應用奈米晶體增強太陽熱能系統之能量儲存

Abstract

太陽熱能熱發電系統可以將太陽光儲存為熱能使其供給無太陽光時之發電需求，故太 陽熱能熱發電系統是一種很有前途的可再生能源資源。目前太陽熱能發電系統之儲能 容量受限於其低比熱容的工作流體，這導致其需要一個尺寸相當巨大的儲能槽。此一 巨大尺寸儲能槽，限制此太陽熱能發電系統應用在一些土地較小的國家，例如：台灣。 同時，通常潛熱的值高於固體感熱，故以潛熱儲存熱能之效率高於應用固體材料的感 熱。通過將奈米粒子嵌入到工作流體中並擷取其潛熱，我們可以大大提高此工作流體 的有效熱容。在這個計畫中，我們將合成鋁鍺合金（鋁 69.7 ％和鍺30.3 ％）奈米粒 子 (熔點為424 C)，並以此奈米粒子的潛熱來增加工作流體的有效熱容量。目前的太 陽能熱發電廠使用熔鹽作為工作流體，其比熱容量約為1.2 kJ/kg-K。通過加入約10 ％ 的鋁鍺合金奈米顆粒進入熔鹽，其比熱容可由1.21 kJ/kg-K 增加到約12 kJ/kg-K。此方 法可以有效增加太陽熱能發電系統之熱能儲存，將來更可以應用於改善全世界之太陽 熱能發電廠之熱能儲存。

A solar-thermal power system which stores sunlight as the thermal energy and releases the energy when sunlight is not available is a promising candidate for the renewable energy resources. The current capacity of the energy storage of a solar-thermal power plant is limited by the low specific heat capacity of the working fluid. This results in a huge size of the storage tank and causes a severe problem for the application of the solar-thermal power plant in countries with small land, e.g. Taiwan. Thermal storage by latent heat is superior to sensible heat because the latent heat of fusion is superior to the sensible heating of solid material. By embedding nanoparticles into the working fluid, the effective heat capacity of the working fluid could be greatly enhanced by taking the advantage of the large latent heat of fusion of the nanoparticles. In this project, the aluminum-germanium (Al 69.7 % and Ge 30.3 %) alloy nanoparticles with melting point of 424 C will be synthesized to harvest the latent heat of fusion during the range of the operation temperature of the solar thermal-power plant. The current solar-thermal power plants use the molten salt as the working fluid having a typical specific heat capacity of ~ 1.2 kJ/kg-K. A 10 % loading of the aluminum-germanium nano-particles into the molten salt could in principle increases the specific heat of the solvent form ~ 1.21 kJ/kg-K to ~ 12 kJ/kg-K by using the latent heat of the nanoparticles. Thus, the proposed method could effectively enhance the thermal storage capacity of the current solar-thermal power plants and will have potential application in all the solar-thermal systems in the world.