Investigation of the Influence Mechanism and Analysis of Engineering Application of the Solar PVT Heat Pump Cogeneration System

Abstract

Amidst the ongoing global energy crisis, environmental deterioration, and the exacerbation of climate change, the development of renewable energy, particularly solar energy, has become a central topic in the global energy transition. This study investigates a solar photovoltaic thermal (PVT) heat pump system that utilizes an expanded honeycomb-channel PVT module to enhance the comprehensive utilization efficiency of solar energy. A simulation platform for the solar PVT heat pump system was established using Aspen Plus software (V12), and the system’s performance impact mechanisms and engineering applications were researched. The results indicate that solar irradiance and the circulating water temperature within the PVT module are the primary factors affecting system performance: for every 100 W/m² increase in solar irradiance, the coefficient of performance for heating (COP_h) increases by 13.7%, the thermoelectric comprehensive performance coefficient (COP_co) increases by 14.9%, and the electrical efficiency of the PVT array decreases by 0.05%; for every 1 °C increase in circulating water temperature, the COP_h and COP_co increase by 11.8% and 12.3%, respectively, and the electrical efficiency of the PVT array decreases by 0.03%. In practical application, the system achieves an annual heating capacity of 24,000 GJ and electricity generation of 1.1 million kWh, with average annual COP_h and COP_co values of 5.30 and 7.60, respectively. The Life Cycle Cost (LCC) is 13.2% lower than that of the air-source heat pump system, the dynamic investment payback period is 4–6 years, and the annual carbon emissions are reduced by 94.6%, demonstrating significant economic and environmental benefits. This research provides an effective solution for the efficient and comprehensive utilization of solar energy, utilizing the low-global-warming-potential refrigerant R290, and is particularly suitable for combined heat and power applications in regions with high solar irradiance.

1. Introduction

Against the backdrop of an escalating global energy crisis, deteriorating environmental conditions, and the persistent intensification of climate warming, the advancement of renewable energy has emerged as a pivotal agenda in the worldwide energy transition. In China, the Energy Law has institutionalized the principle of prioritizing renewable energy development, thereby accelerating the decarbonization of the national energy mix [1]. Among these resources, solar energy—distinguished by its abundance, cleanliness, intrinsic safety, and extensive accessibility—has gained extensive deployment globally. The technological pathways for harnessing solar energy are primarily categorized into photovoltaic power generation and solar thermal utilization.

In recent years, China has achieved remarkable progress in both technological innovation and industrial capacity across these domains. By the end of 2023, the nation’s installed photovoltaic capacity had reached 609 GW, securing the global lead for an unprecedented eleven consecutive years [2]. Similarly, China’s installed capacity of solar thermal systems attained 375 GW, representing approximately 70% of the global market share [3].

With the maturation of building-integrated photovoltaics (BIPV), zero-energy buildings, and renewable energy systems, conventional photovoltaic (PV) and solar heat collection (ST) technologies have increasingly revealed intrinsic limitations—namely, single-output capacity, poor operational flexibility, and low efficiencies in solar energy capture, equipment utilization, and spatial deployment. To address these constraints, researchers have developed photovoltaic–thermal (PVT) technology, which integrates PV power generation with ST harvesting within a single module.

A PVT module typically comprises a PV layer with an integrated heat exchanger on its rear surface. Solar irradiation in the 0.3–1.1 µm wavelength range is absorbed by the PV cells and converted into electricity, while radiation in other spectral bands is predominantly captured by the heat exchanger and converted into thermal energy. This configuration not only cools the PV cells—thereby improving their electrical conversion efficiency—but also enables cogeneration of electricity and heat [4].

The concept was first proposed by Kern and Russell in 1978 [5], who incorporated fluid channels into the rear of PV modules to dissipate excess heat and recover usable thermal energy. Subsequent studies by Florschuetz [6] and Raghuraman [7] on flat-plate PVT collectors laid the theoretical and experimental groundwork for this integrated approach. Research in this field has since concentrated on developing high-efficiency PVT modules and optimizing PVT systems through modeling, simulation, and performance evaluation.

