Solar water heating - heater tank questions

I need to replace a really old electric solar water heater in a domestic hot water system, and I'll buy a conventional electric heater because solar tanks cost much more but are of inferior quality.
Conventional heaters are usually modified for solar use by shortening the dip tube in half and using it as the inlet for the solar-heated water, and the drain opening replaces the normal dip tube for cold water But I found this diagram:
www.solardev.com/images/hotwater_r2_c1.gif
which shows an unmodified conventional tank being used for solar heating. Instead of feeding the solar-heated water into the middle of the tank, in this diagram it goes into the bottom. Will that work well?
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Honestly, if your solar collector system & pump are really old you might as well just cap the solar collector off and put a conventional water heater in. I just did that in my home when the solar water heater went out. I spoke to several solar water heating experts and they basically said my old solar system (late 70's early 80's mfg. date) was useless.
-Tom

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- as they wrote up an estimate for its replacement...

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I replaced the water heater myself and I told them up front all I needed was advice.
-T

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Bob Ward wrote:

Solar companies want about $750 for a 65 gal solar tank, and that's for one without a heat exchanger (which I don't need).
I can understand a system from the early 1980s being worn out, but if it's still in good condition, how it can be useless, provided it was installed right in the first place (my neighbor's had some plumbing connections wrong and a missing check valve)? I doubt that today's solar hot water systems are much better, at least those made for climates where freezing is rare (my freeze protection merely turns on the pump).
What I don't understand about the hookup in that diagram is that it shows water going both in and out through the same pipe at the bottom. It's not a misprint because I saw the same for an Australian system.
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TT wrote:

The solar collectors are as good as new (glass, copper, and aluminum), the pump still works fine (changed impeller, shaft, and seal), and in the warmer months the electric backup heat hardly runs at all. I have enough valves installed to let the solar part be bypassed easily, but that would mean spending at least $100 more in electricity. Why did those experts say that your old system was useless?
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