Right now he is probably right. The current grid storage solutions are usually Lion or LiPho and neither is really cheap enough and the entire power system will scew towards enormous overproduction with less storage as a result. But there are plenty of grid size storage solutions being developed that have the $ per KWH that will make it more viable.

One possibility is that we use all that excess power for carbon capture or hydrogen production so that we can burn CO2 producing fuels or hydrogen when the sun and wind aren't blowing for days at a time. It's all viable the pieces exist it's about building them more than anything.