Substantial work has focused on optimizing PVT module structural parameters, coolant channel geometries, and PV cell coverage ratios. Raghuraman [7] established a mathematical model for water- and air-cooled PVT collectors to evaluate their thermo-electrical performance and overall solar utilization efficiency. Fujisawa [8] applied exergy efficiency concepts to compare flat-plate ST collectors with both glazed and unglazed PVT designs, finding that PVT collectors achieved superior annual exergy performance. Brinkworth [9] demonstrated significant gains in electrical output through both air and liquid cooling of PV modules. Sandnes and Rekstad [10] advanced module fabrication by directly laminating monocrystalline cells onto black polymer absorber plates, followed by theoretical and experimental performance assessments. Chow [11] developed a dynamic simulation framework for tube–plate PVT collectors with and without glazing, enabling detailed evaluation of thermal, electrical, and combined performance metrics. In China, Pei [12,13] investigated parametric influences—such as glazing configuration, PV coverage, coolant flow rate, and ambient conditions—using both energy and exergy analyses. Liu [14] examined the effect of structural parameters on the integrated opto-thermal–electrical performance of PVT assemblies, while An [15] compared different cooling techniques for PV cells under varying solar irradiance, elucidating the thermal, electrical, and cogeneration efficiency trade-offs.

Beyond component-level design, numerous studies have explored PVT system modeling and optimization. Imre [16] examined architectural integration strategies for PVT modules. Bergene [17] reported that PVT systems can achieve combined efficiencies of 60–80%, markedly higher than stand-alone PV or ST systems. Brinkworth [9] investigated façade- and rooftop-integrated PVT systems, while Thomas [18] demonstrated successful engineering-scale deployment. Comparative investigations [19,20] have analyzed water-cooled, air-cooled, concentrating, and non-concentrating PVT configurations—both glazed and unglazed—through experimental trials, techno-economic assessments, and annual performance evaluations. Zakharchenko [21] optimized PVT designs across multiple PV technologies and cooling approaches. In China, Ji [22,23,24,25,26] proposed multiple variants, including PVT water heaters and PV–Trombe walls, supported by rigorous theoretical and experimental validation. Xu [27] tested a low-concentration PVT heat pump hybrid system, achieving a photovoltaic efficiency of 17.5% and an average heating COP of 4.8. Further studies [28] on concentrating hybrid systems have combined numerical simulation with experimental characterization to examine in-module fluid flow and heat transfer mechanisms.

While considerable research has been conducted on PVT technology and its integration with heat pumps, studies focusing on the detailed influence mechanisms of PVT heat pump systems remain relatively scarce. This gap limits the theoretical foundation available for optimizing system design and control strategies in real-world engineering applications.

Furthermore, the environmental sustainability of the working fluid is equally crucial. The transition towards low-global-warming-potential (GWP) refrigerants is imperative to mitigate direct emissions from heating and cooling systems.

To address this, the present study develops a comprehensive simulation platform for a solar PVT heat pump cogeneration system that employs the low-GWP refrigerant R290 (propane) [29]. This platform enables in-depth investigation of the key factors influencing system performance under different external conditions. Furthermore, using a collaborative innovation center in Hainan Province as a case study, the work analyzes annual energy production, techno-economic feasibility, and environmental benefits. The results provide a theoretical basis and practical reference for the engineering application of PVT heat pump technology, particularly in regions with high solar and ambient temperature.

2. System Description

2.1. PVT Module

The interlayer configuration of the inflated honeycomb-channel PVT module employed in this study is illustrated in Figure 1. From top to bottom, the layered assembly comprises a glass cover plate, an array of PV cells, a PV backsheet, and an inflated heat exchanger plate, all integrally bonded through thermal lamination. On the front side, the module accommodates a 6 × 12 array of monocrystalline silicon PV cells, as shown in Figure 2a. The rear side houses its core heat-exchange component—an inflated plate incorporating a honeycomb-channel architecture, as depicted in Figure 2b.

The honeycomb-channel configuration is derived from a periodic hexagonal-cell topological array. The porous cellular structure facilitates radial redistribution of the working fluid and induces three-dimensional flow perturbations. This geometry maintains intrinsically low hydraulic resistance while markedly increasing turbulence intensity and the contact surface area between the fluid and channel walls. Consequently, convective heat transfer is significantly intensified, thereby enhancing the module’s overall thermal exchange performance.

2.2. Principle of Solar PVT Heat Pump System

The operational principle of the solar PVT heat pump system is illustrated in Figure 3. The primary components of the system comprise the PVT array, evaporator, condenser, compressor, and expansion valve. The key technical specifications of the major system components are listed in

Table 1. Specification of main equipment.

