**2. Methods**

In this study, a systematic review of renewable heat policies in China, spanning from 2000 to 2021, is conducted to understand the framework of China's renewable heat policy and to determine the key drivers in policy making. The review approach is developed by referencing several studies, including Zhu Bei et al. [18], Liu Junxia et al. [15], and Chul Kim [19].

To quantify the effectiveness of existing policies, a policy intensity index (PII) model is employed. A policy intensity index is developed based on the game theory of public policy to quantify the impact of policies. The index was first developed by Libecap [20] in 1978, and then widely used to quantify policy effectiveness. The structure of the PII in this paper is established based on previous studies concerning China's energy saving and clean heating policies [16–18,21], and specific modifications are made to precisely reflect the characteristics of renewable heat policy. The modification contains 2 aspects. Firstly, the score scope is narrowed down to 3 degrees. Secondly, the policies are classified into 3 categories instead of 5 categories, to simplify the evaluation.

Table 1 shows a breakdown of the index indicators, which includes 2 primary aspects: issuance level and target level. The policy's authority level is measured by the level of issuance. The issuance level aims to measure the authority degree of the policy through 3 sub-indicators: document type, issuer level, and coverage of the policy. The target level includes 2 indicators, the refinement and the duration of the targets, with the purpose of assessing the stringency degree of the targets in the policy. Each sub-indicator is endowed with the same score rules, from 1 to 3.

In terms of data processing, we gathered policy documents from official government websites, such as the official websites of the state council (SC), the National Development and Reform Commission (NDRC), the Ministry of Ecology and Environment (MEE), and relevant policy databases. A total of 146 relevant policies were collected. The keywords for text analysis included "policy," "regulation," "renewable heating," "geothermal," "biomass," "wind power heating," "clean heating," and "solar heating". Screen criteria was identified to ensure that the policy type was in the form of law, regulation, opinion, measure, or notice. The collected policies were standardized for further quantitative analysis by issue time, issuer, the number of issuers, target type, coverage, etc. The timeline ranged from 2000 to 2021, with the consideration that few policies were released before 2000.


**Table 1.** The breakdown of PPI indicators.

After each indicator was scored, the policy intensity for a policy was calculated by multiplying all the sub-indicators. The model is shown in the following formula.

$$P\_i = \sum\_{j}^{N} \left( P1\_{j,i} \times P2\_{j,i} \times P3\_{j,i} \times P4\_{j,i} \times P5\_{j,i} \right), i = \left[ 2000, 2021 \right] \tag{1}$$

*Pi* represents the policy intensity of year *i*, while *j* represents the ordinal number of the policy in year *i*. *P*1*j*,*<sup>i</sup>* to *P*5*j*,*<sup>i</sup>* represent the score of the sub-indicator in a specific year of policy *j*.

#### **3. Development of China's Renewable Heat Policy**

#### *3.1. Architecture of Renewable Heat Policies in China*

China's current renewable heat policy system has been formed from scratch after more than 20 years of efforts. The architecture of the system is illustrated in Figure 1, to elucidate the inner relationship of the policies. Generally, policies can be classified into several levels. The first level is law, which lays out a fundamental legal framework for the development of renewable heating. The second level is medium- to long-term strategies or plans. The third level focuses on short-term comprehensive plans, including conventional plans and unconventional plans. The fourth level is sub-plans and special policies. The fifth level refers to local plans and policies.

China introduced the Renewable Energy Law in 2005, and since then renewable energy has become a preferential area for energy development. Renewable law lays a legal basis for renewable heating development. To implement the renewable heating law, central and local governments have formulated a series of policies.

Under the renewable law, medium- to long-term strategies are made. "The Mediumand Long-Term Renewable Development Plan" [22] and the relevant climate and environment strategy mainly addressed the principles and priority tasks for making short-term national renewable energy plans in China.

**Figure 1.** The structure of the renewable policy in China.

Based on strategy and high-level guidance, central governments usually make conventional plans to guide the next five years of development. The first renewable energy development plan was issued in 2012, and China has since began to promulgate a renewable development plan for each five-year period. These plans generally include mandatory goals that should be achieved by the end of the fifth year. Alongside conventional plans, some unconventional plans were also promulgated to address important and urgent issues. In 2017, the Clean Heating Plan for Northern China (2017–2021) (clean heating plan) was released jointly by nine ministries to facilitate the transformation of clean heating, and to control air pollution caused by coal-fired boilers [23]. The implementation of the clean heating plan spanned three years until the end of 2021 and covered "2 + 26" cities in Northern China.

The targets in these comprehensive plans are usually broken down into more specific targets and presented in sub-plans with specific measures. China has issued special plans for geothermal energy heating, biomass energy heating, renewable electricity heating, solar water, and heating policies [24–28]. Additionally, it is of significance to engage in the implementation of comprehensive plans and supporting policies, such as subsidies and tax credits, to show sufficient support and attention.

Local governments commonly release renewable heat policies according to local conditions under the umbrella of national policies. For example, Inner Mongolia issued the "Notice on wind power for heating to support the utilization of wind power for heating in winter seasons" [29]. Furthermore, local governments are also encouraged to formulate local standards to enhance the implementation of renewable policies and regulations. As of 2015, more than 28 provinces had already issued compulsory regulations requiring new buildings to install solar heating systems [30].

#### *3.2. The Development of Renewable Heating in China*

When the cost of solar water heating systems dropped significantly in the 2000s, renewable heating started to receive more attention from policymakers [30]. Since then, progress in policies has been accelerated to push forward the deployment of renewable energy in the heating sector. The evolution of renewable heat policies has been closely associated with the socio-economic context of the last 20 years [24]. The development of

renewable heating policies can be divided into four stages, as shown in Table 2. The key drivers and the role of renewable heating are different in different stages.


**Table 2.** The four stages of renewable heating development.
