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Heat-energy storage device could make household solar power more feasible

The prototype device utilizes paraffin contained within thin aluminum plates
The prototype device utilizes paraffin contained within thin aluminum plates
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The prototype device utilizes paraffin contained within thin aluminum plates
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The prototype device utilizes paraffin contained within thin aluminum plates

Although solar panels are active while the sun is shining, they typically don't do much once the sun goes down. This is why some systems incorporate water tanks. The water is heated during the day via the panels, then that stored thermal energy (heat) is used to warm the home at night. While the tanks are effective, they also take up a lot of space, making them difficult to fit into peoples' homes. A newly-developed device, however, stores just as much heat in half the space – using paraffin instead of water.

The prototype was designed by researchers from Spain's Universidad del Pais Vasco and Euskal Herriko Uniberstitatea. It contains a commercial type of paraffin, sealed within thin aluminum plates. Water is still involved, although it serves to transport the heat instead of storing it.

Here's how the system works ...

Water is heated by rooftop solar thermal panels and then flows into the house to the thermal energy storage unit. Upon reaching the device, it circulates through channels between the plates. As it does so, the heat in the water is absorbed by the aluminum and passes through to the paraffin – which is in a solid state at the time.

Upon reaching a temperature of about 60º C (140º F), however, the paraffin melts to store the heat energy. When heat is needed later, cool water is circulated through the channels, lowering the temperature of the paraffin. Once it drops below 60º C and re-solidifies, it releases the stored heat. The use of the thin plates allows the thermal energy to be released from the paraffin relatively quickly. Normally, such phase-change materials take a long time to release energy, which has limited their usefulness in thermal energy storage devices.

Along with being able to do the work of a water tank of twice the volume, the storage units could also be built in a variety of shapes – not just cylinders, as is the case with tanks. This means they could be tucked into corners, or even built into false ceilings.

The researchers are continuing to develop the technology, and are looking into replacing the paraffin with other phase-change materials that are capable of storing even more energy, such as fatty acids. They're also building a full-scale prototype, which will be tested via real-world use in a government office.

Source: UPV/EHU

[Ed. note: This article initially suggested that the stored thermal energy would also be used to generate electricity, but has since been amended.]

Although solar panels are active while the sun is shining, they typically don't do much once the sun goes down. This is why some systems incorporate water tanks. The water is heated during the day via the panels, then that stored thermal energy (heat) is used to warm the home at night. While the tanks are effective, they also take up a lot of space, making them difficult to fit into peoples' homes. A newly-developed device, however, stores just as much heat in half the space – using paraffin instead of water.

The prototype was designed by researchers from Spain's Universidad del Pais Vasco and Euskal Herriko Uniberstitatea. It contains a commercial type of paraffin, sealed within thin aluminum plates. Water is still involved, although it serves to transport the heat instead of storing it.

Here's how the system works ...

Water is heated by rooftop solar thermal panels and then flows into the house to the thermal energy storage unit. Upon reaching the device, it circulates through channels between the plates. As it does so, the heat in the water is absorbed by the aluminum and passes through to the paraffin – which is in a solid state at the time.

Upon reaching a temperature of about 60º C (140º F), however, the paraffin melts to store the heat energy. When heat is needed later, cool water is circulated through the channels, lowering the temperature of the paraffin. Once it drops below 60º C and re-solidifies, it releases the stored heat. The use of the thin plates allows the thermal energy to be released from the paraffin relatively quickly. Normally, such phase-change materials take a long time to release energy, which has limited their usefulness in thermal energy storage devices.

Along with being able to do the work of a water tank of twice the volume, the storage units could also be built in a variety of shapes – not just cylinders, as is the case with tanks. This means they could be tucked into corners, or even built into false ceilings.

The researchers are continuing to develop the technology, and are looking into replacing the paraffin with other phase-change materials that are capable of storing even more energy, such as fatty acids. They're also building a full-scale prototype, which will be tested via real-world use in a government office.

Source: UPV/EHU

[Ed. note: This article initially suggested that the stored thermal energy would also be used to generate electricity, but has since been amended.]

7 comments
The Doubter
I don't think this is new or novel. Phase change heat exchange is well-tried and well-used.
LordInsidious
Awesome, the more options we have the more energy conservation can be used by different people and places.
MonacoJim
As mentioned nothing new about phase change energy storage, this was big back in the 90s. Why not fill car radiators with paraffin and pass air or water heated by solar panels over them? (no, the radiators arent left in the car, seal them off and line them up in a polystyrene lined & covered trench with air inlet at one end, & outlet into house the other. 12v fans and first radiator connected to the solar panels) We need cheap simple solutions- theres normally an excess of heat in summer, these could adsorb the heat and cool the air into the house, and in winter release the heat to prewarm the air coming into the house. Sure it will need an air divert valve before the house inlet and a few temp sensors and an Arduino board or Rasberry pi to control it but its not rocket science and theres no NASA sized bill.
Don Duncan
Forty years ago in Israel an inventor discovered using oil instead of H20 to collect solar heat was much more efficient. As for storage, I question the "quick release is better idea". Slow release by radiance is more efficient, and feels better.
CaptD
We are now just beginning to see what R&D will come up with to maximize the storage of Solar (of all flavors) Energy. Imagine what will be discovered and be in use in a decade or two, which is why even considering building new Nuclear no longer makes financial sense, since Solar is already less expensive, much faster to install and has no decommissioning or ☢ waste "baggage" that ratepayers have to also pay for in addition to the reactor and expensive operational upgrades that all reactors require.
andyfreeze
I find it rather patronising how it's always couched in terms of use heat during the day to release at night to heat. I now live in a semi tropical climate and it's always warm at night! What is needed is a way to generate usefull amounts of electricity from the temperature difference of full sun to shade.
Energyman
What about using a material that changes phase at around 120 degrees Centigrade, rigged up to store energy and feed it when necessary to a hotplate arrangement, to create a practical solar powered cooking appliance. Vacuum collector tubes can easily get to 120 degrees, a sufficiently high enough grade of heat to boil water and cook basic foodstuff. Here in Africa, millions of people burn mega-litres of paraffin or mega-tons of wood each day just to prepare basic meals, while the sun shines in abundance. Does anyone off hand know of a suitable material?