Equipment	Parameter	Value
PVT module	Dimensions	1950 × 986 × 25 mm
	Flow channel configuration	Honeycomb type
	Effective flow channel volume	3.0 L
	Flow channel width	10 mm
	Flow channel height	2.5 mm
	Photovoltaic cell type	Monocrystalline silicon
	Rated peak electrical power	330 W
	Photovoltaic conversion efficiency	17.1%
	Temperature coefficient	−0.4%/°C
	Installation tilt angle	40°
	Quantity of modules	330
Heat pump unit	Refrigerant type	R290
	Rated heating capacity	550 kW
	Rated input power	105.2 kW
	Rated coefficient of performance (COP)	5.23
	Refrigerant mass flow rate	5700 kg/h
	Water flow rate on evaporator side	77 m3/h
	Inlet water temperature on evaporator side	20 °C
	Outlet water temperature on evaporator side	25 °C
	Water flow rate on condenser side	95 m3/h
	Inlet water temperature on condenser side	45 °C
	Outlet water temperature on condenser side	50 °C

.

The system operates through two sequential heat exchange processes.

Heat transfer from the PVT module to the circulating water: When solar radiation strikes the PVT module, a portion is converted into electricity by the PV cells, while the remaining energy is absorbed as heat, raising the temperature of the cells and the attached absorber plate. The circulating water is pumped through the network of narrow, interconnected honeycomb channels on the rear plate. This design creates a large contact area between the water and the hot absorber surface. Heat is transferred from the solid absorber plate to the flowing water primarily via forced convection. The honeycomb structure promotes turbulent flow, which significantly enhances the convective heat transfer coefficient, thereby efficiently capturing the thermal energy and raising the water temperature.

Heat transfer from the water to the refrigerant in the evaporator: The heated water exiting the PVT array is directed to the evaporator of the heat pump unit. The evaporator is a tube-in-shell or plate heat exchanger where this water stream flows on one side. The refrigerant (R290) flows on the other side at a lower pressure and temperature. As the warm PVT-loop water passes through the evaporator, thermal energy is transferred across the metal walls of the heat exchanger to the cold refrigerant. This energy causes the liquid refrigerant to evaporate into a vapor. Consequently, the water is cooled and pumped back to the PVT array to be reheated, completing its loop. The now gaseous refrigerant, having absorbed the low-grade heat from the water, is then compressed to begin the condensation and space-heating cycle.

It is noteworthy that the PVT module in this system operates in an indirect heat transfer configuration, where circulating water serves as the intermediary fluid between the PVT absorber and the refrigerant loop. This design contrasts with direct-expansion PVT systems, in which the refrigerant flows directly through the PVT channels. While direct-expansion configurations can potentially reduce thermal resistance and improve heat exchange efficiency, they also introduce challenges such as refrigerant maldistribution, complex pressure management, and higher refrigerant charge—issues that are mitigated in indirect systems. The indirect approach adopted here enhances operational stability, simplifies maintenance, and facilitates integration with conventional heat pump units, making it particularly suitable for medium- to large-scale engineering applications.

2.3. Performance Evaluation of Solar PVT Heat Pump System

In this study, the performance of the solar PVT–heat pump system is evaluated in terms of the heating performance coefficient, heating capacity, electrical efficiency, and thermoelectric comprehensive performance coefficient.

The coefficient of performance for heating is determined according to Equation (1):

$$\begin{array}{c}CO{P}_{\mathrm{h}}=Q_{\mathrm{c}}/W_{\mathrm{c}}\end{array}$$

(1)

where COP_h represents the heating performance coefficient of the system; Q_c represents the heating capacity of the system, in kW; and W_c represents the input power of the heat pump compressor, in kW.

The heating capacity is determined according to Equation (2):

$$\begin{array}{c}{Q}_{\mathrm{c}}=c_{\mathrm{P},\mathrm{w}}{m}_{\mathrm{w}}\left(T_{\mathrm{w},\mathrm{con},\mathrm{o}}-T_{\mathrm{w},\mathrm{con},\mathrm{in}}\right)\end{array}$$

(2)

where m_w represents the circulating water flow at the condensing side of the system, in kg/s; c_p,w represents the specific heat of water, in kJ/(kg·k); and T_w,con,in and T_w,con,o represent the inlet and outlet water temperature of the condenser, respectively, in kJ/kg.

The electrical efficiency is determined according to Equation (3):

$$\begin{array}{c}{\eta }_{\mathrm{e}}={\displaystyle \frac{W_{\mathrm{e}}}{n{A}_{\mathrm{PVT}}I/1000}}\times 100\%\end{array}$$

(3)

where η_e represents the electrical efficiency, in %; W_e represents the power generation of the PVT array, in kW; n represents the number of the PVT array; A_PVT represents the area of the PVT module, in m²; and I represents the solar irradiance, in W/m².

