Projects

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Overview:

Power sector decarbonisation is one of this century’s concerns that our society must face and the only available long-term solution is exploiting extensively Renewable Energy Sources (RES). However, the increasing ratio of renewable energy in the electricity mix has a major impact in the energy systems and networks. The electricity production, especially, the one from RES as wind and solar suffers daily fluctuations which requires a high flexibe, intelligent and smart grid. The upcoming challenge to balance the mismatch between energy supply and demand craves for adjustable, low-cost and efficient Electric Energy Storage
(EES) (Staub et al. 2019).
The well-established technologies for an efficient storage of electricity are Batteries (of different types), Pumped Hydro Energy Storage (PHES), which currently represents 96% of the worldwide storage capacity, and Compressed Air Energy Storage (CAES) with efficiencies significantly above 50% and a high maturity level (Frate et al. 2020). However, the limited raw materials resources, geographic and geological requirements impose restrictions to the broad adoption of these technologies and pushed the development of alternative electricity storage technologies. In this context, Pumped Thermal Electricity Storage (PTES), or Carnot
Battery (CB), is a recent and promising technology to storage electricity as it promises to be cost-effective with a long lifetime (unlike many battery chemistries), and site-independent (unlike PHES and CAES). Although the implementation of EES remains limited at the moment, mainly for financial and technical reasons, it is expected to increase rapidly in the coming years (Dumont et al. 2020).
Carnot battery consists in thermodynamic two cycles. The charge cycle converts the excess of electric energy into heat to a hot reservoir with a heat pump (or another heating system) when electricity production is greater than demand. The discharge cycle is activated when electricity demand outstrips production and the PTES generates electricity from the stored thermal energy (possibly via a Rankine cycle) (Dumont and Lemort 2020). The thermal energy can be stored over several hours up to few days without considerable losses and, so, not losing the required temperature levels (Rahman et al. 2016) and initial studies reported
power-to-power efficiencies of around 50-70% (Staub et al. 2018).
The assessment of the CB technology as an EES is not yet properly addressed due to his novelty. A few different prototypes of Carnot battery have been developed and reported in the literature but only a few configurations have been tested. Different technologies for the charge and discharge processes that affect the system boundary conditions shall be examined and the trade-off between the system cost, complexity and performance determined. Moreover, the ability of the system scalability is crucial for the broad adoption of the technology.

This project aims to assess the technical and economic viability of the state-of-art Carnot Batteries technology as an electric energy storage. First, an overview of this emerging and innovative technology should be carried out to evaluate the current developments, techniques and features of the existent prototypes in the scientific and industrial communities. A previously tested and validated development strategy by the team members will be implemented for the design of a CB lab-scale prototype. The strategy starts with the development of a simplified thermodynamic model to fully understand the complete process including the charge and discharge phases, and screen different working fluids, different configurations and storage mediums. Secondly, a realistic off-design model of the system will be designed, constructed and tested in a wide range of operating conditions to assess the behaviour in part-load operation. Finally, a tecnoeconomic optimization will be carried out to plan the pilot plant. In the end of the project, the specifications of a CB system that can be built in the future should
be attained including the test-rig components selection and a pilot plant design in a CAD software.
For the performing of this project, the team comprises four members of University of Coimbra with a PhD in the area of thermodynamics and also investigators of ADAI. All the members have a background on thermodynamics and an extensive experience in organic Rankine cycle as a result of the participation in several projects and the writing of scientific publications regarding this subject.

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Aware that, both for safety reasons, namely those related to reducing the risk of fire, and for economic-environmental reasons, associated with the fact that forest products are increasingly more valuable and biomass can be used as a renewable energy vector, there will have to be a paradigm shift in the way forest management is carried out in Portugal and that, As a result, the amount of waste resulting from integrated forest management will tend to increase, the consortium will seek to take advantage of the opportunity that opens up with the increased availability of this waste to consider the production of a new energy vector, avoiding the classic solutions of energy recovery. In this phase, the main objective is to assess the technical feasibility and identify the technological challenges facing the production of this energy carrier from the aforementioned forest resource.