Studies on the integration of renewable energy source systems are often conducted with a special focus on the electricity sector. During the recent years however, it has become clear that the least cost solutions for stabilizing the fluctuating power sources, such as wind and solar, is likely strong coupling between the different energy sectors. This concept is known as smart energy. This concepts describes that increased coupling between the energy sectors and taking advantage of cost effective yet efficient energy storage systems is the most cost effective instrument to realize the required flexibility. The work of the project READY focuses on three innovative technologies/solutions in the framework of smart energy systems. In this report, these three concepts are introduced and discussed briefly. Details on the individual concepts are presented as scientific research papers produced as part of the task. In this respect, the first concept is a novel energy storage solution based on combination of high temperature packed bed thermal storage and conventional power plants. In this work, a simple yet efficient energy storage system for renewable energy source power plants such as wind farms is proposed and designed. This system was show-cased for Denmark where district heating(DH)is as important as power generation, and as a result, a considerable portion of the stored energy in low demand times is used to support the local DH-system. In order to have a proper design, the local power production of one of the wind farms of Aarhus city in Denmark as well as its DH-system conditions were taken into account as the case study of this work. This system was later called high temperature heat and power storage (HTHPS). Furthermore, the performance of the HTHPS in terms of energy and exergy efficiencies under realistic operational conditions was investigated where the storage supports a number of wind turbines over a long period. The potential value creation of the energy storage system in the local electricity and heat markets was also assessed. Having both forecasted and realized wind power generation as well as energy prices for the recent years, the system was designed with rigor and a smart biding-strategy was determined for the power plant equipped with the energy storage unit for day-ahead and intra-day markets. The results showed that the system is able to compensate the fluctuations of wind power plants, and present high annual overall energy and electricity efficiencies of 80.2% and 31.4% and the exergy efficiency of 56.1%. Finally, a comparison of this technology with other competent technologies recently proposed was done, founding the HTHPS a promising technology outperforming all others for the operation locations like Denmark.
The second concept focused on finding an innovative solution for the cooling preparation of the Aarhus University Hospital(AUH), which is the largest hospital of the northern Europe. In fact, so far, supplying the heating demand of the absorption chiller of the AUH was challenging as the heat was provided by the local DH-system in which the load is not high enough during summer time. A new configuration of co-generative solar assisted absorption chiller was proposed by which not only the heating demand may be efficiently supplied, but also a significant contribution in supporting the local DH can be made. This innovative system takes advantage of an evacuated tube solar thermal system and no cooling tower. The effect of applying this change in the configuration of the AUH cooling system on the local DH and cooling network was assessed over an entire year. The results showed that the proposed system could make 30% contribution in the heat preparation process of the absorption chiller during the summer and 17% during the entire year and great amount of heat production for DH purpose. The effect of replacing the conventional system by the proposed configuration on the CO2-emission of the AUH was also evaluated. Finally, the two economic criteria net present value (NPV) and internal rate of return (IRR) approaches were used to assess the economically effectiveness of the project, finding it a very feasible and economical system with a payback period of only 3 years and an IRR value of 37%. In the second phase of this work, a unique idea in utilization of the potential of gas transmission system for cooling production. In gas transmission systems, there are some expansion stations in which gas pressure, after being preheated, is reduced considerably. This pressure drop causes temperature collapse in the gas stream. Power productive gas expansion station (PPGES) is the most recent design proponed for these stations. In this work, taking advantage of the temperature fall in the gas stream for cooling purpose is proposed by coupling the station with an absorption chiller. In this case, the chiller could also provide the heating demand of the expansion station. The combined system was designed for integrating the AUH absorption chiller and Viborg gas expansion station. The results showed that the expansion station could provide an annual cooling production contribution of 27% and produce a large amount of free power.
The third covered concept in the work of READY is another innovative storage technology. This is in fact the fifth generation of compressed air energy storage (CAES) called “subcooled-CAES”. The new proposed technology aims at cogeneration of power, heat and cooling. This system may be a very advantageous for locations with high heating and cooling demands, like locations with district heating and cooling systems, and high penetration of renewable energy in the power grid. An extensive design, sizing and thermodynamic analysis of the system for a typical wind farm case study with 300 MW in Denmark was presented. The results showed a great potential of the system to support the local district heating and cooling networks and reserve services in electricity market. The values of power-to-power, power-to-cooling and power-to heat efficiencies of this system are 32%, 32%and 92%, respectively. Thus, the coefficient of energy performance (COEP) taking into account its heat, power and cooling production is 1.56. A simple techno-economic comparison of this system with other CAES generations proved the firm superiority of the subcooled-CAES.
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Deliverable no. D.4.7.1 Report on three mature proofs of concepts for innovative technologies for energy system of the future, ready for demonstration
Please contact: Ahmad Arabkooshar and Gorm Bruun Andresen, Aarhus University