SCE NEM True-Up · 200 Waterford Ave · Aug 2025 – Jul 2026
The bill went from ~$650 to ~$1,200 because the house's net grid position tripled — from 826 kWh to 2,647 kWh of net imports — and 76% of that swing happened in December–February. It wasn't the EV: charging was flat year-over-year. The main driver is hiding in plain sight: the hot tub was broken for most of the base year and came back online April 25, 2025 — so last year's "cheap" winter had no tub, and this year's had one running through a snowy winter that also buried the panels (21 near-zero solar days in January), all priced at rates SCE raised ~12% mid-year.
NEM years run August–July. "Last year" = Aug 2024–Jul 2025; "this year" = Aug 2025–Jul 2026. All figures from SCE hourly interval data (Delivered = grid → house, Received = house → grid). The meter only sees net flows — solar you consume directly is invisible, which matters below.
Month-by-month net position (imports minus exports) tells most of the story. Sep–Oct slipped from small surpluses to deficits, and then Dec–Feb blew out: net imports of 3,108 kWh vs 1,728 kWh the prior winter (+1,380 kWh — 76% of the annual swing). January 2026 alone was net +1,398 kWh vs +611 the year before.
Monthly net grid position, year over year
kWh · above zero = net import (you pay) · below zero = net export (you bank credit)
Two months went the right way: March 2026 (a sunny March vs a stormy March 2025 — exports nearly doubled) and June 2026, when imports dropped 42% — nine days that month the house drew under 10 kWh, so someone was away. Without those two offsets the bill would have been higher still.
Days where the system exported essentially nothing (<0.5 kWh) are a clean proxy for snow-covered panels or storm cover. Last winter had bad stretches too — but January 2026 had 21 of 31 days with zero export, versus 4 in January 2025. January exports collapsed 71% (351 → 101 kWh).
Days per month with near-zero solar export
days with <0.5 kWh exported — snow cover / storm proxy
Snow cover hits twice: exports go to zero and the daytime load the panels would have served silently becomes grid imports. That double-counting is why January imports jumped to 48 kWh/day from 31, even though measured exports "only" dropped 250 kWh.
The obvious suspect gets acquitted first: hours drawing >5 kW (the EV6 charging signature, concentrated 9 pm–2 am) totaled 3,653 kWh last year and 3,675 kWh this year — a 0.6% difference. Charging behavior didn't change.
The real culprit shows up in the quiet hours. Take each day's 2–7 am draw and subtract its floor: what's left is cycling load — equipment that switches on and off. Through April 2025 that residual is ~0.1 kW: essentially nothing cycles overnight. Then on April 25, 2025 it spikes to 2.6 kWh (a cold-fill heat-up), spikes again May 2 (4.0 kWh), and locks in at ~0.5–0.7 kW permanently — the hot tub, repaired and holding temperature ever since. It was off for the entire base-year winter, so last year's baseline was artificially cheap.
Overnight cycling load — the hot tub signature
kW · weekly median of (2–7 am mean − 2–7 am floor) · cycling load above the house's constant base
With the tub identified, the winter numbers make sense: average Dec–Feb draw rose in all 24 hours of the day (+0.3 to +0.9 kW) because a tub holding ~102°F against a Mammoth winter cycles around the clock — roughly 350–500 kWh/month in the cold months, on top of snow-covered panels turning daytime self-consumption into imports. Comparing the mild shoulder months where the tub is the only real difference (Aug, Sep, Oct, Apr), imports ran +80 to +300 kWh/month — pinning the tub's annual net-import impact at very roughly 1,200–1,800 kWh of the +1,821 kWh swing.
Average hourly grid draw, Dec–Feb
kW · shaded band = 4–9 pm peak pricing window
One detail worth your attention: in early July 2026 the tub's overnight cycling dropped by more than half (~0.6 → ~0.25 kW) and stayed lower through August. If you serviced it, replaced the cover, or dropped the setpoint around then — whatever changed, that's the cheaper operating mode. Going into this winter, that difference alone is worth roughly $30–50/month.
Every net kWh this year was priced higher: SCE's average residential rate rose 9.1% in January 2025, then jumped ~13% on October 1, 2025 (31.2¢ → 35.3¢/kWh average), easing slightly to 34.5¢ in January 2026. Your bad months (Dec–Feb) all landed after the October hike. On top of that, the 4–9 pm peak-window net position — the most expensive kWh on any TOU plan — worsened from 1,350 to 1,717 kWh.
Modeling the year with TOU-style rates (peak 4–9 pm, cheap overnight, monthly netting) reproduces the shape of the increase. Approximate attribution of the ~$550 jump:
Modeled monthly NEM energy charge
$ · approximate TOU model — negative months bank credit against positive months at true-up
The structural point worth internalizing: near net-zero, the NEM bill has enormous leverage. Imports rose only 18%, but because you were previously offsetting almost everything, the net position tripled — and every marginal net kWh is billed at full winter retail. A snowy winter will always swing this bill by hundreds of dollars; that's variance, not a trend.
Caveats, honestly stated: your exact rate plan and true-up statement weren't available, so the dollar model assumes a TOU-D-PRIME-like structure and calibrates to the bills you quoted. It matches the delta well but not the absolute level — the ~$650 base year on a nearly net-zero house suggests meaningful fixed/non-bypassable charges, or a plan detail the model doesn't see. Sharing the true-up PDF would let me pin this precisely.
| Month | Imp 24–25 | Imp 25–26 | Δ Imp | Exp 24–25 | Exp 25–26 | Δ Exp | Net 24–25 | Net 25–26 | Δ Net |
|---|
Method: SCE hourly interval data, Aug 1 2024 – Aug 26 2026 (18,144 clean hourly reads; NEM-year comparisons use the matched Aug–Jul windows). EV signature = hours with >5 kW draw. Snow proxy = days exporting <0.5 kWh. Hot tub signature = daily overnight cycling residual (2–7 am mean minus floor), which steps from ~0.1 to ~0.6 kW on Apr 25 2025 and persists — confirmed by the owner's recollection that the tub was out of service for part of 2025. Rate history: Helios SCE rate tracker, 2026 TOU-D-PRIME rates, CPUC GRC proceedings.