Fossil fuels are sources of energy and tradable commodities. (means easy to stick in a barrel, pipeline or tanker and sell.) Renewables tap into sources of free energy (sun, wind, water), and are energy carriers. (it’s all about flow) As energy carriers renewables benefit what’s known as the “experience curve”. This is where increasing production volumes leads to gains in efficiency. That’s why their costs keep falling. Meanwhile, the cost of their energy sources (wind, sun, water) is still free.