The thermoelectric comprehensive performance coefficient is determined according to Equation (4):

$$\begin{array}{c}CO{P}_{\mathrm{co}}=\left(Q_{\mathrm{c}}+W_{\mathrm{e}}/{\eta }_{\mathrm{power}}\right)/W_{\mathrm{c}}\end{array}$$

(4)

where COP_co represents the thermoelectric comprehensive performance coefficient of the system, and η_power represents the thermoelectric conversion coefficient (generally 38%), in %.

3. Establishment and Verification of Simulation Platform for Solar PVT Heat Pump System

3.1. Establishment of System Simulation Platform

The simulation platform for the solar PVT heat pump system is constructed entirely within the Aspen Plus software (V12) environment. The heat pump unit model is built using the software’s built-in modular components, while the PVT module is implemented as a user-defined custom model based on its mathematical formulations of thermal and electrical performance.

3.1.1. Mathematical Model of Solar PVT Module

Considering the cogeneration characteristics of PVT modules, mathematical models of thermoelectric performance of PVT modules are established [30,31].

The thermal efficiency of the PVT module indicates the ratio of its heat-absorbing quantity to the incident solar thermal energy, and the calculation formula of the thermal efficiency of the PVT array is shown in Equation (5):

$$\begin{array}{c}{\eta }_{\mathrm{th}}={\displaystyle \frac{Q_{\mathrm{PVT}}}{n{A}_{\mathrm{PVT}}I/1000}}\times 100\%={\displaystyle \frac{c_{\mathrm{P},\mathrm{w}}{m}_{\mathrm{w},\mathrm{PVT}}\left(T_{\mathrm{PVT},\mathrm{o}}-T_{\mathrm{PVT},\mathrm{in}}\right)}{n{A}_{\mathrm{PVT}}I/1000}}\times 100\%\end{array}$$

(5)

where η_th represents the thermal efficiency of the PVT modules, in %; Q_PVT represents the heat-absorbing quantity of the PVT modules, in kW; A_PVT represents the area of the PVT modules, in m²; n represents the number of PVT modules; m_w,PVT represents the circulating water flow of PVT, in kg/s; and T_PVT,in and T_PVT,o represent the inlet and outlet water temperatures of the PVT modules, respectively, in °C.

The electrical efficiency of the PVT module is affected by the area of the PVT module, solar irradiance, the temperature of the PVT module, and other factors, and its calculation formula is shown in Equation (6) [32]:

$$\begin{array}{c}{\eta }_{\mathrm{e}}={\eta }_{\mathrm{ref}}\left[1-\beta \left(T_{\mathrm{PVT}}-T_{\mathrm{ref}}\right)\right]\end{array}$$

(6)

where η_ref represents the power generation efficiency of solar cells under standard test conditions, in %; β represents the temperature coefficient of the PVT module, in %/°C; T_PVT represents the temperature of the PVT module in °C; and T_ref represents the temperature of the PVT module under standard test conditions, generally 25 °C.

3.1.2. Simulation Platform of the PVT Heat Pump System

The simulation model of the PVT heat pump system was developed using Aspen Plus software (V12), a robust process simulation tool widely employed in energy system modeling. Aspen Plus was selected for its integrated thermophysical property database, which includes accurate fluid properties essential for refrigerant and water cycles, and its ability to interface with external property databases such as REFPROP for enhanced accuracy. The software employs an equation-oriented approach to solve system-wide mass and energy balances, making it suitable for steady-state and dynamic simulations of integrated energy systems.

In this study, component models for the heat pump unit (e.g., evaporator, condenser, compressor, expansion valve) were constructed using lumped-parameter methods, which is a common approach for system-level performance evaluation. The PVT module was implemented within Aspen Plus as a user-defined custom model, based on the mathematical formulations described in Equations (5) and (6). This enabled direct integration of the PVT thermal and electrical performance models into the system simulation, allowing coupled analysis of thermal and electrical outputs under varying solar irradiance and operating conditions. The Aspen Plus model of the PVT heat pump system is illustrated in Figure 4.

The circulating water, driven by a pump (PUMP), flows into the PVT modules where it absorbs both solar and ambient energy, thereby being heated. It then enters the evaporator (EVAP) of the heat pump unit, transferring its thermal energy to the refrigerant, after which it is pumped back to the PVT array to repeat the heating cycle. Within the heat pump cycle, the refrigerant flows sequentially through the evaporator, compressor (COMPR), condenser (COND), and expansion valve (VALVE), completing a vapor-compression refrigeration loop. Meanwhile, low-temperature water from the storage tank is driven by another pump into the condenser (COND), where it absorbs heat from the refrigerant. The heated water then returns to the tank, continuously supplying thermal energy in a closed loop.

