I was investigating today into something similar. The concusion of my research: - Model A uses a way less (about 33%) electricity, because it does not have a

I was investigating today into something similar. The concusion of my research: - Model A uses a way less (about 33%) electricity, because it does not have a lan controller. So it will be useless as a server, but for my application this is the choice. - The RPi does work with 3.3 Volts, but then the USB does not work. Yet again, for me good enough. - Undervolting (the core and ram) and downclocking do not make much sense. It does save nearly nothing and make the board absurd slow. - The biggest powersink seems to be the GPU, but AFAIK it can't sleep. - The most inefficient component are the voltage regulators. Replacing them with dc-dc converters was discussed, i have no experimental results. The easies way is to convert the input to 3.3V without replaying and board components. - Displays use very much power. But they can be turned of if not needed. It seems the solar panel can be significantly smaller, but not for a webserver.