Alternative Forms of Solar Heat Storage

Testing molten salts, concrete and natural stone for thermal storageThe quest for renewable energy sources goes on, and despite the strong allure of solar power and the immense benefits that effectively harnessing the sun itself could bring, it continues to be overshadowed by wind, PV and natural gas.

Further research is needed before solar energy can be deemed as reliable as those aforementioned, but significant progress has been made. One of the chief challenges facing the solar power industry is finding the means to store the sun’s energy in a form that can be converted into electricity, at the levels that would be required to meet the demands of the populace.

Attempts to develop such storage mediums have taken researchers in some interesting directions. Here are examples of some alternative – but surprisingly efficient – forms of thermal energy storage.



The steam engine kicked off the industrial revolution, and perhaps things will come full-circle, as steam may prove to be a key component in the quest for affordable solar energy.

Australian engineers have developed an energy-storage mechanism that combines both solar power and the steam engine. Dubbed ‘Terrajoule’, the system utilizes solar concentrators to create steam, and steam engines to convert it into electricity.

According to Terrajoule CTO Robert Mierisch, the system can provide energy storage at 20% less cost per kWh of electrical of storage capacity than any form of battery storage. Their website claims that by 2015, they will be able to bring peak watt pricing down to $1.50 to $2.00 per watt, making the price competitive with that of the photovoltaic systems.

Furthermore, the Terrajoule system is extremely durable. It is capable of lasting up to 25 years, and utilizes no toxic materials.


Phase-Change Materials

Phase-change materials (PCM) store or release heat energy by changing between liquid, solid and gas state, depending on the material in question. When it comes to thermal energy storage, solid-liquid is the preferred form.

In this case, the solid material will essentially store the heat by melting, and release heat when it freezes. This may sound counter-intuitive, but the nature of the PCM is such that it can continue to absorb heat at a consistent rate even as it melts and transforms into liquid form. The PCM then freezes as the temperature begins to drop, releasing its stored heat as it reverts to solid state.

Researchers in India have utilized such technology in a creative way, fashioning small spherical capsules about 38 millimetres in diameter that combine paraffin wax and stearic acid to achieve the PCM effect.

In other words, they’ve made beads that can store thermal energy, absorbing heat from the sun during the day and releasing it slowly over night. This may provide an easily affordable source of regions that are sunny during the day but nevertheless endure freezing temperatures at night.


Molten Salts

Able to maintain its liquid state at temperatures of 1000 degrees Farenheit, molten salt provides a highly efficient storage medium for thermal energy. It renders weather-interference a non-issue, and can be easily stored due to its constant liquid state.

The world’s largest solar thermal plant recently went online in Arizona. Constructed by Spanish company Abengoa, the Solana Generating Station utilizes molten salts as its storage medium, capable of storing thermal energy collected from the sun during the day for up to six hours into the night.

Though only having recently been adopted for commercial purposes, molten salt as a heat storage medium continues to gain momentum, and may well prove to be the solution the solar power industry is looking for.


Image credit: DLR , CC BY 2.0, Via Flickr

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