They may have been referring to installed capacity in the UK, not worldwide. 30GW by 2019 sounds about right.
Wind supplied 17% of the UK's entire electricity demand in December 2015
There is a premium for reliable sources of electricity generation since you have to have reliable generation to avoid blackouts.
Wind and solar can capture more $fiat per MWh if they purchase Tesla stationary storage and can deliver firm dispatchability (that premium for reliable generation you mention).
Natural gas will make a fine stopgap until we have enough battery storage.
Certainly some markets have prices that vary through the day to give generators the incentive to generate when power is needed most if they have that flexibility.
"Through the auction, government has procured 49.26GW of capacity at a clearing price of £19.40kW" (second link). Note units are kW not MWh.
http://www.nationalgridconnecting.com/keeping-the-lights-on/
https://www.gov.uk/government/news/the-first-ever-capacity-m...
http://www.gwec.net/wp-content/uploads/2012/06/Global-Cumula...
We're adding more than 50GW/year now, which should easily put us over the amount of nameplate capacity nuclear installed worldwide. Within the next decade, wind will surpass Nuclear in actual twh of generation as well.
If you assume nuclear is about 400GW installed worldwide and a 90% capacity factor, then wind would only need 900GW installed to match output at a 40% capacity factor. NREL just realeased data that shows potential capacity factors of 60% on over 2 million acres in the US:
http://apps2.eere.energy.gov/wind/windexchange/windmaps/reso...
Wind and solar are steadily eating world power generation.