A quick google search [1] learns that the CO2 emissions of the solar panel are marginally higher than for a nuclear power plant, but more then 10-fold lower than coal plants. Vattenfall did a study, but it's from 1999, so relies on 20-year old solar technology.
In addition, building a nuclear power plant is amazingly complex. In Europe there are hardly any companies that have the technology and risk-appetite to build one without a solid (financial) support from the government. I recall that in the UK they are building one that is over time and way over budget [2] (spoiler: they started in 2008 and as of now still aren't producing any electricity, and the government-promised price of ~100 pounds/MWh was in 2016 already beaten by solar, implying that over the lifetime the nuclear power plant will cost the consumer 50 billion pounds on subsidies and 20 billion on construction)
And sure, you can't control the sun or the clouds. But with a bit of effort you can create a grid that evens out the impact of the weather. High-voltage power grids in Europe are increasingly interconnected and help fill the gaps in electrical power cross border. Excess solar energy from Germany can simply be transferred to the UK via the Netherlands.
[1]: https://www.startpage.com/do/dsearch?query=co2+emissions+sol...
[2]: https://en.wikipedia.org/wiki/Hinkley_Point_C_nuclear_power_...