To calculate the effect of the RES on electricity ratepayers we used EIA data on the average monthly electricity consumption by type of customer: residential, commercial and industrial.40 The monthly figures were multiplied by 12 to compute an annual figure. We inflated the 2010 figures for each year using the average annual increase in electricity sales over the entire period.[*]

We calculated an annual per-kWh increase in electricity cost by dividing the total cost increase — calculated in the section above — by the total electricity sales for each year. We multiplied the per-kWh increase in electricity costs by the annual kWh consumption for each type of ratepayer for each year. For example, we expect the average residential ratepayer to consume 8,578 kWh of electricity in 2015 and we expect the medium-cost scenario to raise electricity costs by 0.85 cents per kWh in the same year. Therefore, we expect residential ratepayers to pay an additional $73 in 2015.

[*] The growth rate of electricity usage is assumed to be approximately 0.97 percent. This figure is conservative and is less than the growth rate used in Graphic 5.