EPrices/VERSION.md

EPrices – Version History

v1.2.2 — 2026-04-28

Stability patch addressing spontaneous reboots during tomorrow price fetch at ~13:55. No new sensors, no secrets changes, no entity ID changes. Drop-in replacement for v1.2.1.

ESP32 task watchdog timeout increase

Increased the ESP-IDF task watchdog timeout from the default (~15 seconds) to 40 seconds and disabled idle task watchdog checking on both CPU cores. This prevents false-positive watchdog resets during heavy JSON parsing when full price data arrives (~13:55 and subsequent retry attempts).

Root cause: The first API call at 13:25 typically returns no data (Energy-Charts usually hasn't published tomorrow's prices yet), so no heavy parsing occurs. By 13:55, complete data is available, triggering the full parsing chain that exceeded the default watchdog timeout.

JSON string building optimised

Replaced O(n²) std::string += concatenation in recompute_today and recompute_tomorrow with pre-allocated fixed-size char buffers via snprintf(). Eliminates heap fragmentation and peak memory spikes during JSON building for the 8 JSON text sensors.

Periodic yield() calls

Added explicit yield() calls at strategic points during parsing and recompute operations to prevent the task watchdog from triggering during CPU-intensive operations.

Heap monitoring logs

Added ESP_LOGI calls to log free heap at key points during parsing and recompute operations using heap_caps_get_free_size(MALLOC_CAP_8BIT).

See CHANGELOG.md for full implementation details.

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v1.2.1 — 2026-04-07

Stability and housekeeping patch. No new sensors, no secrets changes, no entity ID changes. Drop-in replacement for v1.2.

ESP32 main task stack size increase

Doubled the FreeRTOS main task stack from 8192 to 16384 bytes via CONFIG_ESP_MAIN_TASK_STACK_SIZE. Eliminates the stack overflow scenario most likely responsible for the spontaneous reboot observed in production on 2026-04-06 during a simultaneous NVS load + HTTP fetch/parse cycle.

Price vector heap pre-allocation at boot

Added .reserve(96) on all four price vectors (price_timestamps_today, price_values_today, price_timestamps_tomorrow, price_values_tomorrow) in the on_boot lambda. Prevents repeated heap reallocation during NVS load and HTTP parse operations, reducing heap fragmentation and peak allocation pressure during the boot sequence.

Hourly JSON sensor cleared state unified

Today JSON Hourly Prices EUR⁄kWh and Tomorrow JSON Hourly Prices EUR⁄kWh now publish "" when cleared, matching the existing behaviour of all six 15-minute JSON sensors. Previously they published "[]".

See CHANGELOG.md for full implementation details.

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v1.2 — 2026-04-06

HTTP fetch stuck-flag watchdog

Fixed a production-observed reliability issue where a TCP-level stall during an HTTP fetch could lock is_updating_today or is_updating_tomorrow at true for several minutes, silently blocking all auto-retry triggers and manual button presses for the duration.

A 120-second watchdog was added to both worker loops. If either is_updating_* flag has been held for more than 120 seconds, the worker force-clears it and sets the status message to "Fetch timeout – will retry", allowing the next scheduled retry or manual press to proceed immediately.

New globals: is_updating_today_since, is_updating_tomorrow_since.

Tomorrow auto-retry attempt counter fix

tomorrow_retry_count was not being incremented in the 13:55 and 14:55–19:55 hourly retry triggers, causing the Tomorrow API Fetch Attempts diagnostic sensor to undercount after the first scheduled attempt at 13:25.

Status message improvements

• tomorrow_update_status_message initial value changed from "Waiting for 13:20" to "No data yet"
• clear_tomorrow_prices end message changed from "Cleared – awaiting next 13:20 window" to "Cleared – awaiting fetch window"

See CHANGELOG.md for full implementation details.

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v1.1 — 2026-04-06

Negative price provider fee

Added separate provider fee support for negative spot prices via a new eprices_neg_prov_fee secret key. Positive and negative market prices now use independent fee multipliers, correctly modelling contracts where the provider's fee structure differs between the two cases.

Price calculation:

• Positive: (raw / 1000) × (1 + prov_fee) × (1 + vat_rate)
• Negative: (raw / 1000) × (1 - neg_prov_fee) × (1 + vat_rate)

VAT is applied to both, consistent with net billing where VAT is calculated on the monthly net sum (linear equivalence applies).

See CHANGELOG.md for full implementation details.

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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