A rate structure unlike other utilities
SDG&E's EV-TOU-5 was designed around a specific behavioral premise: if you make the price gap between peak and off-peak windows large enough, and if you give drivers the tools to charge automatically during the cheap windows, most of them will comply. The rate structure carries that premise into unusually aggressive numbers.
The Super Off-Peak windows are wide and unusually timed. Weekday Super Off-Peak runs midnight to 6 AM (standard overnight window) and 10 AM to 2 PM (unusual midday window). Weekend Super Off-Peak runs continuously from midnight straight through 2 PM. This is not standard TOU design — most utilities put Super Off-Peak strictly overnight. SDG&E's midday window is a deliberate supply-side price signal aligned with California's utility-scale solar generation, which peaks in those hours.
The On-Peak window is narrow and expensive. Just five hours daily (4 PM to 9 PM), but priced at 80.3¢/kWh in summer and 53.3¢/kWh in winter. This is the window California's grid struggles most: solar generation is dropping off, air conditioning demand is peaking, and gas peaker plants are covering the shortfall.
The subscription structure filters for committed users. EV-TOU-5 carries a $24 monthly fixed fee. That fee filters against low-mileage or occasional EV drivers, for whom the fixed cost exceeds any savings. But for a household charging meaningful volume, the fixed fee is trivial compared to the per-kWh savings from Super Off-Peak access. SDG&E offers three alternative structures (EV-TOU / EV-TOU-2 without fixed fees but with higher Super Off-Peak rates, TOU-ELEC for whole-home electrification, and dedicated EV submetering) for households where the primary EV-TOU-5 structure doesn't fit.
What the enrollment data actually shows
According to SDG&E's 2024–2025 Load Impact Research, nearly all new EV owners electing an EV-specific rate choose EV-TOU-5 over the alternatives. The older EV-TOU-2 structure has seen virtually zero enrollment growth despite being simpler (no fixed fee). Drivers explicitly prefer paying the $24 monthly fixed fee in exchange for guaranteed access to the sub-14¢ Super Off-Peak tier.
This preference is analytically important. It tells us that EV drivers who are willing to engage with utility rate design at all are willing to pay for optionality — they'd rather have the cheapest possible off-peak rate available (even at a fee premium) than the marginally-cheaper zero-fee option that caps their upside. The drivers self-select for the plan that rewards charging discipline most aggressively.
That self-selection also means SDG&E's EV-TOU-5 data represents an already-motivated subset of drivers, not the general EV-owning population. Which makes what the data shows about behavior even more useful — it isolates what happens when drivers who want to optimize meet a rate structure that lets them.
The 6:1 threshold that changes behavior
The most analytically important finding in SDG&E's Load Impact Research is the relationship between rate ratio and behavioral compliance. Utility rate design has long assumed that any TOU differential produces some load-shifting response, but the shape of that response curve was not well characterized. SDG&E's data now maps it clearly.
At a 2:1 On-Peak-to-Super-Off-Peak ratio (peak costs twice as much as off-peak, typical of softer TOU designs offered by many utilities across the country), only about 70% of enrolled EV drivers meaningfully shift their charging load away from peak evening hours. Roughly one-third continue charging during peak windows despite paying more for that electricity.
At a 6:1 ratio — which aligns with EV-TOU-5's summer 80.3¢ On-Peak versus 13.1¢ Super Off-Peak pricing — 90% of enrolled drivers immediately shift their charging loads to overnight and midday windows. The behavioral response curves upward sharply between 2:1 and 6:1, then flattens. Pushing the ratio beyond 6:1 provides only marginal additional load-shifting gains.
What this means for rate design nationally. Utilities designing new EV rate programs now have a specific benchmark: hit approximately 6:1 to capture the substantial majority of available load-shifting behavior. Anything softer leaves meaningful load in peak windows. Anything more aggressive doesn't buy much more shifting but does concentrate financial risk on drivers who miscalculate. The 6:1 threshold is not a theoretical optimum — it is an observed inflection point in real driver behavior at scale.
The design implication for supply-side signaling. SDG&E's midday Super Off-Peak window is designed to move charging load into hours when California utility-scale solar generation exceeds demand. When enrolled drivers respond to that price signal by scheduling charging into midday windows, they are effectively becoming demand-response resources for renewable integration — absorbing generation that would otherwise curtail. This is what "vehicle-grid integration" looks like in practice, delivered through rate structure rather than through separate demand-response programs. It is quiet infrastructure integration that most drivers don't recognize as such.
