A heat transfer liquid concentrate comprises, in addition to at least one glycol, a) from 0.05 to 10, preferably from 0.1 to 5, % by weight of one or more aliphatic amines of the formula (I),  where R1 to R3 may be identical or different and are hydrogen, optionally branched C1-C9-alkyl or C1-C9-hydroxyalkyl, b) from 0.005 to 3, preferably from 0.01 to 1, % by weight of one or more silicates which may have been stabilized, c) from 0 to 3% by weight of one or more corrosion inhibitors selected from the group consisting of the hydrocarbon-triazoles and of the hydrocarbon-thiazoles, d) from 0 to 5% by weight of one or more alkali metal, ammonium or substituted ammonium molybdates and e) from 0 to 1% by weight of one or more polymeric hard water stabilizers. The concentrates, if required after prior dilution with water, are particularly suitable for use in solar plants in which a heat transfer liquid is in direct contact with the glass of the solar plant.