Further assume that this energy is generated by a power plant that burns natural gas, and that the efficiency of production of the electrical current is 20% (i.e., only 20% of the heat energy from burning natural gas ends up as electrical energy).
(a power plant; burns; natural gas) (the efficiency of production of the electrical current; is; 20%)
a power plant the efficiency of production of the electrical current
burns is
natural gas
20%