Why automation is doing more work than price signals
Here is the finding that reframes conventional utility thinking about rate design: price signals alone do not achieve optimal load shifting. SDG&E's research shows that the drivers achieving 90%+ compliance are overwhelmingly using automation — vehicle-integrated charging timers (Tesla Charge Stats, most manufacturer apps), third-party smart chargers (ChargePoint Home Flex, Wallbox), or utility-managed programs that handle scheduling automatically.
Drivers relying on manual behavior — plugging in at 6 PM when they get home from work, unplugging in the morning — show significantly lower compliance rates. Not because they don't understand the rate structure, but because manual scheduling around 9 PM plug-in windows and 6 AM unplug windows proves inconvenient in daily life. The price signal is present. The intention is present. The friction wins.
This has implications utilities are only beginning to internalize. Rate design without automation infrastructure captures maybe 60-70% of the theoretically available load-shifting benefit. Rate design with widespread automation captures 90%+. Which means the utility policy question is not just "what should our rate structure look like?" but "how do we ensure enrolled customers have access to charging automation?"
Some utilities are responding by bundling smart chargers into their EV rate program enrollment (Xcel Energy Colorado's Home EV Charger Rebate at $500 with income-qualified enhancements up to 100% of hardware cost is one approach). Others are working directly with vehicle manufacturers to enable OEM-integrated charging schedules that align with local utility windows. SDG&E's Vehicle Grid Integration programs pursue this through direct integration with charging platforms rather than driver-managed configuration.
The broader lesson: the rate structure is a necessary condition for load-shifting behavior, but automation is what makes the rate structure actually work. This is a design principle that will shape utility EV programs across the country as they mature past the "publish a rate and hope" phase.
Why California utilities are designing rates this way
SDG&E's rate structure is not an outlier by accident. It reflects specific characteristics of the California grid that other regions are increasingly encountering.
Utility-scale solar generation dominates California's midday supply curve. During spring and early summer, midday generation frequently exceeds midday demand — not by design but as a consequence of successful renewable deployment. When supply exceeds demand, wholesale prices in California's day-ahead and real-time markets can drop dramatically, occasionally into negative territory. That surplus generation has to go somewhere: it is either used, curtailed (paid to shut off), or exported to neighboring states at unfavorable prices. Every additional kWh of midday load absorbed by EV charging reduces curtailment and improves grid economics for all ratepayers.
Evening peak load is expensive to serve. As solar generation drops after 4 PM, demand for cooling, cooking, and residential activity climbs. California covers the evening peak with a combination of imports, hydroelectric, storage discharge, and gas peaker generation. Peaker plants are expensive per-kWh, high-emissions per-kWh, and only run during peak windows. Every kWh of EV charging that happens during 4-9 PM peaks the grid unnecessarily and requires peaker generation to cover. Every kWh shifted out of that window reduces peaker dispatch.
The rate structure passes both signals directly to drivers. The 13.1¢ Super Off-Peak rate reflects the low marginal cost of electricity during solar-surplus and overnight low-demand windows. The 80.3¢ On-Peak rate reflects the high marginal cost of covering peak demand with peaker gas generation. When SDG&E prices these windows at a 6:1 ratio, drivers are not being punished for evening charging — they are receiving accurate price information about what their electricity costs the system to produce and deliver in that moment.
This is where U.S. utility rate design is headed generally. Renewable penetration is increasing in every state. Peaker generation is becoming increasingly uneconomic as battery storage and demand response scale. The economic case for wide rate spreads that pass supply-side price signals directly to end users grows stronger as grids become more variable and demand becomes more shiftable. Utilities from Arizona (SRP) to Colorado (Xcel EV Accelerate) to Michigan (DTE Overnight Savers) are already moving in this direction with less extreme spreads. SDG&E is at the front of the curve.
The household the design assumes
Every rate structure implicitly assumes a target customer profile. SDG&E's EV-TOU-5 assumes a specific one, and it's worth naming: an owner-occupied single-family household with a garage-installed Level 2 charger, an EV with smart-scheduling capability, ideally rooftop solar with net-metering, potentially a home battery, and the technological engagement to configure automated charging schedules.
For this household, EV-TOU-5 is exceptional. Effective per-kWh cost lands around 12-13¢ for charging — among the lowest in the U.S. — while the household captures full value from solar generation exported at retail rates during Super Off-Peak windows. The rate structure is designed for and rewards this household profile.
For households outside this profile, EV-TOU-5 works less well. Renters without utility account control cannot enroll. Apartment residents whose parking is metered separately from their dwelling cannot easily manage charging schedules. Condo residents on submaster utility structures often cannot enroll individually. Households with older EVs lacking scheduling capability, or with charging equipment that lacks smart controls, capture less of the rate's benefit. Households whose vehicles are used by multiple drivers with irregular schedules face compliance challenges. Households without home charging at all — relying on workplace or public DC fast charging — don't interact with EV-TOU-5 pricing at all.
