1 For the first 10 kWh per day on average in summer or 16 kWh per day on average in winter, you pay the rate of $0.0376 per kWh. 2  For additional use over 11 kWh per day on average in summer or over 17 kWh on average in winter, you pay the rate of $0.0793 per kWh.OTE: The normal billing period ranges from 57-63 days. To figure the average kWh use per day, Seattle City Light takes the total number of kWh used and divides by the number of days in the billing period.