Codan Radio Radio Repeater Systems Training Guide - Manual (Page 34)

TRAINING GUIDE | RADIO REPEATER SYSTEM
Chapter 3: Repeater System Equipment Page 26
d) Solar Power
You will fi nd some level of government or agricultural or environmental bureaucracy will be able to
supply you with solar insolation (the number of bright sunshine hours (BSH) per year) and average
annual temperature at some data point near your proposed site. If this data point is, for example, in
a fog shrouded valley, or your proposed site is on a mountain-top which is often obscured by cloud,
adjustments (of perhaps +/- 10%) will have to be made to the available fi gures.
Enter site name, data point, BSH and any adjustments on the Solar Sizing Worksheet (a completed
worksheet is shown on the next page). Calculate the peak hours of sunshine per day as shown. We
have used 1927 average yearly bright sunshine hours at a data point called “Lytton”, about 56 km (35
miles) from our proposed BRIDGE ARS. Our example shows an adjustment of +5% for our site, as
the data point, being in a deep valley, is likely to be in shadow earlier in the day than the repeater site.
The next fi gure that you will require for your calculations will be the average annual temperature at the
data point, use our example, 9 °C (48 °F). Our site is at 1372 meters (4500 ft.) and the data point is
at 281 meters (922 ft.), a difference of 1091 meters (3578 ft.). The normal adiabatic lapse rate (change
in temperature with elevation) is -0.5 °C per 100 meters. Therefore, our adjusted temperature will be 9
- (1091/100) x 0.5 = 3.5 °C. Percent duty cycle, as calculated in part b) above, is entered as 0.08 based
on our 9 operating hours per day. Calculation of current (I) used is taken directly from the repeater
manufacturer’s technical specifi cations. Our fi gures for standby are 24 (hours) x .036 A for VHF and
.048 A times 24 for UHF, totaling 2.0 Ah. Total transmitter current for our site is 1.2 A x 9 (hours) x 0.08
(duty cycle) for VHF and 1.0 A x 9 x 0.08 for UHF, totaling 1.6 Ah. The total (receiver and transmitter)
daily requirement is entered as 3.6 Ah. Enter the repeater operating voltage, the battery type, volts per
cell and number of cells required (in series), and calculate the days of storage. One month is adequate
for this fi gure, as you are assuming that there will be no sunlight for recharging in this period. However,
you may want to double the battery size to accomodate for variables. From the battery manufacturer’s
technical specifi cations, fi nd the fl oat voltage fi gure and enter it on the sheet.
Some solar panels already have an internal reverse current diode installed. If not, one will be necessary
and a fi gure of 0.65 volts should be entered as a loss. If heavy duty Ni-Cad cells are used, a regulator
is not required, although a simple zener diode bypass regulator may give peace of mind if you are
worried about overheating. If another type of battery is used, you may have to include a regulator, with
its attendant voltage loss, in the power supply design. When the maximum charging current of the
module is less than approximately 2% of the battery capacity (e.g. panel producing 1.4 A and a battery
of 100 Ah capacity or more) a regulator is not required. Enter the panel manufacturer’s name and panel
model number (just for reference later), the nominal panel voltage (from the manufacturer’s data), and
calculate the panel current as shown. Calculate the module current output per day by multiplying the
average peak hours of sunshine per day by the panel current (using the manufacturer’s power graph).
The total daily power requirement divided by the module current will then give you the number of panels
required. Our example shows 0.5 or one panel required. We could re-calculate for a lower output panel
if desired or re-calculate to see how high a duty cycle one panel will permit (in our example, this works
out to 33%).
With advances in design, the mounting angle is not as critical as it was previously. A useful rule of thumb
is to mount your panel at an angle to earth equivalent to your latitude plus fi ve degrees. Remember
to point the panel(s) true south, towards the sun at noon (this is true for most sites in Canada and
the United States but is dependant on your geographical location). Different types of panels require
different mounting techniques. Follow the manufacturer’s recommendations. One panel available that
has proven useful is built on a fl exible thin sheet, thus mounting on a curved surface (see the following
section on accommodations) is possible.