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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.

Table 9-2 Solar Panel Power Output
Rated Rated Rated Open Short Dimensions Panel
Power Voltage Current Circuit Circuit (H W D Weight
(Watts) (Vmp) (Imp) Voltage Current in inches) (lbs)
(VOC) (Isc)

20 W 12 V 1.29 A 22.9 V 1.54 A 29.5 13.0 1.3 13.0
40 W 12 V 2.41 A 22.2 V 2.59 A 50.9 13.0 1.4 22
50 W 12 V 3.15 A 19.8 V 3.35 A 48.0 13.0 1.3 17
70 W 12 V 4.25 A 21.4 V 4.70 A 47.3 20.8 2.2 23
100 W 16.7 V 6.00 A 21.0 V 6.70 A 56.93” 20.8 2.2 26
216 Part III ” Playing with Access Points

Solar power ratings assume operation at a Maximum Power Point (MPP), which is generally con-
sidered 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 out-
put power somewhere in the 80 to 90 percent efficiency range during peak hours of sunlight.

Finding PV sources
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 residen-
tial 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:

Shell Solar SP75
BP Solar BPSX-70U

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.

Solar power is obviously based on sunshine. Solar providers will know a lot about your local sun-
light coverage. That is, incoming solar radiation or “insolation” will vary from place to place on
the globe. Talk to a local solar specialist about hours of sunlight for your area. Maps and figures
are also available online. One such resource is provided by Solar4Power at The global map they™ve
posted online shows insolation values for every part of the globe.

Configuring Your Solar System
To understand the various configurations for solar power, we will cover a few different applica-
Chapter 9 ” Building a Solar-Powered Wireless Repeater

Solar Module

Over Current
Protection /Safety

Charge Regulator
DC Loads
Systems Control


AC Loads

FIGURE 9-7: Diagram of a directly connected solar system.

A directly connected system is shown in Figure 9-7.

No battery storage
Load operates in sync with sunlight
218 Part III ” Playing with Access Points

Peak operation during summer and middle of the day
Special inverter can add AC power

Typical applications:

Ventilation fans
Water pumping

A stand-alone system is shown in Figure 9-8.

Battery storage allows operation at night or during bad weather
Charge regulator prevents battery from over-charging and over-discharging
System controls can include circuit protection and remote monitoring
Inverter can add AC power

Typical applications:

Telecommunications telemetry
Outdoor lighting
RV or boat electric power source
Remote homes or storage facilities

There are also a number of hybrid systems.

Generator plus rectifier allows battery charging for full energy availability in any climate
or season
Generator can be multifuel source (natural gas, diesel, propane)
AC bus allows direct AC power to loads from generator through transfer switch, while
also recharging the battery through the rectifier
DC Bus has all power flowing through battery (DC), avoiding complex transfer switch-
ing and any anomalies in the power load

Typical applications:

Large telecommunications stations
RV with generator

The wireless repeater in this chapter will be designed using the stand-alone model.
Chapter 9 ” Building a Solar-Powered Wireless Repeater

Solar Module

Over Current
Protection/ Safety

Charge Regulator DC Loads
Systems Control


AC Loads


Battery Storage

FIGURE 9-8: Diagram of a stand-alone solar system.
220 Part III ” Playing with Access Points

FIGURE 9-9: The enclosure cabinet.

Installation Overview
The heart of the system is the solar panel, while the body is the enclosure cabinet. The enclo-
sure will house all of the electronics and keep them safe from the weather and other predators.
The enclosure will be directly connected to the solar panel and wireless antennas. Flexible con-
duit is recommended for the solar panel junction box interface, while Times Microwave LMR-
400 cabling is suitable for the antenna connections. If your enclosure has “knockouts” for
conduit, so much the better; otherwise, drill out the holes for your pigtails and electrical con-
Figure 9-9 shows the enclosure layout. Components are spaced evenly for ease of maintenance.
Electrical wiring exits the enclosure on the left. Antenna cabling exits on the right through
bulkhead pigtail connectors connected to LMR-400 cable.

