PvMonitor

A headless .NET 10 web service that monitors a Fenecon Home photovoltaic system via Modbus TCP, persists telemetry to SQLite, and exposes a Minimal API for querying live and historical data.

Personal portfolio project for exploring .NET in depth — Minimal APIs, EF Core, BackgroundService, layered architecture, and FluentModbus.

Features

• Reads live telemetry (battery SoC, battery/grid/production/consumption power, grid mode) from the Fenecon FEMS device over Modbus TCP
• Register map is data-driven (registers.json) — supporting a new device means a new JSON file, not new code
• Sentinel-value aware: OpenEMS undefined values (0xFFFF, 0x7FC000, …) are treated as missing, not zero
• Will store readings to SQLite via EF Core
• Exposes a Minimal API with OpenAPI support

Stack

Concern	Technology
Runtime	.NET 10
Language	C# 14, nullable reference types
Web framework	ASP.NET Core Minimal APIs
ORM	Entity Framework Core 10 + SQLite
Modbus	FluentModbus
Logging	Microsoft.Extensions.Logging
Testing	xUnit

Architecture

The solution follows a layered, domain-first architecture. Dependencies flow inward toward PvMonitor.Core.

PvMonitor.sln
├── src/
│   ├── PvMonitor.Core/      # Domain types and interfaces. No external dependencies.
│   ├── PvMonitor.Modbus/    # FluentModbus implementation of IModbusReader.
│   ├── PvMonitor.Storage/   # EF Core implementation of ITelemetryRepository.
│   └── PvMonitor.Api/       # Composition root. Minimal API + BackgroundService.
└── tests/
    └── PvMonitor.Tests/     # xUnit tests.

Core → nothing · Modbus → Core · Storage → Core · Api → all three

Getting Started

Prerequisites

• .NET 10 SDK
• A Fenecon Home (or compatible OpenEMS device) reachable over the network
• (Optional) Dev Container — a .devcontainer config is included for VS Code

Configuration

Copy the placeholder settings and fill in your device details:

cp src/PvMonitor.Api/appsettings.json src/PvMonitor.Api/appsettings.Development.json

Edit appsettings.Development.json:

{
  "Fenecon": {
    "Host": "192.168.1.x",
    "Port": 502,
    "UnitId": 1,
    "PollIntervalSeconds": 10
  }
}

Run

dotnet run --project src/PvMonitor.Api

The port is determined by src/PvMonitor.Api/Properties/launchSettings.json. The current defaults are http://localhost:5137 and https://localhost:7252. The actual URL is printed to the console on startup.

API

Method	Path	Description
GET	/telemetry/now	Read live telemetry from the device right now

OpenAPI is available at /openapi/v1.json in the Development environment.

Example response

{
  "timestamp": "2026-04-29T14:32:10+00:00",
  "batterySoc": 72,
  "batteryPowerWatts": -1200.0,
  "gridPowerWatts": 0.0,
  "productionPowerWatts": 3400.0,
  "consumptionPowerWatts": 2200.0,
  "gridMode": 1
}

Sign conventions:

• batteryPowerWatts: negative = charging, positive = discharging
• gridPowerWatts: negative = export, positive = import
• productionPowerWatts: always ≥ 0
• gridMode: 0 Unknown · 1 OnGrid · 2 OffGrid · 3 OffGridGenset

Register Map

Modbus register definitions live in src/PvMonitor.Modbus/registers.json and are loaded at startup:

Register	Channel	Type
302	_sum/EssSoc	uint16
303	_sum/EssActivePower	float32
315	_sum/GridActivePower	float32
327	_sum/ProductionActivePower	float32
343	_sum/ConsumptionActivePower	float32
417	_sum/GridMode	enum16

Development

# Build everything
dotnet build

# Run tests
dotnet test

# Format the solution
dotnet format

# Add a database migration
dotnet ef migrations add <Name> \
  --project src/PvMonitor.Storage \
  --startup-project src/PvMonitor.Api

# Apply migrations
dotnet ef database update \
  --project src/PvMonitor.Storage \
  --startup-project src/PvMonitor.Api