In this paper, the rated installed capacity of the heat pump unit is 550 kW, and the temperature of the prepared hot water is set at 50 °C. Combined with the mathematical model of the PVT module, this model can simulate the operating characteristics of the heat pump system under different environmental temperatures, solar irradiance, and PVT circulating water temperature by adjusting the inlet and outlet water temperature of the evaporation side, water flow rate of the evaporation side, and refrigerant flow rate. Based on this, the performance influence mechanism of the solar PVT heat pump system can be studied.

3.2. Verification of System Simulation Platform

The simulation model was validated against experimental data reported in the literature for a comparable PVT heat pump system [33]. The referenced system comprises a PVT array and a borehole array, which together serve as the compound heat source/sink for a water-loop heat pump. Through valve control in the hydraulic circuit, the system can operate in multiple configurations, including a mode in which the PVT array directly supplies heat to the heat pump—a configuration that aligns with the system studied in the present work. Under typical heating operation, its coefficient of the heating performance ranged from 5.8 to 6.3.

In this work, the same performance indicators—heating capacity and COP—were compared between the present simulation results and the experimental measurements reported in [33]. As shown in Figure 5, the maximum deviation between simulated and experimental values does not exceed 10.0%, which falls within the widely accepted uncertainty margin for thermodynamic system simulations reported in similar studies. Therefore, the established system model can be considered sufficiently accurate and reliable for the subsequent simulation analyses conducted in this study.

4. Analysis of Performance Influence Mechanism of Solar PVT Heat Pump System

For the solar PVT heat pump system, the performance of the system is mainly affected by environmental temperature, solar irradiance, and the temperature of circulating water of the PVT modules. In this paper, the solar PVT heat pump system is used to prepare 50 °C hot water. The solar irradiance is set to 1000 W/m², 800 W/m², 600 W/m², 400 W/m², and 200 W/m², respectively, and the ambient temperature changes between 20 °C and 35 °C. The circulating water temperature of the PVT module is set to 20 °C, 22 °C, 24 °C, and 24 °C.

4.1. Analysis of Influence Mechanism of System Thermal Performance

This section analyzes the influence of ambient temperature, solar irradiance, and circulating water temperature in the PVT module on COP_h and the heating capacity of the solar PVT heat pump system.

4.1.1. Analysis of Influence Mechanism of System COP_h

The influence of ambient temperature, solar irradiance, and circulating water temperature in the PVT module on COP_h of the solar PVT heat pump system is shown in Figure 6.

As the solar irradiance increases, the heat-absorbing quantity of the PVT array correspondingly escalates, prompting an elevation in the operational frequency of the heat pump unit’s compressor. This results in a gradual enhancement of the heat pump unit’s partial load ratio, thereby transitioning the unit towards its high-efficiency operational zone, which in turn leads to a progressive increase in the COP_h. However, with a further augmentation of solar irradiance, the heat-absorbing quantity of the PVT array continues to rise, causing the partial load ratio of the heat pump unit to increase further. Consequently, the heat pump unit begins to deviate from its high-efficiency zone, resulting in a gradual decline in COP_h. At lower solar intensities, for every 100 W/m² increase in solar irradiance, COP_h increases by 0.33, representing an increment of 13.7%. Conversely, at higher solar intensities, for every 100 W/m² increase in solar irradiance, COP_h decreases by 0.38, indicating a decrement of 10.0%.

As the circulating water temperature within the PVT module gradually increases from 20 °C to 30 °C, the system’s evaporative temperature correspondingly rises, thereby leading to a progressive enhancement in the COP_h. For every 1 °C increment in the circulating water temperature within the PVT array, the COP_h increases by 0.36, representing an augmentation of 11.8%.

Conversely, the ambient temperature exhibits a relatively minor influence on the system’s COP_h. This phenomenon is primarily attributed to the minimal impact of ambient temperature variations on the heat collection capacity of the PVT module. Consequently, the circulating water temperature within the PVT array undergoes only slight changes, resulting in a negligible effect on the evaporative temperature of the solar PVT heat pump system. Therefore, the system’s COP_h experiences only minor fluctuations.

