Direct energy conversion in combination with Concentrating Solar Energy (CSP) is a promising combination to go to higher efficiencies. The Alkali Metal Energy Converter (AMTEC) is such a device developed several years ago at KIT-INR. The ATEFA (AMTEC Test Facility, see Fig. 1) is aimed at further investigation and development of AMTEC converter. ATEFA is designed to operate in a wide temperature range of 600 – 900 °C and up to 0.5 bar overpressure. For safety reasons the facility is sheathed by stainless steel (see Fig. 1 left).The AMTEC test cell is divided through the BASE (ceramic electrolyte) in two main regions. The inner side of the BASE tube is filled up with liquid sodium, which serves as anode, and heated up to high temperatures 600 – 800 °C. ATEFA is operation including maintenance shut downs to change test section (indicated red in Fig. 1 right).
|Figure 1. ATEFA in AMTEC laboratory (left); ATEFA internals (right)|
On the way to obtain a matured design of the AMTEC converter for the industry, still many aspects need to be investigated and optimized. The two drawbacks of the cell are i) low cell efficiency (~ 20 %) in contrast to the high theoretical efficiency (~ 40 %) and ii) fast power degradation in time. Both are strongly bound to electrolyte and cathode. The electrolyte is responsible for ~ 60 % of the power loss while the electrode is in charge of the ~ 20 %. Regarding the cell efficiency, a fundamental part is lost through heat radiation and conduction. The ion conductivity of the BASE needs to be likewise taken into consideration as well as the electrical losses in electrode, current-collector and leads. Furthermore, alternative solutions need to be found for the joining between the ceramic BASE and the metallic structure of the cell. The junction must withstand temperatures of 800 – 1000 °C in a corrosive medium, which is an issue that has not been solved yet for long-standing cells.
The main objectives of the project are:
- Study and test surface coating materials on BASE (electrodes)
- Study and test current collector structures / materials
- Analysis of the electrochemical properties of AMTEC cell
- Study of electrical performance of AMTEC cell
- Development of long term AMTEC cluster for SOLTEC-3