Results
What every number means and how Cali-Graf calculates it.
- Read the resultsAfter Calculate, the result opens with the yearly savings, the electric bill today and with solar, and how much of the usage solar covers. Below are the price and payback, charts for bills, energy and 25 years, and every number in detail.
- Bills by billing periodNumbers by period, at the bottom of the result, lists every billing period of the first year with solar — its dates, usage, solar production, and the bill today and with solar. LADWP has 6 two-month periods, SCE 12 months.
- Savings over 25 yearsThe 25-year forecast adds up yearly bills with and without solar as rates rise and panels age. Bill savings, 25 years counts bills only; 25-year savings in the price tile also subtracts what the customer pays for the system.
- Warnings on the resultsNotes under the savings flag what deserves a second look — a system bigger than the home needs, panels that don’t count in the calculation, and bills shown without the city utility tax.
- Why the calculator asks you to recalculateA result belongs to the inputs it was calculated from. Change the roof, the usage, the equipment, shade analysis or the rate increase — or let the utility rates update — and the calculator marks the result as out of date until you press Calculate again.
- Why the first-year forecast is a rangeFor SCE homes, bills tell how much the home used each month but not at which hours. Cali-Graf calculates the year for many hourly patterns that all match the bills, shows the middle one in the tiles, and the likely range — P20 to P80 — under the bills.
- The battery in the resultsWith a battery, the result adds a bill With battery next to today and with solar. For SCE it usually shows extra savings from the evening peak; for LADWP it shows that the battery doesn’t change the bill and its value is backup power.
- Result details: roof faces, taxes and engine notesDetails, at the bottom of the result, lists the roof faces that went into the calculation, the city utility tax that isn’t in the bills, and the calculation engine’s notes on rates, weather and equipment.
- How production is calculatedCali-Graf models every hour of a typical year for each roof face — NREL weather, the sun’s path, Google’s shade at each panel, panel heating and the exact panel and inverter models — then subtracts the system losses.
- How the bill after solar is calculated: LADWPLADWP nets solar against usage 1:1 in each two-month billing period. Extra solar becomes a dollar credit that rolls forward to later bills but is never paid out — and it pays only the base energy rates and the access charge, not the adjustment factors or taxes.
- How the bill after solar is calculated: SCE NEM 3.0New SCE solar is billed under the Net Billing Tariff (NEM 3.0) on TOU-D-PRIME. Power from the grid is paid at full PRIME prices, power sent to the grid earns hourly export prices, and once a year a true-up settles the energy.
- How accurate are the numbersThe bill calculation is checked against real utility bills — LADWP bills within ±3 cents, most SCE bills to the cent. The utility is found right for 99% of tested homes. Production hasn’t yet been checked against monitoring data of installed systems.
- Why results differ from other softwareTwo tools can model the same roof and give different numbers. The usual reasons are the rates (which year), the shade (measured per panel or a flat guess), the system losses, the utility’s credit rules, and whether the bills are modeled period by period or as an average.