People often underestimate the amount of storage you need for renewables. Depending on the geographic location you might be looking at tens of TWh. The cost for renewables then suddenly becomes much higher.
I recommend everyone who is using the cost argument to actually do the math on this first. It might be an eye opening experience. It certainly was for me.
Could you share your numbers as well? According to [1], the UK currently needs about 300TWh per year. Lets say we go entirely solar+wind+battery(whatever that means) and assume that battery has to bridge a gap of at most 7 days (meaning no wind and no solar at all during this time, which is at most a few days at a time). This adds up to 300/365*7= 5,8TWh of max capacity. Lets take it safe, round up and say we need 10TWh (which is already not "tens of TWH", but "ten"). [2] Says that grid-scale batteries come at around 350$ per kWh right now. kWh -> TWh is factor 1 billion (10^9), meaning if we want to build 10TWh of storage, it will cost 3,5 Trillion Dollars. Impressive number indeed. But there are multiple asterisks here.
1. This calculation takes into account that there is no exchange with mainland europe and no gas power plants or other sources of power (e.g. hydro or hydro storage). This sharply reduces the need for batteries.
2. Battery costs will fall in the next decades, compared to nuclear, which will take a long time (if ever) until costs will fall.
The problem is that the math is often done using faulty assumptions, such as expecting to rely solely on batteries to store enough energy to last several months.
In practice there are never long periods with and zero wind and zero solar and zero import capacity. Place the right price on electricity during peak demand, and suddenly the market is more than happy to install an overcapacity of wind & solar. Gigawatt-capacity cables to neighboring countries? Already being built!
A country like the UK needs an average electricity input of 45GW. It is totally fine to serve that with 60GW of wind operating at 25% capacity, 60GW of solar operating at 25% capacity, and 15GW of import operating at 100% capacity.
I recommend everyone who is using the cost argument to actually do the math on this first. It might be an eye opening experience. It certainly was for me.