Sources we use

Primary sources

• Internal Revenue Service (IRS)

  Federal tax law and tax-credit guidance.

• California Public Utilities Commission (CPUC)

  The state regulator of California's investor-owned electric utilities: tariffs, net billing and consumer-protection decisions.

• California Energy Commission (CEC)

  The state energy agency, including California's building energy code.

• The electric utilities

  Each utility's own published tariff schedules and rate pages.

• Lawrence Berkeley National Laboratory (LBNL)

  Research on installed solar and storage prices.

Checking a figure yourself

Pages link to the sources they cite, so a figure can be checked against the publisher's own page and the date it was checked.

When a source changes

Rates, credits and program rules move. Material corrections are logged, with dates, on the corrections page.

The wider reference list

The methodology page lists the wider set of references the site consults.