Green Energy

The electricity generation industry measures everything in power because the main constraint is powerto meet peak load. A 1GW gas peaker that is only going to be used for 400 hours a year is 1GW. So is a 1GW coal plant that runs at 40% power 6000 hours a year. So is a 1GW solar farm that outputs peak power 1000 hours a year and 20-80% for 3000 hours.

Performatively misunderstanding this concept is just as bad, if not worse, than not including the duration figure and is usually done to try and pretend the 1GW gas peaker running at 4% capacity factor for two hours a day during summer at peak load somehow cannot be replaced by a 500MW solar farm producing at 17% and a 500MW 2hr battery with energy to spare.

If you see 2.8GW storage, and you trust it's not just a sham project. Then you know that somewhere in the range of 2.8GW to 10GW of nameplate renewable capacity can be added to the grid. 20GWh doesn't convey any information.

Ideally you'd mention both (and include efficiency, seasonality, input power etc.), but this particular pearl clutch is less correct than the headline and is rooted in coal and gas industry propaganda. If only one number is mentioned, then capacity is the most informative.