Definition of solar thermal energy

The sun is the nearest star to the earth and the only luminous celestial body in the solar system. It brings light and heat to the earth and is the root of all life on the earth. The sun transmits energy to the earth’s surface in the form of light radiation. Solar energy belongs to renewable green energy and is an “inexhaustible” energy. Under standard sunlight conditions in the daytime, the power generation efficiency is 10%, so the annual solar power generation available on the whole earth’s surface is 114 × 1015 kwh, about 100 times the total energy consumption in the world today.

Advantages and disadvantages of solar thermal energy

1. Universal

The sun shines all over the land without geographical restrictions. It can be developed and utilized directly, regardless of land or sea, mountains or islands, without mining and transportation.

2. Harmless

The development and utilization of solar energy will not pollute the environment. It is one of the cleanest energy sources, which is extremely valuable in today’s increasingly serious environmental pollution.

3. Gigantic

The solar radiant energy reaching the earth’s surface every year is about 130 trillion tons of standard coal, and its total amount is the largest energy that can be developed in the world today.?

4. Long term

According to the current rate of nuclear energy generated by the sun, the storage capacity of hydrogen is enough to last for tens of billions of years, and the life span of the earth is about billions of years. In this sense, it can be said that the energy of the sun is inexhaustible. Dispersity

Although the total amount of solar radiation reaching the earth’s surface is large, the energy flow density is very low. On average, near the Tropic of cancer, when the weather is sunny in summer, the solar radiation irradiance is the largest at noon, and the average solar energy received on an area of 1 square meter perpendicular to the sunlight direction is about 1000W; If it is averaged day and night throughout the year, it is only about 200W. However, in winter, it is only about half, and in cloudy days, it is only about 1/5, so the energy flow density is very low. Therefore, when using solar energy, a set of collection and conversion equipment with a large area is often required to obtain a certain conversion power, and the cost is high.

5. Instability

Due to the limitations of natural conditions such as day and night, season, geographical latitude and altitude, as well as the influence of random factors such as sunny, overcast, cloud and rain, the solar irradiance reaching a certain ground is intermittent and extremely unstable, which increases the difficulty of large-scale application of solar energy. In order to make solar energy become a continuous and stable energy, and finally become an alternative energy that can compete with conventional energy, it is necessary to solve the problem of energy storage, that is, to store the solar radiation energy in sunny days as much as possible for use at night or in rainy days. Energy storage is also one of the weak links in the utilization of solar energy.

6. Low efficiency and high cost

Some aspects of the development level of solar energy utilization are feasible in theory and mature in technology. However, some solar energy utilization devices have low efficiency and high cost. In general, the economy cannot compete with conventional energy. In a considerable period of time in the future, the further development of solar energy utilization is mainly restricted by economy.

  Advantages and disadvantages of solar thermal energy and its utilization

Utilization of solar energy

(1) Photothermal utilization

Its basic principle is to collect the solar radiation energy and convert it into heat energy through the interaction with materials. At present, there are four types of solar collectors used most, including flat plate collectors, vacuum tube collectors, ceramic solar collectors and focusing collectors (trough, dish and tower). Generally, according to the different temperatures and uses that can be achieved, the solar thermal utilization is divided into low temperature utilization (200 ℃), medium temperature utilization (200 ~ 800 ℃) and high temperature utilization (800 ℃). At present, the low-temperature utilization mainly includes solar water heater, solar dryer, solar distiller, solar heating (solar house), solar greenhouse, solar air conditioning and refrigeration system, etc., the medium temperature utilization mainly includes solar cooker, solar thermal power concentrating and collecting device, etc., and the high-temperature utilization mainly includes high-temperature solar furnace, etc.

(2) Power generation utilization

New energy the large-scale utilization of solar energy in the future will be used to generate electricity. There are many ways to use solar energy to generate electricity. There are two main types that have been used.

1. Optical thermal electrical conversion. That is to use the heat energy generated by solar radiation to generate electricity. Generally, the solar collector is used to convert the absorbed heat energy into working medium steam, and then the steam driven gas turbine drives the generator to generate electricity. The former process is optical thermal conversion, and the latter is thermal electrical conversion. This method is simple, low-cost and high return, and is suitable for large-scale promotion in China.

2. Optical electrical conversion. Its basic principle is to use photovoltaic effect to directly convert solar radiation energy into electric energy. Its basic device is solar cell. Unfortunately, the efficiency of this power generation method is only 10%, and its cost is greater than its service life, so it has no economic value. In the process of manufacturing solar cells, secondary pollution often occurs.

(3) Solar cell

Material requirements: resistant to ultraviolet radiation, and the light transmittance does not decrease. The components made of tempered glass can withstand the impact of a 25 mm diameter ice ball at a speed of 23 m / s.

Usage: solar power generation is widely used in solar street lamps, solar insect killing lamps, solar portable systems, solar mobile power supplies, solar application products, communication power supplies, solar lamps, solar buildings and other fields.

Solar energy may become the main source of electricity before 2050, thanks to the sharp drop in the cost of power generation equipment. According to the IEA report, by 2050, solar photovoltaic (PV) systems will contribute up to 16% of the world’s electricity, and solar thermal power generation (STE) from solar power plants will provide 11% of the electricity.

(3) Photochemical utilization

This is a kind of photo chemical conversion method that uses solar radiation energy to directly decompose water to produce hydrogen. It includes photosynthesis, photochemistry, photosensitive chemistry and photolysis.

Photochemical conversion is the process of converting chemical energy into chemical energy due to the absorption of light radiation. Its basic forms are photosynthesis of plants and photochemical reaction of using chemical changes of substances to store solar energy.

Plants rely on chlorophyll to convert light energy into chemical energy to achieve their own growth and reproduction. If the mystery of photochemical conversion can be revealed, artificial chlorophyll can generate electricity. Solar photochemical conversion is being actively explored and studied.

The process of converting solar energy into biomass is realized through the cooperation of plant light. Giant algae.

(4) Fuel utilization

Since june2011, the European Union has been committed to the development and production of “solar” fuel by using the high-temperature energy provided by the sun and using water and carbon dioxide as raw materials. Up to now, the R & D team has successfully realized the whole process production of renewable fuel in the laboratory scale for the first time in the world, and its products fully comply with the EU aircraft and automobile fuel standards, without any adjustment and modification to aircraft and automobile engines.

The “solar energy” fuel oil prototype developed and designed is mainly composed of two technical parts: the first part uses the high-temperature energy generated by the concentration of solar rays, supplemented by metal oxide material additives with the independent intellectual property rights of eth Z ü rich, to convert water and carbon dioxide into syngas in the self-designed solar energy high-temperature reactor. The main components of syngas are hydrogen and carbon monoxide; In the second part, according to the Fischer Tropsch principle, the waste heat high-temperature syngas is converted into “solar energy” fuel products that can be commercialized in the market.

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