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We often use electronic device and home appliances with electricity as a power source. Basically here in Japan, "AC 100 V outlet" is mainly used for charging. The electricity generated by the power plant is delivered to home through "alternating current" or "AC". We are wondering if there is a question at this point. While electricity has direct current (DC) and alternating current (AC), DC is used to provide electricity for primary batteries and rechargeable batteries. Mobile phones, digital cameras, and PCs operate on DC power. Home appliances also operate by converting AC power into DC power internally.
More significantly, solar panels that are getting popular recently generate DC electricity. In addition, Enefarm employs DC power supply to generate electricity from hydrogen or gas containing hydrogen. In order to use DC power supply at home, it is connected to a commercial AC power supply from the outside and then, the AC is converted into DC to use for home appliances. As a result, such a process requires a lot of times.
With direct current sent through the transmission line, there would not have caused such a trouble. Why is the electricity sent from the power plant as alternating current to the commercial power source? There is a historical story.
The electrical products developed by Thomas Alva Edison (1847-1931), who is widely known for the inventor king, were operated on DC power so far. Aiming to transmit the generated electricity as direct current, he started his business in the 1880s using direct current to transmit electricity.
On the other hand, the inventor of the alternating current, Nicola Tesla (1856-1943) who was supported by George Westinghouse, Jr. (1846-1914) promoted power transmission through AC, causing a battle of DC vs AC called "War of the Currents".
After all, DC power transmission was replaced by AC power transmission. The reason is that DC power transmission has disadvantages where the conversion equipment of DC transmission is more expensive than AC one. Also, in terms of short-distance transmission, the loss of DC conversion equipment got higher compared with AC transmission. Considering that the large-capacity transmission was extremely inefficient, it was rather difficult to transform DC power, and as the result, AC transmission has won in the "War of the Currents".
We recognize that DC power transmission had many problems compared to AC power transmission. Having said that, the situation is drastically changing along with the development of various technologies.
Firstly, the total power loss of DC power transmission has been reduced in the case of long-distance power transmission, even considering losses of conversion equipment. The transition was occurred by using longer transmission line compared to the time of Edison. In other words, as for the loss of power generation, the conversion equipment was larger than the transmission network in the short-distance so far. But in the case of long-distance transmission, the loss in the transmission network was rather larger.
Secondly, the development and miniaturization of the buck-boost DC/DC converter helped facilitate the transformation. Moreover, the bi-directional power supply has evolved, and AC/DC interconversion can be also done easily. Following this, it is getting easier to connect to existing power transmission systems mostly on alternating current using grid connection. In addition, DC/DC conversion mechanism has been improved. Besides 12 V DC, the supply voltage of EV can be adopted 280 V or 360 V, which is available with batteries of various automotive devices by stepped down the voltage.
Finally, there are new electrical appliances with a large amount of DC high power generation as well as power supply such as solar panels, hydrogen power generation from gas, and home storage batteries. At present, thanks to DC/AC conversion and grid connection, DC is used for household products. But in the near future, it is highly expected that smart grids with domestic DC system can be built by using EV as part of a large capacity battery.
If Edison were still alive or if there were an entrepreneur as a contender of Edison, what do you expect from their power transmission system?
For example, in the case of a developing country where the power grid will be developed from now on, it will be more advantageous to carry out long-distance power transmission with DC from the beginning. If each household is independently generating solar power, etc., all transmission systems should be built with DC power. And it would be better that only voltage conversion is carried out in each region and a smart grid with direct current will be constructed.
In this case, it is important that voltage is unified into 2 or 3 types to introduce mass production of DC/DC converter, leading to the cost reduction. Now, solar panels, hydrogen power generation by gas, large-capacity batteries like EV, and home appliances operate at various types of voltage.
As a result, the development of DC power transmission and the creation of equipment compatible with certain standardized voltages will open new business opportunities for home appliance manufacturers. Regarding the shape of outlets currently different in the world, the criteria of outlet shape should be unified based on the voltage so that people can use the equipment without a mistake. What is more, there is no need to prepare a shape conversion plug for local use when traveling abroad.
In addition, Edison's invention has a light bulb plug shape (ex. E17 or E26), which is commonly used in the world. From now on, there is a possibility of profitable business to unify the outlet shape by the voltage in constructing a DC power transmission system. Actually, devices with relatively low voltage such as smartphones, digital cameras, and even personal computers are mostly offered by USB power supply.
In this case of Japan, it is necessary to consider whether the existing transmission network with the current 50 Hz/60 Hz will continue or install a new network for DC transmission.
If you prefer to make use of the existing power transmission network, the transmission of electricity generated by solar panel in each local area needs to be operated respectively through local smart grids on DC power aiming for local production for local consumption. And the excess of electricity will be sent to AC commercial power with grid connection.
Solar power companies do the same thing with this. In this system, it is absolutely indispensable for local community to meet the local power demand by its own by purchasing the last one mile of the power infrastructure in the local area for direct current transmission, making the most of the benefits. There is a possibility now that the cost of power generation by solar power generation is falling while the power generation by fossil fuels or nuclear power is getting more expensive in accordance with the measures against global warming and safety measures including decommissioning, and so on.
Of course, you might as well take the opposite way. The last one mile of the power infrastructure uses the existing AC power transmission, and the national power transmission network line is performed via DC power transmission. However, since there are transmission lines of respective Japanese power companies under the present circumstances, you can use DC power transmission as backup. In particular, when there was a shortage of power in the Tokyo Electric Power District after the Great East Japan Earthquake, the government transferred electricity from West Japan to East Japan. Despite this, due to lacking 50 Hz/60 Hz convertible capacity, sufficient power failed to be provided.
Therefore, in case of a disaster, it might be a better option if the DC transmission networks are used as backup. After expanding throughout the country, the DC power transmission lines are to be connected to the AC power transmission networks of each electric power company by grid connection. It seems possible to readily implement a power transmission network that is resistant to disasters as well as compatible with natural energy. Presumably, knowing that the conversion of AC power is conducted in the 50 Hz/60 Hz boundary area, Edison must have been started DC power transmission there with standardizing the transmission voltage.
On the other hand, if you don't use the existing power grid, you will first build a regional smart grid with DC power transmission, and then, you will connect the regional smart grids with a DC power grid. Such a network system will be taken in developing countries as introducing a power grid there.
In this case, if the transmission voltage levels of regions are different, the conversion is required to connect the grids. Of course, as the improvement of the performance in DC/DC converter itself is also accelerated, it may not be a big burden, but unifying the voltage level is absolutely important in that the mass production of small variety of products leads to the cost reduction.
In view of this circumstance, there would be a possibility that a new movement would come changing the historical outcome of the "War of the Currents" that Tesla won over 100 years ago. Actually, under the slogan "Build the environment where the Internet can be used all over the world", SpaceX established by Eron Mask promotes a Starlink program to launch a large number of communication satellites.
Likewise, new projects are underway in the power industry. For example, a project to create solar and wind power plants in the Sahara and the Middle East has been implemented for over 10 years referred to as "Desertec" in Europe. While this project does not work well so far because of funding and security issues, reportedly the company has started a project in Tunisia in 2017. That is why, it is no wonder that some company in the power industry will take the same action.