Where a Cali-Graf Proposal's Numbers Come From: The Public Data Chain

Source: in Los Angeles County, the county's Address Points; elsewhere, Google's Geocoding API.

What it changes: where the home is — and from that, almost everything else: the utility and its rate zone or region, the city's utility users tax, the weather location and which aerial image and height data are loaded. An address-point suggestion comes with its exact point; an address found through Google is placed by Google, which is why Cali-Graf asks the seller to check that the pin sits on the right roof.

Source: the California Energy Commission's map of electric load-serving entities, LADWP's table of residential zones by ZIP code, and city-level data for SCE baseline regions and Clean Power Alliance.

What it changes: which rate book applies and which tier or baseline allowance the home gets. The same usage produces a different bill in LADWP Zone 1 or Zone 2, in a different SCE baseline region or in a Clean Power Alliance city. Cali-Graf shows the result under the address — for example LADWP · Zone 1 or SCE · SCE generation · Baseline region 9 — and gets the utility right for 99% of homes; the rare miss sits on a utility border.

Where it can go wrong: near borders. Where a ZIP code is split between LADWP and SCE, the city decides — a Los Angeles neighborhood is LADWP, Santa Monica or Culver City is SCE — and Cali-Graf goes by the city a home legally belongs to rather than its mailing name, so a Van Nuys address counts as Los Angeles. City-owned utilities such as Glendale, Burbank and Pasadena are recognized, but their bills can't be calculated yet: the line under the address turns red, and the roof can still be designed. The utility can't be changed by hand yet; when the line differs from the customer's bill, check first that the pin sits on the right roof.

Source: Google's Solar API — the aerial photo, the 3D height map of roofs and trees, and the shade around the home.

What it changes: the geometry and the shade. Each roof face's pitch and direction are measured from the height data, and shade from trees, chimneys and neighbors is worked out for every panel's spot. A newer tree or a demolished building that the image doesn't show will skew both, which is why the image date is shown and the trace should be checked against the real roof.

Source: California Residential Code R329.6 and the Los Angeles Fire Department's rules for homes.

What it changes: where panels can go — and so how many fit. Under the California code, the ridge setback grows from 18 to 36 inches when solar covers more than a third of the roof, and Cali-Graf lays the panels out again when that happens. The plan reviewer and the local fire department have the final say on each job.

Source: a typical year of hourly sun and temperature from the National Solar Radiation Database (NSRDB) of NLR — the U.S. Department of Energy's national laboratory, formerly NREL.

What it changes: how much sunlight reaches the roof each hour, and how hot the panels run. It is a typical year, not a forecast: real years are sunnier or cloudier.

Privacy note: the weather service receives only the approximate center of the home's ZIP code. A separate terrain service, the European Commission's PVGIS, receives the location rounded to about 100 meters to measure hills on the horizon. Neither receives an address or a name.

Source: NLR's PVWatts engine in its System Advisor Model (SAM), with the California Energy Commission's panel and inverter models.

What it changes: the kilowatt-hours the system makes, hour by hour, for each roof face — after panel heating, the exact inverter's efficiency and power limit, and Cali-Graf's 7.77% real-world losses. How the pieces fit together is in hour-by-hour production per roof face.

Source: the customer's own Green Button file when there is one; otherwise ResStock, NLR's hour-by-hour model of a large, representative sample of U.S. homes, using its single-family homes in Los Angeles.

What it changes: how much solar the home uses directly and what it sends to the grid — which, under SCE's Net Billing, decides the bill, because a kilowatt-hour exported at noon earns far less than one bought at 7 p.m. Without a Green Button file, Cali-Graf picks the 30 ResStock homes whose year looks most like the customer's bills, scales each to match the bills exactly and uses their middle result; for SCE homes it also shows the spread of those 30 scenarios. Time-of-use kWh from SCE bills narrow it, and for TOU-D-PRIME customers it picks similar homes with an electric car charging at night. A yearly total alone carries no shape, which is why bills give a more accurate result than one number.

Source: the California Energy Commission's Solar Equipment Lists for panels, inverters and batteries, plus the manufacturers' datasheets for compatibility limits.

What it changes: power, efficiency and temperature behavior in the production model; whether the panel, inverter and battery work together (a panel's cold-morning voltage is checked at −10 °C, 14 °F); and the yearly degradation used in the 25-year forecast. The same CEC lists power Cali-Graf's public equipment directory.

Source: LADWP's residential rates and adjustment factors; SCE's tariff books and its export prices under the Net Billing Tariff; Clean Power Alliance's published residential rates; each city's utility users tax rate.

What it changes: the dollars. Rates are applied by billing period — six two-month LADWP periods or twelve SCE months — with each utility's credit rules. The city utility users tax is shown separately rather than hidden inside the bill. 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 in Details → Engine notes under the result. Checked against real bills, Cali-Graf's engine comes within ±3 cents on LADWP and matches most SCE bills to the cent — see how accurate Cali-Graf is.

Source: the IRS page on the Residential Clean Energy Credit.

What it changes: nothing is subtracted for it. The 30% federal credit isn't available for systems placed in service after December 31, 2025, so Cali-Graf's price, payback and savings include no federal credit, and SGIP or local rebates aren't added either. Background: the 30% solar tax credit ended.

Product facts on this page come from Cali-Graf's own help center and the pages linked below; figures in examples come from the stated inputs. Features, limits and supported utilities change; each was verified October 16, 2026.

1. Cali-Graf Help — Data sources
2. Cali-Graf Help — How the hourly usage profile is built
3. Cali-Graf Help — How production is calculated
4. Cali-Graf Help — Supported utilities and areas
5. Cali-Graf Help — Fire setbacks on the roof
6. Cali-Graf — Privacy Policy (weather and terrain services)
7. Google — Solar API overview
8. NLR (formerly NREL) — National Solar Radiation Database
9. NLR (formerly NREL) — System Advisor Model (SAM)
10. NLR (formerly NREL) — ResStock
11. European Commission JRC — PVGIS
12. California Energy Commission — Solar Equipment Lists
13. SCE — Tariff books
14. IRS — Residential Clean Energy Credit