Here Comes the Sun

By Amy Mayer

November 26, 2007

From remote villages to train yards and vineyards, solar power shines in Wi-Fi deployments.

The ubiquity of Wi-Fi, particularly with the coverage a mesh network can provide, is primarily limited by the ability to get power to each access point. Increasingly, in environments as diverse as small villages in developing countries, vineyards in California, and Chicago Transit Authority maintenance yards, the power of the sun is fueling nodes where AC power is unavailable or unaffordable.

Solar-powered Wi-Fi takes on different guises depending on the specifics of a situation. But typically an access point requires a small solar panel, an inverter to convert the sun's energy to electricity, and a battery to store that power. Those things connect with the router or other hardware and the point functions the same as one powered solely by disposable batteries or AC power.

Protection and security

For Solis Energy of Orlando, Florida, perimeters of buildings and outlying tarmacs at airports have brought customers in the door.

"Specifically in the solar, it's been for security systems," says CEO and founder Robert Reynolds. An engineer, Reynolds made the transition into solar powering wireless systems after helping his son, then in junior high, with a science project. The potential applications of solar power seemed marketable, and after assessing the situation with a colleague, Reynolds launched Solis.

When a Wi-Fi AP is desired in a location without power, Reynolds says, the cost of having wired electrical power run to the location far exceeds the cost of a solar set-up. And the "solar power plant" that he markets for various applications works well for Wi-Fi because the needed power wattage is low.

"In the use of a Motorola Motomesh duo with a canopy backhaul," he says, just 24 watts of power is needed. "Our solar power plants for the ‘Sunbelt’ states use 210 watt solar panels." A higher capacity solar panel might be necessary in an area with fewer sunny days. Reynolds says typically customers who initially think they want to deploy solar power purely for environmental reasons discover that in a location where electrical power is available, the additional expense for the solar hardware becomes cost-prohibitive. It's really only economically practical where no AC power source exists.

Wildlife and fire monitoring

One such location is the wilderness surrounding Laguna Beach, California, an area devastated by a wildfire in 1993. The community sought a strategy for monitoring remote areas to allow for early warnings if fires formed. Working together, the Laguna Broadcasting Network and Tropos deployed a solar powered Wi-Fi network.

"Having solar power was an incredible advantage for Laguna Beach," says Tropos marketing director Denise Barton. The sensitive environment—and the cost—made running power out to the points impossible. So the client accepted the cost of $1,500-$2,500 per node for solar power and ended up with an entirely solar-powered wireless mesh network that allows video surveillance of a 20-square-mile area. It's even backhauled to a solar powered transmitter (with battery back up). Barton says a mounting bracket on the Wi-Fi router allows for co-location with the solar solution. Tropos works with SunWize Technologies and Alpha Technologies for solar hardware.

Barton shares Reynolds' observation that customers are choosing solar for logistical reasons rather than green ones.

"If there isn't readily-available power, or if it's difficult to get access rights," she says, "solar is a very attractive option."

That proved to be the case for the Chicago Transit Authority, Barton says, when they worked with Tropos to deploy a network that would allow inspectors with wireless handhelds to keep track of tasks in their maintenance yards.

"They wanted to get a network up quickly. The expense and time involved in running cable was not desirable." Now, about a dozen yards around the city have mesh networks that connect to a gateway for backhaul. It's all solar-powered.

Barton says Tropos has been working with solar solutions for about three years and is seeing increasing interest from municipal deployments that want to expand and from more niche clients like a marina that wants boats in port to be able to access the Wi-Fi network. For users, solar powered APs are indistinguishable from any other.

"It's completely seamless to anyone using the network."

Solar, sensing, and Wi-Fi

In a different context, the relationship between solar power and Wi-Fi can involve vast solar arrays being used to power entire buildings. To ensure such a solar deployment functions optimally, constant monitoring of myriad factors is necessary. Sensicast offers wireless sensors that can be used to monitor large solar systems. Gary Ambrosino, Sensicast's CEO, says it's important for the sensors to be self-powered.

"That's something that's often overlooked," he says. If the array goes down and the sensors rely on it, then the sensors will go down, too. It will be more difficult to diagnose what happened. While currently sensors rely on battery power, "we're going to announce a solar-powered sensor in the first quarter of next year," Ambrosino says. Sensicast is working with Konarka on a non-silicone-based solar solution.

