Space Based Solar Power - Path Attenuation
Microwave power from space must contend with atmospheric attenuation. The Space Solar Power Satellite (SSPS) will not be directly overhead a temperate-latitude rectenna; a lower elevation above the horizon increases attenuation.
The attached graph is originally figure 101 from Blake (1972), and reproduced as Figure 2.19 on page 2.48 in the second edition of Radar Handbook by Merrill Skolnik, TK6575.R262 1990
The graph is for a radar beam leaving and re-entering the atmosphere. The decibel loss is halved for a one-way transit of the atmosphere, space to sea-level rectenna. The graph does not include rain; the effect is small for light rain, but heavy rain will significantly attenuate the power beam from an SSPS, especially if it is close to the horizon. In that case, the power beam should be deflected to another rectenna where rainfall is not a problem. That is what electrical grids are for.
Heavy rain is infrequent, even here in Oregon. If rainfall is heavy everywhere simultaneously, you do not need electrical power; you need a boat. If it keeps up everywhere for weeks, you need two of every kind and a Very Large Boat. 
