LSM14: How lithium can change the solar landscape

By Emma Hughes
Published: Wednesday, 28 May 2014

While industrial minerals like quartz, silica, feldspar and silicon carbide have traditionally been linked with solar energy applications, it is lithium that could see a 10-fold increase in demand through use in CSP working fluids.

Lithium could soon see increased use in the solar energy industry as a working fluid component in concentrated solar thermal systems.

By replacing traditionally-used organic heavily oil fractions or solar salts, a lithium-based molten salt could increase lithium carbonate equivalent (LCE) demand by about 1m tpa, according to Jon Hykawy, president of Stormcrow Capital Ltd.

Speaking on the side-lines of the IM Lithium Supply & Markets conference, held in Montreal, Canada, last week, Hykawy told IM that traditional working fluids have comprised organic heavy oil fractions or solar salts, both of which come with positive and negative attributes.

“Organic oil fractions are heavy, expensive and break down at about 400°C. If you spill them on the desert floor they basically turn into oily soil that you have to truck somewhere to dispose of,” Hykawy said.

The high break-down temperature means that the system is efficient, but it is still limited to 400°C and, if a spillage occurs, it can be an expensive problem.

“Solar salts, which are cheap, have a much lower melting point – at around 130°C – but they break down at around 150°C. If you spill [molten salt] you can pick it up and reuse it. But if it freezes, you’ve got a problem, as trying to melt all of the salt in all of those pipes is going to take a long time,” he told IM.

As a result, many researchers have been looking at alternative salts that melt well below the boiling point of water and have a property called eutecticity, which means all of those individual salts melt at the same temperature, even though each of them has a different melting temperature.

“A couple of formulas have been found, which typically contain four or five different types of salt. One of them is always lithium nitrate (LiNO3),” Hykawy explained.

“What lithium does for you is it lowers the melting point, but also lowers the viscosity of the salt, meaning you don’t have to use as much energy to pump it through the system. They also have exceptionally high operating temperatures – well above 500°C, typically,” he added.

Lithium therefore offers several advantages over traditional working fluids as the electricity produced is cheaper, the system is no longer in danger of freeze-up and if there is a spillage, the salt turns hard and is able to be reused.

solar 
SolarReserve's Crescent Dunes 110MW CSP project located near Tonopah, Nevada, US.
Image: SolarReserve 

Specifications


If the best salt used contains 25% LiNO3, then 32,000 tonnes of salt contain 8,000 tonnes of LiNO3, or about 4,300 tonnes of LCE.

“This would create a 10-fold increase in lithium demand, just for that application, equating to 24.6m tones LCE, or about 1m tpa,” Hykawy told IM.

“It would be nice if the lithium industry could actually deliver this in the chemical form needed, rather than asking them to buy lithium carbonate and then getting them to convert it to lithium nitrate. I think this would boost the lithium industry over time,” he added.

How CSP systems work

CSP systems use optics such as lenses or curved mirrors to concentrate a large amount of sunlight onto a central solar tower or collector, which uses this energy to heat a working fluid to drive a heat engine – usually a steam turbine.

This heat engine is connected to an electrical power generator or powers a thermochemical reaction.

While space restrictions are as relevant for CSP systems as they are for any other large-scale renewable energy alternative, the fact that CSP can be used anywhere there is sunlight – not necessarily sunshine – means they are a viable option worldwide.

Hykawy explained that in the reflecting tower applications are relatively compact and a user can get a factor of 10,000 increase in solar insolation on that tower, while for a parabolic reflector the best that can be expected is a factor of a few hundred augmentation of the sun’s energy.

“The biggest impediment is that the sun only shines for half the day, so you’re really looking to build the heat load and then spread that out over the entire 24-hour period,” he told IM.

This means that, unlike solar photovoltaics systems, which require battery power when the sun goes down, CSP systems can continue to generate energy at night. This is because the system has built up heat throughout the day.

“Over time I think you’re going to see [CSP] take off. It is inexpensive, it is base-load, and it’s not solar PV, where if the sun goes behind a cloud you’ve lost half the output from the field. As long as the sun shines, they can continue to produce power and even when the sun goes down, they can continue to produce power,” Hykawy told IM.

For more information on the use of industrial minerals, like lithium, in renewable energy applications, pick up your copy of IM’s Critical Materials for Green Energy supplement magazine, out this August.