**5. Two Types of Distributed Energy Systems**

According to the above-mentioned distributed energy system based on solar energy utilization, photovoltaic and photovoltaic thermal utilization can generate different grades of energy such as electricity and heat to meet various needs of users. Whether in urban or rural areas, in western or eastern China regions, solar energy through building walls, house roofs, etc., is a viable way to produce energy. Therefore, the following will propose two types of typical distributed energy supply systems based on wind, photovoltaic and photovoltaic thermal utilization.

#### *5.1. Heat Pump and PVT Integration Solutions*

In remote or rural areas of western China, good wind and solar resources are shown in Figures 7 and 8. Meanwhile, the energy and electricity consumption are relatively decentralized, and the demand for electricity and heat from retail households is prominent. Therefore, to satisfy the electricity and heat demands of households, wind turbines, PV and PVT can be integrated to form a distributed energy system with the complementary scenery. As shown in Figure 11, this distributed integrated energy system includes wind turbine power generation, photovoltaic power generation, a high-efficiency electric heating device composed of PVT and heat pump, and energy storage devices such as batteries and heat storage, which together meet the electricity and heat needs of users. For the PVT-heat pump subsystem, the working medium flows through the photovoltaic panels, which on the one hand, reduces the temperature of the photovoltaic back and improves the efficiency of photovoltaic power generation. On the other hand, the heated air goes into the evaporator of the heat pump to further enhance the electric–heat conversion coefficient of the heat pump.

**Figure 11.** The integration of heat pump, wind, PV, PVT, and energy storage units.

Meanwhile, energy storage is significant for this distributed energy system, including electricity and heat storage devices. The electricity storage equipment can be electrochemical batteries to improve user-side wind power and photovoltaic power generation. In addition, the thermal storage equipment can be water storage or ice storage to meet the different thermal needs of users. That is, this electricity and heat storage device ensures the stable electricity and heat output of this distributed energy system and guarantees the energy demand of customers without carbon emissions.

#### *5.2. Fuel Cells and PVT Integration Solutions*

Unlike the western areas in China, wind power resources are relatively scarce in the eastern or coastal areas, as shown in Figure 7. Therefore, solar energy should be better utilized in household energy consumption. Due to the intermittent nature of solar energy utilization, a certain amount of energy storage technology is required to guarantee the stability and reliability of energy consumption by users. In addition, solar energy should be stored directly as electricity or converted into fuels, such as hydrogen and methane.

Therefore, this research proposes an alternative distributed energy system containing PV, PVT, and fuel cells shown in Figure 12. The fuel cell is a high-efficiency combined heat and power generation technology [46,47]. Among them, building PV and PVT can be used to generate electricity. Using natural gas and solar fuel, etc., the combined heat and power supply is carried out by means of fuel cells. For example, fuel cells can use solar fuel (natural gas or hydrogen) to directly convert the chemical energy of the fuel into electricity without producing mission pollutants and can provide both electricity and heat with an efficiency of over 80%. The combination of PVT and heat pump can improve the coefficient of performance of the heat pump that produces the heat for users. Besides,

batteries and heat storage are introduced to overcome the temporal mismatches between the solar energy distribution and the electricity and heat needs of the users.

**Figure 12.** The integration of PV, PVT, FC, and energy storage units.

Figures 11 and 12 propose two types of distributed energy supply systems based on wind power and solar power, so they do not have carbon emissions. Meanwhile, these two types of distributed energy supply systems are two possible conceptual solutions based on the basic situation of renewable energy distribution and household energy consumption in China and are not real systems. However, they provide a feasible reference for the design of real systems in the future. In the future, we still need to plan and design, working conditions optimization and operational control from the technical and economic point of view for the actual user needs and the geographical characteristics of the location.

#### **6. Conclusions**

In the context of carbon neutrality, making full use of renewable energy is key to further improving China's human development index. To improve China's HDI under the carbon neutrality constraint, effectively reducing household energy consumption and selecting appropriate household energy supply options are significant. Therefore, this research obtained some conclusions


(4) Two types of typical distributed energy supply systems can be provided by integrating efficient energy conversion, storage, and exchange devices, such as electric heat pumps, PV, PVT, heat storage, electricity storage, and fuel cells, all of which are clean, efficient, low-carbon, and safe. In conclusion, the proposed two distributed energy systems can achieve carbon neutrality while meeting the energy needs of households.

**Author Contributions:** Conceptualization, Y.Z.; Data curation, S.W.; Formal analysis, Y.Z.; Funding acquisition, Y.Z.; Methodology, Y.Z.; Writing—original draft, Y.Z.; Writing—review & editing, W.S.; visualization, J.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research is support by Capacity Building of Science and Technology Innovation Services Basic Research Operation Fund (PXM2020\_014213\_000017) and Research Foundation for Youth Scholars of Beijing Technology and Business University (QNJJ2020-150).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Restrictions apply to the availability of these data. Data was obtained from Chinese General Social Survey and are available at http://cgss.ruc.edu.cn/ with the permission of Chinese General Social Survey.

**Conflicts of Interest:** The authors declare no conflict of interest.
