To be realistic in order to get to 100% renewables you need storage to cover the intermittency. It's not nearly as much as the fossil fuel and nuclear lobby makes it out to be, but it is real. The great thing is that the cost curve is so steep and we're so far along it now that you can quote absolute worst case renewables plus storage and it's still the least cost option. And in reality you're correct, nuclear can't ramp up and down either and there's just as much intermittency in demand as in supply, so nuclear would need to either overbuild and dump power into the ground most of the time or have storage as well.
Does it really though? The levelized cost of combined cycle gas is right around $38 (https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf). And keep in mind, any renewable project will happily sign a contract to deliver that power to you at the same price for 20 years. No natural gas plant would do that in a million years, if they did the contract price would be a heck of a lot higher than the $38 you pay for renewables plus storage. And again, there's no cost curve you can reasonably expect gas plants to come down for construction and O&M costs and hedging the gas out beyond a couple years is prohibitively expensive so there's no reliable cost curve on that either.
The way I see it, the renewables and the fission can work hand in hand to provide the first line of power. The rods are going to fission at their rate. You cannot stop them or slow them down from doing their thing. So they feed the grid constantly. Then you have the renewables like solar. As the solars + nukes + wind turbines are feeding the grid, it is the NG and other fossil fuel plants that can control their own rate of feeding to make up for the lack of what the renewables cannot provide. I would figure that would save on carbon emissions, and in fact that may be the way it is done now, just guessing. That is why I do not understand the need for "storing" the power. The grid should be fully co-op. As the renewables lose their output due to lack of wind and sun, the NG plants can ramp up a bit to fill in the power demands. And the nuke rods (balls) will just keep doing their thing.
For more specialized and “Grid tie” applications, that can work. For more common single home systems, having a battery bank will provide power after a succession of cloudy days.
Oh, you mean on the home front? I was thinking of solar farms and the like from the commercial supply side. Well, sure, if you got the solar stuff on your roof and a battery bank in your home, the idea is sound. Except it won't work because people are as wasteful with electricity as they are with food. How many lights in your house right now are on but you are not using them? I bet most people in the USA cannot honestly answer "none", were they to be asked that question. And that is just lights! Imagine all the other appliances. Like the stereo receiver they forgot was on. Or the DVD player...etc etc etc.
I question the value of solar farms at current efficiency rates except perhaps in the most specialized applications. However, on rooftops with a hot water system, especially in rural areas, solar can make a lot of sense.
What "efficiency" are you questioning? Solar farms can generate electricity for a fraction of the cost of coal and cheaper than the cheapest fossil fuel or nuclear plants on a levelized per MWH basis. How is that not "efficient" in any universe?