Two alternatives are examined, based upon Northwest Power Planning Council data on incremental cost and heat rate. The first measures the cost of having PGE dispatch Beaver (combined cycle gas) ahead of Boardman (coal), in spite of the higher cost of operating Beaver. The second measures the cost of keeping Centralia offline during periods when it is run for export, at a price 3 mills/kwh above the incremental running costs.
These two units are approximately the same size. Assuming that there are 1000 hours/year when PGE and the other Boardman partners need the output of one, but not both, of these units, Boardman is the lower cost plant to run, at 26.1 mills/kwh versus 29.3 mills/kwh for Beaver. If HGC paid the difference, the sponsors would presumably be indifferent between the units, and be willing to operate Beaver instead. Over 1,000 hours of substitution per year, CO2 savings would be 341,000 tons at a cost of $1.75 million, or about $5/ton.
The Centralia coal plant is sometimes operated when power is being exported from the region, typically at a price about 3 mills/kwh above the variable running cost of Centralia. Assuming that the Centralia sponsors are willing to operate the plant if power can be sold for 3 mills/kwh above the variable running cost, but are unwilling to do so at a price 1 mill/kwh above the variable running cost, HGC should be able to secure shutdown of Centralia under these circumstances at a cost of 2 mills/kwh. Such a shutdown would presumably cause more generation in California using natural gas, at a typical heat rate of 10,000 BTU/kwh. Assuming that 1,000 hours of Centralia operation per year could be displaced in this manner, the CO2 savings would equate to about 742,000 tons at a cost of about $4/ton.