Alternating or direct current? The matter is still not settled!

The debate that raged at the end of the 19^th century about the best type of current to develop has resurfaced in recent years. Depending on the type of energy produced, how it is used and the distance it has to travel, it can sometimes be more efficient to distribute direct current in networks. Experiments are ‘currently’ in progress...

The war of the currents: a debate that goes back to the 19^th century

Although it was first discovered in antiquity, electricity has only been in widespread use since the end of the 19^th century, initially for lighting and communication. The transmission of electricity over a significant distance, recorded in 1882, was achieved using direct current at the International Exposition of Electricity in Paris¹.

In the 1890s, the development of electricity continued. In the United States, Nikola Tesla designed a reliable and economical alternating current generator, which transformed direct current into alternating current. George Westinghouse, a multi-millionaire entrepreneur and engineer, bought the patent rights from him².

Over the next few years, supporters of direct current, including the inventor Thomas Edison, clashed with those in favour of alternating current, including Tesla and Westinghouse. Alternating current was criticised as being more dangerous, whereas its advocates claimed that it lost less energy over long distances³. Above all, a commercial war raged over the use of patents.

In the end, by 1892-1893, alternating current has largely prevailed. It was the most cost-effective solution at the time since it involved using less copper⁴ and less energy was lost during transmission.

Despite this, some structures and communities continued to operate with direct current into the middle of the 20^th century – such as the capital of Finland, Helsinki, until 1940⁵.

Nowadays, alternating current is used throughout the world in domestic power supply, notwithstanding some minor differences in voltage (V, electrical pressure) and frequency (Hz, the number of times per second that the current changes direction), depending on the country. For example, in North America, electricity is distributed with 120 V at 60 Hz, whilst in Europe, the standard is 230 V at 50 Hz. In Asia and Africa, power supply varies between 220 V and 240 V at 50 Hz and, in South America, there is a mix of 127 V and 220 V, depending on the country.

Progress in electricity transmission in the 20^th century

With the development of high voltage direct current (HVDC) power lines in the 1950s, direct current started to be used again in long-distance power transmission. The first commercial HVDC power line, a 50-kilometre-long submarine cable, went into service in 1954 between the island of Gotland and mainland Sweden⁹. It was the first of a long series of underground and submarine lines in the world, such as those linking France and the United Kingdom or Denmark and Norway.

In the 1970s, technological developments enabled land-based HVDC power lines to be built. This meant that it became possible to use direct current in electric power transmission over very long distances. For certain projects, there are financial advantages in choosing direct current over alternating current.

Are we witnessing a return to direct current?  

Using direct current comes with advantages and can in some cases avoid wasting energy. Indeed, the development of global solar capacity (a new record of 600GW was added in 2024, a 33% increase on 2023¹⁰) implies an increase in electricity produced in direct current form.

At the same time, the growing use of electric-powered vehicles (+ 27% worldwide in 2024 compared with 2023¹¹) and energy storage in batteries, the widespread use of LED bulbs and computer hardware that requires direct current all mean that many infrastructures, especially in the tertiary sector, mostly use direct current.

It is therefore conceivable for buildings to produce electricity in direct current and distribute it in this form via an internal network, without going through a two-stage conversion to alternating current. Significant power conversion losses would thus be avoided.

On peut ainsi imaginer des bâtiments produisant de l’électricité en courant continu et qui la distribuent directement sous cette forme dans un réseau interne, sans passer par une double conversion en courant alternatif. Des pertes de conversion importantes seraient ainsi évitées.  

Cegelec, a subsidiary of VINCI Energies, has already identified many cases where direct current is being used without conversion in closed networks: overhead solar canopies powering EV charging stations, street lighting, office buildings or data centres can use such systems to make significant energy savings¹². For example, charging stations, supplied with direct current without conversion through solar panels installed above them, can charge EV batteries.

More and more microgrids – independent power networks supplying houses, buildings or neighbourhoods – are popping up. In France, Enedis lists more than 490,000 “self-consumers”¹³ (people generating their own electricity), who in some cases might benefit from being able to use direct current without conversion.

As technological developments continue, electrical power networks are adapting to the overall growth in demand and global consumption of electrical energy. Although alternating current was the standard for over a century, a return to the use of direct current is becoming a distinct possibility in the global energy landscape. Direct or alternating current: a choice to be made depending on the origin of the electricity produced, what it is used for, the distance to covered and the transmission power.

Sources :

¹ BnF Passerelles : “Une découverte majeure : l’électricité “ – https://passerelles.essentiels.bnf.fr/fr/metier/8d6b068d-5d3f-47bc-b023-19ab3ca7261f-electricien/article/d8607fa7-61f1-4a1c-91ab-d8dd5358e8fd-une-decouverte-majeure-electricite  

² Connaissance des énergies : “Nikola Tesla“ – https://www.connaissancedesenergies.org/fiche-pedagogique/nikola-tesla 

³ Ibidem.  

⁴ Thomas P. Hughes, Networks of Power, Johns Hopkins University Press, 1993.   https://en.wikipedia.org/wiki/War_of_the_currentshttps://en.wikipedia.org/wiki/War_of_the_currentshttps://en.wikipedia.org/wiki/War_of_the_currents

⁵ Wikipédia : “War of the currents” – https://en.wikipedia.org/wiki/War_of_the_currents 

⁶ Depco : “Voltage and Frequency by Country”  – https://www.depco.com/resources/voltage-and-frequency-by-country/  

⁷ Chapman, Stephen J., Electric Machinery and Power System Fundamentals, McGraw Hill Higher Education, 2001. Hambley, Allan R., Electrical Engineering: Principles and Applications, Pearson College Div, 2007.  

⁸ Kaptitude : “ Le risque électrique “ – https://www.kaptitude.com/blog/le-risque-electrique/  

⁹ Technique de l’ingénieur : “ Le HVDC : une revanche posthume pour Edison “ – https://www.techniques-ingenieur.fr/actualite/articles/le-hvdc-une-revanche-posthume-pour-edison-7188/ 

¹⁰ SolarPowerEurope : “New report: World installed 600 GW of solar in 2024” – https://www.solarpowereurope.org/press-releases/new-report-world-installed-600-gw-of-solar-in-2024-could-be-installing-1-tw-per-year-by-2030   

¹¹ Eco Motors News : “Les chiffres clés de la mobilité électrique en 2024-2025 “ –https://www.ecomotorsnews.com/international/les-chiffres-cles-de-la-mobilite-electrique-en-2024-2025 

¹² Cegelec, groupe VINCI : “Présentation power point “La révolution du courant continu”   

¹³ Les Échos : “La révolution silencieuse du courant continu “ – https://www.lesechos.fr/idees-debats/sciences-prospective/la-revolution-silencieuse-du-courant-continu-2100539