Rural Electrification & Microgrids

Research Overview
 
Local electricity generation is one of the key challenges of technology for developing regions. Although we were driven by the need to power rural connectivity solutions, the approach described here makes sense for any remote ICT project with power needs up to about 100 W, which includes most home solar systems, as well as single PC projects, such as kiosks.
The primary concern is to provide reliable electricity for our WiFi-based long-distance (WiLD) links, particularly relay points. The relay point may be in the middle of a remote area where no grid power is available. Furthermore, even in areas served by the grid, power is often unreliable.

AC Microgrid Smart Meter Management System
Please contact javirosa@eecs.berkeley.edu for questions. We'd be glad to collaborate on improving the Microgrid Management System to meet your requirements.
Software
Source code available under the GPL
Hardware
Hardware available under Creative Commons Share-Alike
Solar Charge Controller
Note: Detailed report on the TIER Solar Controller is here (in PDF).
Summary of Features

  • Maximum power point tracking
  • Panel, battery and load status reporting through Ethernet (and serial)
  • Provides power over ethernet
  • Low voltage disconnect, trickle charge

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Maximum power point tracking
The charge controller implements maximum power point tracking using a PIC microntroller. Power point tracking is seen to have increased solar panel output up to 15% compared to a simple direct connection between the solar panel and the battery. Switch-mode power conversion used with the power tracking has a typical efficiency of 95%.
Status reporting through Ethernet (and serial)
Voltages and currents of the solar panel, battery and load are reported through the Ethernet connection of the device. Status reports may also be monitored through the serial port.
Power over Ethernet
The devices provides power over Ethernet through the RJ45 port (assuming battery is sufficiently charged). Typical output voltage is 12 volts. PoE is disconnected when battery voltage drops below the minimum safe voltage.
Device specifications

  • Maximum input voltage (solar panel connection): 36 V
  • Maximum current output capacity: 5 A
  • Load output voltage (PoE): 11.3 V to 14.3 V
  • Dimensions: 7.6 cm x 7.6 cm x 2 cm
  • Ethernet: 10 Mbps, PoE at pin 4/5 (+) and pin 7/8 (-)
  • Serial: RS232, 19.2 kbps, 8N1
  • Low voltage output (PoE) disconnect at 11.3 V
  • Trickle charge at 14.3 V

Version 2: Adjustable Voltage Output
To address the need to power different types of routers, the previous board has been revised. The revised board (shown below) can be configured to output, through the PoE 12V-48V. Power capacity through the PoE is limited to 24W. 12V output is still available through the load terminal.
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Version 3 (Current Version)
You can find a set of files related to this version here, including:

  • A PDF describing the controller's operation and including an general schematic.
  • PNG overview schematic image.
  • EAGLE files for the board and its layout.
  • PIC Microcontroller program assembly source and compiled binary.

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Version 4 (Work In Progress)
See this page for details on the planned 4th revision of the solar charge controller.
Building, Testing and Monitoring