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• Experience and lessons summarized on the first solar district heating system in rural Beijing. • A solar-assisted GSHP system is a reliable solution for district heating. • Solar collectors contribute to heat balance of the soil heat storage. • An optimized scenario with a reduction of overall operating cost by 10.9% proposed. • The combination of domestic hot water and space heating is worth promoting in China. Experimental and theoretical investigations have been carried out on the first large scale solar assisted ground source heat pump (SAGSHP) for heating and cooling of a village in the outskirts of Beijing. Long term performances of the system without and with solar heating were monitored. A TRNSYS model of the SAGSHP system was developed and validated against the measured data. Based on a parametrical investigation using the model, an optimized solution was proposed. It is shown that adding a domestic hot water system to the original SAGSHP system will not only help to secure thermal balance of the ground but also reduces primary energy consumption for hot water by 70%. The system COP increases by 9.4% from 2.42 to 2.65 and the annual overall operating cost decreases from 892,000 CNY to 794,000 CNY with only a small increase in equipment cost. Under the premise of ensuring thermal balance of the ground, there is an optimal match between the size of the ground heat storage, the collector area and the tank volume. Experience and lessons learned from the project are conducive to successful implementation of similar projects in the future. [ABSTRACT FROM AUTHOR]

China is the second-largest economy country, and the largest country worldwide in total solar energy system capacity installed. More than 70% of total solar collector capacity worldwide is installed in China. The production of solar collector in China had decreased significantly from 64 million m2 in 2012 to 37 million m2 in 2017, corresponding to a reduction of around 40% of the market in 2012. There are very limited comprehensive studies in existing literature, which have investigated the reasons on the decline of Chinese solar thermal market. This study aims to identify the reasons from both the demand and the supply sides in details. Furthermore, with the rise of emerging markets, such as the rapid development of the "Clean Heating Initiative" for space heating in North China, solar heat industrial process, and the mandatory installation of solar domestic hot water system for residential buildings below 100 m in urban area, the Chinese solar thermal market is expected to recover soon, called "U-shaped curve" in this study. The market share of flat plate collector and evacuated tube collector is predicted to change in the near future. The research and development of flat plate solar collectors will increase continually in the market other than evacuated tube solar collectors like the past 10 years. The main driver for the solar thermal market development in China in the near future will be the demand from the urban area. • The largest solar thermal market worldwide has been presented. • The market share of flat plate collector will continue to grow gradually. • Market factors from both supply and demand sides are analyzed in detail. • Scenarios is predicted in short, middle and long terms. [ABSTRACT FROM AUTHOR]

To find an optimal economic solution for solar district heating (SDH) in China, an evaluation model based on the levelized cost of heat (LCoH) is developed. A Python program is developed to calculate the LCoH of SDH systems using the quasi-dynamic test method. Based on these calculations, the trend of LCoH with solar collector area under different heating load intensities, heating terminal units, heated areas and land rents is discussed. The optimal solar collector area and the solar fraction are determined for combinations of solar thermal with four types of auxiliary heat sources, including air source heat pumps, ground source heat pumps, gas boilers and gas boilers with seasonal heat storage. The calculations show an economic optimal solar fraction of 11%–33% for a SDH system with heat pumps. High dependency of LCoH on network temperature is found for a SDH system with gas boilers. Seasonal heat storage minimizes LCoH of a SDH system with gas boilers at 100% solar fraction. The findings can be used as a reference for local authorities, consultants and engineers in the early energy planning to determine the optimal proportion of solar energy in a district heating system with the lowest operating cost. • An optimal solar fraction of 11%–33% for a SDH system with heat pumps. • High dependency of LCoH on network temperature for a SDH system with gas boilers. • Heat storage minimizes LCoH of a SDH system with gas boilers at 100% solar fraction. • The higher the heat demand, the greater the solar contributed economic benefits are. • With biomass >1100 CNY/ton, the biomass heating system reduces LCoH by adding solar. [ABSTRACT FROM AUTHOR]

High-rise buildings have a significant impact on the surrounding environment. Building-integrated solar water heating (SWH) systems are effective ways to use renewable energy in buildings. Impediments, such as security concerns, aesthetics and functionality, make it difficult to apply SWH systems in high-rise buildings. At present, only China uses SWH systems on a large scale in such buildings. What are China's experiences and lessons learned in applying SWH systems in high-rises? Are these experiences scalable to other countries? This study used a combination of field investigation, literature review and case study to summarize 36 systems that had been in operation for 1–14 years. System types, collector types, installation methods, types of auxiliary heat sources, economic performance and various basic principles were summarized. The economic performance of SWH systems in high-rise buildings was analyzed and verified by a case study in Shanghai. The results show that the installation of SWH systems in high-rise buildings is feasible and reliable. Individual household systems (61%) were more popular than centralized systems (25%) and hybrid systems account (14%). The average area of solar collectors per household was 2.17 m2/household, the average design solar fraction was 52%. Flat plate solar collectors (53%) was the most commonly used collector, while electric heating elements (89%) were the most common auxiliary heat sources for SWH systems, followed by gas water heaters and air source heat pumps. The cost of SWH systems per m2 of a building area was between 22 CNY/m2 to 75 CNY/m2. China's unique practical experience gives a reference for other countries in their efforts to make high-rise buildings more sustainable. [ABSTRACT FROM AUTHOR]

Highlights • The largest solar district heating market worldwide has been presented. • Characters of solar district heating plants in Denmark were summarized. • Possibility of solar district heating in smart renewable energy system was shown. • Potential trend of solar district heating plants in Denmark was discussed. Abstract Large solar collector fields are very popular in district heating system in Denmark, even though the solar radiation source is not favorable at high latitudes compared to many other regions. Business models for large solar heating plants in Denmark has attracted much attention worldwide. Denmark is not only the biggest country in both total installed capacities and numbers of large solar district heating plants, but also is the first and only country with commercial market-driven solar district heating plants. By the end of 2017, more than 1.3 million m2 solar district heating plants are in operation in Denmark. Furthermore, more than 70% of the large solar district heating plants worldwide are constructed in Denmark. Based on the case of Denmark, this study reviews the development of large solar district heating plants in Denmark since 2006. Success factors for Danish experiences was summarized and discussed. Novel design concepts of large solar district heating plants are also addressed to clarify the future development trend. Potential integration of large solar district heating plants with other renewable energy technologies are discussed. This paper can provide references to potential countries that want to exploit the market for solar district heating plants. Policy-makers can evaluate the advantages and disadvantages of solar district heating systems in the national energy planning level based on the know-how and experiences from Denmark. [ABSTRACT FROM AUTHOR]