I have been looking at / researching what I can about batteries, solar-systems, wind-generators, wiring, etc for quite a few years now. I have been using a calculator to try to figure out what works in theory vs. what works in reality. This morning I found a quote that explains very well what I have learned over the years: For a solar-panel to "push" power into a battery, it must be able to do so faster than what the draw out of the battery is. My 80-watt solar panel on my camper pushes (calculated) 5-amp of power into the batteries at high-noon. For me to replace my 80-watt panel with a 120-watt panel, I would only gain approx. 3-amp of power (about 8-amp calculated). To put on a pair of 120-watt panels would give me about 16-amp (calculated) worth of power into the batteries. Now, if I run all the lights / pump / furnace in the camper at the same time, the power-draw exceeds the maximum amount of power that the panel can provide, so, the power must come from the batteries, draining the power from them (think of the battery as a water-reservoir). If the solar-panel doesn't have enough time to refill the battery before the end of day, the amount of available power leaving me with less than a full "reservoir" of available power. For a short night in the summer where the power-draw is low, I should have more than enough power in the batteries with my current setup. For a long night in the winter (and a very short charging day-time) the power-draw could bring the batteries down to "dead" state where there isn't enough available voltage to run the camper. To compensate for that, I could add even more batteries to the mix for more "reservoir" available but I would still need to add more solar-panels to make sure that there is sufficient "flow" into the batteries. It is a never ending cycle of adding more till you reach a point of "more than enough" - and at that point you can stop spending money on wiring, panels and batteries and start living again. How do you decide when it is enough? Trial - trial - trial. Live it and you will figure out fairly quickly what is enough. But, sometimes that answer isn't good enough. Sometimes hard-numbers are needed and an electrical-engineer might need to be hired to really work your system over to locate areas of phantom power draws. If you cannot afford to hire one, see about talking to some teachers / students at the local college to see if they could help you out with the math as part of a "practicle" portion of the class. Closing-thoughts We have members here who are living off of solar-panels and batteries and they have shared their experience with all of us. If you are seriously considering making your own power, search the forum and answers will slowly appear. Good LUCK!!