Techno-economic optimization and analysis of a high latitude solar district heating system with seasonal storage, considering different community sizes (original) (raw)
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Design and Optimization of a De-Centralized Community Sized Solar Heating System for Nordic Region
Proceedings of SWC2017/SHC2017, 2017
There is a need to accelerate the application of advanced clean energy technologies to resolve the challenges of climate change. Solar heating is a feasible solution among clean energy technologies. These technologies are not yet highly used in high latitudes due to various challenges. This paper focuses on the community sized solar district heating system configuration for cold climates. The proposed configuration consists of a partially decentralized heating system. Each individual house heat pump was connected between large centralized solarcharged low temperature tank and smaller decentralized individual high temperature tank in each house. Additionally, the large centralized tank was directly charged by solar-charged borehole storage during winters. Dynamic simulation approach was used through TRNSYS software coupled with MOBO (multi-objective building optimizer) for NSGA-II optimization algorithm. The purchased electricity and investments were two objectives minimized. The impact of the energy system on the renewable energy fraction, purchased electricity and investments as a function of the building heating demand, collectors and photovoltaic areas, short-term tanks storages and boreholes volumes were evaluated. Results showed that purchased electricity varied 47 kWh/m 2 /yr-25 kWh/m 2 /yr and renewable energy fraction 75%-91%.
Applied Energy, 2018
Solar thermal energy is widely recognized as one of the most important renewable energy resources. However, in high latitudes, due to various climatic and mismatch challenges, such solar district heating networks are difficult to implement. The objective of the paper is to optimize and compare two different design layouts and control strategies for solar district heating systems in Finnish conditions. The two different designs proposed are a centralized and a semidecentralized solar district heating system. The centralized system consists of two centralized short-term tanks operating at different temperature levels charged by a solar collector and heat pumps. Borehole thermal energy storage is also charged via these two centralized tanks. In contrast, the semi-decentralized system consists of one centralized low temperature tank charged by a solar collector and a borehole thermal energy storage and decentralized high temperature tank charged by an individual heat pump in each house. In this case, borehole thermal energy storage is charged only by the centralized warm tank. These systems are designed using the dynamic simulation software TRNSYS for Finnish conditions. Later on, multi-objective optimization is carried out with a genetic algorithm using the MOBO (Multiobjective building optimizer) optimization tool, where two objectives, i.e. purchased electricity and life cycle costs, are minimized. Various design variables are considered, which included both component sizes and control parameters as inputs to the optimization. The optimization results show that in terms of life cycle cost and purchased electricity, the decentralized system clearly outperforms the centralized system. With a similar energy performance, the reduction in life cycle cost is up to 35% for the decentralized system. Both systems can achieve close to 90% renewable energy fraction. These systems are also sensitive to the prices. Furthermore, the results show that the solar thermal collector area and seasonal storage volume can be reduced in a decentralized system to reduce the cost compared to a centralized system. The losses in the centralized system are 40-12% higher compared to the decentralized system. The results also show that in both systems, high performance is achieved when the borehole storage is wider with less depth, as it allows better direct utilization of seasonally stored heat. The system layout and controls varied the performance and life cycle cost; therefore it is essential to consider these when implementing such systems.
Renewable Energy, 2017
This paper proposes various community-sized solar heating systems configurations for cold climate. Three configurations were proposed, (I)a heat pump connected to two tanks in parallel, using charged borehole storage, (II)a heat pump connected between two tanks, using charged borehole storage to directly charge the lower temperature tank, and (III)two heat pumps used in series, one between the tanks and the other between the lower temperature tank and ground. In configurations (I) and (II) the vertical borehole field is used as a seasonal storage, in (III) it is used to extract heat only. The studied energy flows are heat and electricity. The border consists of energy production systems, heating grid and buildings. The impact of the considered system solutions on the heating renewable energy fraction, on-site electrical energy fraction, purchased energy and full cost as a function of the demand, solar thermal and photovoltaic areas, tanks and borehole volumes has been evaluated. The dynamic simulations results shows that an average renewable energy fraction of 53-81% can be achieved, depending upon the energy systems' configuration. Furthermore, Energy System II utilizes less energy compared to other systems. In all three systems medium-sized solar thermal area is more beneficial instead of large area.
Renewable Energy, 2018
Solar energy use in Nordic countries suffers from a high seasonal mismatch of generation and demand. However, given a large enough community, seasonal thermal storage could be utilized to store summertime heat gains for use in winter. This simulation study examined a Finnish case of fully electric solar heating, where heat pumps (HP) powered by photovoltaic (PV) panels were used for generating heat for both immediate use and for seasonal storage through a borehole thermal energy storage (BTES) system. Multi-objective optimization of LCC and energy use was performed by a genetic algorithm and TRNSYS simulations. Comparison was done between communities of a 100 and 500 buildings. The need for purchased electricity was between 40 and 26 kWh/m 2 per year for the optimal configurations. For the same cases the life cycle cost was between 220 and 340 V/m 2. Up to 98% renewable energy fraction was obtained for heating, showing that even in Finland it is possible to provide practically all heating by solar energy. The PV-type heating system was also compared to a solar thermal heating system from a previous study and it was found that the new design had as much as 36% lower life cycle cost.