"We're exploiting thin-film solar technology," he says, which he expects to be reasonably priced. Initially, choosing a solar sensing system may ring in at five percent more than a battery-powered one, but when the cost of disposable batteries and the expense of sending someone out to change them are considered, he estimates a customer could, over ten years, save around 30 percent. "The economics are very, very good."

The solar-powered sensors will also be applicable in a wide range of environments where something other than a solar array is being monitored. Though Sensicast contributed to the first certified net-zero electric commercial building in the country, Ambrosino, too, says it's economic and not environmental reasons that generally drive clients toward solar power.

The farmer in the dell

In northern California, Grape Networks already has solar-powered sensors on the job keeping track of soil moisture, humidity, and temperature in vineyards. Grape Networks president and CEO Peter Tsepeleff says the original Wi-Fi network monitoring system only tracked information on temperature and humidity and, therefore, used little power. But adding soil moisture tipped the power demand beyond two double-A batteries.

"We had to go with solar," he says, or batteries would have needed to be changed impractically often.

Now, the solar-powered nodes have a small panel co-located with the modules. The sun charges four rechargeable double-A batteries. The whole set-up fits into a piece of 2-inch by 6-inch PVC pipe that is rugged enough to hold up outdoors. Solar nodes and battery-powered ones send information through a Zigbee-compatible 2.4Ghz signal mesh network so vineyard managers know whether to worry about mildew and other factors that could threaten crop quality. Deploying a solar node adds about 30 percent to the cost of the module, Tsepeleff says, but echoing the others, he adds that "the cost of going out there and replacing batteries more than makes up for the cost of the solar panel."

Tsepeleff says the business started with grapes because wine is such an important cash crop in California—and now vineyards in Europe have expressed interest. But the technology could be applied in a range of places. He says stone fruit (peach, apricot, etc.) orchards are a secondary market but he's entertained interest from the medical and defense industries that also have a need to monitor information in areas where power isn't available. 

It takes a village

Bruce Baikie is a computer-industry veteran whose day job involves greening-up Internet data centers. So he's spent some time exploring ways to make technology more efficient or sustainable. He also travels around the world and he says he began to wonder why solar power wasn't being used more in developing areas. The answer he discovered? Cost.

"As I looked, I couldn't find anything [affordable], so I pulled together a small team in Silicon Valley," he says, to engineer a better way.

"We all, on our own, got together to solve this problem," he says. The result is Green WiFi [sic], a start-up that has received some financial support from One Laptop Per Child.

What he and his crew came up with they call an "intelligent charge controller."

"We've been able to shrink the solar panel down and shrink the battery down so our cost per AP location is about $500," he says, or about one-third the cost of systems they'd seen. They make the smaller hardware sufficient by managing power consumption more aggressively.

"The router of choice as you do these low-cost networks," Baikie says, is the Linksys WRT54-GL. The charger controller has an Ethernet port that allows it to connect to the router. The charge controller monitors how much power the battery has and how much the router needs. There are four stages of power management that the devices can employ to reduce consumption, for example overnight.

Despite misspelling the trademarked term “Wi-Fi,” Green WiFi's focus is bringing power to schools in developing countries. The first 1000 intelligent charge controllers will be manufactured in the coming months and rolled out to five sites in the first quarter of 2008. One Laptop Per Child made a financial contribution to help Green WiFi move into production because it is putting solar-powered, Wi-Fi enabled laptops in the hands of children in remote communities. One Laptop Per Child saw the value of getting low-cost solar solutions into villages at the same time.

Baikie says that although his group has applied for a patent, they have no interest in challenging companies bringing solar power to Western markets.

"We never see ourselves competing against them at all."

Solar power is neither new nor newly in vogue. But it does seem to be steadily increasing in popularity, in part because people want to take technology farther and farther afield and in part because growing concern about unbridled power consumption prompts at least a few people to investigate other options. Because the nature of Wi-Fi gets people and equipment outside of their proverbial—wired--boxes the prospects for a bigger role for the sun seem, well, bright.

Amy Mayer is a freelance writer and independent radio producer based in Greenfield, Massachusetts. Read and listen to her work at her website.



Comment and Contribute
(Maximum characters: 1200). You have
characters left.