FIELDLINE RESEARCH
Illustration: looking down an aisle between rows of battery enclosures toward the project substation and its transmission line
An aisle between rows of battery enclosures, looking east to the project substation.Illustration: Fieldline Research

Field notes · Energy storage

Field notes: inside a 400 MWh storage site

The batteries arrived first and waited all summer. The date was set by the transformer.

By Miriam OkaforSite visit, September 10

The site sits on about nine acres of former pasture in the western part of the Midland Grid footprint, two miles from a 230 kV substation. From the county road it looks like a storage yard: eight rows of white enclosures on concrete pads, a gravel ring road and a fence. The developer asked us not to name the project.

It is a 100 MW system with four hours of storage. That makes it 100 MW in a grid operator’s queue report and 400 MWh in the way we count projects. When we visited, construction was finished on the battery side and the crew was waiting to energize.

The batteries came first

There are 96 enclosures, each holding about 4.2 MWh of lithium iron phosphate cells in racks, with a cooling unit on the end wall. They were delivered about five months after the order, in line with the median lead time Vale Systems reports for enclosures this year. Most of them stood on their pads, fully installed, from spring through the summer.

Site plan: eight rows of twelve battery enclosures with three inverter skids per row, a project substation with one main power transformer, a control building and the site fence 96 battery enclosures about 4.2 MWh each 24 inverter skids one for every four enclosures Main power transformer 120 MVA, arrived August Line to the grid
1 / 2Site plan. Each row holds twelve enclosures and three inverter skids. Collection cables run along the rows to the project substation on the east side.

Between every four enclosures is an inverter skid, 24 in all. Each converts the batteries’ direct current to alternating current at 34.5 kV. The site manager called the battery side “the part that went to plan.”

The transformer came last

The project substation is the part of the site that sets the date. Its main power transformer, rated 120 MVA, steps the collection voltage up to 230 kV for the line to the grid. The developer ordered it when the interconnection agreement was signed, 31 months after the project entered the queue. The quoted lead time was 15 months.

Illustration of the main power transformer on its pad in the project substation, with the gantry and the line to the grid behind it
2 / 2The main power transformer on its pad. It arrived in August, about two months after the date the developer had planned to energize.

The crew used the wait to finish testing on the battery side, which should shorten commissioning once the substation is ready. Energization is now planned for November.

What the site shows

One visit does not change what our sample measures, but it makes the order of events easy to see. The batteries were the quickest part to buy and install. The queue took the longest. The transformer decided the final date. Developers described the same pattern in our survey, where 62% of projects named the connection queue as their main constraint and, among the 58 projects with a signed agreement, 24 named equipment delivery. The full numbers are in our October outlook.