"Before researching this topic, I didn't know a volt from an amp"
I have only used solar power on one occasion; to keep electrical components running during a 28-day unsupported expedition, so although my knowledge is restricted to this one instance I will try to share the benefit of my experience as it could apply to wider usage.
The solution we required was to be able to run and recharge a large number of appliances for a possible 35-day period in temperatures as low as - 40 degrees Celsius. Before researching this topic I didn't know a volt from an amp, in the weeks that followed I was to discover that there was more to this than simply plug-and-go.
To begin with, it is necessary to state that in sub-zero temperatures it is possible for a battery to lose up to 90% of its charge, however the effect can be countered by re-warming the battery, in which case the usable charge would return to similar levels once thawed out. The obvious solution to this would be to keep batteries warm inside a sleeping bag at night or inside a jacket during the day.
I was lucky in finding an expert who was able to ask the right questions, namely; what is the total power consumption you anticipate daily, what are the volt/amp/wattage's of all the components that you need to run and the hours that you will run them for? This allowed me to take all the requirements and put them in a table to get the final figure for which I would have to provide.
Building the solar battery
The components we were running included; satellite phone, tough-book, camcorder, cameras, GPS and the obligatory I-pods. The end figure for daily power consumption allowed my tech-geek to calculate the total surface area of panels, operating at such and such a percentage efficiency for so many hours of sunlight at that latitude per day, minus the expected percent of cloud cover for that time of year, with a generous margin thrown in to compensate for the degradation in performance which would be caused by the cold.
The next consideration was the battery. For this I considered a car or motorcycle battery with a transformer that could vary the output voltage to charge each of the items. The variable voltage is necessary because some items like I pods required a current of 5 V whereas others like a tough-book might require 16 V. Putting 16 V into an I-pod could fry it whereas putting 5 V into a tough-book would be useless.The next problem was from the cold; while the solar panels didn't lose too much efficiency the battery would charge at a vastly reduced speed and never reach full capacity unless kept warm, insulation was out of the question as the minute warmth generated by the battery during charging would be obliterated by the - 40* C temperatures. So, the batteries had to be kept under a jacket while on the move.
For this I turned to a military equipment sponsor and designed with them a battery bra this was sort of like an under-arm pistol holster, but with two zipped bags that hung under each arm-pit. The material used had to be waterproof to prevent the electrical equipment from attracting condensation; if it was taken from out of the cold and placed inside a warm jacket or sleeping bag (think of what happens to a cold beer when you take it out of a fridge) the damp condensation would cause damage to any electrical gear over time. With this combination of gadgets the solar panels could be strapped to the outside of our sledges while we moved and the output cable would go up inside the jacket to plug into the reservoir battery while it was kept snug and warm inside the battery-bra (I used to envy these warm batteries).
Science and Design
Every system was duplicated to allow for failures. In the end we had more battery surplus than we could use. However out of three I-pods, not one survived the cold. Apart from these, all the electrical systems were kept running, but this required a painstaking amount of care and attention, it has to be remembered that these components are not designed for expeditions and can easily be broken if not treated carefully. Although my safety margins were perhaps too generous I am glad that I was too cautious rather than not enough. We could have probably gotten away with one solar panel and battery combination and one Freeloader Pro, but Murphy's law states that if you don't bring a spare you will need it.
The lessons I learned from this were to exhaustively research the requirements and then to exhaustively research the options. In the remote places we go, survival is only possible due to a combination of; skills, knowledge and equipment, like a fire triangle; take away one of those and the whole will collapse. So, you have got to get the equipment right and to do that is worth the time it takes, also its worth spending time to shop around and find the best price. Secondly its worth finding out who the experts are in what you are trying to do and getting several opinions, people are usually happy to talk about their subjects and flattered to be asked so make use of this free resource.
Parting thoughts
I hope this was useful and would welcome any feedback from others who have had different experiences that might contradict my own. Please don't take this as gospel and go making decisions about your safety margins based on what I have written here, the whole point is to be able to make your own informed judgements based on research into your specific requirements which will probably be very different from what mine were.
Good luck and stay safe