Lee’s – KM6UFF Presentations & Calculators

Page 1 is a sampling of appliance wattages and a guess as to how many hours it normally is used. Just add up the watthours of the appliances/devices that you want your battery/solar to power and go to page 2.

Page 2 is a list of watthours from .1kwh to 5kwh and the applicable battery size in amp hours. You have to decide what battery voltage you want to use; 12, 24 or 48 lithium. I don’t include a lead acid column but if that’s what you want then double to triple the recommended lithium amp hour rating. Twelve volt has an advantage in that many things run off 12v without the need for an inefficient inverter. Twenty four volt systems need half the size wire and charge controller for the same power. Most 12v charge controllers will also do 24v. Some will also do 48v which needs even smaller wiring. You also have to choose how many cloudy days (0-4) you want to plan for.

Page 3 will help you figure out your location’s worst case Sun-Hour rating. We want to size the off-grid solar system for the worst case (winter) so it will work any month. Sun-Hours isn’t the same as daylight hours. You will need to know this to properly size the solar array for your chosen battery.

Page 4 will tell you what wattage the solar array needs for the particular battery voltage & amp-hours and available sun at your location.

Page 5 is a simple matrix that tells you what kind of panels work with which voltage battery and with what type of solar charge controller. The older PWM charge controllers are fussy about being properly matching to the battery and panels. There are used 60 cell solar panels available that will not work with a PWM but will work for any battery using a MPPT charge controller. MPPT is also more efficient.

Page 6 Will take the solar array watthours from page 4 and guide you to a size, quantity and configuration of the solar panels needed to create that array. There are 6 large data squares. Two for 12v, 3 for 24v and 1 for 48v battery options. The 2 top squares tell you how to set up “12v” 36 cell solar panels. The middle 2 squares use “20v” 60 cell panels. The bottom 2 squares use “24v” 72 cell solar panels. Find the square that applies to the battery voltage and type panel you want to use and locate page 4’s wattage in the WATTS column in that square. The individual size panel wattage is in the 2nd column from the left. The series/parallel configuration is at the top of the column. The minimum wire gauge for the array is one square to the right of the array wattage.