Solar access points bridge digital divide
Power traditionally has been a major challenge for wireless communications systems, particularly in rural deployments and in disaster situations where commercial power and backup systems have been rendered inoperable. One solution that is gaining momentum concerns the use of solar-powered access points.
One such technology is the SWAP900, developed by IR Data Corp. It is a solar-powered, ruggedized 802.11/g access point with secure local access for Wi-Fi-enabled computers, said Doug Bradford, the company’s president.
It promises security with built-in AES encryption protocols and Web-based authentication, so only authorized users are able to access the network, Bradford said. Data is relayed between access points using a data-throughput-optimizing mesh network operating at 913 MHz.
“We came up with a system that is 900 MHz in order to get the long-range and penetration through dense trees,” Bradford said.
SWAP900 employs SunPower’s solar-array technology to power the unit during the day. The unit then switches to lithium ion batteries at night. The solar panels recharge the batteries in two to three hours and do not have to be in direct sunlight to fully charge. However, this is based on recharge tests held in the southwestern states, not in cooler climates in the north. And the solar panels do have a tendency to overheat, Bradford said.
“We need to do further testing in areas that do not have the high-solarization index, which is different for northern latitude states versus southern latitude states,” he said. “We also found early on solar cells become less efficient when they heat up. They weren’t charging the batteries as fast as we would have liked.”
Michael Calabrese, vice president of New America Foundation — an organization lobbying to open airwaves for unlicensed access to facilitate affordable municipal- and community-wide wireless broadband — agreed the SWAP900 does have room for improvement. But his reasons concern spectrum allocation.
“The way they are architecting this makes sense,” Calabrese said. “But it would be far more powerful and more available if there were lots of channels available in that frequency range, not just the one at 913 MHz.”
He said the technology shows promise for use in rural environments and in developing countries.
“The United States is the most wired country in the world, so the solar-powered access point will be most relevant in remote areas,” he said. “Overseas, I think it will play a much bigger role.”
Calabrese also sees solar-power access points as a technology capable of supporting social programs in third-world nations, such as One Laptop per Child (OLPC). OLPC is a nonprofit association with the aim of distributing $100 laptops — created by members of the Massachusetts Institute of Technology’s Media Lab — to schoolchildren in third-world countries so they can access the Internet. A mesh of the solar-powered nodes mounted on rooftops could keep a wireless network between villages running, he said.
“It’s one thing to provide a $100 laptop to an African village,” Calabrese said. “But if the village school doesn’t have electric power, then you can’t get on the Internet.”
The SWAP900 was originally marketed to golf courses in the Palm Springs, Calif., area that were looking for a way to provide wireless coverage, Bradford said, not for social-justice causes. However, several features make the device relatively easy to use, leading to more widespread deployment in underserved and underdeveloped areas. For instance, the access point auto-discovers and self-configures, so non-technical people can install it. It also is lightweight, weighing only 12 lbs. with batteries (not including the antenna weight), and can be mounted on poles, rooftops or towers facing the sun.
Byron Stafford is a solar engineer with the National Renewable Energy Laboratory, the Department of Energy’s renewable energy and efficiency research and development laboratory. He sees another promising aspect of the technology: cost. Economics, he said, will be the driver behind widespread adoption of solar-access points, especially overseas.
“We’re not talking about how many cents per kilowatt hour that we’re paying; it’s the installation labor costs,” Stafford said. “Because for solar wireless, one person — and they don’t have to be an electrician — can set up the site.”
He questioned why the technology hasn’t hit the marketplace sooner. “You have a wireless system for connectivity and then you still have to run a power line? It just doesn’t make sense,” he said.
He also sees the SWAP900 as a technology capable of setting up communications quickly after a man-made or natural disaster.
“I’m going out on a limb here, but after an emergency or hurricane … you can deploy this mesh network almost any place,” Stafford said. “Set some poles up, and you’re in business as long as you have a good link back to the backbone.”
The SWAP900 includes antennas, batteries, solar cells and software for remote management through the secure Web interface. Most orders include 20 to 50 nodes depending on the deployment, Bradford said. Each node costs $3495.