Your calculation does not make much sense (GWh isn't even a unit of power). One would have to look at actual power production and consumption curves in order to estimate the required storage capacity. Battery storage is still very exotic, pretty much the entire capacity is provided by hydro nowadays.
Current-gen solar panels average about 30 W/m² over the year in Japan's latitude and climate. So a solar park the size of the Fukushima exclusion zone would produce around 7 GW on average which is more than the combined nameplate capacity of the six reactors (5.3 GW). Supplying the entire country with electricity (~114 GW) would require about 3800 km² of solar panels, or about 1% of Japan's area.
GWh is the most relevant unit: the quantity of energy we need around the year. GW of nominal output is relevant for nuclear or fire-based power that can produce 24h/24 365d/year, but completely irrelevant for wind and solar that provide power only part time.
A 1GW solar plant outs 1GW once every sunny day, at noon. The rest of the day, it produces less, and nothing at all 12 hours a day. A 1GW solar plant roughly produces 3GWh a day. OTOH, a 1GW nuclear plant produces on a yearly average 800MWh every hour, every day and night. So at the end of the year your 1GW solar plant produced a grand total of 1100GWh, while your 1GW nuclear (or coal-fired, or gas-fired) power plant produced 7000GWh.
Plus your solar panel will provide energy mostly around noon, need it or not. While the nuclear (or gas, or coal) plant will provide power exactly when you need it.
Wind is even worse than solar, because production yield isn't even particularly predictable. So when wind blows, electricity goes into the grid without any consideration for the need for it. That's why its price drops to negative at times: because we don't need it. That's not because wind is wonderfully efficient or something. It's because building wind farms is a fantastic misallocation of resources. We're literally spending money for electricity worth almost nothing, and it won't ever recoup its costs.
That's why Germany, after having dumped 300 billions euros on wind farms in 20 years, stop building them altogether in 2018. At some point some accountant did the math.
It is completely obvious that renewables require significantly more storage capacity than other power sources. However, a lot of experts seem to believe that this is not nearly as big of an issue as you are implying.
As for wind energy, you are completely wrong. In 2019 25% of Germany's electricity was generated by wind (compared to 13% nuclear). This has significantly reduced the fossil fuel consumption and CO2 emissions.
The main reason for halting construction is that conservative politicians have passed idiotic NIMBY regulations that now make it very difficult to build new on-shore wind farms. Somehow they even managed to convince a signify fraction of the population that wind turbines are somehow dangerous (probably the same fraction that believes in electro-smog).
If Germany had invested 300 billions in nuclear instead of wind, they would have 0 emissions electric power right now.
It makes relative sense in Germany because they still rely a lot on coal for power generation. If they hadn't stopped nuclear power in its tracks, they would have achieved a much bigger reduction of their emissions, too.
If you take the example of Spain you can easily see that they fired up 1GW of gas plant for every GW of wind farm. Because some days there isn't any wind. You can't lower your emissions to zero with wind and solar.
Europe has very little room left for hydro storage. Most dams that could be built have been built long ago. That drastically limit the efficiency of more wind and more solar power. Nuclear, on the other hand, doesn't need much backup. In fact in France it needs less than 2% of backup (EDF has the know-how to modulate power very accurately to match consumption entirely on nuclear power) so it would already be possible to do 0 emission with 95% nuclear and 5% hydro and nothing else.
The other elephant in the room is that nuclear energy relies on having cheap sources of Uranium available. This works fine for the almost negligible amount of nuclear energy being generated today. Scaling this up to a significant fraction of the world energy consumption would require usage of breeder reactors which nobody has been able to get to work at the required industrial scales.
Nuclear energy is capital-intensive, but not resource intensive. The cost of the plant dwarves the cost of uranium to run it. In this way, it's similar to wind.
France had 2 working breeders reactors, Phénix and SuperPhénix, and they worked at industrial scale. They were cut off for purely political reasons.
https://en.wikipedia.org/wiki/Superph%C3%A9nix
Current-gen solar panels average about 30 W/m² over the year in Japan's latitude and climate. So a solar park the size of the Fukushima exclusion zone would produce around 7 GW on average which is more than the combined nameplate capacity of the six reactors (5.3 GW). Supplying the entire country with electricity (~114 GW) would require about 3800 km² of solar panels, or about 1% of Japan's area.