new device for solar thermal panels

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Hello all, it seems that there is a real danger to operating solar thermal panels in northern climates when they are sized to provide a decent amount of hot water in the winter and then operated in the summer. When summer comes around there is too much hot water available and there is a risk of overheating the panels and damaging them.

Therefore the drainback system has been developed. However it may be wise to stick with a close loop glycol system in the north.

I was thinking there may be a need for an automatic tarp that can cover a panel as required based on outlet temperature. Does this sound like an interesting development that could be of use?

Cheers,

Jacques
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: new device for solar thermal panels

    One option is to mount the panel more vertical--It will catch the winter sun and much less of the summer sun. Having an overhang to provide shade can help too...

    Anything mechanical (automatic tarp) will require maintenance--which I tend to avoid if at all possible.

    If you have a water based system (open loop) vs glycol type (closed loop), you could just place a T&P Valve (temperature & Pressure valve such as for a hot water heater) at the top of your panel and simply vent the hot water out if the panels start to overheat...

    With a glycol system, overheating antifreeze can cause problems--and you cannot just "vent" that expensive stuff to the ground if the thing over heats.

    But--I wonder how often over heating in the summer is with a solar hot water system... I know that for some collectors (the vacuum thermos bottle type) they can generate very high heat and need the protection or the antifreeze (or other components) can fail.

    Do "simple" insulated flat plat collectors need similar protection (T&P valve--I know that many systems include a pressure relieve valve--is this enough or are they really T&P valves instead?)?

    The Solarroofs.com kits include a Pressure (150 lb) only valve--and they say their panels (at least with fresh water) do not have any ill effects from stagnation up to 120F ambient temperatures.

    If you use anti-freeze (cold climate), your glycol may begin to break down before the panel "has a problem".

    And, in any case, it looks like they want 50 PSI of pressurization to support a maximum of 250F stagnation temperature.

    Looking around the Dow Chemical site, there is DowFrost and DowFrost HD which are rated to a maximum temperature of 250F/325F respectively.... So, depending on your maximum temperatures you expect, and which type of anti-freeze you choose--It looks like you may not need to worry about stagnation temperature with some of the simpiler flat plate collectors (Solar Roofs is on the low end of the cost scale--but still a good product).


    I guess, you need to check with your equipment supplier and see what their recommendations are for your area/installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: new device for solar thermal panels

    Bill, thanks for an interesting reply.

    Jacques
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