diff --git a/solar-analysis/Dockerfile b/solar-analysis/Dockerfile
index 35cc155..66197d2 100644
--- a/solar-analysis/Dockerfile
+++ b/solar-analysis/Dockerfile
@@ -1,9 +1,13 @@
-FROM python:3.11-slim
+# SITER-Solar analysis container — runs the CURRENT bash analyzer.
+# (2026-09-06, #826: entrypoint previously ran the DEPRECATED
+# solar_estimate.py, which also assumed 400W panels. Retired.)
+FROM alpine:3.20
+
+RUN apk add --no-cache bash curl jq bc
 
 WORKDIR /app
 
-RUN pip install --no-cache-dir requests
+COPY siter-solar-analysis.sh /app/siter-solar-analysis.sh
+RUN chmod +x /app/siter-solar-analysis.sh
 
-COPY solar_estimate.py /app/
-
-ENTRYPOINT ["python", "solar_estimate.py"]
+ENTRYPOINT ["/app/siter-solar-analysis.sh"]
diff --git a/solar-analysis/siter-solar-analysis.sh b/solar-analysis/siter-solar-analysis.sh
index 063ad5b..71925d0 100755
--- a/solar-analysis/siter-solar-analysis.sh
+++ b/solar-analysis/siter-solar-analysis.sh
@@ -49,8 +49,8 @@ readonly DEFAULT_ARRAY_TYPE="0"
 
 # Financial parameters
 readonly PROJECT_COST="4100"
-readonly CURRENT_MONTHLY_BILL="301.08"
-readonly CURRENT_ANNUAL_CONSUMPTION="23952"
+readonly CURRENT_MONTHLY_BILL="264.47"  # 15-month avg from v2 plan billing table (was 301.08, stale)
+readonly CURRENT_ANNUAL_CONSUMPTION="22614"  # 15-month avg x12 from v2 plan (was 23952, stale)
 readonly CONSUMPTION_RATE="0.085"
 readonly EXPORT_RATE="0.04"
 readonly SELF_CONSUMPTION_PCT="0.60"
diff --git a/v2-siter-solar-plan.md b/v2-siter-solar-plan.md
index 24b965c..492042d 100644
--- a/v2-siter-solar-plan.md
+++ b/v2-siter-solar-plan.md
@@ -8,14 +8,14 @@
 This document outlines a solar energy installation project for SITER, designed to offset a portion of monthly electricity costs through solar generation. The system will utilize 16 solar panels across 8 custom-built ground-mount racks, paired with a Sol-Ark 5K hybrid inverter that integrates with the existing Base Power battery backup system.
 
 **Total Project Investment:** $4,100.00
-**Estimated ROI Period:** 9.1 years (based on updated billing analysis)
+**Estimated ROI Period:** 10.2 years (baseline 4.0 kW system, updated billing analysis)
 **Estimated Monthly Savings:** $37.61 (14.2% bill offset)
 
 **Existing Infrastructure:** SITER currently operates with a Base Power battery backup system and automatic transfer switch (ATS), installed in 2025, providing resilience and a fixed energy rate of **$0.085/kWh** through a 3-year contract (Oct 2025 - Oct 2028).
 
 **Updated Billing Data (15 months):** Average monthly consumption of 1,885 kWh (~22,600 kWh/year) at average effective rate of $0.140/kWh.
 
-**NREL PVWatts Analysis:** Based on location data for SITER, a 16-panel system (4.0 kW DC with 250W panels) is projected to produce ~6,000 kWh/year, offsetting approximately 14% of current consumption.
+**NREL PVWatts Analysis:** Based on location data for SITER, a 16-panel system (4.0 kW DC with 250W panels) is projected to produce ~6,000 kWh/year, offsetting ~26.6% of current consumption kWh (~12.7% of the bill).
 
 ---
 
@@ -36,7 +36,7 @@ This document outlines a solar energy installation project for SITER, designed t
 
 ### Objectives
 
-- Reduce monthly electricity expenses through solar generation (~14% offset with current panels)
+- Reduce monthly electricity expenses through solar generation (~12.7% bill offset with current panels)
 - Integrate with existing Base Power battery backup infrastructure
 - Leverage Base Power's 4¢/kWh solar buyback program for excess production
 - Complete installation with minimal upfront capital expenditure
@@ -370,6 +370,8 @@ The ground-mount configuration at this site has significant advantages:
 
 The site's open exposure and ground-mount flexibility make it an ideal solar location.
 
+> **Cost caveat (2026-09-06 audit, #826):** the scenario payback rows above and in §ROI assume the SAME $4,100 project cost at every array size. Larger arrays need more panels+racking, so the improved paybacks at 4.8–8.0 kW are optimistic ceilings; per-scenario BOM costing is queued.
+
 ### Monthly Production Profile (NREL)
 
 | Month | AC Output (kWh) | Daily Avg | Solar Rad (kWh/m²/day) |