Here’s my working. There are about 31.56 million seconds in a year, and so

30 GWh/year ~ 31.56 GWh/year = 31x10^9 Wh / year
= 31x10^9 Wh / 31x10^6 s = 10^3 Wh/s = 1 kWh / s = 3600 kWs / s = 3.6 kw

I used the duckduckgo autocalculator just now, and 30/31.56*3.6 is about 3.4, so it’s much closer to 3.4kW.

(It’s not power output, it’s manufactured storage output. I think of it as like a factory that produces 3.4 litre capacity jugs per second, but they’re not jugs, they’re actually batteries.)

If these were sold at lithium ion prices, that would net them about 120*3.4 USD/s, or roughly 1.5 million USD/s.

Or to calculate another way, they could make a 120kWh battery, (which would give a family car a range in the region of 450 miles), every two minutes.