EPrices/VERSION.md

EPrices – Version History

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