Carbon Dioxide Emissions from the Import of Electricity

 Only 2% of the electricity consumed in Rhode Island in 1990 was generated in-state, rising to 20% in 1996, after Ocean State Power and the repowered Manchester Street Station came online.  Although the Rhode Island emissions inventory contains only greenhouse gas emissions directly produced in-state, the Workbook requests an estimate of the emissions resulting from the electricity that was imported.  Obviously, these data will be essential for estimating the impacts of demand-side management of electricity.

 In the years covered by this inventory, three major electric utilities supplied over 99% of the end users of Rhode Island: Narragansett Electric, Blackstone Valley Electric and Newport Electric.  The electricity they provide is supplied to them through the New England Power Pool grid.  The individual utilities purchase their electricity from a number of different power plants through the grid, based on demand and least-cost generation.  The name of the power plant and the amount of electricity purchased is reported to the Rhode Island Public Utilities Commission in monthly Fuel Adjustment Clauses.  The fuel the plants consume is reported annually by the New England Power Pool in their Capacity Energy Loads and Transmission reports.  We obtained these data from the RIPUC directly.  The amount and origination of electricity for each utility for the years 1990 through 1996 are presented in the imported electricity appendix.

 The efficiency of generation (the amount of carbon emitted per unit of electricity generated) came from two sources:  E-GRID97 (http://www.epa.gov/acidrain/egrid/) and Richard Kennelly of the Conservation Law Foundation.  Conversion factors for some generating units listed by the RIPUC appeared in neither set and for these the average efficiency for fossil fuel units was used.  The calculations used to estimate the carbon emissions are shown in the imported electricity appendix.  Note that the efficiencies of generating units using more than one fuel will vary with the fuel mix, but for these calculations we had available only annual average efficiencies.

 The electricity consumption data for 1990 – 1996 period are given in the Electricity Consumption table, with amounts generated in-state and amounts imported shown separately.  The EIA reports the amount of electricity imported into Rhode Island, and their data are listed in the bottom row of the table.  The EIA estimates are much lower than the RIPUC data, most dramatically in 1996, where EIA reports only 35% as much electricity imported as the RIPUC.  Dean Fennell of the EIA said that the only explanation he had to offer was that the EIA data reflect only retail sales, and that wholesale of electricity (e.g. from one utility to another in-state) would lead to double-counting.  As far as we can tell, this kind of wholesaling is not significant in Rhode Island.

Since in every case where we were able to check EIA data we have found it to be significantly in error, the EIA data for electricity importation were not used in the total emissions calculations.  E-GRID97 reports instate generation in ’96 at 3,301 MKWH, which is consistent with the production of the Manchester St. plant as reported by the RIPUC (3,257 MKWH), and does not include Ocean State Power or Pawtucket Power.

 Electricity Consumption in Rhode Island, in MKWH

The Carbon Emissions table lists the amount of carbon emissions (in MCTE) resulting from electricity consumption in RI, allocated between in-state sources and generation sources outside the state.  For the purposes of designing an action plan for emissions reduction, the total emissions will be most useful.  These total emissions increased 10% from 1990 to 1996, while total electricity consumption increased only 7%.  We found this surprising, given the increase in the use of natural gas as fuel for generation.  In part, this difference results from a decrease of in the amount of electricity imported from nuclear plants: 7,100 MKWH in 1990 and 5,800 MKWH in 1996. 

Carbon Emissions from Electricity Consumed in RI (MTCE)