Holistic performance evaluation of integrated solar systems for sustainable building practices

Abstract: The integration of solar technologies into building surfaces is among the recommended strategies of the International Energy Agency for achieving Net-Zero Emissions by 2050. Given the variability of solar technologies in the market, namely, PV panels, PVT panels, and solar thermal panels (SDWH), and the high dependence of these technologies' performance on site characteristics, arriving at an optimal decision and a better understanding requires a thorough and comprehensive evaluation approach. This study provides a holistic approach to the performance evaluation of photovoltaic (PV), photovoltaic/thermal (PVT), and solar thermal systems for building integration. The evaluation encompasses the 4E criteria: Energy, Exergy, Environment, and Economy, ensuring a multidimensional analysis of each system's performance. By leveraging empirical data and advanced simulation tools, the study examines the energy yields, exergy efficiencies, environmental impacts, and economic feasibility of each technology under Moroccan market conditions as a case study. The findings offer valuable insights for stakeholders aiming to optimize solar integration for sustainable building practices. This research not only aids in selecting the most suitable solar technology for specific applications but also contributes to the broader goal of sustainable development and energy transition in Morocco.

Keywords: Solar energy, Numerical simulation, DWH, Energy efficiency, Environmental performance, LCC, Payback period.

Introduction

Based on the latest data published by the International Energy Agency, almost one-third of global final energy consumption is attributed to the operation of the building sector [1]. This energy use primarily involves heating, cooling, and the operation of various household appliances. Meanwhile, these types of energy demands can be met sustainably through the use of building-integrated solar technologies. Hence, of the most encouraged strategies for building sector decarbonizing is the increase of renewable energy resources installed capacity [1]. Accordingly, several countries have defined nationally determined contributions, towards their climate targets, that concerns the increase of buildings integrated solar capacity [2].

The mature solar technologies for buildings use are PV panels, PVT panels, and Solar Thermal panels. With each technology specification, advantages, and limitations they all exhibit a high-performance dependence on sites characteristics. Through a literature review, the weather conditions [3], the government’s policies [4], the market prices[5], and the conventional resources tariffs were all stated to influence the performance of each of the solar technologies[6]. Combined they contribute to the fact that what could be energetically beneficial will not always translate to being economically and/or environmentally beneficial [7]. 

Hence, in order to make a well-informed decision in regard to what would be the best solution of solar technology for integration into the buildings, a holistic approach should be adopted, where performance dependant inputs-as mentioned above- should be considered and performance from a multidimensional perspective should be evaluated.

For this purpose, the aim of this study is to provide a holistic approach to compare and analyse the energetic, exergetic, economic, and environmental performances of three solar systems for building integration: PV, PVT, and Solar thermal systems. And as a case study, the Moroccan building sector characteristics were taken into consideration.

Methodology

To estimate the energetic performance of the three studied systems, PV, PVT, and Solar Thermal, the well-known Trnsys software for dynamic simulations was adopted. A simplified generalized representation of components simulated are represented in Figure 1. For PV and PVT, the thermal behaviour in terms of cells temperature under the dynamic weather conditions were taken as input to a Sandia Lab code developed in Matlab software-for better and more reliable electrical yield estimation [8]. The two mathematical models were validated, and good agreement was found between experimental and numerical models’ output. Hourly weather data for a whole year in terms of ambient temperature, wind velocity, and solar irradiation were taken from Meteonorm software for the six climatic zones of Morocco [9]. A typical house of a family of five members was considered, and technical characteristics of the studied systems were gathered. Annual simulations were conducted, and 4E analysis was followed. For energetic performance analysis, the useful thermal energy, the thermal efficiency, the electrical power, the electrical efficiency, and the solar fraction were calculated following the equations defined in Table 1. For exergy analysis, similarly, the total exergy input, the electrical exergy output, the thermal exergy output, the thermal exergy, and the electrical exergy were considered. And for environmental performance the potential of CO₂ emissions mitigation was estimated as defined in Table 1. For the economic performance, and in order to dive deeper into the comparison between the studied solar technologies, two approaches were adopted, the Payback Period analysis, and the Life Cycle Cost analysis. For both approaches several scenarios inspired from the case of the Moroccan building sector were considered, as represented in Figure 2. And they were regarding, subsidy over the initial cost of the installations, the conventional systems replaced-usually used by the houses, and the subsidy currently adopted by the Moroccan government through which the consumer pay only a third of the real price of the gas purchased.

Figure 1.simplified and generalized representation of components simulated for the three studied systems [7].

Table 1. The equations used for the energetic, exergetic, and environmental analysis.

Results and discussion

As mentioned, the analysis was conducted for the six climatic zones of Morocco. In Figure 3, the results regarding the annual energy yield in kWh per climate region per system and the results of the environmental analysis in terms of potential CO₂ mitigation are represented. As it can be seen, the Solar Thermal system produces the highest annual thermal energy, due to its higher thermal efficiency that varies between 40% to 46% depending on the climate zone. The PV system produces almost the same amount of electrical energy as of the PVT one, where for the first one the annual electrical efficiency varied between 10.2 % and 11%, and for the second one it ranged between 10.2% to 10.5%. The PVT system was found to produce higher total energy compared to PV system due to the dual production of heat and electricity, with that it has the highest total exergy efficiency that attend 12.3%. While for the solar thermal, the maximum was only 3.5%, and for the PV system it was 11.12%. Regarding the environmental performance, as it can be seen in Figure 3, the PV system was found to mitigate the least amount of emissions due to its lower energy efficiency. The PVT and the Solar Thermal systems exchange the first and the second position depending on the conventional system they are supposed to replace, either it is a butane gas boiler or an electrical heater, where the latter has a higher CO₂ emission coefficient. Economically, the PV system was found to have the shortest PBs, that varies around two years for the scenarios where the initial cost is considered with a 20% subsidy, and around 4-5 years for the scenarios when no subsidy is considered. The economical performance of the PVT and the Solar Thermal systems are highly sensitive to the conventional systems considered to be replaced.  When the solar systems replace an electrical heater, both systems have PBs, while PVT system is better than Solar Thermal. And regarding the LCC, economical savings are achieved for all studied scenarios, with again PVT performing better. Meanwhile, When the solar systems are supposed to replace a gas heater, the Solar Thermal system is found to be non-viable economically, while PVT have BPs that varies between 19-22 years. LCC wise, the two solar systems PVT and SDWH are more expensive than the conventional energy system.

Conclusion

A well-informed decision from a private consumer, or a well-adjusted policy from a stakeholder, regarding solar technology integration into the building sector, demand a thorough analysis of performance. Hence, in this study a multidimensional analysis based on a 4E approach: Energy, Exergy, Environmental, Economical performance, was proposed and conducted. Taking into consideration the case study of the Moroccan building sector. Trnsys and Matlab software were used for mathematical modelling, and technical specifications of the studied systems, namely, PV, PVT, and Solar Thermal systems were considered. A summarized ranking of performance of the systems is presented in Table 2, where from a holistic point of view it can be seen that the PVT solution is the most suitable solar technology for building integration in the Moroccan case.

Table 2. The ranking order of the three solar systems studied based on their performances.

References

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