The way I will be setting this up will not allow the system to freeze. You cannot use straight water in such a heating system in northern Minnesota where winter temperatures reach 40 below zero every year. The solution needs to be a glycol mixture (for everyone else reading, glycol is antifreeze). A 60% glycol mixture insures that the system is fully protected to 40 degrees below zero, but I have added a little something as a backup!!
Using the wind/solar setup, and a 110-volt water heater element, I am able to add heat to the system at night from the battery bank, however, this is not the only heat being added to the system at night!!
See, radiant floor heating only requires 130 degrees in the liquid flowing through it, to heat the floor. The system I am designing will heat the water to 170 degrees or more, so, the logical thing was to slow down the heat for the radiant flooring, and at the same time, store the excess heat for later use. I would really have to draw a picture to explain the entire design, but if you have some imagination, I will try to explain it here.
The water is initially heated and immediately put into a highly insulated 55 gallon hot water tank that sits directly behind the parabolic trough, outside. This tank is, for no better terminology, my water temperature regulator. When the water in the outside tank reaches 130 degrees, it is automatically released into the actual heating system for the radiant flooring.
In the house, there is another tank. A 105 gallon electric hot water tank. This tank is used for excess storage of the heated water, but also as a regulator. On the cold line side of the 105 gallon tank, there is an actual non-electric regulator that sits between the hot line and the cold line. This regulator is set for 130 degrees. If the water coming into the system is above 130 degrees, the non-electric regulator kicks on, and adds cold water to the heated water to bring it down to 130 degrees to insure proper operating temperature.
The end line from the radiant flooring (the cold end) is hooked to the cold end of the non-electric regulator as well as the 105 gallon tank via a “T”. This allows me to use the cooled water from the radiant floor heating to help regulate the water temperature from the solar trough. Any excess heated water is allowed to bypass the “T” and go into the 105 gallon hot water tank that is in the house for night time “storage”. Then, a line from the cold side of the 105 gallon tank runs back outside to the solar trough to be heated.
Now, a couple of key things: The inside 105 gallon hot water tank is set up on an automatic switch that is automatically tripped when the sun goes down or sun comes up (using a small solar panel works great for this since it throws off electricity when the sun is shining and no power when the sun is not.).
When there is no sun, the switch is tripped and the battery bank from the wind/solar takes over to heat the water via the 110-volt heating element in the 105 gallon hot water tank. When the sun comes up, the switch is tripped again and stops the battery bank from heating the water so that the heated water now comes from the solar trough. Simply automated system that uses the sun, itself, to determine when and how the water is to be heated. Be it through the electric side (battery bank) or the solar trough heater. This same switch is used to stop the water flow from the interior system to the solar trough at night so that the cold water from the outside tank is not being introduced to the system. These “switches” are nothing more than simple relay switches that are readily available at more electronic stores.
For those that do not know how a relay works, here is a website that kind of explains them. They are a simple device that automatically turns on and off when a small amount of power is flowing to it.
Currently, only because I have to build more solar panels, the pump for this system (a TACO 007 pump that runs on about 37 watts of power) is running on grid power. Once I build additional solar panels and add to the battery bank, this entire system will be off-grid and running completely on solar power.
One note for those of you that are interested in plans like this: Do NOT BUY solar panels!! The cost of them will drain your bank account quickly!! It is actually very simple to build your own solar panels, and the cost is FAR below the cost of a commercial solar panel. Example: You can buy tabbed solar cells on Ebay. 2 KW of them can run as low at $900, and all you have to do is solder them together. On the other hand, 2 KW in solar panels from a commercial sale, could cost you in excess of $10,000 depending on where you are buying from.