In the design of trigeneration plants for buildings, two fundamental issues must be addressed: the synthesis of the plant configuration (installed technologies and capacity, etc.) and the operational planning. Given the variety of technology options available and great diurnal and annual fluctuations in energy demands, finding the optimal supply system of energy services is a complex task. Cost allocation in multi-product systems requires special attention because the way in which allocation is made will affect the prices of the final products and, consequently, the consumers' behaviour. When a polygeneration plant is designed to serve different products, it is possible to achieve a lower total cost. However, if potential consumers are free to participate, the system's management should ensure that every participant shares the benefit of joint production. In trigeneration systems this implies that all consumers should achieve, at least, a lower cost for their demanded energy services than operating separately. The present work proposes a Mixed Integer Linear Programming model to determine the optimal configuration of trigeneration systems that must cover the energy demands of electricity, heating and cooling of a residential complex located in Zaragoza, Spain. The model considers the possibility of using a set of proposed alternative technologies within a superstructure and considers the optimal operation throughout a typical meteorological year. The objective function to be minimized is the total annual cost. The results indicate that compared to consumers standing alone, the optimal trigeneration system can achieve 10.6% cost saving. Ten different cost assessment methods to the three final energy products of the analyzed trigeneration system are rigorously compared. Cooperative game theory shows that all consumers benefit. Using the Shapley values as the distribution criterion, the savings for electricity, heating and cooling consumers are 4.8%, 20.9% and 11.1%, respectively.

The development of new clean energy production systems is one of the research priorities in the energy sector. There are numerous works that evaluate the efficiency of new energy production plants from the environmental point of view. Among them, large-scale Concentrated Solar Power plants occupy a relevant place. However, medium-size plants, between 100 KW and 10 MW, have not been evaluated as intensively, resulting in a lack of knowledge in the estimation and dissemination of inventory data and environmental assessments, especially those including Organic Rankine Cycle (ORC). This work evaluates the environmental impacts caused by two solar ORC cogeneration plants that supply electrical and cooling energy for a shopping centre located in Zaragoza (Spain), using the Life Cycle Assessment methodology. One system is hybridized with a biomass boiler and the ORC operates at full load, the second one is not hybridized and the ORC can operate at partial load depending the availability of the solar energy. The selected life cycle impact assessment methods are Global Warming Potential, ReCiPe 2016, and Cumulative Energy Demand. The results allow for evaluating and comparing the environmental loads of the two medium size cogeneration systems in order to help different stakeholders to make well-informed decisions with regard to the environment. The system without hybridization presents better environmental performance in all the applied methods, 76.7 % of CO2 emissions, 67.5% of environmental impacts according to ReciPe and 5.7% of cumulative energy demand with respect to the system with hybridization. The findings show the importance of the impacts caused during the manufacturing phase of the equipment, which are more relevant than those produced during the operation phase of the plants for all environmental indicators analysed.

The residential sector plays an important role to mitigate climate change due to its high energy consumption. Polygeneration systems are a suitable alternative enabling efficient use of natural resources with low environmental impact. However, their deployment depends, among other factors, on the economic cost and the legal restrictions. This work analyses the potential reduction of greenhouse gases emissions, expressed in CO2‐equivalent emissions CO2eq, in residential buildings installing polygeneration systems and considering the current Spanish self‐consumption regulation. This is achieved through a multiobjective optimization, applying a Mixed Integer Linear Programming model, considering economic, environmental and legal aspects. Obtained results provide interesting replicable lessons, and show the interest of collective installations, in which remarkable CO2eq emissions reductions, above 65% with respect to conventional systems, can be achieved at an affordable cost. Technologies such as photovoltaic, reversible heat pumps, biomass and thermal energy storage are competitive when properly integrated. Furthermore, the sale of renewable electricity to the grid under a net‐billing scheme, with suitable electricity sale prices, is an appropriate approach, aligned with the European climate and energy policy. Nevertheless, the current Spanish self‐consumption regulation is mostly appropriate for small‐medium size residential buildings. Evaluation of different technologies such as renewable energy, heat pumps, energy storage, among others, in the pathway to achieve sustainable energy systems for residential buildings considering the current Spanish legal restrictions, stablishing guidelines for the proper design of polygeneration systems for residential buildings at an affordable cost, aligned with short term EU objectives on climate change, as well as with the objective of reaching affordable carbon neutral energy systems for buildings in the long term of 2050.

Hybrid polygeneration systems offer a great opportunity to meet growing energy demands with cost efficiency and environmental benefits. The identification of the optimal solution (configuration and operational strategy) is strongly affected by the relationship between the system and its surroundings. Previous studies have analyzed the influence of boundary conditions on the synthesis of polygeneration systems for buildings. However, local regulations are often disregarded or oversimplified in those studies. Therefore, this paper aims to evaluate the influence of legal conditions on the integration of renewable energy technologies in polygeneration systems for buildings. A comprehensive synthesis model is developed, including different types of legal conditions, such as power exchange modalities, subsidies/surcharges on energy prices and investment costs, and total ban on fossil fuels. Then, the model is applied to the case study of a Brazilian hospital. The current Brazilian net metering scheme is implemented. Results show that natural gas cogeneration is an attractive solution to cover the hos-pital's energy demands with or without the possibility of selling/exporting electricity. Also, the Brazilian net metering scheme, by itself, is not enough to ensure renewable energy deployment. An in-depth discussion about the conditions that would promote renewable energy integration is reported and recommendations are made on how current policies can be improved, including the need to explicitly address renewable technologies, the application of minimum renewable fractions, and the role of renewable heat/cooling. While the case study considers the specific circumstances in Brazil, it provides insights that can be extended to other countries or applications.

Renewable energies can play a very important role in the development of a new energy model contributing effectively towards a more sustainable development in the mid and long term. In this context Central Solar Heating Plants with Seasonal Storage (CSHPSS) are able to provide space heating and Domestic Hot Water (DHW) to residential buildings with high solar fractions (>50%). These systems are already being used in Central and Northern Europe, as well as in Canada, where there is an important experience in district heating systems. The study presented herein presents an environmental assessment, applying the Life Cycle Assessment (LCA) method, of a CSHPSS, which should cover the space heating and DHW demand of 500 dwellings of 100 m2, located in Zaragoza, Spain. Environmental burdens through the life cycle of the system are estimated based on greenhouse gas emissions, and comprehensive environmental indicators as the ReCiPe and Cumulative Energy Demand (CED). These indicators allow to evaluate the reduction of the environmental load achieved by the CSHPSS analyzed with respect to conventional space heating and DHW systems, as well as to identify the most critical aspects from the environmental perspective. In this article, the environmental behavior of the CSHPSS is decoupled into the two demands covered, heating and DHW, in order to quantify the environmental impact of each generation system. A detailed life cycle inventory is presented with the aim of promoting the development of increasingly efficient technologies from the environmental point of view, not only in the operation phase but also in the construction of the equipment. Furthermore, an in-depth analysis is performed to evaluate the variation of the environmental impact depending on the climatic conditions. The CSHPSS is also dimensioned in different Spanish cities and a LCA is carried out for nine locations. The results can help different stakeholders to make decisions in order to optimize the renewable energy generation systems taking in account its whole life cycle and to point out the necessity to evaluate the environmental impact essentially in the production phase for all renewable energy systems. Share Link: https://authors.elsevier.com/a/1dK0I3QCo9bNRq