Regarding the ROI and subsidies, I guess you would need to compare them to the billions received by the incumbents :)
The power crisis in South Australia has been extremely costly. The cost for the proposed fast start gas power plant was 380 million.
The state-wide blackout cost businesses 367 million.
http://www.abc.net.au/news/2016-12-09/sa-blackout-costs-coul...
This battery will cost taxpayers 50 million over 10 years, apparently. Seems like a pretty good deal.
http://www.abc.net.au/news/2017-12-01/tesla-giant-battery-of...
What worked in the article?
It only says the battery supplied less than 2% of the lost power for about 5 seconds before regular power generators took over.
It is supposed to kick in and help support the South Australia power grid when power drops. It did that, faster than the designated backup did.
It worked as designed.
What worked in the article?
It only says the battery supplied less than 2% of the lost power for about 5 seconds before regular power generators took over.