The present invention relates to heat-transfer concentrates for solar installations, containing a) from 92 to 99% by weight of at least one polyglycol of the formula R--O--(CH.sub.2--CH.sub.2--O).sub.n--H, in which n is an integer of from 3 to 500 and R is H, a C.sub.1- to C.sub.4-alkyl group or an aromatic radical having 6 to 12 carbon atoms, b) from 1 to 8% by weight of at least one corrosion inhibitor, with the proviso that its content of ethylene glycol and 1,2-propylene glycol is less than 0.2% by weight.