standards and guidelines for communication sites - Radio And ...

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES ALTERNATE POWER SOURCES
6.6 ALTERNATE POWER SOURCES
Certain sites without access to commercial AC power utilities can use solar and/or wind-generated
power. The solar panels and/or wind generator charges batteries that provide power to site equipment.
Propane or liquid natural gas (LNG) generators can be used, especially in colder climates, to back up
the solar/wind system.
Because solar/wind systems provide limited power, it is important when planning the power system to
calculate the predicted power usage for the site. Solar power is best suited for small sites with low
power requirements where the physical size and cost of the standalone power system does not become
impractical. The site's transmitter duty cycles shall be planned so as not to exceed the maximum
average current requirements.
Wind generators can be used to back up a solar panel system. If there are sunless days with wind then
battery charging can still take place. Such a system could take advantage of more sun in the summer and
more wind in the winter. Wind generators should be mounted higher than buildings or other obstructions
where wind flow is more efficient.
6.6.1 SYSTEM PLANNING
Development of a stand-alone power system should be contracted with a firm experienced in the design
of alternate power systems. To design a system capable of supplying the site's power needs, the
contracted firm needs the following information:
• Total typical ampere-hours (Ah) used by all site equipment over a 24-hour period. (1 ampere used
continuously for 1 hour is 1 Ah.)
• Voltage the power system must be capable of providing. (Communications sites of this type
typically use 12 volt or 24 volt battery systems.)
• The average number of consecutive sunless days expected at the location.
The daily AH rating is calculated as shown in the following example. Given the following
characteristics for a single-repeater site:
Single repeater requires 7A for Tx (ATx) and 1A for Rx (ARx)
Radio link requires 1.6A for Tx and 1A for Rx
Duty Cycle (Tx/Rx) of 20%
Using the following formula: [(ATx × %Tx) + (ARX × %Rx)] x 24 hrs = average
Ah required
For the example characteristics given, the repeater requirement is:
[(7 x 0.2) + (1 x 0.8)] x 24 =52.8 AH/day
Radio Link requirement is: [(1.6 × 0.2) + (1 × 0.8)] x 24 =26.9 Ah/day
Total requirement is: 79.7 Ah/day
68P81089E50-B 9/1/05 6-25