1. Introduction
In recent years, due to political and economic events in the world that have largely hit European Union (EU) countries, in particular, the armed conflict between Ukraine and Russia, interest in renewable energy sources (RES) technologies has increased significantly. The relevance of RES installation technology growth in the EU is affirmed by a number of actions, funds and policies [
1]. The latest legislative changes in the EU assume the achievement of very ambitious goals, including the usage of RES in the total energy mix up to at least 40% by 2030, cutting greenhouse gas emissions to 55% from 1990 levels and reaching climate neutrality by 2050 [
2]. These activities are expected to have a remarkable impact on stimulating sustainable development in the UE countries but also reducing energy-import dependency [
3]. The EU has identified the energy transition as a critical strategic goal in its efforts to address climate change and enhance energy security [
4]. As RES technologies continue to evolve and become more widely adopted, their impact is likely to become even more significant.
Currently, systems with PV panels and heat pumps (HPs) of various types are the most dynamically developing sector in environmentally friendly technologies. In particular, PV energy is gaining interest internationally and in the EU as a provider of low-cost, energy-efficient and clean energy [
5]. In 2021, 18.7% of the world’s total PV capacity, which corresponds to 158 GW, was installed in EU [
6]. Germany leads the way with PV capacity installed of 58.5 GW, second is Italy with 22.7 MW and third is France with 14.7 GW [
6]. The expansion of the PV installations market is particularly visible in Poland, which ranked 10th in the world regarding investment made in new PV power capacity installed in 2021 [
2]. It is expected that there will be further growth of PV capacity in Poland, reaching approximately 7.3 GW in 2030 and 16 GW in 2040 [
7].
Over the past few years, HPs technology has also made great inroads into the EU market by increasing energy efficiency, reducing greenhouse gas emissions and promoting RES. HPs are now particularly seen as devices that can significantly reduce energy consumption in buildings for both heating and cooling purposes. According to the European Heat Pump Association, the HPs market in Europe has been growing steadily over the last decade and in 2021 have exceeded 34%, surpassing two million units sold per year for the first time [
8]. This big growth has been driven by several factors, including increasing energy prices, energy efficiency regulations and the push towards decarbonization. ASHPs have the largest share in the HPs market in 2021, which is equal to 94% with the remaining 6% being ground- or water-based [
4]. ASHPs are considered less expensive compared to other existing HP-based technologies.
There is a need to develop solutions that will help maximize the use of energy generated from RES and reduce or even limit existing development barriers [
9]. Such issues include the problem of insufficient use of generated electricity in PV on-grid microinstallations (<50 kWp) in residential buildings. The coefficient of SC is used to determine the degree of use of the generated energy in a PV installation. It can be calculated as the share of the self-consumed energy
ESC in total energy generated
Egen in the PV system as shown by the following equation:
SC parameter is calculated over an assumed period of time, usually during a given day, month or year. It can be a value between 0% and 100%, where 100% means that all
Egen is consumed by the loads and 0% means that the entire stream of generated electricity was transferred to the grid (in on-grid PV system). The greater the SC value, the higher the profits associated with the operation of PV systems [
10]. It also brings other positive aspects, which include the reduction of energy losses in the network, increased grid stability due to lower load fluctuations, reduced energy costs for consumers due to self-sufficiency and lower electricity storage capacity, enabling reduction in the capacity of conventional power plants in the long term to promote the integration of renewable energy and reduce the need for power system infrastructure improvements [
11]. Additionally, the growth of SC in PV installations is a major issue due to the fast-growing number of such systems and the overloading in the distribution grid [
12], which can lead to grid instability and, in extreme cases, problems with electricity availability and inverters operation [
13].
In the literature, some ways to grow SC parameter in PV systems have been reported. In the article [
2], the authors pointed out that installing a smart monitoring system for tracking energy usage patterns and identifying areas for improvement maximizes SC. Moreover, in shifting energy consumption devices (washing machines, dishwashers, dryers or electric vehicles) to daytime hours when energy from solar radiation is being generated [
12] and using energy management tools that adjust and optimize in real-time, energy consumption and usage will have a positive effect on this parameter [
14]. Similar conclusions were presented in the paper [
15], where a model for adequate matching of PV power for prosumers was proposed, taking into consideration the day-ahead load distribution. On the other hand, in the paper [
16], the authors indicated that determining the appropriate size of the PV system and installing a battery storage system which can store excess energy produced during the day for later use, increases SC during non-sunlight hours. An interesting proposal related to hydrogen generation can also be found in the paper [
16], in which the authors suggested producing green hydrogen during water electrolysis from solar-generated electricity. Moreover, a good solution is skilfully combining PV systems with RES-based electrical equipment, such as HP, to produce heat and/or cooling [
17].
