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Glycol solar fluid questions

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  • Glycol solar fluid questions

    Hello Experts,

    My solar panel system uses Glycol as the solar fluid to collect heat from sun shine. Unfortunately it was drained out by somebody. I want to refill it. I have some questions for you guys/experts. The solar system is in Boston, MA.

    1. Are there many different Glycols in the market?
    2. Which one I should use?
    3. Do I need to mix the Glycol with some water? If yes, what's the percentage?

    More details about my solar system, please refer to this post:



  • #2
    Re: Glycol solar fluid questions

    never really dealt with solar before,

    but there is Ethylene glycol and the propylene glycol,

    both are used as and antifreeze solution, ethylene is the normal for automotive uses, even tho the propylene glycol is becoming more popular as it damage to water supplies is less of a hazard,

    the Ethylene glycol will destroy your kidneys if ingested, you have heard of the warning of animals or pets drinking antifreeze out of a car and how it can kill them.

    the propylene glycol is even use in some food additives, it is what most RV antifreeze is, even tho it is used in many applications that ingestion takes place, there is the question of purity and additives come in to play so In the event of accidental ingestion, emergency medical services should be contacted.

    Food Additives - Names Starting with P

    Polyethylene Glycols - Antisticking Agent, Binder, Carrier, Carrier Solvent, Coating Agent, Disintegrating Agent, Dispersing Agent, Filler, Film Former, Flavoring Adjunct or Adjuvant, Formulation Aid, Glaze, Lubricant, Plasticizer
    uslay you can buy anti freeze straight or premixed, if you mix it follow the directions on the container or literature that comes with, it. if premixed it has treated and purified water in the mix, (I have bought auto motive premixed by the 55 gallon drum, actually diesel formulation for the tractors)
    and you can buy straight by the drum as well.

    some will depend on your area and you how cold it gets in your area,
    one thing I learned when I switch over to propylene glycols antifreeze in my tractors, is a normal hydrometer will not test properly for proper mixture, (there may be ones now, but I use a Antifreeze Optical Refractometer to test for the strength of the coolant/antifreeze). (note: the url is for information purpose only not a recommendation) I also say where hydrometers are not available as well.

    my guess is that there are anti freezes that are designed for heating systems

    as automotive and truck antifreeze has additives that are designed to keep a cars cooling system happy, not necessary a home heating system,

    I would suggest a antifreeze that is "safe" "non toxic" if for some reason it is some how mixed with the hot water or potable water system, (and not use a Ethylene glycol such as a normal automotive antifreeze)
    U.S. Department of Energy - Energy Efficiency and Renewable Energy
    A Consumer's Guide to Energy Efficiency and Renewable Energy
    Solar Water Heating System Freeze Protection
    Solar water heating systems, which use liquids as heat-transfer fluids, need protection from freezing in climates where temperatures fall below 42ºF (6ºC).

    Don't rely on a collector's and the piping's (collector loop's) insulation to keep them from freezing. The main purpose of the insulation is to reduce heat loss and increase performance. For protecting the collector and piping from damage due to freezing temperatures, you basically have two options:

    Use an antifreeze solution as the heat-transfer fluid.

    Drain the collector(s) and piping (collector loop), either manually or automatically, when there's a chance the temperature might drop below the liquid's freezing point.

    Using an Antifreeze Solution
    Solar water heating systems that use an antifreeze solution (propylene glycol or ethylene glycol) as a heat-transfer fluid have effective freeze protection as long as the proper antifreeze concentration is maintained. Antifreeze fluids degrade over time and normally should be changed every 3–5 years. Since these systems are pressurized, it is not practical for the average homeowner to check the condition of the antifreeze solution. If you own this type of system, have a solar heating professional check it periodically.

    Draining the Collector and Piping
    Solar water heating systems that use only water as a heat-transfer fluid are the most vulnerable to freeze damage. "Draindown" or "drainback" systems typically use a controller to drain the collector loop automatically. Sensors on the collector and storage tank tell the controller when to shut off the circulation pump, to drain the collector loop, and when to start the pump again.

    Improper placement or the use of low-quality sensors can lead to their failure to detect freezing conditions. The controller may not drain the system, and expensive freeze damage may occur. Make sure that the sensor(s) have been installed according to the manufacturer's recommendations, and check the controller at least once a year to be sure that it is operating correctly.

