fully discharged, up to close to 1500 volts when it’s fully charged.  

You’ll see here in this system as a whole, we have five repeating AC blocks on this row and another five on this row, meaning that we have a total of 100 MWh on this side, and this one makes it 200 MWh for the entire system. 

It’s common to arrange the AC blocks in a row like this so that the underground conduit that connects each of the medium voltage transformers can run in a row and connect one to the other, to the other, to the other.  

Want to catch the rest of the BESS model tour? Enroll in the Foundations of Battery Energy Storage Systems course.