Solar water heating

Solar water heating is a technology with independent intellectual property rights, the most mature technology, the fastest industrialization development in the domestic market, and the largest market potential in the field of solar thermal utilization in China.

It is also China’s only self-developed technology that has reached the international leading level in the field of renewable energy. The following uses statistical data in 2007 as an example to analyze the industrial structure, main products, quality supervision and market conditions of China’s solar water heaters.

The solar water heaters actually used at present can be divided into two types: evacuated tube and flat plate according to the collector structure. Among the 23 million m² solar water heaters produced in China in 2007, the output of vacuum tube water heaters was 21.9 million m² and the output of flat water heaters was 1.07 million m², accounting for 95% and 5% of the total output respectively.

In the total output of evacuated tube water heaters, the proportions of all-glass evacuated tubes, heat pipe evacuated tubes and U-shaped evacuated tubes are shown in Figure 1.

China has established a complete national standard system for solar thermal utilization products, covering all product series such as household solar water heaters, solar water heating systems, solar collectors and vacuum solar collector tubes. At the same time, authorized by the General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China and the National Certification and Accreditation Administration Commission, two national quality inspection centers for solar water heaters have been established – National Solar Water Heater Quality Supervision and Inspection Center (Beijing) and National Solar Water Heater Product Quality Supervision and Inspection Center (Wuhan). Since 2004, these two national centers have been entrusted by the General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China to conduct inspections on solar water heaters for five consecutive years. The national supervision and spot checks on product quality have played a good role in regulating the market.

China’s solar hot water market can be divided into two major segments. One is a domestic solar water heater-directly purchased by the user, using a store or shopping mall sales model, and installed by a dealer; the other is the solar water heating system integrated with the building-engineering construction mode. At present, most of the engineering departments of solar energy companies carry out the design and installation for related projects. In the future, it should be transferred to enterprises for supply. The design institutes and equipment installation companies are responsible for the formal mode of design and installation. Since 2003, China’s solar hot water project market share has developed steadily, and the proportion of the project market in total output is shown in Figure 2.

Solar refrigeration and air conditioning

Since the late 1970s, Chinese scientific and technological workers have conducted in-depth research on various types of solar refrigeration, developed corresponding experimental devices and prototypes, and built a number of demonstration projects. The technical types include solar absorption refrigeration, solar absorption refrigeration, passive cooling, underground cooling source cooling and solar dehumidification air conditioning.

China’s research and practice of solar refrigeration and air-conditioning began with solar ammonia-water absorption refrigeration systems. More than 20 units have successively carried out work and accumulated valuable experience. The first solar refrigeration and air-conditioning project completed in China was the solar nitrogen-water absorption refrigeration and air-conditioning system built in Beijing No. 3 Cotton Mill in 1979.

Another type of refrigerator suitable for solar energy utilization is an absorption refrigerator with lithium bromide-water as the working medium. At present, the quality of lithium bromide absorption refrigerators produced in China has reached the international advanced level. In order to adapt to the characteristics of using low-temperature heat sources from solar energy, the Guangzhou Institute of Energy Research, Chinese Academy of Sciences, began to develop a new type of hot water two-stage absorption lithium bromide refrigerator in 1982. The 70kW, 350kW and 1000kW two-stage absorption lithium bromide refrigerators manufactured in 1993, 1994 and 1997 respectively have been successfully operated in the actual air conditioning system. The salient features of the unit are the low temperature of the required heat source and the large difference in the utilization temperature of the heat source.

Solar adsorption refrigeration uses solid adsorbents (zeolite molecular sieves, silica gel, activated carbon, calcium chloride, etc.) on the adsorption (or chemical absorption) and desorption of refrigerants (water, etc.) to achieve a refrigeration cycle. The regeneration temperature of the adsorbent is between 80~150℃, which is suitable for the use of solar energy.

Another technical route of solar refrigeration and air-conditioning is to use focused solar collectors and high-temperature hot water or steam absorption chillers to work together. However, due to the unstable performance and quality of the focused collector product itself, the implementation effect is not ideal, and it needs to be improved through technical research. In addition, China has also carried out a lot of research and development work in the technical fields of solar dehumidification air-conditioning, passive cooling and underground cold source cooling, so as to integrate China’s actual conditions and track the world’s cutting-edge level. In recent years, the solar-assisted heat pump regenerative adsorption dehumidification system has begun to be used for drying grain in the silo, which has exerted good economic benefits.