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Bifacial solar panels installed on flat rooftop of industrial buildings are an effective way to boost the yield. The albedo of the flat roof determines to great extent the bifacial gain. However, because it changes due to soiling and moss growth, the power output of bifacial PV installations over time is difficult to calculate. For the purpose of evaluating and rating the effect of bifacial PV rooftop systems, a small plant with 20 modules including dummies was installed. To guarantee an optimized output, a commercial bifacial PV module supporting construction was placed on a flat roof that was painted white. By using an east-west orientation, an optimum for the use of available roof space was reached. The yield for each module was determined with power optimizers and the extracted data, provided by the monitoring portal, were analysed. The data were collected for each day over a time of one year. Three different modules, both east and west orientated, were investigated. The bifacial module with a transparent backsheet compared to a module with the same bifacial cells but with a black backsheet, showed initially a benefit of 17% for the east and 15% for the west orientated panels. After one year of operation, a measured benefit of 7% for the east and 5% for the west orientated panels remained due to albedo loss because of moss growth and pollution. The use of panels with 92% bifaciality resulted in a higher yield of up to 3% compared to panels with 70% bifaciality.

The press-pack packaging technology has been adopted in recent years for insulated-gate bipolar transistors (IGBTs) to be utilized in high voltage–high current applications, such as high-voltage direct current (HVdc) electric power transmission. Traditionally, the heat management of such systems is based on water coolant; however, there are numerous challenges associated with that method, such as the requirement to deionize the water to prevent electrical potentials and inherent problems of corrosion and leakage in the cooling piping structure. This article presents the design and development of a liquid metal heat sink for press-pack IGBTs. The use of a thermal management system based on liquid metal increases the heat dissipation capability without corroding the cooling structure. Analytical work is performed on the design of the heat sink. Moreover, the thermal performance of the heat sink is experimentally validated against a commercial water-based cooling system. The presented results show that the cooling performance of the liquid metal system is increased, whereas the shortcomings of the water-based system are eliminated.

Integration of Photovoltaics (PV) with Energy Storage Systems (ESS) and Demand Side Management (DSM) is an innovative way that could transform a building into a self-sufficient nanogrid. Such an approach could act as an energy rehabilitation solution and contribute to alleviating the technical problems posed to the electrical grid from high consumption of buildings and high PV injections. The scope of this paper is to investigate the potential for achieving high level of building self-sufficiency using hybrid PV-ESS-DSM solutions. Towards this direction this work analyzes the self-consumption and self-sufficiency rates for various installations equipped with PV and ESS with different climatic and load demand characteristics. Moreover, the potential for increasing these indices under DSM is examined aiming to maximize the utilization of renewable energy produced on-site.

Photovoltaic (PV) installations grow exponentially, and the mismatch between generation and demand will adversely affect the stability of the grid. This paper presents a modified operational mode of a grid-connected hybrid PV and battery energy storage system (BESS) in Cyprus. The BESS is coupled with residential rooftop PVs and is functioning under an operational mode aiming to decrease the peak power fed into the grid by storing the excess PV generation. The stored energy is then used to cover the mismatch between generation and demand, thus also increasing the on-site PV self-consumption. Given the favourable environmental conditions in Cyprus, with increased PV generation especially during summer, a significant amount of excess PV generation exported to the grid is still observed, as the BESS is usually fully charged before noon. For this reason, a modification of the operational mode of the aforementioned BESS was performed, aiming to reduce the building’s interaction with the electricity grid during peak export hours by delaying the BESS charging process. An analysis of the system’s operation during that period and its contribution towards grid interaction limitation is presented.

Power modules are the most common components to fail in power converters that are employed in mass transportation systems, thus leading to high unscheduled maintenance cost. While operating, high junction temperature swings occur that result in high thermomechanical stress within the structure of the power module, reducing the lifetime of the module. Liquid metals as a cooling medium received so far little attention in the area of power semiconductor cooling, despite being able to remove high heat fluxes. This paper shows for the first time how liquid metal is used to reduce actively the junction temperature swing. A magnetohydrodynamic (MHD) pump has been designed for this purpose allowing active control of the flow rate of the liquid metal that impinges against the baseplate of the module. The pump has been 3-D printed and is attached directly to the power module. A closed-loop temperature control system is implemented, able to estimate the insulated-gate bipolar transistor's junction temperature, and thus, controls the MHD power. This paper presents simulation and experimental results showing reductions in the temperature swing over the full load cycle with 12 °C as the highest observed reduction rate. This paper also shows detailed designs of the MHD pump and the controller hardware.