    To ensure that the collector loop drains completely, there should also be a means to prevent a vacuum from forming inside the collector loop as the liquid drains out. Usually an air vent is installed at the highest point in the collector loop. It is a good practice to insulate air vents so that they do not freeze. Also make sure that nothing blocks the airflow into the system when the drain cycle is active.

    Collectors and piping must slope properly to allow the water to drain completely. All collectors and piping should have a minimum slope of 0.25 inches per foot (2.1 centimeters per meter).

    In integral collector storage or "batch" systems, the collector is also the storage tank. Placing large amounts of insulation around the unglazed parts of the collector and covering the glazing at night or on cloudy days will help to protect the collector from cold temperatures. However, water in the collector can freeze over extended periods of very cold weather. The collector supply and return pipes are also susceptible to freezing, especially if they run through an unheated space or outside. This can happen even when the pipes are well insulated. It is best to drain the entire system before freezing temperatures occur to avoid any possible freeze damage.

    See Heat-Transfer Fluids for Solar Water Heating Systems to learn more about the different types of heat-transfer fluids.

    For more information about residential solar systems, see:

    Solar Water Heaters
    Solar Space Heating Systems
    Heat Exchangers for Solar Heating Systems
    Learn More
    Related Links
    How do I protect my solar system from freezing weather?
    Florida Solar Energy Center

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    Content Last Updated: September 12, 2005
    Last edited by BHD; 08-08-2007, 02:51 PM.
    Push sticks/blocks Save Fingers
    "The true measure of a man is how he treats someone who can do him absolutely no good."
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    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and the current state of the economy............the light at the end of the tunnel, has been turned off.


    • #3
      Re: Glycol solar fluid questions

      note: I jsut re-post the information that would have value to this discussion, where and +++++ is is a missing paragraph from the original document
      U.S. Department of Energy - Energy Efficiency and Renewable Energy
      A Consumer's Guide to Energy Efficiency and Renewable Energy
      Heat-Transfer Fluids for Solar Water Heating Systems
      Heat-transfer fluids carry heat through solar collectors and a heat exchanger to the heat storage tanks in solar water heating systems. When selecting a heat-transfer fluid, you and your solar heating contractor should consider the following criteria:

      Coefficient of expansion – the fractional change in length (or sometimes in volume, when specified) of a material for a unit change in temperature
      Viscosity – resistance of a liquid to sheer forces (and hence to flow)
      Thermal capacity – the ability of matter to store heat
      Freezing point – the temperature below which a liquid turns into a solid
      Boiling point – the temperature at which a liquid boils
      Flash point – the lowest temperature at which the vapor above a liquid can be ignited in air.
      For example, in a cold climate, solar water heating systems require fluids with low freezing points. Fluids exposed to high temperatures, as in a desert climate, should have a high boiling point. Viscosity and thermal capacity determine the amount of pumping energy required. A fluid with low viscosity and high specific heat is easier to pump, because it is less resistant to flow and transfers more heat. Other properties that help determine the effectiveness of a fluid are its corrosiveness and stability.

      Types of Heat-Transfer Fluids
      The following are some of the most commonly used heat-transfer fluids and their properties:


      Water is nontoxic and inexpensive. With a high specific heat, and a very low viscosity, it's easy to pump. Unfortunately, water has a relatively low boiling point and a high freezing point. It can also be corrosive if the pH (acidity/alkalinity level) is not maintained at a neutral level. Water with a high mineral content (i.e., "hard" water) can cause mineral deposits to form in collector tubing and system plumbing.

      Glycol/water mixtures
      Glycol/water mixtures have a 50/50 or 60/40 glycol-to-water ratio. Ethylene and propylene glycol are "antifreezes." Ethylene glycol is extremely toxic and should only be used in a double-walled, closed-loop system. You can use food-grade propylene glycol/water mixtures in a single-walled heat exchanger, as long as the mixture has been certified as nontoxic. Make sure that no toxic dyes or inhibitors have been added to it. Most glycols deteriorate at very high temperatures. You must check the pH value, freezing point, and concentration of inhibitors annually to determine whether the mixture needs any adjustments or replacements to maintain its stability and effectiveness.


      Content Last Updated: September 12, 2005
      Push sticks/blocks Save Fingers
      "The true measure of a man is how he treats someone who can do him absolutely no good."
      attributed to Samuel Johnson
      PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and the current state of the economy............the light at the end of the tunnel, has been turned off.