Solar Power for Alvarion Equipment
by Dave Clelland

When you size solar power, you have to calculate a few things first.

1. Each BreezeACCESS 2.4 AU, BreezeNET Pro.11, and BreezeNET DS.11 access unit, or access point consumes about 11 watts of continuous power. Each BreezeACCESS LB will consume about 38 watts of continuous power. Add up the watts of continuous power consumption that your planned site will use. Remember to include any hub, switch or router that may be installed in the site as well.

2. Multiply watts consumed by 24. This will give you the watts/day of power required.

3. Find out the average number of hours of daylight during the winter in your location. You need to generate 24 hours worth of power in the number of hours of daylight you have during the shortest days of the year. Here in Edmonton, we have 7 hours of daylight in the winter, so a solar array that I would build must completely recharge my batteries in those 7 hours. Again, an example: a. Suppose I have 2 BA-II AU's, back hauled with a DS-11 system. This means my radios will consume 33 watts of power. In one day I will consume 792 watts. In my area, I have 7 hours of daylight in the winter, so my solar panels need to provide 792/7 = 113.1 watts per hour- round that up to 120 watts per daylight hour.

4. Go to your local solar panel distributor. They will have panels based on 20 watt, or 40 watt increments. Connect the right number of panels in parallel to make up the correct wattage - in our example we might use 3 40 watt panels at our site. a. A 40 watt Siemens panel is about 4ft by 2ft., and puts out about 12 volts. You need to make sure you have a regulator, and a low voltage disconnect on your panels and between your batteries and your load. b. For all Alvarion equipment, I recommend inverting the DC power to AC, then using standard 120vAC to power the radios, and any switch, or other network device you might use.

5. Size the batteries such that one 24 hour period without sun will only draw the batteries down about 5%. This does not mean you have 20 days worth of backup power, but you do not want the voltage to drop too much when a day with heavy clouds obscures the sun. a. In our example, we are using 33 watts of power. Batteries are sized in amp hours, so we need to convert our watts to amps (Power = volts X amps, or Power / volts = amps). 33/12=2.75 amps of current. In one hour, we would drain 2.75 amp hours of energy from the battery. We would use 66 amps per day. Using the 5% rule, I would install a battery set capable of delivering at least 1300 amps / day, or 55 amp hours of energy. Your local battery specialty shop, or a company that provides standby power will be able to help you purchase the correct batteries for your area.