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The difference between photothermal and photovoltaic power generation

Solar photothermal power generation refers to the use of large-scale array parabolic or dish mirror to collect solar heat energy, through the heat exchange device to provide steam, combined with the traditional turbo-generator technology, so as to achieve the purpose of power generation.

The cost of solar power generation can be greatly reduced by adopting solar photothermal power generation technology, which avoids the expensive silicon photoelectric conversion process. What’s more, this form of solar energy has an advantage that other forms of solar energy conversion cannot match. The water heated by solar energy can be stored in huge containers and still be able to turn steam turbines for several hours after the sun goes down.

Principle of photothermal power generation

The principle of solar photothermal power generation is that the sun rays are concentrated through the reflector to the solar collection device, and the heat transfer medium (liquid or gas) in the collection device is heated by the solar energy, and then the water is heated to form steam to drive or directly drive the generator to generate electricity.

The difference between photothermal and photovoltaic power generation

  1. Different principles of power generation

Conventional photovoltaic power stations use solar panels to absorb visible light in the sun to form photoelectrons and generate current. Photothermal power generation uses a medium such as molten salt or oil to absorb the heat from sunlight and uses a steam turbine to convert it into electricity.

  1. The difficulty of connecting the grid is different

At present, the solar photovoltaic power generation system can improve the output characteristics by adding heat storage units or by supplementary combustion or combined with conventional thermal power, so that the output power is stable and the power is adjustable. However, photovoltaic power generation is greatly affected by the intensity of sunlight, which brings great pressure to the power grid after being connected to the Internet. Its form of power generation is unique, and it is difficult to merge with traditional power plants. In terms of grid-connection difficulty, photothermal power generation has more advantages than conventional photovoltaic power generation. Improve the output characteristics of photothermal power generation through heat storage (trough and tower photothermal generation). During the day, the excess heat is stored, and at night, the stored heat is released to generate electricity. In this way, the continuous power supply of photothermal power generation can be realized, and the current is stable. The peak regulation problem which is difficult to be solved by photovoltaic power generation and wind power generation can be avoided. According to different heat storage modes, the utilization hours and generating capacity of the power station can be improved to some extent, and the regulating performance of the power station can be improved.
The output characteristics of photothermal power generation can be improved by secondary combustion or combined with conventional thermal power. Solar thermal power stations can use fossil fuels or combined with conventional thermal power operation, so that it can continue to generate electricity at night or in continuous cloudy days, and even can be operated with stable output to bear the base load, so that the annual use of electricity up to 7,000 hours.

  1. Different degrees of environmental pollution

Photothermal power generation is a clean production process, which basically uses physical means to convert photoelectric energy and has little harm to the environment. The CO2 emission of solar photothermal power station during its whole life cycle is only 13~19g/kWh. However, the fatal weakness of photovoltaic power generation technology is that solar cells in the production process of large environmental loss, high energy consumption, high pollution production process.

  1. Different levels of technological maturity

Conventional photovoltaic technology has been stable in the development of our country, the technology is relatively mature, but thermal power generation, although the rise of very early in a foreign country, but in our country, it is still in the stage of constant innovation and improvement of technology.

  1. Different directions of use

Photovoltaic – suitable for distributed, small-scale, high-end cities; Small local power supply
Photothermal – suitable for centralized, large-scale, general areas; The whole region, province, and even the whole country have a large scale of power supply. Just using the solar heat energy of 100 square kilometers of Xinjiang desert can supply electricity for the whole of China. The Xinjiang desert is 424,800 square kilometers;

  1. Different industrial chains

Photovoltaic – silicon production, purification, slicing, products, related industry chain professional single;
Light and heat — steel, glass, cement and so on, involving a number of industries, similar to real estate, related industry chain is long, very rich;

Solar thermal power generation and photovoltaic power generation

Investment cost

The investment cost of photovoltaic power generation is much higher than that of photovoltaic power station. At present, the unit cost of large-scale photovoltaic power stations constructed in China is about 8000 yuan/kW, and the solar thermal cost is about 22,000 yuan/kW. The photovoltaic power stations in the United States are about 2400 to 3000 dollars/kW, and the solar thermal cost is about 5100 to 6200 dollars/kW, and the solar thermal cost is basically 2-3 times that of photovoltaic power stations. In addition, the photothermal power station is highly sensitive to scale, and only under the premise of a large enough scale can economic benefits be effectively realized. At the same time, its overall investment threshold is high, 100 megawatt plant investment needs nearly 500 million dollars. It is precisely because of the large investment and high risk of photovoltaic power stations, even if they reach the parity level of Internet access, compared with photovoltaic power stations, there are still very few investors, which will objectively delay their cost reduction.

Construction conditions

The photothermal power station has high requirements for construction conditions, and the installation elasticity of photovoltaic is relatively large. Solar thermal power generation is mainly installed in places with good direct solar radiation (DNI). Desert is the best choice, but these places are often remote and have weak power demand. Therefore, transmission channels need to be built to send power out, which will not only increase the cost, but also can only enjoy the electricity price on the generation side. At the same time, because the solar thermal power station belongs to the tracking system, the local climate conditions are also relatively high requirements.

Photovoltaic power stations can use both direct light and scattered light, and have a wide choice of installation areas. For example, they can be installed in load centers, rooftops or industrial buildings, and enjoy user-side electricity prices. Therefore, it is more competitive to sell it at the generating side price compared with the photovoltaic power station.

Environmental protection

Solar thermal power station requires a large amount of land and water, and has high requirements for environmental protection. According to the current construction situation of photovoltaic power stations in the United States, each MW needs about 40-50 mu of land, almost twice that of photovoltaic power stations, and requires very flat land. In terms of water use, while both PV and photothermal require water for module or mirror cleaning, the photothermal power station also requires additional water for cooling, which consumes about 2.9-3.2 litres /kwh, almost 4 times that of natural gas power generation. Dry cooling technologies are also being developed, such as air cooling to solve the water problem, but the technology is not yet mature, and it is likely to reduce electricity production and increase the cost of electricity generation by about 3-8%. In addition, due to the large space occupied by the photovoltaic power station, it will affect the local wildlife, biodiversity and other impacts, and also prone to environmental disputes.

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