Krzysztof Mik

This paper investigates the use of a hybrid renewable heat-supply system based on photovoltaic–thermal collectors, an industrial heat pump, thermal energy storage, and electrical energy storage for a small- to medium-scale district-heating network. A dynamic lumped-parameter model was developed and applied to hourly data from an existing network. The photovoltaic–thermal collector model accounts for low-temperature operation, wind effects, precipitation, and condensation-related heat gains, while the heat pump is represented using compressor performance characteristics under variable source and sink temperatures. The analysis focuses on whether the proposed configuration can meet summer heat demand and reduce reliance on a conventional peak or backup source during shoulder periods. The results show that, during an extended non-heating season, the system can supply approximately 90–100% of the district-heating demand while maintaining a daily mean coefficient of performance in the range of approximately 2.0–3.1. The photovoltaic–thermal field and electrical energy storage do not provide full electrical self-sufficiency, but they reduce grid electricity import; in July and August, the electricity autarky coefficient is approximately 48–49%. The results indicate that the proposed system can serve as a seasonal renewable heat source for district heating. Further refinement of the configuration, operating setpoints, and control strategy could improve its shoulder-season performance.

Two types of full-size photovoltaic modules for on-grid systems with maximum DC voltage of 600 V have been developed and prepared for production. With carefully selected materials and dedicated manufacturing processes the weight of 3.5 and 3.2 kg, the power as high as 220 and 200 Wp and efficiencies of 20.1 and 21.3% were obtained. Together with standard mounting systems the devices make it possible to build non- intrusive installations on low-load capacity roofs with various types of covering, particularly in large-scale lightweight buildings.

The compliance with international standards does not necessarily ensure a long-term reliability of photovoltaic modules. Field tests are required to make the standard tests more adjusted to the evaluation of new concepts. Numerous researches focus on long-term performance of standard modules, but only few studies are dedicated to lightweight modules. Therefore, the field operation of a PV system consisting of 28 lightweight modules of 4 different types (denoted as P1, P2, P3 and P4) has been being monitored for a year in warm temperate climate conditions. Over this period, the modules were tested by visual inspection, thermography and electroluminescence imaging and their electrical parameters were measured to compare results with the outcome of simulations in PVsyst. Visual inspections revealed yellowing and delamination of a few P2 and P4 modules. Thermography exposed many hot spots and failure of substrings in case of P2 modules. Also, the electroluminescence imaging showed numerous defects, mostly various micro cracks, which affected all modules’ types. Nevertheless, excluding P2 modules, the others generated higher yield than estimated by the simulations. Analysing year-to-year degradation, results for P3 and P4 were in line with results predicted for standard PV modules in similar climates.

Dynamic growth of photovoltaic capacity in Poland encourages many entities to invest in photovoltaic systems. However, in the case of buildings with low roof-bearing capacity it can be problematic or even impossible to mount conventional PV modules due to their relatively high weight. Hence, the use of lightweight PV modules is a potential solution. In this paper four different prototype silicon lightweight modules of novel structure manufactured by the Xdisc S.A have been investigated in terms of their electrical and thermal features. The measurements showed that all prototypes have efficiency exceeding 19.5% and power in range of 214 to 242 Wp at standard test conditions. Their area density is about 3.5 kg/m² which is typical for lightweight modules. In turn, the Power-to-Weight Ratio exceeds 40 W/kg threshold and in one case reaches almost 58 W/kg. Thanks to the measurements, the prototypes could be modelled in PVsyst (PVsyst SA, Satigny, Switzerland). The performed simulations of an example PV system revealed that installations based on prototypes have comparable performance to a conventional installation. Nevertheless, at current prices they are less profitable than the standard system and it shows the need for future cost reductions in the manufacturing process. The proposed materials selection may be the starting point for search of inexpensive substitutes of these materials which still conserve modules high performance. A system based on the prototypes can still prove advantageous when simplicity and promptness outweigh higher initial costs.

A photovoltaic thermal solar collectors (PVT) and heat pump combined system consists of numerous elements. In this context it is important to properly model respective elements. To the best of our knowledge there is no relative research that has optimized PVT geometry to maximize heat generation for the ground regeneration. Therefore, the authors decided to investigate the influence of bottom insulation and air gap thickness on heat generation in case of glazed and unglazed PVT. The results show that the optimum construction of the PVT should be based on the unglazed technology of solar collector and on minimum insulation thickness. Obviously, the thickness of insulation needs to be optimized to the specific conditions like for instance type and depth of borehole heat exchangers or parameters of the heat pump.