Modernize depreciation studies

[cmgosnell]

We have some depreciation studies that we have collected from FERC and PUC's across the country. But depreciation studies are only filed every few years. We want to "modernize" depreciation studies. In order to do this, we need to know how much capital additions (annual additions to the plant balance/original cost) and potentially the scale of interim retirements have been made each year.

Assumptions

• We assume the depreciation rate, the net salvage rate and the reserve rate stay constant.
• We assume the capex data (represented in capex_total) in FERC is cumulative over time.

Capital Additions

We can calculate capital additions for plants that report in the steam table from FERC's capex_total line. The capex_total should be a cumulative total over time, so in theory we can calculate annual differences to generate an annual capital addition.

A consideration here: sometimes only a part of the plant is represented in the depreciation studies. This matters because when we allocate the capex additions we are allocating to all sub-generators in whatever slices of plants are reported in FERC1 steam. We'll have to come up with a methodology for appropriately allocating the annual capex when the FERC records have capex associated with generators that are not actually in the depreciation studies. This matters because we are currently only planning on modernizing records that have associated depreciation records.

Connecting FERC Capital Additions to Depreciation Records

FERC plant tables and depreciation records are reported with differing levels of granularity - ie the same utility may report a whole plant to FERC and separate units in a depreciation study. Because of this, we have connected both the depreciation studies to the EIA plant-part list. We are also actively developing modular scaling methods to scale the depreciation and FERC data to the same plant-part level. We can use this connection to connect the annual capital additions to the depreciation records.

Retirements

.... this is a whole other issue that we could ignore entirely or attempt to extract some amount of meaning out of aggregated utility-level
data...

Actually doing the modernization!

Once everything is connected, basically we need to generate "fake" depreciation records up till the present year (or any other year of data we want to be modernizing to) with no data, but only their modernized ID's and connections to the EIA plant-part list. Using the EIA connection, we can connect the FERC plant data with annual capital additions. Then I believe we will have all of the ingredients to modernize the depreciation records.