Only about 20% of the cost of coal and 5% of nuclear comes from the fuel. Almost all costs are fixed costs. They need to be paid regardless of whether people use the power or not. But in the current system, those who use solar or wind and only use base power occasionally aren't paying those costs. Instead everyone else has to cover those costs, which is why the price of electricity skyrockets wherever there are more 'renewable' (or specifically, 'intermittent') sources.
This is why electricity costs 10c per kwh in many parts of the US, but 40c per kwh in European countries with lots of windmills.
basically it is a huge market distortion. The real cost of base power is a fixed yearly fee to get access, then 2c per kwh after that (i.e the 20% fuel cost). If this is what was charged no one would use wind or solar at all. (or you would have people using solar but disconnected from the grid, which would be great too).