4.1.2. Analysis of Influence Mechanism of System Heating Capacity

The influence of ambient temperature, solar irradiance, and circulating water temperature in the PVT module on the heating capacity of the solar PVT heat pump system is shown in Figure 7.

With the escalation of ambient temperature, the thermal efficiency of the PVT module experiences a slight increase, which in turn leads to a marginal rise in the heat-absorbing quantity of the PVT module. This results in a modest enhancement in the system’s heating capacity. For every 1 °C increase in ambient temperature, the system’s heating capacity increases by 0.083 kW, representing an increment of 0.17%.

In contrast, as the solar irradiance increases, the heat-absorbing quantity of the PVT array undergoes a significant enhancement. Consequently, both the operational frequency and the partial load ratio of the heat pump unit exhibit substantial increases, leading to a marked improvement in the system’s heating capacity. On average, for every 100 W/m² increase in solar irradiance, the system’s heating capacity increases by 53.58 kW, indicating an increment of 50.9%.

However, with the rise in the circulating water temperature within the PVT module, the thermal efficiency of the PVT module decreases, resulting in a reduction in its heat-absorbing quantity and, subsequently, a decrease in the system’s heating capacity. For every 1 °C increase in the circulating water temperature within the PVT module, the system’s heating capacity decreases by 2.57 kW, representing a decrement of 2.2%.

4.2. Analysis of Influence Mechanism of System Electrical Performance

The power generation and electrical efficiency of the solar PVT heat pump system are important indexes to evaluate the electrical performance of the system, and they are mainly affected by solar irradiance and circulating water temperature in the PVT module. The influence of solar irradiance and circulating water temperature in the PVT module on the power generation and electrical efficiency of the solar PVT heat pump system are shown in Figure 8 and Figure 9, respectively.

As the solar irradiance increases, the power generation of the PVT array correspondingly escalates. For every 100 W/m² increment in solar irradiance, the power generation increases by 8.84 kW, representing a significant enhancement of 52.1%.

Conversely, as the circulating water temperature within the PVT module increases, the power generation decreases. On average, for every 1 °C increase in the circulating water temperature, the power generation decreases by 0.21 kW, indicating a decrement of 0.80%.

As the solar irradiance increases, the electrical efficiency of the PVT array correspondingly decreases. For every 100 W/m² increment in solar irradiance, the electrical efficiency of the system decreases by 0.05%.

Conversely, as the circulating water temperature within the PVT module increases, the electrical efficiency of the PVT array decreases. On average, for every 1 °C increase in the circulating water temperature, the electrical efficiency decreases by 0.03%.

4.3. Analysis of Influence Mechanism of System Thermoelectric Comprehensive Performance

The thermoelectric comprehensive performance coefficient of the solar PVT heat pump system is an important parameter to comprehensively evaluate the cogeneration capacity of the system, which is mainly affected by the environmental temperature, solar irradiance, and circulating water temperature in the PVT module. The influence of ambient temperature, solar irradiance, and circulating water temperature in the PVT module on the heating capacity of the solar PVT heat pump system is shown in Figure 10.

With the increase in solar irradiance, both the heat-absorbing quantity and power generation of the PVT array increase. Consequently, the partial load ratio of the heat pump unit increases, prompting the unit to gradually operate within its high-efficiency zone. As a result, the rate of increase in the system’s power consumption gradually diminishes, leading to an enhancement in the system’s COP_co. However, as the solar irradiance continues to rise, despite the concurrent increase in both heat-absorbing quantity and power generation of the PVT array, the partial load ratio of the heat pump unit further increases. This causes the unit to gradually transition towards a lower efficiency zone, resulting in a progressive increase in the system’s power consumption, thereby causing the system’s COP_co to decline. At lower solar intensities, for every 100 W/m²; increase in solar irradiance, COP_co increases by 0.51, representing an increment of 14.9%. Conversely, at higher solar intensities, for every 100 W/m²; increase in solar irradiance, COP_co decreases by 0.58, indicating a decrement of 10.4%.

As the circulating water temperature within the PVT module rises, both the thermal and electrical efficiencies of the PVT module decrease, leading to a reduction in the system’s heating capacity and power generation. However, due to the elevated evaporative temperature, the compression ratio of the heat pump unit decreases, resulting in a significant reduction in the system’s power consumption. Ultimately, this leads to an increase in COP_co. For every 1 °C increase in the circulating water temperature within the PVT module, the system’s COP_co increases by 0.54, representing an increment of 12.3%.

