If two documents for your SDG&E-area solar PPA show different system sizes, first check the rating labels. A DC panel rating and a CEC-AC rating can describe the same equipment using different methods. Ask the provider to reconcile the figures before assuming that panels were removed or that the PPA price changed.
This is a useful check when comparing qualifying no-upfront solar-plus-battery offers: match the equipment first, then compare the production forecast and payment terms.
What does CEC-AC mean?
California DGStats explains that a system's CEC-AC rating is calculated from the modules' PTC rating multiplied by inverter efficiency. PTC means PVUSA Test Conditions. That is a different rating basis from the panels' standard-test-condition, or STC, DC nameplate wattage.
For an illustrative calculation only, assume 20 identical panels, each rated at 400 watts STC and 360 watts PTC, with an applicable inverter efficiency of 97%:
- DC nameplate total: 20 × 400 watts = 8,000 watts, or 8 kW DC.
- Total PTC rating: 20 × 360 watts = 7,200 watts.
- CEC-AC calculation: 7,200 × 0.97 = 6,984 watts, or about 6.98 kW CEC-AC.
Those assumed numbers describe the same 20 panels. They are not specifications for a particular product, an annual energy forecast or a guarantee of instantaneous output. Use the actual listed ratings for your design; do not apply a universal percentage conversion to every proposal.
Request one equipment reconciliation
Ask the provider for a short comparison showing the panel manufacturer, exact model, quantity, STC wattage, PTC rating and inverter model used in each document. The California Energy Commission's equipment lists provide equipment data, but inclusion is not a Commission warranty of performance or durability.
If the model or panel count differs, ask whether that reflects a documented design revision. If only the rating method differs, request clear labels on the proposal so you can compare offers consistently. Treat the inverter's own AC nameplate rating as a separate item to identify, rather than automatically calling it CEC-AC.
For an SDG&E-served property, keep the equipment reconciliation with your utility application records. SDG&E's installation center directs solar and battery projects through its DIIS interconnection process. Have the installer explain the rating requested by each application field; this example does not establish an approved system size or authorize an equipment change.
Compare payments using energy and contract terms
Kilowatts describe power ratings. PPA energy prices are commonly expressed per kilowatt-hour of generated energy. Neither the 8 kW nor the 6.98 kW figure above supplies the annual kWh needed for a payment estimate.
Request the site's production forecast, the contract's billing measurement and any separate battery charges. Our guide to solar offset percentages explains why matching annual usage also does not eliminate every utility charge.
A suitable PPA can provide solar and storage without an upfront equipment purchase, with the provider retaining ownership. Review ongoing payments, possible escalators, term, eligibility, maintenance, replacement and transfer provisions. No-upfront availability depends on the actual offer; savings and free electricity are not guaranteed. The CPUC solar guide supports comparing financing and continuing costs.
Check backup separately
Solar ratings do not establish battery runtime. Ordinary grid-tied solar generally does not supply outage power alone. Compatible backup equipment, supported circuits, available charge and load limits matter; solar recharge depends on conditions. Tesla's outage guidance explains these practical limits.
Review your proposal with West Coast Alternatives. Bring both equipment schedules and the PPA terms so the comparison starts with clearly identified ratings.