Alternating and direct current

Alternating current is the type of electric current in which the direction of the flow of electrons (polarity) changes periodically, at regular intervals, with an oscillating pattern that is represented as a sine wave. Due to this changing polarity, alternating current flows in both directions in an electric circuit.

The frequency of this oscillation in a period of one second (how many cycles are produced in a second) is one hertz (Hz). In many countries, including Spain, the frequency is 50 Hz. In others in Asia and America, such as in the United States, it is 60 Hz.

Alternating current is the most suitable to transport electrical energy, which is then converted to different voltages through transformers. This type of current is the one that is used to transmit electricity from power plants to urban areas. It is also the one that reaches our homes, the one that powers appliances, and the one that gives us light at home.

Unlike what occurs with alternating current, in direct current the flow of electrons is transported in a constant direction. There are no changes in polarity and, moreover, the flow of electrical energy is uniform, so the energy supply is stable.

This constant voltage makes it suitable for sensitive electronic devices. It is the type of current that batteries, solar panels, and some generators supply us. It is the one that is stored in the batteries of our cellphones and laptops, and the one that the electronic devices of our homes use, such as the television, after transforming the alternating current of the electrical network of our home.

Although we have already noted some characteristics that differ between alternating and direct current, this would be a summary:

• Alternating current changes polarity in a periodic manner, while direct current remains constant in the same direction.
• The waveform of alternating current is sinusoidal, while that of direct current is represented as a straight line.
• Direct current is generated in batteries, solar panels, and some generators; alternating current, however, is generated in power plants.
• Alternating current is more suitable, as it is more efficient, for transporting energy over long distances. Direct current isn't used for this purpose because it is less efficient, greater loss of energy is produced.
• Alternating current is more easily convertible to different voltages through transformers.
• Alternating current is the one that is used in the electrical grid and, for example, which our kitchen's appliances consume. Alternating current is the one that electronic devices use internally and the one that is stored in batteries and batteries of devices such as cellphones.

As you see, alternating current and direct current have, because of their characteristics, different uses. At Repsol, we use both alternating current and direct current, depending on the transportation or energy storage needs, to save it or make it reach where necessary.

At this point, you will understand better why alternating current can't be stored: by changing polarity, and therefore being transmitted in different directions, it isn't possible to store it. Direct current does allow it.

Different energy sources also generate different types of current. For example, the type of current of the electrical energy produced by wind turbines (windmills that produce wind energy) is alternating current, which is then converted into direct current through rectifiers, which facilitates the storage of electricity in batteries.

In the case of solar energy, however, the sun's rays are transformed by the photovoltaic panels into direct current electricity. Afterwards, in order to be able to harness it for its common use in the electrical grid, an inverter converts this direct current into alternating current.

Now that you know more about the two types of electric current and also about solar energy, you may be interested to know about Repsol's projects aimed at fostering the production and supply of this type of renewable energy. On the one hand, we can install solar panels on your home or business, through our Solar360 program, which will allow you to save in electrical energy while you are supplied with an environmentally friendly energy.

On the other hand, we offer you the possibility to connect to a solar community and consume solar energy produced locally and close by, while you save on your bills, with our Repsol Solmatch program.