Friday, August 30, 2013

Hawaii Energy Storage 8: The fascinating world of phase change materials

They’re not batteries, they’re not thermal storage systems, but they still store energy.

You haven't heard much about phase change materials. You will.  Phase change materials are a range of compounds that have a huge energy signature when they change forms, or change phase, from liquid to solid or solid to liquid.

A common example is ice in a cooler. As long as ice is melting, it is absorbing heat from the beer and the outside of the cooler, and it keeps the temperature of everything around freezing. The temperature stays stable as long as the ice is changing phase and turning into water. Once the ice is gone and the melting process stops, the stuff in the cooler warms up.

You can develop materials that change phase at almost any temperature, and they work both ways--they can keep things cold, or alternatively, can keep things hot.

Japanese researchers at a recent energy storage conference said they are studying phase change materials to keep bentos hot. In this application, the materials changes from liquid to solid at the assigned temperature. As the food starts to cool, the phase change starts, the liquid changes to solid, and the process throws off heat. As a result, your bento stays at the assigned temperature and can't get cold.

You have heard of lithium ion batteries in laptops and Boeing jets that heat and even explode. You’ve felt your cell phone battery heat up. One researcher said a phase change material blanket could automatically a begin liquefying when a battery heats up, thus keeping it cool and preventing the explosion.

Researchers said you can dramatically increase the capacity of a home water heater by inserting rods with phase change materials inside. The phase change material stores a great deal of energy, and releases it as it changes phase. In this application, as the water temperature drops when you take a shower, the phase change material—presumably inside pipes in the water heater--begins solidifying, releasing heat into the water, without having to turn on the electric coils.

This means you could charge up a water heater when power is plentiful and cheap, and it could produce far more hot water for longer than standard water heaters of the same size.

I talked to a man whose company uses phase change materials to keep medical supplies cold for a week while they are being delivered to the military or third world countries.

A New Zealand researcher is mixing phase change compounds into drywall, keeping a house from getting too warm in summer or too cold in winter--without having to use electricity. It basically makes half inch drywall act like a thick concrete wall.

A German researcher talked about designing a modern supermarket to reduce lighting loads and improve cooling loads. They build icemakers into their big coolers to buffer their temperatures, and so they can turn off the power during times of high-cost power and still keep food cold. On stormy nights, when German windfarms produce more power than there is load, the price of electricity to supermarkets goes negative; they are paid to take power—they make ice with it.

When power rates go up, they can use the phase-change characteristics of the ice to keep the food cold without buying expensive electricity.

Next: Wrapping up energy storage

© Jan TenBruggencate 2013

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