Data sources

Every number in a calculation goes back to a public source. The utility rates are checked against real customer bills.

The home and the roof

Address and location

Address suggestions in Los Angeles County come from the county’s Address Points. Other addresses are found with Google’s Geocoding API.

Aerial photo, heights and shade

Google’s Solar API: the photo, the 3D height map of roofs and trees, and the shade around the home — Aerial image and height data.

Fire setbacks

California Residential Code R329.6 and the Los Angeles Fire Department’s rules for homes — Choose fire setback rules: California, City of LA or custom.

Energy

Weather

A typical year of hourly sun and temperature from the National Solar Radiation Database of the National Laboratory of the Rockies (NLR, formerly NREL).

Production model

NLR’s PVWatts engine in its System Advisor Model — How production is calculated.

Hourly usage

A Green Button file when you have one; otherwise Los Angeles homes from NLR’s ResStock — How the hourly usage profile is built.

Panels, inverters and batteries

The California Energy Commission’s Solar Equipment Lists, and the CEC panel and inverter models in NLR’s System Advisor Model.

Utilities and rates

Which utility

The CEC’s map of Electric Load Serving Entities, and LADWP’s table of residential zones by ZIP code — How the utility, rate zone and region are found.

LADWP rates

LADWP’s residential rates and adjustment factors.

SCE rates

SCE’s tariff books and its export prices for the Net Billing Tariff.

Clean Power Alliance rates

CPA’s published residential rates.

City utility tax

Each city’s utility users tax rate, from uutinfo.org and the State Controller’s city UUT data.

Federal tax credit

The IRS page on the Residential Clean Energy Credit — Federal tax credit.

Which rates a calculation used

Utilities change their prices several times a year, so the same home can come out a little different later. The rate plans a calculation used are listed under the result, in Details → Engine notes.