Clean energy generation and local digital infrastructure should be visible, touchable, and freely accessible in everyday public spaces. Rather than commercial "smart benches" that hide closed electronics behind proprietary vendor NDAs and expensive recurring service contracts, we build an open-hardware public hub and microgrid where every screw, cable, circuit schematic, and line of code is completely transparent, repairable, and free for community replication.

Portable Open-Hardware Structure & Synchronous MPPT Controller

The station is engineered using modular aluminum structural extrusion (2020/2040 profiles) and weather-treated timber, making it reproducible in any community maker workshop using basic hand tools: - High-Efficiency PV Array: An adjustable 120W monocrystalline photovoltaic canopy (22.5% module efficiency) designed to capture direct and diffuse solar irradiance while serving as a rain awning. - Synchronous Buck MPPT Regulator: An open Maximum Power Point Tracking buck regulator switching at 20 kHz with conversion efficiencies exceeding 98%. Utilizing an adaptive Perturb & Observe (P&O) tracking loop, the controller dynamically locates the maximum power operating point ($P = V \times I$) across changing irradiance, temperature swings, and partial cloud cover. - USB-C Power Delivery (PD) & Fast Charging: Four independent, short-circuit-protected DC-DC buck-boost regulators delivering standard USB-PD voltage rails (5V, 9V, 12V, 15V, 20V) at up to 65W per port to cleanly power laptops, handheld transceivers, medical devices, and smartphones.

Safe LiFePO4 Storage Architecture (12V / 24V Modular Banks)

For electrical energy storage, we use Lithium Iron Phosphate (LiFePO4) cells arranged in a 4S configuration (12.8V nominal, 20Ah / 256Wh) or an expandable 8S topology (25.6V 100Ah) for larger stationary deployments: - Intrinsic Thermal Safety & Lifespan: LiFePO4 exhibits outstanding chemical stability with an elevated thermal runaway threshold (>270°C) and zero risk of self-sustaining combustion, delivering over 3,500 full depth-of-discharge cycles (80% DoD) without notable capacity fade. - Smart BMS with Active Balancing: Integrated Battery Management System with cell-level voltage monitoring (HVD: 3.65V, LVD: 2.50V) and a 1.2A flying-capacitor active balancing module that equalizes cell charges without resistive heat generation. - Hardware Low-Temperature Charge Lockout: Dual NTC thermistor probes strictly disconnect charging current when ambient cell temperature drops below 0°C, eliminating catastrophic metallic lithium plating on the graphite anode, while safely permitting discharge down to -20°C.

Industrial RS485 / Modbus Telemetry

Unlike consumer devices that rely on proprietary mobile apps, the charging node interfaces using the robust industrial standard Modbus-RTU over a galvanically isolated RS485 bus: - Real-Time Register Polling: The edge computer queries the solar charge controller via RS485 at 9600 baud, reading live holding registers: PV array voltage ($V_{\text{pv}}$), solar current ($I_{\text{pv}}$), battery charge/discharge current, battery state-of-charge (SoC%), daily cumulative kWh yield, and heatsink thermal status. - Per-Port Current Shunt Monitoring: High-side I2C digital power monitors (INA226) log delivered power across each USB-C charging channel with 16-bit resolution. - Zero-Cloud Local Storage: Time-series telemetry is recorded into a local InfluxDB instance on the node and rendered via a lightweight local Grafana dashboard. - Long-Range LoRa Beacons: Every 15 minutes, the node serializes a compact 32-byte binary telemetry packet and broadcasts it over the 868 MHz Meshtastic / LoRaWAN mesh, feeding live stats to the community map.

Raspberry Pi 4 Edge Server & Local Offline Services

Housed in an IP65 weather-tight vented compartment sits an energy-efficient single-board computer (Raspberry Pi 4 Model B, 4GB RAM) powered directly from the solar DC bus via a dedicated 5.1V / 3.5A buck regulator: - Brownout Immunity (Read-Only Root Filesystem): The OS (DietPi / Alpine Linux) runs with root on a read-only overlay (overlayfs). Abrupt power drops or low-voltage disconnects never corrupt the storage medium or operating system. - Autonomous Wi-Fi Portal: Standalone local Wi-Fi provided by hostapd and dnsmasq, offering digital services to any visitor within a 50-metre radius without requiring an upstream internet uplink. - Kiwix Knowledge Mirror: Offline copies of Wikipedia, open medical handbooks, DIY repair manuals, and full OpenStreetMap vector tiles for North Macedonia. - Microclimate & Soil Ecology: Integrated Bosch BME280 sensor logging barometric pressure, temperature, and relative humidity, combined with capacitive soil probes in surrounding planters. - Open Schematics: All KiCad PCB layouts, structural CAD designs, and Modbus ingestion scripts are maintained in our public git repository.