Pay-As-You-Go Distributed Solar System

A decentralized, token-based solar power solution designed for rural areas, built to deliver electricity to households that can’t afford full monthly bills, one token at a time.

Built Between 2016–2019

This project came out of a real-world problem: how do you deliver solar electricity to low-income homes in a way that’s affordable, tamper-proof, and offline-friendly?

Tech Stack (Then & Now)

2016–2019 (MVP):

  • Microcontroller: STM32 (bare-metal C)
  • UI: Android (Java)
  • Backend: PHP API + MySQL
  • Comms: GSM module (SIM800L)
  • Storage: EEPROM for token caching

Modernization Plan (2024+):

  • Backend Rewrite: Java Spring Boot API (secure + scalable)
  • Mobile UI Refresh: Kotlin/Jetpack Compose or Flutter
  • Add-ons: QR token scanning, OTA firmware updates, mobile-based admin dashboard

What It Does

  1. Customer buys a token using mobile USSD or app.
  2. PHP API (legacy) or Java Spring (new) generates a unique token.
  3. User enters token into the Android interface via Bluetooth or keypad.
  4. STM32 controller verifies the token, energizes a relay, and powers the load.
  5. When the token expires, power is cut automatically.

Highlights

  • Offline-ready: Works with GSM or SMS , no internet required.
  • Tamper detection: Interrupts power on bypass attempts.
  • Micro-payments: Enables buying power in small units (e.g., $0.5 at a time because Zimbabwe and our US dollars).
  • Low-power design: Optimized for 12V DC solar systems.
  • EEPROM caching: Retains balance and token data during blackouts.

Lessons Learned

  • Real-world GSM is messy: signal strength and latency matter.
  • Token generation must be secure but lightweight.
  • STM32 with direct relay control is powerful but needs precise timing.
  • Building a UX for non-tech-savvy users means simplicity is everything.
  • PHP was fast to prototype but not scalable , hence the Spring Boot rewrite.

Future Potential

  • Integrate blockchain or token ledger for village-level energy credits.
  • Add remote monitoring via LoRa or NB-IoT.
  • Community energy-sharing between users with surplus.

“This project taught me that real-world innovation isn’t always about bleeding-edge tech , sometimes it’s about solving fundamental problems with whatever tools you’ve got.”

📌 Follow along weekly right here or catch me on LinkedIn. I’m documenting the grind so you don’t have to make the same mistakes I did.