An open-source - community built micro-inverter

Manifesto

The project goal are :

• Having the first open source PV micro-inverter
• Finally a design easy to repair that is no longer a black box
• Redeem your data sovereignty, you will no longer depend on a proprietary cloud to follow your solar production and consumption.

Open, for everyone, forever

• This project is propulsed by its community.
• The collective work generated is meant to remain open.
• Design files are made with open source software - Namely kiCAD.
• Mechanical interfaces and components are modeled using FreeCAD.
• Simulation files use ngSpice.

In that sense, the owntech foundation aims at protecting this technical common.

Specifications

This section is inspired from

Comparison of micro-inverters with rated output power between 350VA and 400VA:

Model	HM-350	HM-400	IQ7A	EVT300	TSOL-M800
Manufacturer	Hoymiles	Hoymiles	Enphase	Envertech	TSUN
Number of solar panels	1	1	1	1	2
Recommended input power (W)	280-470+	320-540+	295-460	180-420+	2 $\cdot$ 280-440
$V_{MPPT,min}$ (V)	33	34	38 (18)	24	33
$V_{MPPT,max}$ (V)	48	48	43 (58)	45	48
Start-up voltage (V)	22	22	22	-	-
Operating volage range (V)	16-60	16-60	16-58	18-54	16-60
Maximum input current (A)	11.5	12	12	12	11.5
Maximum input short circuit current (A)	15	15	20	15	15
Rated output power (VA)	350	400	349	300	600
Peak efficiency (%)	96.7	96.7	97.7	95.4	96.7
CEC weighted efficiency (%)	96.5	96.5	97.0	95.0	96.5

uVerter Target specifications

Category	Requirement	Notes
Grid	220 V AC to 250V AC / 50 to 60 Hz	Hardware not compatible with 110V grids
Grid compliance	Grid-code compliant	Exact certification scope depends on country / standard
Rated apparent power	450 VA	Software-limited power cap supported
Input DC operating range	16 V – 58 V	PV module operating window
Recommended PV input power	350 W – 550 W	Depends on module and thermal conditions
Efficiency	> 95%	Target at nominal conditions
Power factor	≈ 1	Near-unity PF at rated power
THD	< 5%	Total harmonic distortion at rated conditions
Isolation	Galvanic isolation	Electrical isolation between PV and grid
Operating temperature	-40 °C to +60 °C	Derating may apply
Repairability	No invasive potting	Designed to be serviceable / inspectable
Connectivity	Wi-Fi	Local-first monitoring (no proprietary cloud required)

Renderings

Control overview

The control overview shows the uVerter as two coordinated stages: a PV-controlled DC/DC front end that regulates the panel operating point and raises the DC bus, followed by an AC control stage that shapes a grid-compliant AC output. Measurements and commands flow through Data I/O and the grid-compliance controller so the inverter can synchronize to line/neutral, limit harmonics, and maintain safe operation while power flows from the PV input to the grid.

Firmware overview

The firmware/src/main.cpp file is the entry point for the uVerter firmware: it configures the sensors and power stages, sets up the real-time and background tasks, and runs the state machine plus control loops that drive the boost and inverter legs based on measurements and synchronization status.

• Real-time control runs in loop_critical_task() at 100 µs to read sensors, enforce protections, regulate the boost stage, compute duty cycles, and update grid-sync variables.
• Supervisory logic runs in loop_application_task() to manage modes (idle/startup/power/error), handle transitions, and expose telemetry through the user data API.

Compiling

Micro-inverter uses PlatformIO as it's build and dependency management system.

From the command line

1. Create and activate a Python virtual environment.

    python3 -m venv .owntech-venv
    source .owntech-venv/bin/activate
   

2. Install PlatformIO.

    pip3 install platformio
   

3. Compile the code. Dependencies (including Zephyr and Owntech libraries) are downloaded automatically.

    cd micro-inverter/firmware/
    pio run
   

In Visual Studio Code

1. Install the "PlatformIO IDE" extension
2. Open the firmware directory via PlatformIO's home screen (not with VSCode's File -> Open)
3. Press the "Build" button in the PlatformIO toolbar (found on the bottom left)

Contribute

Spread the word

• ⭐ Star this repository

• Share the project with PV / power electronics / open-hardware communities

• Mention it in meetups, forums, maker spaces, or your local energy co-op

Give feedback and report issues

Help us improve by opening GitHub issues:

• Bug reports (schematic/PCB mistakes, BOM mismatches, mechanical interferences)

• Documentation gaps (unclear steps, missing diagrams, confusing naming)

• Feature requests

Choose a contribution path

Start with — a living list of work items the community can pick up.
Whether you’re a student looking for a thesis topic, an engineer wanting to review a safety-critical design, or a maker growing skills in hardware and firmware: you’re welcome here.

Bring what you have: time, curiosity, test equipment, careful eyes, lived experience installing or repairing PV gear.
Let’s build an inverter that isn’t a black box — and keep it open, for everyone, forever.

Safety first

Disclaimer

This project is shared as-is, without any warranty of any kind, and without any guarantee of compliance with safety, EMC, or grid-connection regulations. By building, modifying, or using this design, you accept full responsibility for verification, testing, certification (if applicable), and safe operation.

Do not connect a prototype to the public grid. Grid connection must only happen after appropriate validation, protections, and (where required) third-party certification.

Mind the risks

Building a micro-inverter is an advanced DIY project. It combines high energy, high voltage, fast switching, and grid interaction — a mix that can injure, start fires, or damage property

Key hazards include:

• Electric shock and electrocution Internal stages can reach hundreds of volts. Multiple nets are high voltage. Some capacitors can stay charged after power-off. Treat the system as live until proven discharged and measured.

• Fire and thermal runaway Faults can turn traces, connectors, inductors, or semiconductors into heaters in seconds. Thermal issues can escalate quickly.

A community note

We want this project to be open — not reckless. If you spot a safety issue (creepage/clearance, insulation, thermal margins, protection logic, connector ratings, etc.), please report it. Safety improvements are contributions that protect everyone.

Standards and directives

Relevant EU directives for CE

• Directive 2001/95/EC: General Product Safety
• Directive 2014/30/EU: Electromagnetic Compatibility (EMC)
• Directive 2014/35/EU: Low Voltage (LVD)
• Directive 2014/53/EU: Radio Equipment (RED)
• Directive 2011/65/EU: Restriction of the use of certain Hazardous Substances (RoHS)

Low Voltage Directive (LVD)

EN IEC 62109-1:2010 Safety of power converters for use in photovoltaic power systems - Part 1: General requirements

EN IEC 62109-2:2011 Safety of power converters for use in photovoltaic power systems - Part 2: Particular requirements for inverters

Electromagnetic Compatibility (EMC)

EN 62920:2017+A11+A1:2021 Photovoltaic power generating systems - EMC requirements and test methods for power conversion equipment

ETSI EN 301 489-1 ElectroMagnetic Compatibility (EMC) standard for radio equipment and services; Part 1: Common technical requirements

ETSI EN 301 489-17 ElectroMagnetic Compatibility (EMC) standard for radio equipment and services; Part 17: Specific conditions for Broadband Data Transmission Systems

Radio Equipment Directive (RED)

ETSI EN 300 328 V2.2.2 Wideband transmission systems; Data transmission equipment operating in the 2,4 GHz band; Harmonised Standard for access to radio spectrum

Grid Regulations

As grid regulations are country specific, please refer to

Licence

This project is licenced under CERN-OHL-V2-S open source hardware licence. Licence file can be found under License/cern-ohl-v2-s.