Static electricity

Static electricity, sometimes referred to as simply static, (TV: The Power of the Daleks) was a form of electricity used by many species, most notably the Daleks. Lightning was a form of static electricity. (TV: Smith and Jones)

Relationship with the Daleks
The Second Doctor once explained that static electricity "was like blood to the Daleks"; they required it not only to power their machines, but to live. Even the use of static electricity as a mundane power source seemed ludicrous to human scientists, let alone the even deeper connection that existed between Daleks and static. However, Dalek technology was fully capable of converting other forms of energy into static that they could exploit. (TV: The Power of the Daleks) In 1866 on Earth, Edward Waterfield conducted experiments with static electricity and time travel. Theodore Maxtible mentioned the efforts of Faraday into the field. This caused his time machine to accidentally summon Daleks through time and into his home. (TV: The Evil of the Daleks)

Several accounts stated that the Daleks used static electricity as the power source of their casings, (TV: The Daleks, The Power of the Daleks, PROSE: Doctor Who in an Exciting Adventure with the Daleks) although the Eighth Doctor once alluded to static electricity having only been "a phase of their development". (PROSE: Alien Bodies) The Daleks most notably used static electricity in their city on Skaro when the Doctor first encountered them there; moreover rather than use an internal power source, they picked up power through the floor. The First Doctor, Ian Chesterton, Barbara Wright and Susan Foreman realised this by the smell they made when moving and were reminded of dodgems at a fairground. They disabled a Dalek by pushing it onto a Thal cloak, insulating the Dalek base from the electricity. They then used the empty Dalek shell to escape the city. (TV: The Daleks)

On Vulcan, scientist Lesterson found a capsule in a mercury swamp containing three dormant Daleks, which had been trapped there for hundreds of years and which he soon brought back to life by giving them electricity which they were able to convert into static. The Vulcan colony did not have metal floors from which the Daleks could extract static electricity, for which reason the Daleks had the colonists lay down power cables for them to use as they began to take over the settlement. (TV: The Power of the Daleks) One account states that these Daleks had originated from a period posterior to the Imperial-Renegade Dalek Civil War, thereby suggesting that some Daleks continued to rely on floor-trasmitted static electricity for most of Dalek history. (PROSE: War of the Daleks) By the time of the 22nd century Dalek invasion of Earth, the Daleks used discs on their backs to supply them with static electricity; these required recharging periodically. (TV: The Dalek Invasion of Earth)

Hellcombe Factory was run at static electricity by the Daleks. The factory came alive and produced legions of British Proto-Daleks. (COMIC: The Dalek Project)

However, many later Dalek soldiers displayed no need of travelling along static-infused metal floors for power, nor displayed the satellite dishes, suggesting that they had found alternative power sources. (TV: The Chase, The Evil of the Daleks, Dalek, Into the Dalek, et al.) For example, one account noted that the Dalek casing was powered by the inner creature's telekinesis. (TV: Death to the Daleks)

Other uses of static electricity
The Trods were also powered by static electricity. (COMIC: The Trodos Tyranny)

In 1974, the Third Doctor and Sarah Jane Smith used static electricity and the Earth's satellites to shield the planet from a poison cloud that remained of a galactic cyclone and destroy the Zircon fleet. According to another account, it was the Fourth Doctor and Joan Brown. (COMIC: Doomcloud)

Cessair used a static electrical charge as a primitive but effective force field. (TV: The Stones of Blood)

Behind the scenes
While never explicitly stated that the Daleks evolved beyond a need for static electricity, later stories would drop this aspect. In addition, TV: Death to the Daleks stated that the Dalek casing was powered by the Dalek creature's telekinesis.