The ambient temperature exhibits a relatively minor influence on the system’s COP_co. This is primarily because the variations in ambient temperature have a minimal impact on both the heat-absorbing quantity and power generation of the PVT module, thereby resulting in only slight changes in the system’s COP_co.

5. Solar PVT Heat Pump System Engineering Application

5.1. Engineering Application Overview

The solar PVT heat pump system is applied to supply 50 °C hot water at a collaborative innovation center in Hainan Province, China. The system’s total heating capacity is 5500 kW, comprising ten sets of solar PVT heat pump units, each with a rated heating capacity of 550 kW. The number of installed solar PVT modules amounts to 3300 units. The collaborative innovation center in Hainan Province, China, experiences relatively high ambient temperatures and strong solar irradiance throughout the year. The environmental conditions are depicted in Figure 11, with the annual maximum temperature reaching 36.4 °C, the minimum temperature at 10.0 °C, and an average temperature of 24.3 °C. The annual maximum solar irradiance is 1024.3 W/m², with a total annual sunshine duration of 4554 h, and the period during which the solar irradiance exceeds 200 W/m² spans over 2200 h. These local environmental conditions provide an excellent foundation for the high-efficiency heating performance of the solar PVT heat pump system.

5.2. Annual Production Capacity Analysis of Solar PVT Heat Pump System

Utilizing the solar PVT heat pump system simulation platform established in this study, in conjunction with the annual meteorological parameters of a collaborative innovation center in Hainan Province, China, the annual capacity characteristics and performance of the system in this region can be ascertained, as illustrated in Figure 12. The system’s annual total heating capacity amounts to 24,000 GJ, with a maximum heating power of 5728.0 kW, enabling the production of 1.15 million tons of 50 °C hot water throughout the year. The annual total power generation is 1.1 million kWh, with a maximum generation power of 947.2 kW. The total annual power consumption of the solar PVT heat pump system is 1.23 million kWh, with a maximum input power of 1123.2 kW. Considering the power generation from the PVT array, the system’s actual annual electricity purchase from the grid totals 0.12 million kWh. The annual average COP_h of the solar PVT heat pump system is 5.30, with an annual operational duration of 2252 h and a maximum COP_h of 6.12. The system’s COP_co has an annual average value of 7.60, with a maximum value of 8.92. In summary, the application of the solar PVT heat pump system at the collaborative innovation center in Hainan Province, China, demonstrates the capability for green, efficient, and low-carbon heating.

5.3. Economic Analysis of Solar PVT Heat Pump System

This study employs the Life Cycle Assessment (LCA) method [34] to comprehensively evaluate the economic viability of the solar PVT heat pump system applied at a collaborative innovation center in Hainan Province, China, and compares it with the economic performance of traditional air-source heat pumps in the same region.

The Life Cycle Cost (LCC) encompasses the costs associated with the initial investment, installation, operation and maintenance, and decommissioning phases of the system. The calculation formula for LCC is as follows [35]:

$$\begin{array}{c}LCC=C_{\mathrm{INV}}+{\displaystyle \sum _{n=1}^N}{\displaystyle \frac{\left(C_{\mathrm{in}}-C_{\mathrm{out}}\right)}{{\left(1+DR\right)}^n}}\\ C_{\mathrm{in}}={\displaystyle \frac{SR}{N}}\\ C_{\mathrm{out}}=OC+MC+{\displaystyle \frac{SC}{N}}\\ OC=m_{\mathrm{w}}{C}_{\mathrm{w}}+W_{\mathrm{c}}{C}_{\mathrm{e}}\end{array}$$

(7)

where LCC represents the Life Cycle Cost; C_INV denotes the initial investment of the system (the total initial investment for this system is CNY 11.4 million [36]); C_in signifies the annual cash income and C_out represents the annual cash expenditure; DR stands for the discount rate, which is set at 5% in this study [36]; n indicates the number of years; SR denotes the salvage revenue from equipment disposal, calculated as 10% of the initial investment [36]; N represents the operational lifespan of the system, which is taken as 20 years in this study [36]; OC signifies the annual operating cost of the system (the annual operating cost for this system is CNY 6.3 million, including an annual water cost of CNY 6.2 million and an annual electricity cost of CNY 0.10 million); MC represents the maintenance cost of the system; and SC denotes the system disposal cost, calculated as 5% of the system’s initial investment [36].

For the air-source heat pump system, the initial investment of the air-source heat pump is CNY 4.0 million, with an annual operating cost of CNY 8.1 million and an annual maintenance cost of CNY 79 thousand [37]; the salvage revenue upon disposal is CNY 396 thousand.