This is neither critique nor endorsement of the rate structure — it is honest observation. Rate design cannot serve every household profile equally, and SDG&E has made explicit choices about which profile the structure serves best. Understanding those choices helps drivers evaluate whether the rate is right for their specific situation, and helps policymakers understand the equity dimensions of how utility rate structures interact with housing type, vehicle age, and household technology adoption.
Why SDG&E has become the national reference case
Every major U.S. utility currently designing or updating EV rate programs is looking at SDG&E's data. This is unusual — utilities historically design rate structures based on their own local grid economics and rarely reference other utilities' programs directly. SDG&E's EV-TOU-5 has become an exception because it delivered two things simultaneously: an unusually aggressive design and unusually rigorous behavioral research documenting the design's effects.
Utilities across the country are extracting three specific lessons. First, the 6:1 rate ratio benchmark for capturing majority load-shifting behavior. Second, the automation dependency — that rate design without complementary charging automation infrastructure captures only partial benefit. Third, the supply-side signal alignment — that Super Off-Peak windows should track when the local grid actually has surplus generation, not just when historical demand is lowest.
The design will not translate perfectly to every utility. Utilities without significant renewable generation on their systems may not have the same midday surplus that justifies SDG&E's unusual midday Super Off-Peak window. Utilities in colder climates face different seasonal load patterns. Utilities in less technologically-engaged markets may face lower automation adoption rates that limit rate-structure effectiveness. But the underlying principles — aggressive spreads, supply-side alignment, automation-enabled compliance — will show up in more utility rate designs over the next 3–5 years across the country. SDG&E is not the future for every utility, but it is a leading indicator of where the industry is heading.
For EV drivers specifically, this means the SDG&E rate design story is worth understanding even outside California. A driver in Michigan or Georgia or North Carolina evaluating their utility's current EV rate program can benchmark it against SDG&E's structure and reasonably predict how their local program might evolve over time. The specific numbers will differ. The design principles increasingly will not.
What we're watching next
Two dimensions of SDG&E's EV rate program will shape our understanding of utility EV design over the next 24 months.
First, enrollment trajectory and behavioral compliance in updated cohorts. The August 2026 rate schedule increased Super Off-Peak windows to their current expanded structure (midday window now 10 AM – 2 PM rather than shorter prior version). Subsequent Load Impact Research will show whether the wider Super Off-Peak windows produce further load-shifting benefit or whether the 6:1 threshold effect saturates at current levels. If the wider window meaningfully increases charging during midday hours, SDG&E will have generated additional evidence that supply-side price signaling produces meaningful behavioral response — useful data for utilities in other regions considering similar restructures.
Second, the CCA (Community Choice Aggregator) generation supply mix and its interaction with EV rates. Most San Diego residents now receive generation service from San Diego Community Power (SDCP) rather than SDG&E, though SDG&E continues to handle delivery and set the EV-TOU-5 rate windows. The interaction between CCA generation choices (which prioritize renewable procurement) and utility rate structure (which signals demand-side response) is an evolving story that deserves its own analysis — which we'll publish separately. For EV drivers on EV-TOU-5, the practical takeaway remains straightforward: the EV rate structure applies regardless of who generates your electricity.
Related coverage
- San Diego: Honda Prologue vs. Honda Passport — case study anchoring this deep-dive. Shows the practical financial impact of EV-TOU-5 enrollment discipline: a Kendall biotech scientist saves $8,012 over 5 years with disciplined charging, but the advantage compresses dramatically without EV-TOU-5 enrollment or with poor charging discipline.
- Xcel Energy Colorado: EV Accelerate at Home — the closest analytical parallel to SDG&E EV-TOU-5 in another market. Xcel's subscription structure bundles unlimited off-peak into a flat fee (different mechanism, similar goal). Colorado's rate design supports EV economics even after the state's IMVC credit was reduced from $5,000 to $750.
- Colorado state incentives analysis — complementary framing on how policy design at the state level interacts with utility rate design at the utility level. Colorado shifted state EV dollars from market-rate to income-qualified programs; California made the parallel transition years earlier. Both states now rely more heavily on utility rate design to sustain EV adoption than on direct state purchase incentives.
- DTE Energy Detroit: Time-of-Day EV — a less extreme parallel from a very different regional grid. DTE's Overnight Savers reflects Michigan's overnight wind generation surplus, similar to how SDG&E's midday Super Off-Peak reflects California's solar surplus. Different renewable technologies producing different rate window patterns for the same underlying supply-side price signaling logic.