At 07:43 AM 4/27/2011, Justin Richards wrote: >I need to size a solar install to remotely power a 3G Modem and a >Intenna (Intenna is an enclosed wifi antenna with 90 mW UltraWAP). Some other information is needed. The most important thing is: Does the temperature drop below freezing=20 at any time? My preferred battery technology is still Lead-Acid. I use gell-cells=20 (AGM) for small projects and flooded batteries for larger installations. Most of my stuff has to work under Arctic conditions. That means=20 that the battery boxes are EXTREMELY well insulated and have tiny=20 heaters to keep the battery above 10C even when its -30C to -50C=20 outside. It takes surprisingly little power to keep the batteries=20 warm if the insulation is good enough. The freezing point of a fully-charged Lead-Acid battery is=20 significantly better than -50C (all that I am worried about) but=20 decreases as the battery is discharged. The freezing point drops to=20 about -40C when the battery has been depleted to about 80% (20%=20 charge used) and steadily gets worse: about -20C at 50% depletion,=20 somewhat below 0C when the battery is fully discharged. The battery is usually considered to be destroyed if it should ever freeze. So: you have to size the battery so that it never becomes discharged=20 to the point where it might freeze at your lowest expected temperature. This often results in the situation where you have a huge battery and=20 a relatively small solar array. Insulating the batteries reduces=20 this disparity. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .