New way out of solar energy

In Durban, a group of politicians is arguing over who should bear more responsibility for climate change. This makes people feel more and more that relying solely on this kind of top-down climate politics may not be enough to solve the urgent crisis of climate change.

Taking into account the best way to mitigate climate change and rising energy prices, it should be to increase the proportion of non-fossil fuel energy use. Among the non-fossil fuel energy that we can use, the safety of nuclear energy is highly controversial. Wind energy and water energy need careful site selection and environmental impact assessment. There are limited areas where geothermal energy can be used. It seems that only solar energy is a more suitable sustainable energy source. .

Today's solar technology is not entirely without problems. Among the solar power generation technologies, the most used is photovoltaic (PV) power generation. Similar to the photoelectric effect, electrons in a photovoltaic material are excited after they receive light energy and enter different electron orbits so that voltages appear between the two poles of the material.

Heavy metal pollution may also occur during the manufacture of such materials, although unit pollution from solar power is much lower than thermal power plants. In addition, the biggest problem encountered in solar power generation is that it is difficult to increase power generation efficiency. Therefore, a solar power plant with a certain size needs to occupy a large amount of open space. Today, as land resources are becoming increasingly scarce, this is also a major constraint.

Therefore, for solar power generation to have greater development, it is necessary to increase the efficiency of power generation; at the same time, it is also necessary to make power generation equipment easier to assemble and use. Today's photovoltaic technology seems to have encountered bottlenecks in both areas.

First of all, as with the photoelectric effect, electrons only excite light of a certain wavelength will be excited, and the photovoltaic effect occurs. Longer-wavelength light will directly penetrate the photovoltaic material without any effect. Shorter-wavelength light will give too much energy to the excited electrons, causing them to fly everywhere and unable to effectively form current.

Moreover, when the sun shines on photovoltaic materials, it inevitably causes it to generate heat, which also affects the efficiency of photovoltaic materials for power generation. Therefore, the photovoltaic material's power generation efficiency is difficult to exceed 15% to 20%, which means that it generates only a considerable amount of electrical energy. About one-fifth or less of the sunlight energy shines on it.

Photovoltaic panels are also expensive, and they require professionals to design and install them. If you want to use photovoltaic power to reduce your electricity bill, you may have to save a sum of money as an investment.

In the breeding of crops, there is no lack of such examples: a breed's performance is not satisfactory, but it can help improve the shortcomings of another breed and produce excellent hybrids. The same is true for technological progress.

In 1821, the German physicist Seebeck discovered that when two different metallic materials were welded together into a ring and heated, they could attract magnetic needles. He thought this was a "thermomagnetic effect," but the Danish physicist Austrian Stet pointed out that the magnetic field is due to the temperature difference between different metals so that the current appears in the ring, and that this phenomenon is a thermoelectric phenomenon.

This phenomenon was later named the Seebeck effect. The material that can produce this phenomenon is called thermoelectric material. In 1954, Maria Telkes, a Hungarian-American scientist who devoted himself to the study of solar energy, used solar energy and thermoelectric materials to realize solar power generation, but the power generation efficiency was only 1% poor. Later generations did not increase the efficiency of solar thermoelectric materials on the basis of her, but the efficiency of photovoltaic power generation technology soon reached more than 10%, so the application of thermoelectric materials in solar power generation was quickly forgotten. .

In today's photovoltaic power generation seems to have no potential to be excavated, some scientists have thought of thermoelectric materials. As mentioned earlier, long-wavelength parts of sunlight can pass through photovoltaic panels and cannot be used by them. So why not add a layer of thermoelectric material below the photovoltaic panels to capture this part of the sunlight?

Yin Huiming and Yang Dajiang, two scientists at Columbia University in New York, conducted this experiment. They found that thermoelectric materials could indeed capture some of the sunlight that was not absorbed by the photovoltaic panels, but the generated electricity was very weak, and economically it could not even compensate for the increase in the cost of thermoelectric materials.

On the one hand, part of the sunlight passing through the photovoltaic material is originally a part of a longer wavelength and lower energy, and on the other hand, the thermal insulation of the thermoelectric material is not good. After the material is heated on one side, the other side will be very The heat is quickly heated, causing the excited electrons to go around and not form a stable current. To solve this problem, the direct method is to use air-conditioner or water-cooling to cool down the low-temperature end of the thermoelectric material. The user quit. Originally, this equipment was used to generate electricity. As a result, my electricity bill will eventually be used to blow air-conditioning.

To solve this problem, the Massachusetts Institute of Technology proposed to separate the sunlight into wavelengths and send them to the photovoltaic panels and thermoelectric materials respectively. Simply put, this is like using a prism to separate the white sunlight into seven colors: orange, yellow, green, cyan, and violet. The green to purple part is sent to the photovoltaic panel, and the red to yellow part is used to heat the thermoelectric material.

However, it is not difficult to think that if you simply put a prism on top of a solar panel, you have to use several square meters of photovoltaic and thermoelectric panels in order to receive sunlight of 1 square meter. Therefore, to use this method effectively, it is necessary to first integrate a large area of ​​sunlight and separate it by wavelength. Concentrating sunlight requires a complex set of automated devices to track the sun for optimal angles of incidence, which in turn will greatly increase the cost of solar power generation. Only large-scale commercial power generation can afford it. For ordinary people, the solution proposed by ** is to use copper sheets placed in a vacuum glass container to collect heat energy, and the copper sheet is covered with thermoelectric material to generate electricity. Using ordinary thermoelectric materials, this method can also achieve an unprecedented 5% efficiency. Although compared with photovoltaic power generation is still very low, but its low cost advantage can offset this deficiency.

Yin Huiming and Yang Dajiang switched to nanotechnology and modified the structure of materials. An article published in Science magazine in 2002 became the basis of their work. By controlling the growth of semiconductor crystals, scientists can fabricate materials that allow only electrons to pass through without passing photons. In this way, the heat will not be brought from the hot end of the thermoelectric material to the cold end by the photons, and both sides can always maintain a relatively large voltage difference, thereby improving the efficiency of the thermoelectric material. If this thermoelectric material is combined with photovoltaic power generation, and the light energy intercepted by it is used to heat water, the energy efficiency can reach 50%.

Charles Stafford at the University of Arizona hopes to solve the solar power cost issue more thoroughly. His proposal is to completely abandon the use of photovoltaic panels instead of using modified polyphenol ethylene polymers. By selecting a functional group on the molecular chain, such a polymer is expected to allow electrons to flow in a certain direction. Photons are trapped in spider webs in this material, which can also achieve solar energy utilization of 20% to 25%, which is higher than existing photovoltaic power generation systems. What's more, the polymer can be painted on the roof or wall like an ordinary paint. Then the electrode is connected to the corner of the wall, and the user can use solar energy to generate electricity.

If these solar energy methods can be put into use, it will make it possible for ordinary people to use solar energy widely and even help each household save considerable heating and electricity bills. The existing energy landscape will also undergo great changes.