OPENDTU READS YOUR BALCONY SOLAR INVERTER DIRECTLY, SO THE DATA NEVER LEAVES YOUR HOUSE
Your panels report to the manufacturer's cloud by default — this fifteen-dollar radio board takes that data back.
by tbnobody
EnergyHome
- difficulty
- ●●●○○
- time
- an evening
- license
- GPL-2.0
- repo
- repo ACTIVE2,173 stars
●●●○○ · an evening · GPL-2.0 · 2,173 stars · repo ACTIVE
WHAT YOU’LL NEED
- Electronic parts — full list with part numbers in the repo BOM
- Dev board / microcontroller — runs the project firmware
Partner
COMPAREE VERDICT
OpenDTU replaces the manufacturer's gateway box so your balcony solar data stays on your own network. It speaks the inverter's own radio protocol — Hoymiles, TSUN and Solenso only — and serves a local web page, publishes to MQTT, auto-discovers in Home Assistant, and exposes a Prometheus endpoint. The parts are an ESP32 (about 8 euros) plus a radio module (NRF24L01+ for HM series or CMT2300A for HMS/HMT, roughly 4.50 euros), landing near fifteen dollars if you solder it yourself; ready-made boards run about 43 euros. You will need to solder the radio module to the ESP32 and add a capacitor near the module for stable operation — the docs show the pinout but assume basic soldering competence. The single biggest trap is buying the wrong radio chip: the HM series uses NRF24L01+, the HMS and HMT series need CMT2300A, and if you guess wrong the board will flash and boot but never hear the inverter. Once running, the data is yours: per-panel production history, charts, and inverter power limiting through the API, which matters in jurisdictions that cap feed-in. The most likely weekend-wrecker is weak radio range — the NRF24 in particular has short reach, and concrete or metal between the board and the inverter can leave you with no signal at all. The repository is actively maintained, the documentation is detailed for build and flash, and the license permits commercial use, so this is a solid pick if your inverter model is supported and you are comfortable with a soldering iron.
IN THE REPO
NOT IN THE REPO
- —GPL-2.0 license permits commercial use.
- —Firmware repository includes full source, flashing instructions, wiring diagrams and a detailed hardware compatibility list.
- —No PCB Gerbers — the project assumes you will either buy a ready-made board (Ahoy, IKNX, et al.) or hand-wire an ESP32 to the radio module yourself.
- —The radio protocol was reverse-engineered and works with Hoymiles HM / HMS / HMT, TSUN TSOL, and Solenso inverters — if your inverter is not on that list, this will not work.
- —Documentation is thorough for building and flashing, lighter on troubleshooting radio range issues.
- —Active development: last push 3 August 2026, 2,173 stars.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterBluHub reads and burns Blu-ray/DVD/CD, adds USB-C, USB-A, SD/TF and 10 Gbps data — plug and play, grand-piano finish.
Videos
OpenDTU build and live production data
No official YouTube channel or build video from the project author. Community walkthroughs exist but are not linked in the repository.
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Check the supported hardware list in the docs to confirm your inverter model is compatible(HM series needs NRF24L01+, HMS/HMT needs CMT2300A — buying the wrong radio is the most common mistake)
- 2.Order parts or a ready-made board (links in the repository shopping list)(Self-build is about 15 USD, ready-made boards about 43 EUR)
- 3.Follow the pinout diagram and solder the radio module to the ESP32(Add a 100µF capacitor near the radio module or you will see random disconnects)
- 4.Flash the firmware using the web installer(No local toolchain required, the flashing is browser-based)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
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KNOWN ISSUES
- Buying the wrong radio module for your inverter series — HM uses NRF24L01+, HMS and HMT need CMT2300A, and the board will not complain if you flash with the wrong one, it just will never hear anything.
- NRF24L01+ has short range and poor wall penetration — if the board and inverter are separated by concrete or metal you may get no signal at all, and the only fix is moving the board or adding an external antenna.
- Forgetting the 100µF capacitor near the radio module — without it the module draws voltage spikes that cause random disconnects and the logs will blame radio errors instead.
- Assuming the manufacturer's DTU can run alongside OpenDTU — both gateways talk to the inverter on the same channel and will interfere, so you have to pick one.
- Not checking that your country or region allows self-built monitoring equipment for grid-connected inverters — some jurisdictions require certified hardware.
- Expecting instant Home Assistant discovery without enabling MQTT in the OpenDTU settings — auto-discovery relies on MQTT being configured first.
Can I run this alongside the manufacturer's DTU?
No — both gateways use the same radio channel and will interfere with each other. You have to remove or power down the original DTU.
Which radio module do I need?
HM series inverters need an NRF24L01+. HMS and HMT series need a CMT2300A. If you buy the wrong one, the board will flash and boot but never hear the inverter.
Does this work with my inverter?
Only Hoymiles HM / HMS / HMT, TSUN TSOL, and Solenso models are supported. The full list is in the repository's supported hardware doc.
How far can the radio reach?
NRF24L01+ typically manages 10-20 meters in free air but struggles through walls. CMT2300A is better. Concrete and metal kill range — if you have no signal, the board needs line-of-sight or an external antenna.
Can I control the inverter's output limit?
Yes — OpenDTU can set the inverter's power limit through its API, which is useful in regions that cap feed-in to the grid.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
2,173 stars and the radio protocol was reverse-engineered from scratch — which inverter series would you point this at first, or are you already running one?
tbnobody
tbnobody reverse-engineered the Hoymiles radio protocol so that balcony solar owners could monitor their own panels without the manufacturer's cloud service. The project started in 2022 and now supports TSUN and Solenso inverters as well.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM19d agoedited
Practical notes from our verification: the repository is actively maintained (last push 3 August 2026), the documentation is detailed for building and flashing but lighter on radio range troubleshooting, and the single most common trap we see in community discussions is someone buying an NRF24 for an HMS inverter or a CMT2300A for an HM — the board will flash and boot but never hear anything, and the logs do not make the mismatch obvious. The parts prices in the payload come from the project's own published shopping list and move with the market. No official YouTube channel exists; the good walkthroughs are community-made (Alex Kly's footage was used for the reel). If you are self-building, budget an extra ten minutes to add the 100µF capacitor near the radio module — without it you will see random disconnects that look like radio errors.