It contains LOTS of energy that you can release simply by setting the coal on fire, yet it’s stable enough that you can store it loose in a box, unlike nearly every other major fuel.

它含有大量的能量，你可以通过点燃煤来释放，但它足够稳定，你可以把它松散地储存在一个盒子里，不像几乎所有其他主要燃料。