Gustavo Caceres

Thermal energy storage systems (widely known as TES) are a key component of Concentrated Solar Power Plants (CSPs) that generally use a mixture of sodium and potassium nitrates also known as “solar salt” as thermal storage material. Improvements in TES materials are important to reduce CSP costs, and therefore increase energy efficiency and the competitiveness with other technologies. A novel alternative examined by the THEMSYS Initiative (UAI-Earth), SERC-Chile, Solar Energy Program (CORFO), and which can also be found in the paper entitled “Techno-Economic Forecasts of Lithium Nitrates for Thermal Storage Systems” by M. Montané, G. Cáceres, M. Villena and R. O’Ryan), is the use of salt mixtures with lithium nitrate to help reduce the melting point of salt and improve its thermal capacity. This, in turn, allows reducing the volume of materials required. The use of Lithium as a TES material can thus be an option for today’s solar salt technologies and a boost to the current demand for the production of typical electric batteries for lithium suppliers, which is likely to increase.

Based on commercial plant data and the expected evolution of the lithium market, the technical and economic perspectives of this alternative have been evaluated, taking into account the recent developments of Lithium Nitrate and the estimated future price of lithium. Through a levelized cost of electricity –LCOE- analysis, it is concluded that some of the mixtures could allow a reduction in costs of CSP plants of up to 5%, thus improving their competitiveness.

A more detailed explanation can be made based on recent technical results, where mixtures based on Lithium Nitrate, in particular the quaternary (KNO3 LiNO3 NaNO3 MgK) and ternary (KNO3 LiNO3 NaNO3) have proven to have exceptional technical properties and economic performance so as to become a very important option for the growing solar market based on CSP with thermal energy storage systems. Due to its lower solidification point, the operating temperature range of the TES systems could be increased, and both, the risk of solidification of the molten salts and the self-consumed energy could be reduced. This would also help reduce the environmental impact of these plants, as less material may be required. Another advantage, specifically identified for CSP plants, is the possibility of using these melted materials as HTF and switching from an active indirect TES system to an active direct system, thus potentially eliminating the use of a heat exchanger and reducing investment and maintenance costs.

These are robust and encouraging results when considering future expected prices increases for different relevant nitrates, specifically the prices for Lithium Nitrate. According to the market analysis performed for 2017, lithium price forecasts predict a 20% increase, led mainly by the demand for electric cars. In the long term, forecasts point to lithium carbonate price increases below 30% for the period 2015-2025. Taking into account these future projections, these expected increases are substantially lower than those required for Lithium Nitrates to lose competitiveness against solar salt in parabolic trough plants. Some evaluated plants showed reductions of LCOE with increases in the prices of Lithium Nitrates below 30%.

Summing up, while continuing to add value to our raw materials, such as lithium, not only boosts the national economy, but also helps new technologies to be more sustainable and accessible, thus resulting in worldwide impact.

This column was published by SERC Chile researcher Gustavo Cáceres in the Estrategia newspaper. Professor at UAI, also director of THEMSYS of UAI-Earth.

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