Dear Dougal,
I also have the same idea. That's why I bought the ASUS WL-500g Premium (V1) to also be able to have enough connectivity.
Without anything (or maybe with a connected HDD. I forgot which measurement I made) I think I had a consumption of 8W.
http://www.asus.com/Networks/Wireless_R … ifications
And to get more performance you can use (what I though using) this super simple solar tracker (without electronic parts) :
http://www.josepino.com/?simple_sun_tracker
Please take me informed about the solar power (and a plan of what you deployed to manage power supply of your panel) to use with your installation.
Sincerely thanks and have a nice day,
Miguipda ;-)