Capturing more solar heat!

[bobberguy]

If I could increase the heat of some water about 10 or 20 degrees it would make the nights warmer inside the greenhouse! The greenhouse usually heats up to 80 even on a 20 degree day outside!The water in the barrels only gains maybe 5 degrees during the day. As the winter gets deeper the water temp in the barrel drops to a low as 35 to 40 and thus gives of little heat at night! If I could absorbe more heat the water would stay around 50 and i would have a non freezing greenhouse! Lat year when the temp went down below 20 for over a week here was some ice in the water barrels and the temp went to about 31 at night but most of the plants stayed alive!
My idea today is to put a aluminum turkey pan on top the water with about 4 inches o water in the pan. I would spra the top of the pan black so it wold heat up quick in the sun or heat of the green house during the day. My hope s that it will increase the tep of the water in the barrel. I have a aquarium temp tester and will see how much it changes the temp in the barrel compared with one of the other barrels! Any suggestions for adding heat with just the sun! I am also reserching phase change materials wich give off 100 times the energy when they change fro a liquic to a solid like wax!
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en.wikipedia.org/wiki/Phase_Change_Material#Organic_PCMs

[mastercatter]

float a cover of the bubble wrap on top of the water ( kind used to wrap packages in for mailing)..The larger the bubble the more heat is generated by the sun. This system was used to cover above ground pools in the winter to keep it from freezing.

[bobberguy]

That is funny you should say that because I just bought a 30 foot roll at walmart for $4 to try some things with! I will try what you said. Its a good insulator too! Thanks!