Mix Solar Into Existing Hot Water Baseboard System?

Q: I have a normal hot water baseboard system in my house. Brand new oil boiler, multiple zones, very typical. My hot water tank is directly heated from the boiler on demand, so not electric. I was wondering if it were feasible to install a SHW panel to add heat to the system during the day (sunny ones :)) My theory is that if the heating water was passing through the panels during the day, the boiler would stay at operating temperature longer without firing up. The trick would be making sure the water was not passing through the panels whenever they were not actually adding heat to the system. I don't want the panels to turn into nice outdoor radiators at night or on cloudy days.

A: Off the top of my head I would think you would need a heat exchanger between the boiler and the solar. I think the most boilers operate at a higher temps than most solar collectors at least most of the time. That way the water from the boiler is not cooling off in the solar collector. With a heat exchanger you could start and stop the solar pump at the right temps. I would guess that the solar would be a "preheater" to your heating system. If you use flat plate collectors, the water temperature is not as high as your boiler. Evacuated tubes can be hot enough, but cost much more. If you can get a tank up to maybe 130f and use the heat off that to preheat the water before the boiler, that might allow you to set down the boiler and save energy. It depends on the set point for the boiler tank, the temperature out of the tank and the temperature back into the tank after circulating through the baseboards. If the water goes out at 170f and comes back at 130f, there is not enough temperature difference to preheat the return fluid to the boiler with a 130F solar circuit. Thermomax makes evacuated tubes and has several system diagrams. Thanks for the input. It does seem that pre-heating the return fluid, even with Evacuated Tube panels, really would not do much at all. Oh well. I did discover that I could install an evacuated tube panel and tank to pre-heat the water to my DHW indirect fire tank. That would result in the boiler not cycling on as much to heat my water. I think I may give this a go. Anyone have any input on this idea?

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