Batteries for short term storage, hydrogen (stored underground and burned in turbines) for long term storage. Combined cycle is 10% of the cost of a nuclear plant of the same capacity; simple cycle just 5%, so one can back up the entire grid with hydrogen and still pay lower capital cost than for a nuclear grid.
Not according to the EIA ([1] page 8 Table 1b). The cost for 1 MWh of nuclear energy is $63 and for solar $30. The solar cost includes 4 hours of storage (no long term storage).
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