Modeling of an Integrated Renewable-Energy-Based System for Heating, Cooling, and Electricity for Buildings

An integrated numerical model that describes the operation of a renewable-energy-based system for a building’s heating, cooling, and domestic hot water needs is described in this study. The examined energy system includes a vapor compression multi-source heat pump, PVT collectors, borehole thermal energy storage, and water tanks. Energy balance equations for the collectors and the tanks are coupled with correlations for the heat pump and the piping losses within a thermal network approach. The non-linear system of equations that arises is solved by employing in-house software developed in Python v. 3.7.3. The performance of the numerical tool is validated against measurements collected during the pilot operation of such a system installed in Athens (Greece) for two 5-day periods (summer and winter). It is shown that the proposed model can predict, both qualitatively and quantitatively, the building’s energy system performance, whereas limited deviations from the experimental findings are mostly observed when highly transient phenomena occur. The numerical tool is designed with flexibility in mind and can be easily adapted to accommodate additional energy-system configurations and operational modes. Thus, it can be utilized as a supporting decision tool for new energy systems’ designs and the optimization of existing ones

EVALUATING THE FACTORS AFFECTING THE BREAK-EVEN COST OF ON-SITE PV GENERATION AT INDUSTRIAL UNITS

This paper studies the way in which the regulatory framework and market rules affect the feasibility of on-site PV generation for large industrial units. In most European markets net metering and feed-in tariffs for selfconsumed electricity are not possible or are being phased out, providing an incentive to the industry for becoming more flexible in the way electricity is consumed in order to maximise the percentage of the variable electricity generated on-site that is self-consumed. The electricity cost for the industry is the benchmark for PV or any other onsite generation technology and in general on-site solar energy is competitive with that. However, as the regulation develops further, the exemptions of paying the regulated charges for the electricity that is self-consumed are phased out. Also the cost of flexibility required to self-consume all variable on-site generation has to be added to the LCOE of solar electricity, moving it further away from the competitiveness benchmark. Still, as the LCOE of solar electricity reduces continuously mostly due to the reduction of PV system costs, it becomes competitive for more and more users in more and more target markets

Parametric comparison of a CPVT performance evaluation under standard testing procedures - ISO 9806:2017 and IEC 62108:2016 - for an automated and manual 2-axis tracking solar system stand

Currently, a noticeable lack of literature with respect to a wide-ranging comparison of the precision exhibited by automated and manual two-axis tracking solar systems, particularly within the context of adhering to the standard testing protocols delineated by ISO and IEC. To address this research gap, a symmetrical concentrating Photovoltaic-Thermal solar collector underwent a detailed evaluation encompassing two standard testing procedures such as ISO 9806:2017 and IEC 62108:2016. This comprehensive assessment covered thermal and electrical performance parameters, unfolding across two distinct geographical locations: Athens (Greece) and Gävle (Sweden). Within this experimental framework, an automated two-axis tracking solar system stand was employed at the Greek testing site, while in Sweden it was characterized by the employment of a manual two-axis tracking solar system. The collective peak power performance presented marginal divergence within a narrow range of ± 1% across both testing sites. This culminated in an overall peak power output of 1550 Wpeak, which included an electrical peak capacity of 218 Wpeak and a thermal peak power of approximately 1332 Wpeak. Notably, the most pronounced deviation has been materialized in the transversal and longitudinal Incidence Angle Modifier coefficients, with disparities remaining limited to a threshold of < 5%. These findings underscore the commendable precision hallmarking. In summary, the outcomes presented in this study not only contribute to the extant body of knowledge by bridging the existing gap in literature, but also emphasize the precision inherent to manual two-axis tracking solar systems when compared with automated equivalents.

A Fast CFD-Based Methodology for Determining the Cyclic Variability and Its Effects on Performance and Emissions of Spark-Ignition Engines

A methodology for determining the cyclic variability in spark-ignition (SI) engines has been developed recently, with the use of an in-house computational fluid dynamics (CFD) code. The simulation of a large number of engine cycles is required for the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) to converge, usually more than 50 cycles. This is valid for any CFD methodology applied for this kind of simulation activity. In order to reduce the total computational time, but without reducing the accuracy of the calculations, the methodology is expanded here by simulating just five representative cycles and calculating their main parameters of concern, such as the IMEP, peak pressure, and NO and CO emissions. A regression analysis then follows for producing fitted correlations for each parameter as a function of the key variable that affects cyclic variability as has been identified by the authors so far, namely, the relative location of the local turbulent eddy with the spark plug. The application of these fitted correlations for a large number of engine cycles then leads to a fast estimation of the key parameters. This methodology is applied here for a methane-fueled SI engine, while future activities will examine cyclic variations in SI engines when fueled with different fuels and their mixtures, such as methane/hydrogen blends, and their associated pollutant emissions