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Wattpilot Data Exporter ⚡

A lightweight Go web application that fetches EV charging session data from Fronius Wattpilot and calculates monthly charging costs based on the official Austrian government electricity rates (BMF Sachbezug).

Features

  • Monthly dashboard — view charging sessions, total energy (kWh), cost (€), and margin for any month
  • Historical charts — visualize energy consumption and costs over time (data since June 2024)
  • Excel export — download a per-month .xlsx billing report with detailed session data and cost summary
  • Live charging indicator — detects whether a charging session is currently active
  • Data caching and backup fallback — data is cached in local filesystem storage or Azure Blob Storage; monthly backups are stored as data/*_backup.json; use the /refresh endpoint to re-fetch
  • OpenTelemetry observability — automatic HTTP request traces, app-level spans, and structured logs
  • Docker support — multi-stage Docker build for minimal container images

Dashboard Screenshot

Prerequisites

  • Go 1.25+ (or Docker)
  • A Wattpilot API key (WATTPILOT_KEY)

Configuration

Variable Required Description
WATTPILOT_KEY Yes Your Wattpilot data export key
OTEL_EXPORTER_OTLP_ENDPOINT No OTLP/HTTP collector endpoint (for example http://localhost:4318)
AZURE_STORAGE_ACCOUNT_NAME No Enables Azure Blob Storage backend when set
AZURE_STORAGE_CONTAINER_NAME No Blob container name (defaults to wattpilot-data)

You can find the key on your Wattpilot export page — it is the e= query parameter in the URL:

https://data.wattpilot.io/export?e=THIS_IS_YOUR_KEY

Create a .env file in the repository root (see .env.example):

# .env
WATTPILOT_KEY=your_key_here
# Optional: send traces/logs to an OpenTelemetry collector
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318

Observability (OpenTelemetry)

The app includes built-in OpenTelemetry tracing and logging:

  • All incoming HTTP requests are instrumented automatically (method, route, status code, duration, propagation headers).
  • Core business operations (data fetch, monthly calculations, refresh flow) emit spans.
  • slog is bridged to OpenTelemetry so structured logs are emitted through the OTel log pipeline.

Exporter behavior:

  • If OTEL_EXPORTER_OTLP_ENDPOINT is set, traces and logs are sent via OTLP/HTTP to your collector.
  • If it is not set, telemetry is written to stdout, which is convenient for local development and debugging.

Example local collector setup:

# .env
WATTPILOT_KEY=your_key_here
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318

Getting Started

Run locally

go run ./cmd/server

Or use the Makefile:

make run        # fetches fresh data (deletes cached data/data.json first)
make run-cached # uses cached data/data.json if available

The application starts on http://localhost:8080.

Run with Docker

make docker-build
make docker-run

Make sure a .env file with your WATTPILOT_KEY exists in the repository root — it is passed to the container via --env-file.

Deploy to Azure

This project is configured for deployment to Azure Container Apps using the Azure Developer CLI (azd).

WATTPILOT_KEY is stored in Azure Key Vault and consumed by the Container App via a Key Vault secret reference using a user-assigned managed identity. The application writes cached data and backups to Azure Blob Storage using a system-assigned managed identity.

Prerequisites:

Quick start:

# Login to Azure
azd auth login

# Initialize environment (from repo root)
azd init -e wattpilot-prod

# Configure
azd env set AZURE_LOCATION swedencentral
azd env set WATTPILOT_KEY <your-wattpilot-api-key>
azd env set DOCKER_USERNAME <your-dockerhub-username>
azd env set DOCKER_PASSWORD <your-dockerhub-password>

# Provision infrastructure
azd provision

# Deploy application
azd deploy

# Get the deployed URL
azd env get-values | grep AZURE_CONTAINER_APP_FQDN

azd deploy automatically builds, tags, and pushes the container image; no manual CONTAINER_IMAGE value is required.

See AZD-SETUP.md for detailed Azure deployment instructions.

CI/CD (GitHub Actions)

The repository includes a GitHub Actions workflow (.github/workflows/deploy-container-app.yml) that automatically deploys to Azure Container Apps on every push to main.

What it does:

  • On pull requests: builds the Docker image without pushing (validation only)
  • On push to main: authenticates to Azure via OIDC, logs into Docker Hub, and runs azd deploy

Required repository secrets:

Secret Description
WATTPILOT_AZURE_CLIENT_ID Azure AD app registration client ID (with OIDC federation)
WATTPILOT_AZURE_SUBSCRIPTION_ID Azure subscription ID
WATTPILOT_AZURE_TENANT_ID Azure AD tenant ID
WATTPILOT_REGISTRY_USERNAME Docker Hub username
WATTPILOT_REGISTRY_PASSWORD Docker Hub access token

Azure OIDC setup:

The workflow uses workload identity federation (no stored client secrets). The Azure AD app registration must have a federated credential with:

  • Issuer: https://token.actions.githubusercontent.com
  • Subject: repo:jetzlstorfer/wattpilot-exporter:ref:refs/heads/main
  • Audience: api://AzureADTokenExchange

Routes

Route Description
/ Monthly dashboard (use ?date=YYYY-MM to navigate)
/charts Historical charts across all months
/download Download monthly Excel report (?date=YYYY-MM)
/info Info page
/refresh Force re-fetch of data from the Wattpilot API

Official Electricity Rates

Charging costs are calculated using the yearly rates published by the Austrian Federal Ministry of Finance:

Year Rate (€/kWh)
2024 0.33182
2025 0.35889
2026 0.32806

Tech Stack

Project Structure

wattpilot-exporter/
├── cmd/
│   └── server/
│       ├── main.go          # HTTP server, routes & signal handling
│       └── telemetry.go     # OpenTelemetry initialisation
├── internal/
│   ├── handlers/
│   │   ├── dashboard.go     # / handler — monthly dashboard
│   │   ├── charts.go        # /charts handler — historical month-over-month stats
│   │   └── download.go      # /download handler — Excel export
│   └── wattpilot/
│       ├── storage.go       # local filesystem / Azure Blob storage abstraction
│       └── wattpilot.go     # API client, refresh logic, pricing, parsing & backup handling
├── templates/               # HTML templates (dashboard, charts, info)
├── static/                  # Client-side assets (Chart.js, Tailwind CSS, icons, PWA manifest)
├── data/                    # Runtime cache — data.json and monthly *_backup.json files
├── infra/                   # Azure Bicep IaC
├── Dockerfile               # Multi-stage Alpine build
├── Makefile                 # Build, run & Docker targets
├── azure.yaml               # Azure Developer CLI configuration
└── go.mod

Makefile Targets

Target Description
make build Compile the binary
make run Delete cached data and run the app
make run-cached Run the app using cached data
make clean Remove binary and cached data
make docker-build Build the Docker image
make docker-run Run the Docker container

License

This project is provided as-is for personal use.

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