I came across this question in a GCSE physics past paper:

enter image description here At first I couldn't answer the question so I checked the mark scheme and it suggested replacing the blocks with tanks of water to improve the energy output, but not the reason why. Is water better at absorbing IR than metal blocks, because that isn't mentioned anywhere in the physics book for my syllabus

  • $\begingroup$ Molten salts have been suggested and as far as I know there is a tower which uses sodium to store heat, but using mirrors, not an updraft type. Look up the specific heat capacity of candidate materials. $\endgroup$
    – user146020
    Mar 6, 2017 at 16:36

1 Answer 1



The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance.

Water has the capacity to hold more heat than any other material, so more thermal energy would be captured.

  • $\begingroup$ Using water instead of some cement or ceramic blocks might have an effect on the time-course of the energy being "released", but unless it is a better absorber there should be no difference in the amount of energy "captured". The blocks would presumably be more dense so a comparison on a volume basis might come up with a different judgement than looking at differences in heat capacity measured on a mass basis. $\endgroup$
    – DWin
    Sep 23, 2017 at 1:43

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