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VERSION.md

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+# EPrices – Version History
+
+## v1.0 — 2026-04-05
+
+First public release.
+
+### What EPrices is
+
+EPrices is an ESPHome firmware for ESP32 that fetches day-ahead electricity
+spot prices from the public Energy-Charts API and exposes them as Home Assistant
+sensors. No API token, no cloud subscription, no external automations required
+for core functionality — just an ESP32, ESPHome, and your WiFi network.
+
+Prices are fetched for today and tomorrow in 15-minute resolution, converted
+from raw €/MWh to €/kWh with your provider fee and VAT applied, and stored
+persistently in ESP32 NVS flash so they survive reboots without re-fetching.
+
+### Core features
+
+- 15-minute and hourly resolution price arrays exposed as JSON text sensors
+- Current, next, average, highest and lowest price sensors for both today and tomorrow
+- Tomorrow live sensors evaluate at `now + 86400s` — showing tomorrow at the same local time
+- NVS persistence — prices survive reboots without re-fetching
+- Midnight bridge — tomorrow's data automatically promoted to today at 00:00
+- Auto-retry logic — up to 8 HTTP fetch attempts for both today and tomorrow
+- DST-safe — UNIX timestamps and binary search throughout, no hour-slot arithmetic
+- Staleness detection — `Today Current Price Status` shows `Stale` if stored date mismatches today
+- Full diagnostic sensor suite — NVS status, fetch attempts, API fetch times, data loaded
+  times, WiFi signal, human-readable uptime
+- Supports any Energy-Charts bidding zone (SI, DE-LU, AT, FR, HR, HU and more)
+- Provider fee and VAT rate configurable via `secrets.yaml` — no code changes needed
+
+### Sensor highlights
+
+- **Today/Tomorrow JSON Hourly Prices EUR⁄kWh** — 24-value JSON arrays
+- **Today/Tomorrow JSON 15-Min Prices EUR⁄kWh (P1/P2/P3)** — three 32-value JSON arrays
+  covering 00:00-07:45, 08:00-15:45 and 16:00-23:45
+- **Today/Tomorrow Data Loaded Time** — stamped on both NVS load and HTTP fetch
+- **Today/Tomorrow Last API Fetch Time** — stamped on HTTP fetch only; `Never` if NVS only
+- **Today/Tomorrow API Fetch Attempts** — HTTP-only counter, resets at midnight
+- **Uptime** — human-readable: `45 s` → `5 min` → `3 h 22 min` → `12 d 4 h` → `4 months 12 d`
+
+### Files
+
+| File | Purpose |
+|---|---|
+| `eprices.yaml` | Main ESPHome configuration |
+| `eprices_nvs.h` | NVS helper — save/load price arrays to ESP32 flash |
+| `secrets.yaml` | Local secrets — not committed to git |
+| `CHANGELOG.md` | Full sensor and entity ID reference for v1.0 |
+| `README.md` | Installation guide and full sensor reference |
+| `ENTSO-E-PRICES-MIGRATION.md` | Optional — migration guide from the predecessor project |