However there are a few drain back systems that only use water.
Antifreeze solar panels.
All glycol products used in solar fluid mixes come with a dilution chart an example of which is shown below.
An antifreeze change may be required for your solar system.
Hydrocarbon oils hydrocarbon oils have a higher viscosity and lower specific heat than water.
The antifreeze is normally non toxic propylene glycol as opposed to toxic ethylene glycol.
It has a long track record over many decades in this application and is widely available from a number of sources.
These types of systems are pressurized and should only be serviced by a qualified solar heating professional.
What type of solar system do you have is it sealed or drainback a correctly installed drainback system should not require antifreeze sealed systems require a good quality antifreeze that will not break down with the high temperatures of solar it should also be a premixed antifreeze it is no good injecting a small quantity of antifreeze into the system as it will not mix and so will not protect the system premixed glycol is the best for solar and it should be used to fill the complete.
They require more energy to pump.
Antifreeze fluids degrade over time and normally should be changed every 3 5 years.
The photovoltaic solar panels or pv solar panels convert the sun s energy into electricity which then can be used to heat water.
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.
Propylene glycol pg has become the most common heat transfer fluid used in closed loop solar heating systems that contain antifreeze.
The heated water would be stored in a simple insulated home built tank and the heated water would be circulated to pex tubing placed in the concrete floor when needed.
Recommended dilution 40 providing total volume of 12 litres for use in solar systems.
5 litres solar antifreeze.
It is vital that you consult the chart to avoid mixing too little or too much glycol into your system too little will risk consequences in cold weather too much will reduce the mix s efficiency.
When the warmer water reaches the valve the port closes and water discharge stops.
Neat propylene glycol with additive package.
Antifreeze fluids degrade over time and normally should be changed every 3 5 years.
It s non toxic biodegradable and relatively stable.
This cycle will repeat as often as necessary to help prevent freezing.
However you should always mix as much water as possible with your choice of glycol product as simple water is the ideal solar fluid.
Currently i m planning to construct a small green house 12 x16 x8 and wanted to heat the green house using evacuated tubes.
Should be sufficient for most single and double panel systems.