Energy Conversion and Management, 2019
Climate change is one of the biggest challenges at the present time, and to tackle such issue, solar energy and efficient buildings, in general, can be used. The goal is to design and optimize photovoltaic based decentralized district heating system and later compare it-economically and technically-against three different optimized typologies of solar district heating system in Nordic conditions. The photovoltaic based decentralized system consists of one centralized low temperature tank charged by photovoltaic and air-water heat pumps and a borehole thermal energy storage, while the decentralized high temperature tank charged by an individual water-water heat pump in each house. The centralized warm tank charges the borehole thermal energy storage. The other three systems are photovoltaic based centralized, roof-mounted solar thermal based centralized and roof-mounted solar thermal based decentralized district heating systems. In solar thermal based systems, collectors are used to directly charge the short-term storage tanks instead of the photovoltaics/heat pump combination. The proposed system is simulated using TRNSYS software. Lastly, purchased electricity and life cycle costs of the system are minimized using multi-objective optimization and the genetic algorithm. The results indicated that the decentralized photovoltaic based system outdoes all the other systems in terms of techno-economic performance. The purchased electricity can be reduced by 22% while at the same time life cycle cost can be reduced up to 40%, compared to the worst optimized system (solar thermal based centralized system). Moreover, the decentralized photovoltaic based energy system has a payback period of 9-27 years, compared to the solar thermal based system and the conventional single building-heat pump system, i.e. around 17-58 years and 15 years, respectively. The highest renewable energy fraction for heating can be close to 99% for this system. The decentralization and electrical based district systems are better in terms of life cycle cost, payback period and in terms of technical performance, compared to traditional single house and solar thermal based district heating systems.
A Model for Simulation and Optimal Design of a Solar Heating System with Seasonal Storage
A thermo-economic model for the simulation and optimization of a Central Solar Heating Plant with Seasonal Storage (CSHPSS) is presented. The model, written in Matlab, is used to investigate the effects of different design variables on thermal performance and cost. Daily and seasonal variations of solar irradiation at different latitudes are considered, and an original approximate model for thermal stratification is included. The simulation model has been also integrated with a non-linear constrained optimization procedure, in order to determine the optimal choice of design variables for different locations and operating conditions.
Energy Conversion and Management, 2022
Utilizing solar energy for heat supply can reduce CO 2 emissions and mitigate global climate change. In the Nordic region (e.g., Iceland and Finland), a tremendous seasonal mismatch exists between the availability of solar radiation and building heating demand. This paper proposes a local hybrid energy system based on solar energy for a residential district. It applies a borehole thermal energy storage to store solar energy in non-heating seasons, and uses stored energy for part of total heating demand in a residential neighbourhood in heating seasons. Photovoltaic panels are used to generate electricity for heat pump operation. To find out cost-optimal and ecofriendly solutions, the local energy system was first modelled and simulated in TRNSYS. Then, genetic algorithms were applied to optimize the system performance and costs. In optimal solutions, 38%-58% of total heating demand could be covered by on-site heat energy with the levelized cost of energy of 110-184 €/MWh. On this basis, importing additional electricity from grid to increase the utilization rate of air-to-water heat pumps can further increase the on-site heat energy fraction to 41%-88% with the levelized cost of energy of 108-201 €/MWh. Compared with the situation of fully district heating input, the proposed system can annually reduce CO 2 emissions by 102-217 tons with the rate of 31-66%. Although the initial cost of the studied system is higher than that of district heating, the local hybrid energy system is worth further developing considering decentralizing heat energy production and reducing CO 2 emissions.
Optimization of operating strategies in a community solar heating system
Applied Mathematical Modelling, 1985
Minimization of auxiliary energy costs is discussed for heating in a district solar heating system with effective heat storage. The minimization problem is approached by dynamic programming which gives an optimal operating strategy for the auxiliary energy system. The effects of different pricing schemes of auxiliary energy (electricity) have been studied. The results show that with an adequate heat storage capacity, the optimization of the auxiliary energy use in a community solar heating system may lead to considerable cost savings.
2016
Buildings represent 40% of the Union’s final energy consumption; the member states should establish a strategy to improve the energy performance in buildings and reduce the consumption of non-renewable primary energy. In Spain, the implementation of the Technical Building Code (CTE) compels to install solar thermal collectors in new buildings providing a minimum solar contribution of domestic hot water (DHW). In north and center European countries, e.g. Denmark, Germany and Austria, new installations also supply heat for the space heating needs. The approach of central solar heating plants with seasonal storage (CSHPSS) is the storage of solar thermal energy from the period of higher offer (summer) to be consumed in the periods of higher demand (winter). These installations are integrated into district heating systems that supply heat for a large number of dwellings and reach a solar fraction of 50% or higher. In this thesis the experience gained in Europe on centralized solar distr...