# Regional Adaptability Analysis of Solar Roof Utilization Technologies in China
## 4 Conclusions  
This paper developed a new evaluation method for solar roof utilization technologies, considering the various influential factors, inclusive solar radiation, thermal climate division, and economic development level. Eighteen typical buildings from 13 different climate zones were evaluated using the proposed method. For utilization of the building rooftop, the following findings are obtained:  
1. The average adaptability index values for solar thermal technology and solar PV technology are 2.54 and 1.63, respectively. Solar thermal technology has a shorter nominal investment payback period; therefore, it is more preferred in most of the investigated scenarios, especially in residential buildings and hotel buildings with a hot water demand.
2. The average payback time of a solar PV system for all the investigated buildings is 12 years. The payback time for a PV system could be as low as 5 years and as high as 26. The longer investment payback period is seen for Chongqing and Xingyi city because of poor solar radiation resource.
3. Technical specifications or application standards regarding roof utilization in China should be launched by relevant national departments to guide and regulate the reasonable use of building roofs. It is considered essential to promote the development of roof  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Roo Resource Utilization** & **Building No. 8** & **Building No. 9** & **Average** \\ \hline Solar thermal technology & 1.93 & 2.96 & 2.45 \\ Solar PV technology & 1.35 & 2.05 & 1.7 \\ \hline \hline \end{tabular}
\end{table}
Table 11: Adaptability index of the test case.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Benefits** & **Solar Thermal** & **Solar PV** \\ \hline Absolute amount of energy saving (10\({}^{3}\) kWh) & 141.30 & 107.69 \\ Relative amount of energy saving (\%) & 24.33\% & 18.92\% \\ Emission reduction (kg) & 120,105 & 91,536.5 \\ \hline \hline \end{tabular}
\end{table}
Table 12: The results of the test case based on software simulations.  
utilization technologies. Provincial or municipal governments should develop five-year or ten-year development plans for roof utilizations considering local economic development, climate conditions, solar resources, energy conservation and emission reduction, urban sustainable development, and urban ecological environment, as well as the function of buildings and adaptability of roof utilization technologies.
* Since a larger difference may exist between the simulation and the practical application, it is recommended to carry out further detailed investigations in order to develop a sophisticated database of adaptability of roof utilization technologies for references in the future engineering practice.  
Conceptualization, J.H. and J.F.; methodology, J.F.; software, Q.L.; validation, J.H.; investigation, J.H.; data curation, Q.L.; writing--original draft preparation, J.H. and Q.L.; writing--review and editing, J.F. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Shandong Provincial Natural Science Foundation, grant number ZR2021 ME051 and the National Natural Science Foundation of China grant number 51608290.  
Not applicable.  
Available upon request.  
The authors declare no conflict of interest.