Roswell Bob
Solar Enthusiast
Is anybody using paraffin as a thermal storage medium?
Not necessarily.Mass and insulation are the key.
I believe you have that backwards. Paraffin absorbs heat as it melts and gives off heat as it cools.Not necessarily.
The unique property the paraffin has is a phase change at a relatively high temp. When the paraffin melts, it gives off a large amount of energy. When the paraffin hardens (Freezes) it absorbs a large amount of energy. The phase change energy absorbed or released is huge and can exceed the thermal mass energy by multiple times. Consequently, you could get a huge amount of thermal storage in a small system. Water probably has a higher phase change energy than paraffin, but it's phase change temperature is inconveniently low for a thermal storage system. Paraffin on the other hand melts and freezes at a temp that is very good for solar thermal systems.
Having said that, there are also challenges. Not the least of which is that the wax cant be the solar collection fluid. You would have to have water or oil going through the solar heat collector and then use some type of heat exchanger in the wax. You would then use the same fluid and heat exchanger for extracting and distributing the heat.
There is little chance the system would ignite the paraffin, but if there was a fire from some other source, I could see where it could get bad... The system would have to be designed with this in mind.
Overall, I agree that the complexities probably out weigh the benefits in most situations, and that is probably why it has never caught on.
I had to google: 1 kg paraffin = 40 litres water when doing the above.For example if the collectors heat a fifty gallon drum of water, then that drum is surrounded by wax, the wax would melt during the day, than as it hardens, it would give off that heat into the drum
Oops..... your right, I got it backwards..... I am not sure how I did that.... Sorry about the confusionbelieve you have that backwards. Paraffin absorbs heat as it melts and gives off heat as it cools.
Yup something like that would work.....A drum of Paraffin with a drum of watter inside of it.... but I would put insulation around the outside of the Pariffin drum as well. Once the paraffin melts it is probably not a very good conductor.While it wouldn't work as a fluid in a collector. It could work as a insulator around a storage tank. For example if the collectors heat a fifty gallon drum of water, then that drum is surrounded by wax, the wax would melt during the day, than as it hardens, it would give off that heat into the drum. Thus allowing the water to stay hot much longer.
I like the radiator idea. You could just lower it inside a steel drum, then fill the drum with paraffin. I am designing a system that will have two fifty gallon drums of water, that will be heated by vacuum tubes. That water will be used to heat underground tanks that feed my radiant floor heater. I'm trying to come up with a containment system for the paraffin outside the tanks.Oops..... your right, I got it backwards..... I am not sure how I did that.... Sorry about the confusion
Yup something like that would work.....A drum of Paraffin with a drum of watter inside of it.... but I would put insulation around the outside of the Pariffin drum as well. Once the paraffin melts it is probably not a very good conductor.
I was thinking some kind of radiator or loops of tubing in an insulating drum of paraffin, but the concept is the same
I would think the spread between peek and off-peak price would have to be pretty big to make a reasonable return on investment.If time of use metering becomes the norm then using electricity at off peak hours to heat the home may make paraffin storage worth the effort.