I spent almost 3 months at London a while back, only two things I was missing are food and solar. Lately I went back London after Olympic, the food is no longer is problem ( beat most cities at north American if not all). Is solar no longer is problem after Olympic?
Here are procedures to select batteries and solar panel;
1.Solar Radiation (Watts/m2)Solar Radiation, noaa.gov
go though history daily report, found out Solar Radiation data. use system total Watts with Solar Radiation data to define solar panel size and batteries.
2.Use low power RF-link instead of GPRS.