Siton 210 — Photovoltaic MPPT Inverter
An open-source project for solar water heating
What is Siton 210?
Siton 210 is a photovoltaic MPPT inverter designed for heating domestic hot water (DHW) in a boiler. It converts DC power from solar panels into AC square-wave current with variable duty cycle, powering the boiler heating element. Using MPPT (Maximum Power Point Tracking) technology, it continuously finds the optimal operating point of the panels, maximizing solar energy harvest — even in poor light conditions.
Why Siton 210?
Operating Principle
The inverter uses a Full H-Bridge with four MOSFET transistors switching in cross pattern at 50 Hz. The Arduino Nano control unit measures voltage and current from the panels, calculates actual power, and by gradually adjusting the duty cycle (3–98%) searches for the Maximum Power Point (MPP). If power increases after raising the duty cycle, it continues increasing — if power drops, the direction reverses. This achieves maximum efficiency even in variable weather conditions.
DC input from PV panels
MPPT control
AC output 50 Hz
Water heating
Technical Specifications
DC Input
| Max. input voltage | 400 V DC |
|---|---|
| Max. input current | 10 A DC |
| Continuous operating current | 8–9 A DC |
| Maximum power | 2 800 W |
AC Output
| Output voltage | ±400 V AC |
|---|---|
| Duty cycle range | 3 – 98 % |
| Output frequency | 50 Hz |
| Protection | OCP ~24 A + 16 A fuse |
Control & Communication
| Control processor | Arduino Nano (ATmega328P) |
|---|---|
| Control section power supply | 12 V / 200 mA DC (Self-consumption: 0.3–0.4 W) |
| Communication | RS485 — EasyTransfer (9600 Bd) / Modbus RTU (9600 Bd, 8N1) |
| Display | LCD 16×2 + ATtiny85 |
| Temperature sensor | KTY81/210 |
Key Components
Power MOSFET Transistors
4× SPW47N60C3 (47N60) — form a Full H-Bridge for DC to AC conversion
MOSFET Drivers
2× IR2104 (or IR2110) — drive the high and low side transistors of each bridge half
Control Unit
Arduino Nano (ATmega328P) — MPPT algorithm, measurements, display, communication
Current Measurement
ACS712/20A module — Hall effect sensor for non-contact DC current measurement
Input Capacitors
3× 470 µF / 450 V — smoothing the input voltage from PV panels
Protection
Overcurrent protection with LM258 op-amp (set to ~24 A) + 16 A glass fuse
Display
LCD 16×2 with ATtiny85 backlight control — shows voltage, current, power, temperature
Solar Panel Wiring
Panels are wired in series (not parallel) to achieve higher voltage. Recommended configurations:
Classic panels (250–280 Wp)
6–8 units in series, voltage ~240 V, current ~8.5 A
Modern panels (400–500 Wp)
5–6 units in series, voltage ~200–250 V
Heating element
Choose a 2–3 kW / 230 V element (min. resistance ~15 Ω). Recommended: Eliko GRBT 2000 W.
Energy Savings Calculator
Estimate how much energy and money Siton 210 can save you per year
How to Build Siton
Order PCB and components
Download Eagle PCB files from the Downloads section. Order PCB manufacturing from any fabricator (JLCPCB, PCBWay). Purchase components from the BOM list.
Assembly and soldering
Populate the PCB according to the schematic — start with SMD components, then THT. Pay attention to MOSFET and IR2104 driver orientation.
Program the processor
Using an ISP programmer (e.g. USBasp) and the AVRDUDESS tool, upload the firmware (HEX file version 5.4.xx). ATmega328P fuses: L=0xFF, H=0xDA, E=0xFD.
Wiring and testing
Connect PV panels (series), heating element, 12 V power supply and KTY81/210 temperature sensor. Verify function on the display — the inverter should start searching for MPP.
Connecting to SitonMonitor
For online monitoring, add an ESP8266 (NodeMCU) module that reads data via RS485 or directly from the serial line and sends it to the SitonMonitor server via WiFi.
Register on SitonMonitor
Create an account and add a new inverter. The system will generate a unique API key for you.
Upload firmware to ESP8266
Download the ESP firmware from the Documentation section, set up WiFi credentials and API key.
Connect ESP to the inverter
Link the ESP8266 to the inverter via RS485 converter (or direct serial connection). Data is sent every 30 seconds.
Monitor data online
Log in to SitonMonitor and track power, energy, temperature and other parameters in real time.
Operation & Maintenance
Siton 210 is designed for maintenance-free operation. With proper component sizing and passive cooling, the heatsink reaches about 40–50 °C at 1800 W output.
Downloads
All source materials for building Siton 210 can be found on the project website:
Start Monitoring
Have a Siton built? Register and start monitoring your system performance online.