Electronic Problem

A twenty watt solar panel needs to be placed on the top of a walk up tower 30 ft tall. The battery is on the ground along with the Campbell data loggers. Where should the solar panel regulator go and what size wire from the solar panel to the ground should be used.

The regulator is a sunsaver. What size regulator do you need to buy.

http://www.solarelectricsupply.com/Charge_Controllers/Morningstar/Sunsaver/index.html

Solution

Watts= volts * amps

20 watts = 12v * x

X=1.66 amps so a 10 amp regulator is more than sufficient.  Could use a 6 amp regulator.

 SunSaver-10 volts12 Amps 10

The current from the Solar panel will be at a maximum 1.66 amps if the battery is completely dead. The output from the solar panel ranges from 12 to 16.8 volts depending on the solar radiation. The voltage drop can not be more than a maximum of 4.8 volts and it would be better to keep the voltage drop to 1-volts.

Voltage drop for different size wire is a function of the resistance of the wire.

V= IR

1.0= 1.66 R

R= .60 ohms total resistance from the length of the wire from the solar panel to the regulator and back to the solar panel = 60 ft.

Resistance per 1000 ft  18 awg = 6.5 ohms or  6.5/1000*60= 0.39 ohms. Consequently 18 awg or larger can be use to connect the solar panel to the regulator.

http://www.stealth316.com/2-wire-resistance.htm

Solar panels can be bought with the regulator at the solar panel or using an external regulator as in this example.

If the regulator is at the solar panel then the voltage drop from the output of the regulator to the battery can only be 0.1 volts because you want the battery to be fully charged

V=I*R

0.1= 1.66 R

R= 0.06 ohms

Resistance  for 10 awg (american wire gage) = 1.0 ohms /1000 ft = 0.06 ohms per 60 ft.

Number 10 wire is hard to work with. If the voltage drop could be 0.2 volts what size wire could be used.

What should you do, but a solar panel with a regulator build it or external and where should you place the regulator.