I'm thinking of using a solar hot water system as a pre heater for an existing electric storage system. Sort of a half way step . Any problems with doing this?

 

Please expalin more. Why does your "electric storage system" need pre-heated water going to it??

 

In the case where you water is below ambient temperature an uninsulated tank can be used to allow the water to rise to ambient prior to entering the heater tank. The warmer water entering the heater will allow it to produce hot water a bit longer, recover faster and use less energy. There is some additional energy savings with this if you are using AC (cold water cools house). I have no idea how effective this is but it is something I would like try.

Using solar heated water in the "unheated" tank should be better but if the solar will take the water much above ambient temperature in the summer you may want to insulate the first tank.

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It doesn't "need" it. It is just a cost cutting exercise. In a couple of years you won't be able to buy electric storage water heaters (in Aus)
So I,m thinking of a solar to pre-heat the water resulting in reduced heating costs for the electric heater. The electric heater is only two years old so it still has plenty of life yet. When it dies simply take it out of the loop & run soley on solar.

 

Ah I get it now. It's an electric hot water storage system. I think it would work pretty well. Any heat supplied by the solar pre heater will not need to be provided by the electric element in the storage heater. But the total increased surface area of 2 tanks will lose more heat energy then just (say) a stand-alone solar-electric heater where all the hot water is stored in ONE tank with modern efficient insulation.

Many years ago I had a neighbour who had a flat black tar+concrete roof and about 200 feet of hosepipe on his hot roof feeding into his hot water system. And walls of his house made from local sandstone (from his own property) about 2 feet thick. Most people thought he was a bit crazy but I guess he was many years ahead of his time...