We felt right from the start that we wanted to live more off-grid than anything else. So far that has not been as much as we would like. Although while we travel from destination to destination the capability of being pretty self sufficient is comforting. 

 Energy management is very key to living this lifestyle. With a good understanding of your electrical needs is a primary goal. For instance knowing that the refrigerator draws 11 amps at 12 volts of electricity converts to roughly 132 watts. This can be figured out by either looking up a Watt/Volts/Amps conversion calculator or just using a Watts (P) to Amps (A) formula. 

DC watts to amps calculation formula

The current I in amps (A) is equal to the power P in watts (W), divided by the voltage in volts (V).  Formally it reads as this:

I=P/V

Simply amps are equal to watts divided by volts.

amps=watts/volts

or

A=W/V

Or

W=AxV

132=11×12

So now you ask what does this information have to do with solar? Right? Well, simply put, it has everything to with it. If you want to know what size batteries to get to last a certain length of time you will need this information. Back to the refrigerator using 132 watts or 11 amps. Those 11 amps will last about 9 hours on a 100 amp hour (AH) battery and less depending on the type of battery you use. Some batteries are best if only used to 50% DOD (Depth Of Discharge)  so right off the bat your down to 4.5 hours of total run time. NOTE: refrigerators do not run continuously so it can be deceiving. 

Another example would be an electric ceramic heater. The one I am using right now as I write this is a 250 watt heater at 120 volts. So back to the formula we will use the formula of: 

A=250/120

A=2.08

This shows the current FROM the inverter

Or

A=250/12

A=20.8

This shows the current TO the inverter

Conclusions

As you can see by the calculations above, understanding voltage, amperage and wattage is a very important factor in calculating one solar needs. This information not only helps size batteries but also wire size, inverter sizing, solar array sizing and total needs of your system. Also while figuring this out be sure to think of expansion if necessary. We use Renogy for our panels and controllers. Very helpful and informative. We will get into that on the next step in the journey of building a solar off-grid system.

Helpful information

If you cannot find what you need by reading labels on your appliances then there is a quick spreadsheet that will give you average information for most common appliances using 120 volts: 

Appliance	Load Range (Watts)	Average Load (Watts)	Amps
Air Conditioner (each)	1400-2000	1700	14.1
Battery Charger	Up to 2,000	1000	8.3
DC Convertor	300-1200	750	6.2
Refrigerator	600-1000	800	6.6
Microwave Oven	1000-1500	1250	10.4
Electric Frying Pan/Wok	1000-1500	1250	10.4
Electric Stove Element	530-1500	675	5.6
Electric Water Heater (6 gallon)	1000-1500	1250	10.4
Electric Iron	500-1200	850	7.1
Hair Dryer	500-1500	1000	8.3
Electric Coffee Pot	550-750	650	5.4
Television (CRT)	200-600	400	3.3
Radio	50-200	125	1.0
Electric Drill	250-750	500	4.2
Electric Broom	200-500	350	2.9
Electric Blanket	50-200	125	1.0
Portable Heater (Ceramic)	1500-750	1500	12.5
Toaster	1200	1200	10.0
Food Processor	720	720	6.0
Hand Vacuum	240	240	2.0
Crock Pot	230	230	1.9
Satellite Dish and Receiver	200	200	1.7
Heating Pad	60	60	0.5