I have just placed a piece of wood between to be on the safe side but if your fridge is situated near the edge of a radiator and it is 4cm away, it should be ok anyway. My fridge instructions said 2-3 cm away from a heat source.
I think everyone should have a greater understanding of alternative power generators which is something I think the government should do. Many people are sceptical as to whether they work compared with the cost outlay etc. I think with many sustainable energy devices right now, a combination must be used until more efficient systems have been developed but in the meantime, at least some energy is being saved don't you think.