Table 3 lists the electricity prices of flat and TOU rates for purchasing and selling electricity. The TOU rates of electricity are changed in three time periods for residential customers in SA. The off-peak period is between 11:00 p.m. and 8:00 a.m., the shoulder period is between 8:00 a.m. and 6:00 p.m., and the peak period is from 6:00 p.m. to 11:00 p.m.