When investigating the feasibility of the above-mentioned solutions, it is important to bear in mind the savings generated by greater self-consumption, resulting in a shorter investment payback time, which is usually the main parameter considered by investors [
18]. It should also be noted that current battery technologies suffer from short lifetimes and high initial investment costs correlated with the storage capacity [
19]; shifting energy consumption devices to daytime hours in most cases could be difficult or sometimes almost impossible and cause a loss of comfort for users of these devices [
18].
A number of articles have analysed ways and results of increasing SC values. In the study [
20], the comparison of demand response and battery operations focused on increasing SC and storing surplus PV energy have been presented. In the article [
21], the author presented results from grid-connected PV installations without storage systems and special energy management systems where reported SC from around 16% to 50% in a one-year period. The improvement of SC with different approaches (demand-side management, battery storage or a mix) allows obtaining SC from 28% to 78%. In the next article [
19], authors proposed and implemented a predictive control model which improved the PV SC by 19.5%. In a subsequent article [
18], in PV microinstallation in a household located in Poland, the authors reported SC equal to 27% for the PV system facing south and 30% for the PV system facing east–west. The review paper [
10] summarized research in the field of SC in residential PV systems, with two techniques in particular: battery storage and demand side management. In the paper [
17], authors analysed a new control strategy for the operation of an ASHP, based on the actual PV availability. The results showed an increase in system SC by 22% in comparison to a standard control strategy, taking into account a highly insulated building in Bolzano, Northern Italy [
17]. The paper [
22] analysed self-producing and sharing electricity with distributed rooftop PV systems and HP. In conclusion, the authors showed that PV installation could help decrease operating costs for district heating systems with large numbers of HP [
22]. In the article [
23], authors presented the results of SC under various installed capacity conditions, orientation and inclination of the PV panels in Córdoba, Spain. In another study [
24], authors proposed a simulation model for residential PV–battery systems under Spanish regulation. The solutions proposed in the work allowed for achieving SC growth by 25% [
24]. In the simulation work [
25], authors evaluated terms of performance control strategies for the heating system with ASHP and PV installation and utilization of energy in storage in a single-family house. Results show that using developed algorithms leads to greater final energy savings and a higher SC parameter [
25]. A smart charging plan for electric vehicle in residential buildings based on installed PV power output and electricity consumption were presented in [
26]. The main conclusion of the research was that minimizing the net load variability implies increasing the PV self-consumption and reducing the peak loads [
26]. As pointed out in [
27], using a heuristic scheduling optimize system of HP and PV can achieve a high level of SC. The results show that an intelligent control algorithm allows for obtaining SC values from 25.3% to 41.0% during a year [
27].
In spite of the growing interest in SC in PV installation in recent years, studies on this topic are still quite scarce and should be further investigated [
10]. This paper’s aim is to complement previous research and to analyse the results of one year-round operation of a PV array grid-connected hybrid installation with ASHP for a domestic hot water (DHW) system in a residential building in Cracow, Poland, in the context of increasing SC of energy. The term hybrid installation means that RES-consuming devices work together to achieve a reduction in the overall electrical energy drawn from the grid, which contributes to cheaper overall operational costs of the installation [
28]. Models of systems with PV panels and other devices are built and simulated in Transient System Simulation Tool (TRNSYS) 18 software. TRNSYS, thanks to the flexibility of the software and the high number of available components presented as black boxes called “types”, allows the building of sophisticated systems with RES. Simulations were carried out for different scenarios involving different building electricity consumption profiles, PV system capacity and specified runtime management of ASHP. The novelty of this study is the evaluation of the impact of a certain range of conditions on the energy performance of the system, particularly on SC.
This paper is structured as follows: In
Section 2, the simulation model, location and consumption profiles are presented and an overview is provided of the devices and details of the simulation settings used (specification of installation components in TRNSYS and their pre-set main parameters).
Section 3 provides and discusses the results for the considered various systems parameters. The paper ends in
Section 4 with conclusions and recommendations.