In principle, you could get an indefinite rectenna array over the walls of the building. But it won't be very practical since the ambient RF power density is low. The recycled energy would a limited amount of "expensive" energy compare with the large scale and "cheap" solar energy. It is more realistic to coat the building with low cost and thin film solar panels. Regards

How about nights and cloudy days? So RF energy always exits. I mean RF energy harvesting co-power to others as solar, wind, etc.

If your harvesters worked well they would stop all wireless communication between the inside and outside of the building. If it looked like it would be widely adopted it would probably be outlawed because it would reduce the range of broadcast communication, rather like the way a row of trees in the way makes motorways quieter.

If the building has been coated by solar panels, the giant energy would be sufficient to be stored for nights and other scenarios I guess. Co-existing power could be an option, to be honest, 90% of energy will be from solar.

The limit for public exposure to non-ionising radiation is 10 W/m2

That means there might be 1 kw hitting a house from all directions, if everyone was exposed to the top limit, everywhere. Exposure is usually, and hopefully, a lot less than this. The limit is unlikely to be raised because it is set at the level where the radiation doesn't quite result in a measurable increase in body temperature. Converting 10 W/m2 , spread over a 5 GHz bandwidth and from random directions, to something useful is another problem.

The idea may sound nice , but as already said before its very likely no to be cost effective..solar cell (PV ) are much more efficient possibly with some battery to cover the night.

And then there is possible legal aspect: more than 80 years ago certain people having a little garden close to the medium wave transmitter in Berlin (germany)did use a few meter long wire (loop) antennas and they could pick up several Watt from the power of the transmitting antenna. This was enough to run day and night a small light bulb. But obviously the power taken out there does not show up in the far field and does not arrive at the intended final destination. Thus finally this game was forbidden as "theft of electromagnetic energy" [to my knowledge this law is still valid at least in germany today]..maybe similar rules could apply for large scale rectennae in cities..

trying to harvest RF energy is a fools game at best. Power density is pathetically low.

There may be applications where such a concept even with very low amount of energy harvested can make sense..e.g. to keep some low level electronic running "forever" with a few nanoWatt but usually there are strong arguments against this like the use of solar cells even when there is no daylight available (nobody is living is a room without ANY light). And good chemical batteries can last for more than 10 years in a standby mode (now very popular for electronic fire alarms required in every house in France).Thus assuming a lifetime of some electronic gadget of say less than 10 or 20 years and cost issues..the market volume for such energy harvesting would be very modest.