photo by Trent Nelson

On Nov. 9, Rocky Mountain Power filed a proposal with the Utah Public Service Commission to change the way the utility’s net-metering customers would pay for electricity.

The Salt Lake Tribune's calculator uses simplified versions of RMP’s current and proposed power-rate methodologies to allow customers to compare what their monthly bills might look like under either rate structure. The calculator considers only charges and credits for monthly power use and generation, and does not take into account various fees and taxes applied to residential customer’s bills each month, so the totals are an estimate only.

Power purchased

The amount of Rocky Mountain Power-generated electricity used during a given billing period. This number can be found on all electrical bills. On traditional bills, it’s reported as the amount of electricity used, in kilowatt hours. See below for where to find this on your bill.

Sample Rocky Mountain Power bill, no solar, current

Detailed Account Activity item 1 - electric service 123 Fake Address Fake City UT Residential Schedule 1 meter number service period

from to elapsed days meter readings

previous current meter multiplier amount used this month 00000000 Date Date 29 37761 37867 1.0 106 kWh

Power purchased per month

According to information filed by RMP with the Public Service Commission, the average non-solar household uses 725 kWh per month, while the average solar household uses 743 kWh per month.

This calculator uses Rocky Mountain Power's winter rate schedule. In the summer, rates are charged according to a different schedule.

Summer rates

8.9 cents for the first 400 kilowatt hours

11.5 cents for the next 600 kilowatt hours

14.5 cents anything over 1000 kilowatt hours

Winter rates

8.9 cents for the first 400 kilowatt hours

10.7 cents for anything over 400 hours

Peak usage

For residential users, this variable is a new charge. Information about peak demand is not currently reported on residential power bills.

To calculate this new “demand charge," Rocky Mountain Power will look at a customer’s monthly electrical use, identify the hour in which they used the most power, and charge that hour at a rate of $9.02 per kilowatt, based on the average amount of power pulled into the home during that hour. According to Rocky Mountain Power, the average customer’s demand peak would sit at about 3.4 kW using this methodology.

Customers can estimate their peak usage based on these averages provided by Rocky Mountain Power, which the utility says are based on customer data.

Average Monthly Energy Usage Average On-Peak kW 200 kWh or Less 1 201 kWh to 400 kWh 2 401 kWh to 600 kWh 3 601 kWh to 800 kWh 4 801 kWh to 1,000 kWh 5 1,001 kWh to 1,500 kWh 6 1,501 kWh to 2,000 kWh 7 2,001 kWh to 3,000 kWh 9

According to Rocky Mountain Power, this charge would only consider electricity used between the hours of 8-10 a.m. and 3-8 p.m. on weekdays, excluding holidays, during the winter; and from 3-8 p.m. on weekdays, excluding holidays, during the summer.

For those interested in researching their household electrical demand, estimate the energy required by various common household appliances.

Surplus power

This is the amount of power a household with solar panels and a net-metering arrangement pushes onto the grid. It’s not the total amount of power generated by the panels — some power generated is used on-site; only unused power is pushed onto the grid and “sold” to Rocky Mountain Power. See below for where net-metering customers can find this figure on their monthly bill, where it's expressed as negative kilowatt hours.

According to the RMP filing, the average net metering customer provides the grid with about 303 kWh per month.

Sample Rocky Mountain Power net-metering bill, current

Detailed Account Activity item 1 - electric service 123 Fake Address Fake City UT Net Meter - 237 kW Solar Schedule 135 meter number service period

from to elapsed days meter readings

previous current meter multiplier amount used this month 00000000M Date Date 30 14270 14804 1.0 534 kWh 00000000XS Date Date 5075 5206 1.0 -131 kWh Total 403 kWh M = Main Meter S = Subordinate Meter

Power purchased per month

Surplus power generated per month

Calculator made by Tribune web developer Daniella Birch and reporter Emma Penrod.