A wireless repeater can be used to reach out beyond the limits of your wired access point. By pulling energy directly from the Sun with a solar panel, the system can be located out as far as the eye can see.

Revolutionary advancements in harnessing the Sun’s power to createenergy have flourished over the last decade.  Solar power is becoming an accepted and, in some cases, required component in structural designs of the 21st century.

While once only viewed as a novelty, solar power is quickly becoming an integral part of powering human requirements. A combination of improved efficiency coupled with the proliferation of the technology has reduced cost and opened entire new markets for this stable energy source.

It was only a matter of time before solar power was harnessed to drive remote networking components. That time has come and as you create the system described in this chapter (see Figure 9-1), you will be a part of the energy revolution and a friend to our fragile environment.

Implementing solar can be expensive. Yet, with some creative sourcing and some do-it-yourself construction, a solar repeater can be put together for less than you may think.

The items used in this chapter’s project are:

While solar power lends itself to limitless possibilities, this chapter will focus on integrating a wireless infrastructure. Once we’ve opened your eyes to the potential, we encourage you to harness the Sun’s power to provide a reliable and free source of power for your networking and computing needs.

Several new technologies are emerging, including fuel cells and microturbines that can generate electric power in a distributed fashion, that is, from locations close to the end-user. However, solar electric power offers many unique benefits apart from other distributed generation systems.

By crafting a successful solar application, you can reap the benefits that come with using a renewable energy source. As a direct result of improving technology and declining PV prices, practical applications for solar cells have steadily expanded from space missions to remote power and personal electronic devices. Since the mid-1990s, PV has become a practical source of solar electric generation in the $800 billion electric power industry.

Using solar power in your application creates a highly available wireless network without the electrical delivery costs. A system like the one you will build in this chapter can run for years with little more maintenance than the occasional “window cleaning” wipedown of the solar panel.

Before getting in to powering a solar system, you will need to determine where this repeating network node will be located. Much of this information is covered in Chapters 8 and 13, so here we will briefly cover how to determine a repeater site.

The concept of a wireless repeater is simple: use a wireless backhaul to beam a signal to an access point that is accessible by the client. Figure 9-3 shows how this would work. The access point sits where client devices (i.e., a laptop computer) could connect while the backhaul links the signal down to the wired Internet.

When configuring multiple radios in a single location, as used in the repeater enclosure, it is a good idea to select channels as far apart as possible, for example, channels 1 and 11 in the United States. If both radios were on the same channel you would get far too much interference, even though the antennas are pointed in different directions. This separation helps prevent signal overlapping because the radios are physically so close together.

The system will require two antennas on the repeater structure, one for the bridged backhaul, or downlink, and one to link to wireless clients. Depending on distance and interference issues, the bridge link would usually require a highly directional antenna. The access point would need an antenna suited to the coverage area.

This configuration requires three wireless devices (not including the clients).Two devices operate in bridge-mode, while one device acts as an access point. Of course, this is just one configuration of many. It’s conceivable that a wireless signal could be repeated over and over. Although, in practice, a large number of repeaters cause processing time delays that could create synchronization problems with traditional Internet protocols.

A wireless bridge is where two wireless devices are configured to allow connections only to each other. This is usually done by entering the MAC address of each access point into the other access point. See Figure 9-4 for an example. Access points in bridge mode will only accept traffic from the other end of the bridge.

Before getting into the solar installation, configure the wireless equipment in a lab setting. Youwill need to configure the bridges individually, and the access point should also be configured at this point. The wireless radios used in this chapter are basic off-the-shelf D-Link access points. These are not necessarily what you would want to run in this type of situation. Considering the money, time, and effort of integrating a solar system, extra cost on the wireless radio components can be justified. These radios can vary widely. Any wireless hardware can be used for the repeater section.  Refer to Chapters 8 and 10 for examples of hardware used for providing wireless Internet access.

The D-Link product is one of the few on the market with a built-in repeater mode. This repeater mode can function well in some environments. However, a single-radio repeater has less than 50 percent of its bandwidth available due to the simultaneous uplink and downlink. Also, the D-Link product does not work well with two antennas. Indeed, the recent version has only a single antenna connection. Optimally, two radios are needed for a 100 percent 802.11b bandwidth repeater.

Aside from the obvious free source of power, there are several other benefits to “solarizing” this leg of your network infrastructure. First and foremost, having an un-tethered wireless access point will enable great flexibility in how and where you get network services within the local region.

Hilltops are no longer out of the equation. By placing a node on a remote hilltop, line-of-sight and interference issues can be minimal. Additionally, a solar repeater mounted to a tower would have a commanding view over a low undulating landscape like farmlands, desert, or wilderness areas.

For this application, a 70-watt PV system will be sufficiently adequate. This system will be preconfigured to 12 V and produce 4.7 A.We recommend using a PV module with a glass surface that is impact-resistant and allows maximum light transmission.

low-light situations makes it particularly effective for specialized applications and in adverse or changeable environments.

Siemens solar division was acquired by Shell in early 2002. Shell (now Shell Solar) did not begin renaming the Siemens product line until mid-2003. You will still find products carrying the Siemens name. The Siemens branded products will eventually disappear from the marketplace as new products are developed.

These panels are engineered and manufactured for durability and ease-of-use. They are fully framed in anodized aluminum with pre-drilled, strategically positioned mounting holes to ensure secure and easy installations. A clamp-type mounting system can be used, so no drilling is required.

You will also want to use a weather-resistant junction box mounted to the solar module that will accommodate all wiring. It should include moisture-tight strain relief connectors, electrical conduit, and a bypass diode. Figure 9-6 shows the junction box on the SP75. Notice the jumpers and bypass diode. These components connect the panel junction in such a way as to provide 12 V. This particular solar module can also be configured for 6 V operation.

the physical location of your solar system and the availability of consistent sunlight exposure. The row in bold is an optimal choice for the project in this chapter. More power will charge batteries faster, keeping them topped up for cloudy days.Too little power may cause a power outage from drained batteries due to decreased charge capacity.

Solar power ratings assume operation at a Maximum Power Point (MPP), which is generally considered impossible to achieve in real-world deployments. Panel output will vary based on factors such as temperature, panel tilt angle, atmospheric conditions, and even cleanliness. Expect output power somewhere in the 80 to 90 percent efficiency range during peak hours of sunlight.

There are many high-quality products that are suitable for this application. Now that you have established your baseline requirements, we will recommend a couple of options that you can choose from. Of course we have our favorite based on optimal output, quality of construction, and quality service from the vendors, but based on your geographic location; you may need to find options that will meet both your cost requirements as well as time constraints.

PV panels are a somewhat specialized product and generally cannot be picked up at the local retailer. However, some electronics stores can special order solar panels designed for RV battery backup power. Largely due to the demands of retail distribution and availability, systems available at local stores can costs hundreds more than a solar module from a distributor or local solar specialist.

Since your wireless repeater system is relatively small and specialized, you may be able to find a local solar specialist with spare 75-watt panels lying around.We found this one from a residential system installer that was using panels like this for decorations around the office. Buying a solar panel from extra inventory can reduce the price considerably.

Popular models include:

Both of these products provided all the features and requirements outlined above. Either choice will result in a successful exercise and provide years of high-quality power to your system. This is not meant to preclude other quality products, but to use as a baseline for you to look at and compare with.