Hey Roger. I can't claim to be any more insightful that you, but I can offer my opinions that are based only on careful research. The cost for panels truly is very low. I am a little concerned about the quality of some of these panels. However, I've noticed that the cost of highly rated Kyocera panels have dropped substantially as well. I say buying today and storing them is a great idea not merely to take advantage of the low cost today, but to possibly avoid paying a high price later due to the likely increase of general price inflation during the next several years. Basically, it seems to me that a substantial increase in the price is more likely than a marginal decrease.
Calculating how many panels you will need is pretty straightforward. You need to know your average daily electricity consumption and the average solar insolation at your location. The single most important consideration here is getting your electricity consumption down to as low as practical.
See these solar maps to find the solar insolation in your region:
http://www.nrel.gov/gis/solar.html. Make sure to reference the maps for PV and not the ones for concentrating
solar power. You'll find that the average solar insolation is about 5 KWh per square meter per day in most regions in the U.S. Of
course, this is an average. Most PV panels are about 15% efficient, and you have to consider other losses that can be substantial depending on how the system is configured. A conservative estimate for a properly designed off grid system would take the losses at about 50% for a net efficiency of 7.5% from solar insolation to ac electricity (NOTE: 50% is a rather low estimate, but it provides a built in fudge factor - there are many more losses in an off grid system due to battery losses). Another consideration is to design the system based on the average solar insolation available during the winter months and position the panels for maximum solar gain during this time of year. For much of the U.S. this value is only about 3-4 KWh per square meter per day. I
think you can see already why reducing electricity consumption is so important for off grid solar.