∫W power =Q emissions =m coal q,
∴m coal =Q put q =1.638×1012J3.0×107j/kg = 54600kg = 54.6t;
(2) filament resistance:
r = U2P =(220v)2 100 w = 484ω，
∫W = UIt = U2Rt，
∴ Actual voltage across the lamp:
u = WRt = 4× 104j×484ω484s = 200v；
(3) The maximum power of electrical appliances used by Xiao Gang's family.
P=UI=220V×20A=4400W。
Answer: (1) The grid-connected power generation of 455,000 kWh per day is equivalent to the energy released by completely burning 54.6t coal;
(2) The actual voltage across Xiaogang's household appliances is 200 V;
(3) The maximum electric power of the electrical appliances used by Xiaogang's family shall not exceed 4400 W. 。