Intermittency is an ongoing limitation for wind and solar, feeding the reluctance and reservations about moving beyond supplementing existing energy supply to investing in these as primary, baseload sources. I think energy storage, especially large stationary storage, has been the neglected poor relation when it comes to energy R&D. It has different priorities than the kind of battery research that might lead to mass use of electric vehicles, which does have the mobile devices market to stimulate it.
I came across this use of heat pump techologies for electrical storage, to be trialled as a "...1.5-MW/6-MWh electricity storage unit on a U.K. primary substation in the Midlands region" (in UK). From the companies website (where exaggerated claims are possible) "We can achieve a levelized cost of storage (LCOS) of less than $35/MWh stored. We believe this to be the lowest price of any storage technology - including pumped hydro."
Is this evidence that energy storage solutions that can be deployed on a large scale and can significantly help match intermittent supply to variable demand are within reach?