If a solar PPA proposal for your SDG&E-connected home places panels on several roof faces, ask how the production estimate represents each group. A single total system size does not describe the direction, slope and shading of every panel. Matching the forecast to the actual layout helps you evaluate both ongoing PPA payments and the energy available for a battery.
Ask how each roof face enters the forecast
The national laboratory's System Advisor Model system-design documentation describes dividing a photovoltaic array into subarrays with different orientations. Its detailed photovoltaic model can represent up to four such groups, including rooftop sections facing different directions.
That is an example of a modeling method, not a requirement to use that particular software. Ask your designer to explain how their chosen tool represents your proposed layout and associated inverter configuration. Avoid assuming that a forecast labeled with one direction accurately describes panels distributed across several roof faces.
Sources were checked November 1, 2026. This is a proposal-review guide, not a production estimate for a particular property.
Request a roof-by-roof summary
A useful attachment to the proposal would identify:
- Panel count and rated capacity on each roof face.
- Direction and tilt for each group.
- Shading assumptions for nearby trees, structures and roof features.
- Inverter equipment and any shared output limits.
- Monthly production and the combined hourly profile used in the bill comparison.
For a hypothetical example, suppose a layout has eight panels facing east and twelve facing west. Ask the designer to show how both groups enter the calculation. Do not replace that layout with twenty south-facing panels merely because the total panel count stays the same. This example assumes no particular wattage, production difference or savings result.
If panels move between roof sections during design, request an updated estimate and payment comparison. Keep the dated layout with the forecast so you can tell which proposal version the numbers describe. Our weather-assumptions guide covers another input that should remain identifiable.
Why timing matters for an SDG&E bill
SDG&E's Solar Billing Plan explanation says export credits depend on energy delivered to the grid at each hour. It also directs customers with a community-choice generation provider to that provider for import and export pricing.
For a home on the Solar Billing Plan, ask the comparison to combine the modeled production profile with your household usage, applicable prices and proposed battery operation. Confirm your actual tariff and generation provider first; do not apply Solar Billing Plan assumptions to a legacy NEM account without checking.
An annual solar total alone does not show how much electricity the home uses directly, stores, exports or later imports. Request those quantities separately rather than treating every generated kilowatt-hour as an equal reduction in the utility bill.
Compare the PPA and battery together
A qualifying no-upfront-cost solar-plus-battery PPA can help eligible homeowners access a tailored system while preserving upfront cash. The CPUC consumer guide explains that the provider owns the solar system and sells the electricity it generates. Check the rate, any escalator, term, billing method, battery ownership and charges, maintenance, replacement and transfer terms, plus remaining utility costs. No-upfront qualification is offer-specific; electricity is not free and savings are not guaranteed.
Ask how the final roof layout affects expected battery charging while retaining the same household-load and backup-reserve assumptions across comparisons. General battery guidance explains that supported circuits, stored charge and demand limit outage coverage. Ordinary grid-tied solar alone generally cannot supply outage power; compatible backup equipment is required. Recharge depends on conditions, so a modeled annual yield is not a runtime promise.
Bring your roof layout, forecast and utility bill to the West Coast Alternatives homeowner journey to compare the proposed equipment and payment assumptions together.