Assembling Your System
Since this system is to be deployed in an outside remote location, it is recommended that you
first unpack all of your items indoors to ensure that you have all the required pieces and that
they are all in good condition prior to beginning.
Chapter 9 ” Building a Solar-Powered Wireless Repeater

In addition, you may want to build as much of the control cabinet as possible before deploy-
ment to test components and minimize the number of total items that will eventually be car-
ried to your destination.
It is critical to closely inspect your PV panel, because it may be the most fragile and valuable
part of this configuration. Specifically, look for any cracks or breaks in the glass or framing that
may have occurred during the shipping process. If you notice any irregularities, contact your
dealer for immediate replacement. Once you are satisfied that all the contents are present and
in reasonable condition, you are ready to begin.
You should start by assembling the contents of the control cabinet first. This is due to its com-
plexity, and it is the core of your system. Once all of the items are mounted and wired into the
cabinet, the balance of the installation will require little more than erecting the pole, mounting
the PV panel, control box, and antennas to the pole, and then testing. Figure 9-10 shows a dia-
gram of the cabinet layout for this installation.
For ease of installation, and to simplify future maintenance requirements, various lengths of
Velcro Strips are part of the list of materials. This Velcro will be used in place of drilling, nuts
and bolts. Moreover, this approach will eliminate the need to punch holes into your control
cabinet which could later result in problems from leakage.

For that professional look and feel, use an enclosure with built-in standoffs and a mounting
panel. The panel becomes a backboard for drilling and mounting equipment without piercing the
rear of the cabinet.

To Solar To Client

Panel Antenna


110 VAC
Charge To Base Station


Controller DC to AC

Access Point




+ ’ + ’
Maintenance-Free Maintenance-Free
Lead-Acid Battery Lead-Acid Battery
12 Volt / 35 Ah 12 Volt / 35 Ah

FIGURE 9-10: Diagram of the control cabinet enclosure layout.
222 Part III ” Playing with Access Points

The cabinet used in this chapter is an 18 inch 18 inch 6 inch enclosure (18 inches square
and 6 inches deep). We drilled the holes necessary for the pigtails with bulkhead connectors
and for the solar panel conduit. Angle iron was used to adapt the cabinet for U-bolt pole
Hundreds of cabinets are available from suppliers like Hammond and B-Line. Search the
Internet for these companies, or visit the wireless supply companies like Tessco, Talley, and

Step 1: Install the Battery Cell
Install the battery (or batteries in this case) into the cabinet, as shown in Figure 9-11. Apply
4-inch Velcro strips to the battery cell, one strip on each end, and apply corresponding Velcro
strips to the bottom of the control cabinet. Finally, insert the battery cell into the control cabi-
net and test alignment of battery with respect to the cabinet. Be sure that the battery is not
touching either side of the cabinet and the space is relatively equal from side-to-side.

Charge the batteries before installing them into the cabinet. A standard car charger set to trickle-
charge the battery should work fine for topping them off before “the great on-turning.”

FIGURE 9-11: Battery installation.
Chapter 9 ” Building a Solar-Powered Wireless Repeater

FIGURE 9-12: Charge controller installation.

Step 2: Install the Charge Controller
Refer to your internal cabinet diagram for component orientation and organization. You may
choose to design your cabinet differently, and that is fine, just ensure that you have a proper
cable management plan before you get too far into the project. This is extremely important in
future days and weeks when maintenance procedures may be required and taking parts in and
out could be hampered by inefficient arrangements. Figure 9-12 shows the charge controller in
place. Substantial Velcro adhesive holds the charge controller in place.
Wiring from the charge controller connects directly to the batteries as shown in Figure 9-13.
When connecting multiple batteries, connect only the negative ( ) terminals to each other, then
connect only the positive ( ) terminals to each other. Do not cross the streams! This is a parallel
connection where voltage remains the same (12 V) but the current capacity increases (70 Ah).

Only connect positive ( ) to positive ( ) and negative ( ) to negative ( ). Do not short-circuit
the battery. Just like a car battery, these batteries need to be treated with care and connected

+ -

+ - + - + - + -
Battery Battery Battery Battery

Battery Array

FIGURE 9-13: Diagram of charge controller connection
to the battery array.
224 Part III ” Playing with Access Points

FIGURE 9-14: The DC-to-AC inverter installed and connected to the battery array.

Step 3: Install the DC-to-AC inverter
The DC-to-AC inverter converts the DC battery power into AC power for the power strip
and wireless components. The battery directly connects to the DC inputs on the inverter.
Figure 9-14 shows the inverter installed and connected to the battery.
By choosing to use an inverter to provide universal AC power, you have the option of easily
changing out radio equipment. Also, while on-site at the repeater system, extra AC power
comes in handy.

When choosing a DC-to-AC inverter, a low-cost “modified sine wave” inverter works fine with
this type of equipment. However, parasitic power is a factor. Try to find an inverter with low
internal current consumption. Anything with less than 0.2 A (200 mA) is fine.

As you may have noticed, the charge controller and the inverter are both connected to the bat-
tery. Solar energy is used to charge the battery via the controller, while simultaneously, the
inverter pulls electricity out of the battery for the wireless radios.

Step 4: Install the Wireless Radios
The wireless equipment will be stacked with the access point on top of the bridge, so keep that

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