Kariky, Are the DS18B20's wired with the 3 wires as Voltage-Ground-Signal? Or are they in "Parasitic" mode?
I'd just like to know so I can help other people with this in future. I have quite a bit of DS18B20 How-To online here:http://arduino-info.wikispaces.com/Brick-Temperature-DS18B20
What cable are you using?? I would suggest using CAT5 network cable, which has 4 twisted pairs. I would use one pair for +5V and Ground, and the other 3 pairs for DS18B20 Signal and Ground. That would be for the long run to your solar collector, and then break out to the individual sensors with 3-wire cable, or 2 twisted pairs. Keeping the Signal and Ground in twisted pair as far as possible would be good.
These protected DS18B20's for $5 might be good in your environment: http://arduino-info.wikispaces.com/Brick-Temperature-DS18B20#TS
Let us know how it's working...
Regards, Terry King
...In The Woods In Vermontterry@yourduino.com
DISCLAIMER: Mentioned stuff from my own shop...