Phase Change Products Provide Energy-Efficient Temperature Control
Most of the attention currently directed towards clean energy is lavished on renewable electricity generation. The sporadic nature of wind and solar generation also brings the question of storage into consideration, usually in the form of batteries or pumped hydro storage. Electricity in, electricity out. But if it’s heating or cooling you are looking for, then alternative storage solutions open up, not the least being those based on phase change materials.
Phase change materials (PCMs) have a sharp melting temperature and need a lot of energy to make them change from a solid to a liquid. The most common example is water. It takes 80 times more energy to melt one kilogram of ice as it takes to raise the temperature of a kilogram of water by one degree. If you’ve ever slipped a blue frozen block into your Eksy then you’ve used a phase change material, but PCMs can do so much more than just keep your beer cold.
Going the other way, phase change materials can give off considerable amounts of heat as they solidify. There are many different types of phase change materials including salts and oils, each with its own melting point, allowing the same basic technology to be used to deliver either heating or cooling capacity as needed.
How much energy can they store? Depending on the material, between about 150 and 350 kJ per kg. That’s roughly on a par with the energy storage capacity of lead or nickel-based batteries, but without the lead, cadmium or other shortcomings of battery technology. On top of that, the upfront cost of PCMs compares favourably to battery costs, and with a potential lifespan many times that of current battery technologies they shape up as a cost-effective energy storage solution.
So why aren’t PCMs a hot topic in clean energy? “We expected a fairly positive reaction to what we do, but on investigation we found that because we only store energy and not make it, neither we nor our potential customers qualify for government grants or assistance,” says Keith Coakley, Managing Director of Perth-based Phase Change Products Pty Ltd (PCP).
What PCM technology can achieve is well demonstrated on a carrot farm at Gingin near Perth. Carrots need to be carefully chilled if they are to be exported, a process that uses a large amount of energy. Unable to draw any more power from the grid during the day time, the farm required a different approach to cooling their carrots. PCP’s solution was to integrate a PCM with a melting point of -4oC into the chilling system. The PCM is “charged” (i.e. frozen) using cheap, off-peak power in the cool of the night. This stored cooling capacity can then be used to chill water during the day. The system saves the carrot farm $80,000 a year in electricity costs – not just by using off-peak power but also by its ability to effectively store some of the cool of the night for use during the day.
The project was the culmination of a lot of effort, and the challenges for PCP aren’t over yet.
Lack of recognition
“We started in 2005,” says Keith, “and are still a business with 12 shareholders and just two employees. The major challenge we face is being recognised as a viable alternative in the renewable sector.”
Another challenge has been the poor perception of some PCMs. “Others had tried to copy our PCMs without success and these products damaged the industry reputation,” says Keith. “Now we have a far better understanding of what we have and what we can do with our products, but there is still a long way to go to get them recognised as readily available for use in a range of industries.”
PCP produces a number of PCMs with usable ranges extending from -21oC up to 58oC. With applications in process cooling, cold chain management, refrigeration and heating, the uses are wide ranging. PCP’s HETAC system is ideally suited to improving the efficiency of heating and cooling office and apartment buildings, but at this stage the economics don’t favour house-sized applications. “We also find that passive applications of PCMs don’t work out so well,” says Keith. In many applications, ambient temperature changes may not be enough to cycle the materials from liquid to solid and back again, whereas active temperature management can make the most of the PCM’s incredible capabilities.
As with many new businesses, capital has also been an issue. “The timeframe to get a sustainable business off the ground is usually longer than expected,” says Keith. “With the benefit of hindsight, I would have raised more money and employed more people with the appropriate skills in the early days of the business.”
Projections for ever-rising energy prices should help to boost demand for PCP’s solutions. The cost of energy is already the major driver of interest from the process cooling industry. The $330,000 system installed in Gingin is delivering cost savings of $80,000 a year, but the actual payback time may be less than these figures suggest due to the increased export capacity the farm now enjoys.
PCP also works with Chinese partners in the area of telecom shelter and battery cabinet temperature stabilisation. However, Keith still sees lots of other opportunities in Australia. “A number of farmers are waiting to see how the Gingin project performs through a full summer,” he says, expecting demand from the farming sector to increase as the results come in.
Beyond that, building temperature control is an area of great promise. “We run workshops to explain the benefits of PCMs to facilities engineers and are very close to being accepted as mainstream,” says Keith. The current culture is to keep adding air conditioners to buildings that need more heating or cooling, but that’s clearly not sustainable. Minds are starting to change and the PCM age might soon be upon us.