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The Green Wifi Concept: Router - Grid - Solar - Power Control
The approach of Green-WiFi is to use software, hardware, and components easily available and low cost, but assembled and compiled to make smart use of technology. Following the MIT roof net approach, the project started by using off the shelf hardware from Netgear and open source wireless grid software. The Netgear WGT634U Wi-Fi router is based on a Linux. The Netgear router has been discontinued since the project started. We have been using the Linksys WRT54GL model router and plan to upgrade to the Ubiquiti Networks products

Wi-Fi hotspot and wireless grid router
OpenWRT-based WGRT634U 802.11b/g router - Netgear

Linux 2.6 kernel
madwifi-ng driver
OpenWRT ipkg support

Wireless 802.11b/g Grid Network Application (roofnet - MIT)
Srcr is the routing protocol used at MIT for their roofnet project, it finds good paths despite generally low-quality radio propagation. Wireless Grid Network software operate without extensive planning or central management, automatically figures out the fastest way to reach from point A to point B and continuously monitors the network paths, and acts as a NAT for connection from Roofnet to the Internet.

Solar Panel
The Shell ST10 solar panel was used in the prototype unit. This solar module is composed of a monolithic structure of series connected Copper Indium Diselenide (CIS) based solar cells. Great performance under low light conditions, shade and high temperature tolerance that offers reliable power in adverse or changeable conditions. Highly transparent tempered glass delivering more power and ensuring high impact resistance and protection against hail, stones, ice, and storms. Since we started the project this model has been discontinued and we are evaluating models from other manufacturers.

Charge Circuit and Power Management
The SunGuard's 5.5 amp 12 Volt unit was first used to see how a low cost, off-the-shelf unit would work. Without any type of power control to the router, the up time was very short. A few cloudy and raining days and battery drained dead in four days. A modified designed was then used that could control the router over a time period, with shut down and restart. This allowed the router to operate during a specific time period, i.e. when school is open, and specific days, which allowed the weekend to be powered down. This extended the up time to 28 days. Still two weeks of cloudy and raining weather did not meet the goal of +30 days of continues operation. The third design can then control, not only day and time but, user access via the router software and the power output of the device through a web browser interface. Access to these features are locally set or permissions can be set for remote access and control. This version also allows monitoring the battery charge level and will allow the router to stay up if level is above the set level. We are testing what would be optimal level for this with a 10 watt solar panel and 19 amp hour battery.


The Green Wifi Prototype
This prototype #2 was assembled using a PVC frame. The testing is underway on the roof of Bruce's home's roof in San Francisco, California. During the month of March 2006, we had record rain of 27 out of 30 days, so was a good test for weak sun levels and cloudy days.

The Green WiFi node/hotspot prototype #3 will utilizes more advanced power control connected between the 10 watt solar panel to the wifi network router using TCP/IP networking protocol via an interface to the network router Ethernet interface. The system also comprises power control module software running on wifi router, communicating via the Ethernet port. Based on the output of the solar panel(s) and the charge state of the battery backup, the control module and software can interact with the network router to regulate power usage of the wifi router, via software control of the RF output level, time of day, number of DHCP clients attached, and strength of link to a associated node point on a wireless grid network or point to point wireless.

Latest Prototype with NEMA 4 enclosure, Omni-directional Antenna, and Green WiFi ICCM - Sept 2006
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