The comparison of related costs between the solar PVT heat pump and air-source heat pump system is shown in Figure 13. The calculated LCC for the solar PVT heat pump system is CNY 92 million, which is 13.2% lower than that of the air-source heat pump system.

Considering the time value of money, the Dynamic Payback Period (DPP) method is employed to assess the economic superiority of the proposed scheme. The methodology for calculating the DPP is illustrated in Equation (8) [38].

$$\begin{array}{c}{C}_{\mathrm{INV}}={\displaystyle {\displaystyle \sum }_{n=1}^{DPP}}{\displaystyle \frac{\left(C_{\mathrm{in}}-C_{\mathrm{out}}\right)}{{\left(1+DR\right)}^n}}\end{array}$$

(8)

The calculation results indicate that the application of the solar PVT heat pump system at a collaborative innovation center in Hainan Province, China yields a dynamic payback period of 4–6 years.

5.4. Environmental Benefit Analysis of Solar PVT Heat Pump System

Compared to the air-source heat pump system, the solar PVT heat pump system is capable of efficiently producing hot water. The annual carbon emissions of both systems can be calculated using Equation (9) [39]:

$$\begin{array}{c}{E}_{{\mathrm{CO}}_2}=W_{\mathrm{a}}\cdot f\end{array}$$

(9)

where E_CO2 represents the annual carbon emission of the system, in tCO₂; W_a represents the annual power consumption of the system, in kWh; and f is the power carbon emission factor, in kgCO₂/kWh, taking 0.4184 kg CO₂/kWh [40].

Hainan Province, situated in the summer hot and winter warm region of China, has an air-source heat pump system with a COP_h value of 3.1 [41]. This enables the calculation of the annual power consumption of the air-source heat pump system at 2.2 million kWh, with an associated annual carbon dioxide emission of 900 tCO₂, as shown in Figure 14. In contrast, the solar PVT heat pump system has an annual carbon dioxide emission of 48.5 tCO₂, which is 94.6% less than that of the air-source heat pump system, demonstrating a significant reduction in carbon emissions.

6. Summary and Conclusions

This study conducts modeling and theoretical research on a solar PVT heat pump cogeneration system, establishes a simulation platform for the solar PVT heat pump system, and theoretically investigates the impact mechanisms on its cogeneration performance. Additionally, an analysis of the system’s economic viability and environmental benefits is conducted for its application at a collaborative innovation center in Hainan Province, China. Through the aforementioned research efforts, the following conclusions can be drawn:

(1)

Solar irradiance and the circulating water temperature within the PVT module significantly influence the thermal and electrical performance of the solar PVT heat pump system, whereas ambient temperature has a relatively minor impact on its performance.

(2)

At lower solar irradiance intensities, for every 100 W/m² increase in solar irradiance, COP_h increases by 13.7% and COP_co increases by 14.9%. At higher solar irradiance, for every 100 W/m² increase in solar irradiance, COP_h decreases by 10.0% and COP_co decreases by 10.4%. For every 100 W/m² increase in solar irradiance, the system’s heating capacity and power generation increase by 50.9% and 52.1%, respectively, while the electrical efficiency of the PVT array decreases by 0.05%.

(3)

For every 1 °C increase in the circulating water temperature within the PVT module, COP_h increases by 11.8%, COP_co increases by 12.3%, the heating capacity decreases by 2.2%, the power generation of the PVT array decreases by 0.80%, and the electrical efficiency of the PVT array decreases by 0.03%.

(4)

A solar PVT heat pump system with a rated heating capacity of 5500 kW, applied at a collaborative innovation center in Hainan Province, China, has an annual total heating capacity of 24,000 GJ and an annual total power generation of 1.11 million kWh. The annual total power consumption of the solar PVT heat pump system is 1.23 million kWh, with an annual average COP_h of 5.30 and an annual average COP_co of 7.60.

(5)

The LCC of the solar PVT heat pump system with a rated heating capacity of 5500 kW is CNY 92 million, which is a 13.2% reduction compared to the air-source heat pump system. Its dynamic investment payback period is 4–6 years. The annual power consumption and carbon dioxide emissions of the solar PVT heat pump cogeneration system are 116 thousand kWh and 48.5 tCO₂, a 94.6% reduction compared to the air-source heat pump system, demonstrating significant energy conservation and carbon reduction effects.

(6)

This study primarily focuses on the modeling and engineering application of the system in the solar-rich region of Hainan. Future work could involve comparative investigations across different climatic regions to evaluate the applicability and performance of the system.