Not to rain on your parade, but be realistic:
1-Don't count on a 30w consumer solar panel to still power your devices in 3 years, and your batteries will need to be replaced several times over that stretch. 15w for 14 hours is an expensive battery and will deteriorate quickly from frequent deep cycling.
30w? I was thinking more like 130-140w for 4 X6500's (eight FPGU's). That's 10 or 20w more than the total load. So there's a little room for deterioration. I don't expect more than 1.5% deterioration per year. So 15% over a whole decade. Perhaps I will go as high as 150w. The batteries I have to think about some more. Even if it needs a another $500 or $1000 spent on Absorbed Glass Matt batteries, the whole thing is still going to pay for itself several times over, well within the life of the panel. It would pay for itself twice even without batteries and only running in daylight hours. The extra cost of battery backup so it can run 24/7 would be marginal to the initial setup costs. Even allowing for two or three battery replacements over the decade.
2-Unless it's extremely well-placed and on a heliostat, your panel will operate at 100% for a grand total of 0% of the time and will only approach 100% for a small part of the day.
So we need to aim at something more like 85% average over 10 hours. I think that's doable. Also a heliostat might very well be a wise investment. That or solar tracking. As long as the solar panel is reasonably oversize the need for 100% efficiency is averted.
3-Regardless of where you live, it is not sunny 100% of the time. Find out your longitude and latitude and google a solar calculator, enter your info and see what kind of realistic production you can expect.
I'm well aware of this. I've been looking into solar systems for quite a while now. I live in South Australia we have an excellent solar yield.
4-You still gotta run a computer.
That's a negligible overhead in terms of running costs. I'm still not convinced that an on site processor is necessary for a network connected unit. Even still, I cant imagine needing anything as powerful as the processor in a typical palmtop or even an embedded system. If the software can be run over the network, all the better. The point is you don't need a huge power hungry monster that runs on mains power.
Small scale solar is cost prohibitive.
And that's why everybody's doing it if they can afford the upfront cost? C'mon now. Haven't you heard? People are putting $5-15,000 dollar units on the family home, that pay for themselves in under 5 years, cut their electricity bill down to a small fraction and sometimes even generate a small profit. Even selling excess power back to the grid is profitable. If buying power from the grid to mine bitcoins (with power hungry GPU's) is profitable, then cutting out the middle man by turning solar into bitcoins without inverters/grid-power at a tenth of the wattage, must easily be profitable.