Speaking of synergy with hydroelectric (gravity) which can be added to wind/solar farms in close proximity, there is what I think is an even greater potential synergy - since it is not as dependent on proper location.
This goes back to Peter Graneau's proposal presented in Infinite Energy a couple of years ago (issue 94) to add "boosting" to hydroelectric. This article is well worth a re-read. A proof of concept should be not overly difficult. Too bad this one did not get into the ARPA contest. (or if it has gone forward, I am not aware of it). Jones From: Jed Rothwell People here have often remarked that an improved battery would help with wind and solar power, by storing energy and leveling demand. That is true. But other methods of storing energy on a large scale already exist. One of the most cost-effecting and reliable ones is pumped hydroelectric storage. It is about 70% to 85% efficient. Not as good as batteries, but not bad. Sometimes, an old technology is a good way to enhance a new one. Here is article about it: Portugal Inaugurates Alqueva Pumped-Storage Hydroelectric Project Expansion http://www.renewableenergyworld.com/rea/news/article/2013/02/portugal-inaugu rates-alqueva-pumped-storage-hydroelectric-project-expansion "BEJA, Portugal An extension of Portugal's Alqueva pumped-storage hydroelectric plant has doubled its capacity to 520 MW. The new addition -- called the Alqueva 2 -- was announced by utility company Energia de Portugal (EDP) in October 2007 as a means of storing power produced by southern Portugal's booming wind power sector. . . ." 520 MW is a lot. - Jed
