Abstract
This work presents an optimization strategy and the cost-optimal design of an off-grid building served by an energy system involving solar technologies, thermal and electrochemical storages. Independently from the multi-objective method (e.g., utility function) and algorithm used (e.g., genetic algorithms), the optimization of this kind of systems is typically characterized by a high-dimensional variables space, computational effort and results uncertainty (e.g., local minimum solutions). Instead of focusing on advanced optimization tools to handle the design problem, the dimension of the full problem has been reduced, only considering the design variables with a high “effect” on the objective functions. An off-grid accommodation building is presented as test case: the original six-variable design problem consisting of about 300,000 possible configurations is reduced to a two-variable problem, after the analysis of 870 Monte Carlo simulations. The new problem includes only 220 possible design alternatives with a clear benefit for the multi-objective optimization algorithm. The energy-economy Pareto frontiers obtained by the original and the reduced problems overlap, showing the validity of the proposed methodology. The No-RES (no renewable energy sources) primary energy consumption can be reduced up to almost 0 kWh/(m2yr) and the net present value (NPV) after 20 years can reach 70 k€ depending on the number of photovoltaic panels and electrochemical storage size. The reduction of the problem also allows for a plain analysis of the results and the drawing of handy decision charts to help the investor/designer in finding the best design according to the specific investment availability and target performances. The configurations on the Pareto frontier are characterized by a notable electrical overproduction and a ratio between the two main design variables that goes from 4 to 8 h. A sensitivity analysis to the unitary price of the electrochemical storage reveals the robustness of the sizing criterion.
Highlights
Planning in the medium-long term the construction of an integrated thermal and electrical energy production system fed by renewable sources is certainly a tricky but interesting investment decision that occurs under multiple uncertainties
Critical issues typically addressed are: the number of different energy sources to be included into the Hybrid Renewable Energy Systems (HRES); the type of technology of the generation sub-systems; the design parameters of the HRES; the strategies used for decision assessment
The correlation analysis shows the importance of the multi-objective approach in HRES design: a single-objective optimization, e.g., economic goal, would not consider the PV system sizing as a design variable to be optimized, disregarding the significant effect of this variable on the energy system
Summary
Planning in the medium-long term the construction of an integrated thermal and electrical energy production system fed by renewable sources ( known as hybrid renewable energy systems, HRES) is certainly a tricky but interesting investment decision that occurs under multiple uncertainties. Modern HRES are generally integrated (electrical, thermal components and buildings), made of highly-coupled subsystems where different technologies (e.g., renewable energy systems and traditional generators) cooperate for concurrent multiple objectives, such as reliability, cost efficiency, environmental sustainability, indoor comfort, and indoor air quality [12]. This condition calls for a robust and more integrated approach to the evaluation of the best system design, able to deal with the increasing complexity of the decision context, an accurate but efficient dynamic modeling of components interconnections, and decision tools able to address the stakeholders towards the most efficient and cost-effective solutions [13,14,15]
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