• Energy Research

Economic support policies are widely adopted in European countries in order to promote a more efficient energy usage and the growth of renewable energy technologies. On one hand these schemes allow us to reduce the overall pollutant emissions and the total cost from the point of view of the energy systems, but on the other hand their social impact in terms of economic investment needs to be evaluated. The aim of this paper is to compare the social cost of the application of each incentive with the correspondent CO2 emission reduction and overall energy saving. A Mixed Integer Linear Programming optimization procedure is used to evaluate the effect of different economic support policies on the optimal configuration and operation of a distributed energy supply system of an industrial area located in the north-east of Italy. The minimized objective function is the total annual cost for owning, operating and maintaining the whole energy system. The expectation is that a proper mix of renewable energy technologies and cogeneration systems will be included in the optimal solution, depending on the amount and nature of the supporting policies, highlighting the incentives that promote a real environmental benefit.

AbstractIn order to reduce the environmental impact caused by merchant ships, the International Maritimes Organization is imposing new and stricter regulations on NOx and SOx emissions. Therefore, ships propelled by Internal Combustion Engines (ICEs) burning HFO must adopt abatement devices or switch to a cleaner fuel such as MGO. If the use of MGO is considered, a further and more drastic modification of the power system can be analyzed, namely the use of Gas Turbines (GTs) in place of ICEs. GTs are an attractive solution thanks to a reduced weight, size and NOx emissions, but are penalized by a lower electric efficiency. The case of a real cruise ship is considered in the present paper and a detailed quantification of the above mentioned differences is provided by simulating the ship operation for a reference trip.

The paper deals with the modelization and optimization of an integrated multi-component energy system. On-off operation and presence-absence of components must be described by means of binary decision variables, besides equality and inequality constraints; furthermore, the synthesis and the operation of the energy system should be optimized at the same time. In this paper a hierarchical optimization strategy is used, adopting a genetic algorithm in the higher optimization level, to choose the main binary decision variables, whilst a MILP algorithm is used in the lower level, to choose the optimal operation of the system and to supply the merit function to the genetic algorithm. The method is then applied to a distributed generation system, which has to be designed for a set of users located in the center of a small town in the North-East of Italy. The results show the advantage of distributed cogeneration, when the optimal synthesis and operation of the whole system are adopted, and significant reduction in the computing time by using the proposed two-level optimization procedure.

In recent years, ship builders and owners have to face a great effort to develop new design and management methodologies that lead to a reduction in consumption and emissions during the operation of the fleet. In the present study, the optimization of an on-board energy system of a large cruise ship is performed, both in terms of energy and of the overall dimensions of the system, while respecting the environmental constraint. In the simulation, a variable number of identical Organic Rankine Cycle (ORC)/Stirling units is considered as an energy recovery system, bottoming the main internal combustion engines, possibly integrating with the installation of photovoltaic panels, solar thermal collectors, absorption refrigeration machines and thermal storages. The optimization takes into account the effective optimal management of the energy system, which is different according to the different design choices of the energy recovery system. Two typical cruises are considered (summer and winter). To reduce the computational effort for the solution of the problem, a bi-level strategy has been developed, which prescribes managing the binary choice variables expressing the existence or not of the components by means of an evolutionary algorithm, while all the remaining choice variables are obtained by a mixed-integer linear programming model of the system (MILP) algorithm. The entire procedure can be defined within the commercial software modeFRONTIER®.

The paper presents the results of a research regarding the application of cogeneration plants, based on Organic Rankine Cycle (ORC), fed with wood residuals. In the first part of the paper an energy audit of the companies in a furniture industry district, located in the North-East of Italy, is presented. On the basis of these data a typical electricity/thermal demand profile dependent on the number of employees has been determined. In order to evaluate the potential savings achievable with an ORC cogeneration plant, a numerical simulation model has been developed to analyse the energy balances of the components as well as the whole ORC power plant performance. The effects on the system energy and exergy efficiencies of different binary and ternary mixtures of polisiloxane as working fluid and of different operating modes (cogeneration or pure electricity production) have been analysed, also in off-design conditions.

This paper deals about the application of MILP for economic optimization of complex cogenerative systems. In particular, it optimizes both the size and operating strategy of CHP systems and the lay-out of micro district heating networks applied to a urban contest. The proposed model considers the possible adoption of a set of micro-cogeneration gas turbines located in different buildings, and of a centralized cogeneration system thus allowing part of the required thermal energy to be produced in a single site. In addition, thermal and photovoltaic panels can be integrated into the system to improve thermal and electrical energy production, respectively. Each site can be connected to the others through district heating micro-grids. Hence thermal energy can be distributed inside the system. A further objective of the paper is to evaluate the effect of different economic support policies on the optimal solution, and to relate the economic effort implied in each support policy with the expected results in terms of CO2 emissions reduction and primary energy savings.

The International Maritime Organization (IMO) has developed new and stricter rules about environmental impact of big vessels. Those rules are going to widen significantly the so called Emission Controlled Areas (ECA) and to generally gain more control over pollution levels over the seas. The solution that most ship-owners are going to prefer is most likely to be the implementation of pollutant emissions reducing systems, such as Scrubbers and Selective Catalytic Reactor Systems, to dampen emissions produced by the present propulsion systems, based on Internal Combustion Engine (ICE) which burns the cheap but polluting Heavy Fuel Oil (HFO). An alternative solution, based on the adoption of Gas Turbines (GT) in the propulsion system, fuelled by Marine Gas Oil (MGO), can be taken into account, allowing considerable savings in weight and space occupied and lover NOx as well as SOx emissions than those of ICEs, even if with a loss in the engine efficiency (Armellini et al., 2018). In this paper, the possibility of using simultaneously ICEs and GTs as well as the use of trigeneration system is analyzed, with the aim of exploiting the positive feature of both the engine systems. The paper provides a quantitative comparison among different hybrid engines configurations (ICEs and GTs working together) making reference to a large cruise ship as a real case. Considering a cruise ship rather than a cargo ship implies an important and time-dependent thermal energy demand, so that an onboard trigeneration system may result a convenient solution.