Steam plants (my particular area of whatever expertise I have) are not necessarily “more efficient”. That is, the process is: burn fuel, heat water to steam, drive a turbine to drive a generator to produce electricity. It’s an inherently inefficient process, a huge Rube Goldberg machine.
There are, in fact, a great number of direct-fired turbine-generator sets in the US and around the world. Though I don’t know the efficiency numbers for them, they are quite efficient—more so than coal. But the fuel to drive them is also quite expensive, and the machinery itself is barely less expensive than much larger coal-fired boilers and turbine-generator sets. They become cost-effective electricity generators when several combinations of factors come into play:
1. The cost for natural gas (the most common fuel for gas-fired turbines, which is the most common form of direct electricity production) goes down, and supply is plentiful and relatively assured over a long plant life. Because of the world market for natural gas, this isn’t always the case.
2. The power is needed immediately by someone who is willing and able to pay the price for that kind of immediate needs-gratification, meaning that the producer is willing to pay the higher prices for fuel (natural gas being much more expensive per BTU than coal).
3. The power is needed in a relatively constrained area or market. Most gas-fired turbines don’t have the sheer size of large utility electric plants. Steam boilers generally run power plants of up to 1000 megawatts. Gas-fired turbines are smaller.
I’m not going to publicize cost figures, but take it from me that the per-megawatt cost of coal-fired electric power is considerably lower than the per-megawatt cost of gas-fired power. (And even though the gas-fired turbine power is inherently cleaner, because natural gas burns cleaner than coal, the added cost of air pollution controls on coal plants still make for a much lower cost, even over the entire 40-year life of the plant.)
So when you need base loading for a large metropolitan or industrial base and can handle the infrastructure to deliver coal (and resulting bottom ash and flyash at the back end), you’d look to coal as the primary source NOT because of efficiency, but because of lower overall cost.