The choice of AC instead of DC for household electricity is a comprehensive result based on power transmission efficiency, equipment compatibility, and historical technological evolution. The core logic revolves around “how to transport electricity from remote power plants to thousands of households at low cost and low loss”.

1. The core advantage of AC is the efficient implementation of long-distance power transmission.

There is a natural geographical gap between power production and consumption – large power plants (such as hydropower and thermal power plants) are often built in resource rich or far from urban areas, and need to transmit electricity hundreds or even thousands of kilometers to residential areas. During this process, when the current passes through the transmission line, thermal losses will occur due to the resistance of the wires (following Joule’s law: losses are proportional to the square of the current). If losses are not controlled, a large amount of electricity will be wasted during transmission, leading to a surge in power supply costs.

The key value of AC lies in its ability to easily achieve “voltage rise and fall” through transformers (devices with simple structure, low cost, and no moving parts):

• Power plant boosting: The AC voltage generated by the power plant is about 12000V, which is first boosted to high voltage of 115kV, 230kV, or even 765kV through a boosting transformer. According to the power formula, under the condition of constant total power, an increase in voltage will significantly reduce the current, thereby reducing the heat loss of the transmission line (for example, if the voltage is increased by 10 times and the current is reduced to 1/10, the loss is only 1/100 of the original), and the final transmission loss can be controlled within 5%.

• Voltage reduction before entering the household: After the electricity arrives in the city, it is first reduced to around 12kV by the voltage reduction transformer of the substation, which is used for local distribution within the city; Finally, the voltage is further reduced to safe household standards (such as 120V in North America and 230V in China/Europe) through small transformers located in residential areas or streets, to avoid the danger of high voltage to human health and household appliances.

On the other hand, DC, due to its constant voltage and current direction, cannot generate a changing magnetic field – and the working principle of transformers relies on “changing magnetic fields inducing voltage”, so DC cannot achieve voltage rise and fall through conventional transformers. If DC transmission is forcibly used, it can only be transmitted at low voltage and high current, resulting in extremely high line losses (for example, the loss of a 100 kilometer DC line may exceed 50%), forcing power plants to be built near users (usually within 1 mile), which cannot meet the large-scale power supply needs of cities.

2. Natural compatibility between AC and household appliances.

In daily life, household appliances (from large appliances to small devices) mostly rely on AC drive or are more suitable for AC power supply. This compatibility stems from the characteristics and manufacturing cost advantages of AC:

• Suitable for mainstream motor types: refrigerators, washing machines, air conditioners, range hoods and other large household appliances, with AC induction motors as the core power component. This type of motor has a simple structure (without the need for vulnerable components such as commutators), low failure rate, controllable cost, and can directly utilize the alternating characteristics of AC to achieve self starting without the need for additional electronic control components. DC motors (such as early brushed DC motors) require mechanical commutators to switch the direction of current, which is prone to wear and has a short lifespan; Even modern brushless DC motors require complex controllers to function, and historically have been manufactured at much higher costs than AC motors.

• Compatible with heating and lighting equipment: Resistance heating equipment such as electric ovens, water heaters, and electric heaters, although theoretically compatible with AC and DC (current passing through resistors will generate heat), as AC is a unified standard for the power grid, the equipment does not require additional “AC to DC” converters, which can significantly reduce production costs and failure rates. Early incandescent lamps and later fluorescent lamps can also be directly connected to the AC power grid for operation; Although modern LED lights are essentially DC driven, they only need to integrate a small rectifier (with extremely low cost) internally to adapt to household AC without changing the power grid architecture.

3. The “Electric Current War” established the dominant position of AC in the late 19th century, directly determining that AC became the global standard for household electricity.

Behind it was a practical competition of two technological routes:

• Edison’s DC solution limitations: inventor Edison initially promoted DC power supply systems and built early DC power plants in New York. However, as mentioned earlier, DC cannot be transmitted over long distances, and its power supply range is limited to within 1 mile around the power plant. To avoid losses, thick wires are required (which is costly) and cannot meet the needs of urban expansion.

• Tesla’s AC solution breakthrough: Physicist Tesla invented a multiphase AC system and AC induction motor, solving the core problems of AC transmission and application. Entrepreneur Westinghouse Electric adopted this plan and successfully used AC to power the 1893 Chicago World’s Fair (lighting tens of thousands of lights), followed by the construction of the AC transmission system for the Niagara Hydroelectric Power Station (delivering electricity to Buffalo, 35 kilometers away). These cases demonstrate the scalability of AC, completely defeating the DC solution and establishing AC’s global household electricity position.

4. The application boundary of modern DC: still relying on AC power grid.

Nowadays, DC is widely used in solar power generation, battery energy storage, and electronic devices, but it has not replaced AC’s core position in household use.

• DC to AC conversion of renewable energy: solar panels directly generate DC, and household energy storage batteries also store DC, but these electricity need to be converted into AC through “inverters” before they can be connected to the household power grid to supply household appliances – essentially still relying on the unified standard of AC

• Supplement to High Voltage Direct Current (HVDC): Modern ultra long distance transmission (such as cross-border power grids, offshore wind farms to land) uses HVDC (with lower losses than AC), but after the electricity reaches the urban distribution network, it still needs to be converted to AC before it can be used in households.

In short, the modern application of DC is a supplement to the AC power grid, rather than a replacement – the core needs of household electricity (long-distance, low-cost, compatible with multiple devices) are still perfectly met by AC.