# Techno-Economic Analysis of Waste Heat Recovery in Automotive Manufacturing Plants
## 6 Conclusions  
This study presents a proposed system designed to recover and utilise heat from the exhaust air following the RTO process. The system integrates a Carnot battery and PV system. The Carnot battery, in this configuration, consists of three main components, including ORC, TES, and heat pump. The waste heat from exhaust air after the RTO is initially captured in TES. To further optimise heat recovery, a heat pump is employed to extract additional energy from the low-temperature waste heat. This energy is then used to raise the temperature of a secondary fluid, which is also stored in the TES. As a result, the TES is charged from two sources: directly from exhaust air and indirectly from the heat pump. The stored heat in TES can subsequently be used to produce electricity through ORC. This dual-source charging approach enables more efficient recovery and energy generation. It is worth noting that the heat pump can be considered as charging, the TES as storing, and the ORC as discharging part of the Carnot battery. In this way, the parts of the storing system--unlike most electrochemical batteries--are independent, making charging power, discharging power, and storage capacity at uncoupled quantities, giving better flexibility to fulfil the needs of consumers/users. The main results from this study are summarised as follows. * The proposed system demonstrates that the COP of the heat pump ranges from 2.55 to 2.87. For ORC with a recuperator, the efficiency falls between 12.5% and 15.5%, with net output power varying from 444.5 kW to 581.3 kW. As a result, the P2P of the Carnot battery system lies between 0.36 and 0.40, depending on different operating conditions. * The study compares the performance of the Carnot battery system with and without a recuperator in the ORC. The results indicate that the difference in efficiency between the two configurations is low, with an RMSE of 0.0075 and an MSE of 5.5947 \(\times\) 10\({}^{-5}\) for ORC efficiency. In this case, the P2P of the Carnot battery shows a slight variation, with an RMSE of 0.0202 and an MSE of 4.0907 \(\times\) 10\({}^{-4}\). * In addition, incorporating a recuperator in TES results in a \(\zeta\) ratio between 5.86 and 6.16. Without a recuperator, however, the \(\zeta\) ratio rises to a range of 6.15 to 6.54. This comparison indicates that using a recuperator reduces the PCM mass needed for TES,thereby enhancing cost-effectiveness. Also, the results indicate a difference with an MSE of 0.1121 and an RMSE of 0.3348. * The PV system generates between 75.35 and 145.91 MWh of AC energy, resulting in an annual energy production of approximately 1.35 GWh AC. This energy is primarily used to power the heat pump and the ORC pump. Any excess energy beyond the requirements of the system can be redirected for other uses within the manufacturing plant, enhancing overall energy efficiency and potentially lowering operational costs. * The Carnot battery system incorporating the PV component achieves a total annual net generation of around 4.30 GWh. * Four scenarios were evaluated to determine the economic viability of the project, considering configurations both with and without a PV system and a recuperator in the ORC. When operating without PV, the Carnot battery relies on electricity from the grid. The results indicate that all configurations provide strong economic performance, with the following favourable metrics across cases: a SIC below 2000 EUR/kW, an NPV over 500 thousand EUR, a PBP between 6 and 15 years, a low LCOE below 0.070 EUR/kWh, and an ROI between 25% and 160%. Among these configurations, the proposed system, which includes both PV and a recuperator, achieves a SIC of 1960 EUR/kW, an NPV of approximately 654,541 EUR, a PBP of 14.06 years, an LCOE of 0.064 EUR/kWh, and an ROI of 25.48%. This configuration provides a high output power of approximately 1.31 MW, with an estimated annual energy production of 4.30 GWh, reflecting both high energy generation and cost efficiency.