**4. Characteristics of the Distributed Energy Supply System**

#### *4.1. An Alternative Future Energy System*

According to the above macro and micro energy consumption and carbon emission analysis, it can be seen that carbon emission, electricity consumption, and human development index are positively correlated, while there are regional imbalance characteristics of energy consumption and production. Therefore, the development and selection of future energy systems must simultaneously consider human development, regional energy resources distribution, users' energy demand, etc. The improvement of the contradiction between carbon emission and human development is more significant for China.

Recently, the energy demands of the industry, commerce, and residential life have focused more on electricity and heat/cool. Various energy generation units provide electricity, heat, and cool. Based on the current feature of China's energy structure and future development plan, this research provides an alternative sketch of the future integrated energy system under the carbon neutral perspective shown in Figure 9. On the energy generation side, various thermal power, combined heat, and power (CHP), wind power, hydroelectric power, nuclear power, photovoltaic (PV), and solar thermal power are the main power generation ways in China, which can meet large amounts of electricity demand. There are power grid, gas network, and heat network in the energy transport processes. There are electricity, heat, and cool demands on the energy consumption side. Meanwhile, various energy storage units (such as electrochemical energy storage, mechanical energy storage, thermal energy storage, etc.), power to gas units, and electricity to heat conversion units (such as heat pump, electrical heating) are in the integrated energy system. Besides, the power generation units such as wind power and PV are also arranged on the customer side. There are two main types of energy production: centralized and distributed in the future integrated energy system. Meanwhile, the future integrated energy system can achieve efficient, flexible, safe, and stable operation by coordinating source, network, load, and storage.

**Figure 9.** The sketch of the future integrated energy system.

Based on the data shown in Figure 4, China's human development needs to be further enhanced, yet the traditional centralized, fossil fuel-based approach to energy utilization needs to change under the strategy of carbon peaking and carbon neutrality in China. In the context of synergistic consideration of China's social development and carbon neutrality, an energy supply system based on renewable energy is necessary and significant. However, the imbalance characteristic between the renewable energy source and the user demands becomes the main obstacle of renewable energy utilization. Therefore, as a complement to the traditional centralized energy production methods, the development of distributed energy systems is essential to balance the regional contradictions in energy production and consumption and increase the efficient utilization of renewable energy [21,39]. Typically, distributed energy systems are placed on the customer side, and there are various types [40–44]. Therefore, the choice and construct of the distributed energy system are significant and necessary for the household energy consumption in a carbon neutral perspective for different regions in China.

### *4.2. Solar Energy-Based Energy Supply System*

It is well known that solar energy is the most widely distributed energy. Therefore, the solar energy-based distributed energy supply system is desirable and will be a significant viable energy supply option for future household energy demand. However, due to its intermittent nature and unavailability at night, the comprehensive utilization of solar energy is provided and required to satisfy the electricity, heat/cool, and gas requirements of users. This utilization can achieve high efficiency, flexibility, low carbon, and security of the distributed energy system.

Figure 10 shows the comprehensive utilization ways of solar energy. All energy comes from the sun, and solar energy is capable of producing heat and electricity through photovoltaics (PV) and photovoltaic thermal (PVT), and fuels, such as hydrogen and methanol, through photochemistry (PC) and other technologies. In order to solve the problem of indirectness and uncertainty of solar energy, energy storage can be used through electricity storage (ES), heat storage (HS), power to gas (P2G), and other energy storage methods. Finally, it further meets the different needs of users for electricity, heat, cold, and gas through high-efficient energy conversions such as fuel cells (FC), heat pumps (HP), and air conditioners (AC). As the research from Frankea et al. [45], the interdependencies of renewable energy and flexibility options such as hydrogen and batteries may be the most cost-effective solutions for the future Chinese energy system under different scenarios. China's carbon-neutral energy system is mainly based on solar power plants that use batteries and hydrogen reconversion to meet nighttime demand.

**Figure 10.** Comprehensive utilization ways of solar energy.
