Project snapshot
What is being added, what is already on the roof, and what still needs confirmation before the handshake turns into paperwork.
Confirmed economics
Design facts
Battery role
Electrical capacity gate
The economics remain favorable. The remaining gate is electrical design validation: the vendor preliminary load model shows 171.87A on the existing 200A service, but that model used a 3-ton AC assumption and other preliminary inputs. Final drawings still need actual equipment nameplate data, final feeder/breaker sizing, and electrician/AHJ acceptance.
What the installer has represented
What still needs to be true
Electrical load planning companion
An owner-side planning model comparing the vendor preliminary load schedule, corrected actual-load assumptions, and future EV charging options against the existing 200A service limit.
Planning read
The economics remain favorable. The remaining electrical question is planning clarity: solar and batteries do not add household load, and a new load center/subpanel improves physical circuit organization without increasing the existing 200A utility service capacity.
Vendor clarification note
The vendor clarified that the new load center is intended to relocate circuits and does not increase total service capacity. Future additional Level 2 charging may require load management or a service upgrade.
Vendor baseline values below are numeric values transcribed from a vendor-provided preliminary load schedule. The private plan document is not published.
| Assumption | Vendor preliminary | Corrected actual | Future EV planning |
|---|
Adjust planning assumptions
Actual HVAC and water heater nameplate data should replace planning defaults. Plug loads and home lab loads may not be handled the same way in formal code calculations, but they matter for owner-side operational headroom.
Questions for electrical designer
- What is the final calculated amperage after replacing the preliminary 3-ton / 5,400W AC assumption with the actual 5-ton heat pump nameplate data?
- Is auxiliary/emergency heat included, if present?
- Is electric water heating included if required?
- How is EV charging treated in the final load calculation, including the vendor preliminary 11,500W placeholder?
- Does the current scope support a future 40A Honda charger without reworking the new load-center work?
- Would future 60A-80A EV charging require load management or service upgrade?
- Are the final load center rating, feeder breaker, feeder sizing, and any load-management equipment reflected in the permitted drawings?
Your last 12 SMUD bills
Billing period analyzed: June 10, 2025 through June 9, 2026. This is the macro-level reality check. Your house is a high-load site with useful room for more solar because current exports are small relative to total consumption.
Annual energy flow
Existing solar supplied about 22.4% of gross household usage. Most of that solar was self-consumed, which is good. The new array should mostly offset imports, not merely flood SMUD with cheap export energy.
Monthly bill and usage trend
Bars = bill dollars. Line = gross household kWh. Summer plus EV plus HVAC is where civilization starts invoicing you for comfort.
Time-of-use exposure
The battery can help shift energy away from expensive periods, but your current peak exposure is not massive. The big guaranteed value remains the VPP payment.
Annual SMUD imports by TOD bucket
Interpretation
Only 8.9% of annual imported kWh landed in the 5-8 p.m. peak window. Weighted peak rate is about 26.1¢/kWh; weighted non-peak import rate is about 14.5¢/kWh. Even if every current peak kWh were shifted, the theoretical annual rate-arbitrage ceiling is only about $179/year.
That is why this model uses a modest battery optimization value, not fairy dust.
Actual time-of-use ledger
This restores the nerdy part that actually matters: annual imported kWh by SMUD rate bucket, current rate, share of imports, and modeled charge exposure. This is why the battery is valuable, but not because of giant arbitrage.
| TOU bucket | Annual imported kWh | Share of grid imports | Rate used | Modeled energy cost | Interpretation |
|---|---|---|---|---|---|
| Summer off-peak | 3,580 | 20.7% | 15.50¢/kWh | $555 | Large summer baseline bucket. More solar can offset this, but value is moderate. |
| Summer mid-peak | 1,854 | 10.7% | 21.39¢/kWh | $397 | Useful solar/battery target, especially afternoon and early evening shoulder load. |
| Summer peak | 643 | 3.7% | 37.65¢/kWh | $242 | Most expensive bucket, but not enough volume to carry the ROI alone. |
| Non-summer off-peak | 10,288 | 59.6% | 12.85¢/kWh | $1,322 | Dominant import bucket. New solar offsets some of this at a lower avoided value. |
| Non-summer peak | 896 | 5.2% | 17.76¢/kWh | $159 | Peak but comparatively mild. Battery helps, just not dramatically. |
| Total imports | 17,261 | 100% | Weighted avg 15.5¢/kWh | $2,675 | Energy-only exposure before fixed charges, taxes, credits, and bill structure. |
Interactive ROI calculator
Adjust the assumptions that actually matter. The defaults are deliberately conservative-ish: 3,900 kWh/year new solar, 90% self-use, 15.5¢ avoided import rate, $100/year incremental battery optimization, and a $47/year SSR export-value drag.
Monthly source table
The boring table that keeps the pretty dashboard from becoming interpretive dance.
| Bill | Period | Bill $ | Gross use | From SMUD | Solar gen | Sent to SMUD | Net billed | EV credit kWh |
|---|
Known unknowns and decision gates
These are not reasons to kill the deal. They are the last few places where sloppy language can turn a good project into future annoyance with a permit number.
Sources and calculation notes
Self-contained file, but not self-deluding. The public page publishes aggregate bill math, public SMUD references, and redacted numeric planning assumptions only.
Public-safe source handling
- Bill analysis is published only as aggregate monthly and annual values; raw bills and account material are not published.
- Project assumptions are published only as redacted numeric equipment and load-planning values; private plan documents and screenshots are not published.
- The vendor preliminary load baseline is numeric-only and remains owner-side planning context, not a stamped service calculation.