What happened

Shares of ESS Tech (GWH -3.71%) surged nearly 20% by 11:15 a.m. ET on Friday. Powering the battery company's rally was its second-quarter financial results. 

So what

ESS Tech achieved a major milestone in the second quarter. The manufacturer of iron flow batteries recorded revenue for the first time, recognizing $686,000 in the quarter through the sale of three energy warehouses. 

Overall, the company completed the delivery of all six energy warehouses ordered by SDG&E in the quarter. The utility purchased them to couple with solar energy and supply a steady power source to a local grid. The company also delivered an energy warehouse to its partner TerraSol Energies, which it will deploy on behalf of another customer to support a solar energy project. 

ESS Tech also signed several contracts for future customer orders. TerraSol Energies has contracted for a second energy warehouse that will sit next to the one ESS delivered in the second quarter. Meanwhile, the company entered a relationship with Energy Storage Industries (ESI), which ordered more than 70 energy warehouses. ESS started shipping them to that customer last month. ESS also signed a contract with Tampa Electric to deliver an energy center to support a solar energy project. 

Now what

ESS Tech is finally starting to monetize its battery storage technology, recognizing revenue for the first time in the second quarter. Sales should grow briskly in the future, given all the sales contracts it has lined up. These sales could give the stock the power to continue rising sharply in the coming quarters.