Her er flere eksempler på energihøstere:

ke3ij.com: A "Free-Power", Batteryless, One-Transistor AM Radio that works off of AC hum and 'spherics. 6/1/2007 by Rick Andersen, KE3IJ:
Citat: "...
It is essential that the antenna be nice and long and that an EARTH ground be used (or a cold water pipe). We're trying deliberately to pick up as much AC hum as possible, since it is the power source!
..."

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Electrostatic Motors Are Powered By Electric Field of the Earth. By C.L. Stong, October 1974:
Citat: "...
I made the motor as light and frictionless as possible with the objective of operating it with energy from the earth's field. The field was tapped with an antenna consisting of 300 feet of No. 28 gauge stranded wire insulated with plastic. It is the kind of wire normally employed for interconnecting electronic components and is available from dealers in radio supplies.
..."

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Energihøster IC til at omforme fra lav spænding til højere:

Feb 1, 2010, powerelectronics.com: Ultralow Voltage Input Power Converters Support Energy Harvesting:
Citat: "...
Linear Technology's LTC3108, a highly integrated dc-dc converter, is intended for energy harvesting. It can harvest surplus energy from extremely low-input-voltage sources such as thermoelectric generators (TEGs), thermopiles, and small solar cells.
...
This allows it to boost input voltages as low as 20 mV, to levels that high enough to provide multiple regulated output voltages for powering other circuits.
..."

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Lysdiode energihøster fra krystalgitter vibrationer (varme):

February 27, 2012, physics.aps.org: Synopsis: Optical Device is More Than 100% Efficient:
Citat: "...
Experiments demonstrate a semiconductor device that emits more power as light than it takes in electrically.
Physicists have known for decades that, in principle, a semiconductor device can emit more light power than it consumes electrically.
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The researchers chose a light-emitting diode with a small band gap, and applied such small voltages that it acted like a normal resistor. With each halving of the voltage, they reduced the electrical power by a factor of 4, even though the number of electrons, and thus the light power emitted, dropped by only a factor of 2. Decreasing the input power to 30 picowatts, the team detected nearly 70 picowatts of emitted light. The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers.
These initial results provide too little light for most applications. However, heating the light emitters increases their output power and efficiency, meaning they are like thermodynamic heat engines, except they come with the fast electrical control of modern semiconductor devices. – Don Monroe
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Parthiban Santhanam, Dodd Joseph Gray, Jr., and Rajeev J. Ram. Phys. Rev. Lett. 108, 097403 – Published 27 February 2012. Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency.
https://journals.aps.org/prl/abstract/10.1...

Diskuteret her.

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Massachusetts Institute of Technology. "A new way to harness waste heat: Electrochemical approach has potential to efficiently turn low-grade heat to electricity." ScienceDaily:
Citat: "...
Since the voltage of rechargeable batteries depends on temperature, the new system combines the charging-discharging cycles of these batteries with heating and cooling, so that the discharge voltage is higher than charge voltage. The system can efficiently harness even relatively small temperature differences, such as a 50 degrees Celsius difference.
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In a demonstration with waste heat of 60 degrees Celsius the new system has an estimated efficiency of 5.7 percent.
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I kilderne på denne side er der flere beskrivelser af elektrostatiske motorer drevet af atmosfærisk elektricitet.

Jeg er helt på det rene med, at det jo nok kun er muligt ved jævnstrøm

Nej, man kan netop ikke høste energi fra jævnstrøm, med mindre man bevæger energihøsteren i forhold til ledningen.

Når man snakker energi, må man skelne mellem potentiel energi og kinetisk energi.

Energien i et elektrisk felt forårsaget af lederens spænding er potentiel energi, som kan opfattes som en kraft mellem ledningen og energihøsteren. Da energi er kraft gange vej, er det indlysende, at man ikke kan høste energi fra en konstant kraft, med mindre man ændrer vejen dvs. bevæger energihøsteren i forhold til ledningen.

Energien i et magnetisk felt forårsaget af en strøm eller en permanent magnet er kinetisk energi, som kun kan udøve en kraft, hvis den ændres(!), så man kan heller ikke høste energi fra et stationært magnetfelt. Hvis man kunne det, ville en permanent magnet hurtigt miste sin magnetisme.

Man kan i princippet godt høste energi fra en ledning, der fører vekselstrøm; men normalt består en ledning af to eller flere ledere, der har den egenskab, at den strøm, der går den ene vej i én eller flere ledere, præcist modsvares af en tilsvarende strøm den anden vej i de resterende ledere - ellers kobler HFI relæet ud, så det resulterende magnetiske fjernfelt er 0 bortset fra små ubalancer og derfor uhyre svært og ineffektivt at høste energi fra. Det elektrostatiske fjernfelt afhænger af spændingsbalancen, som er rimelig god ved en 3-faset belastning, men ikke ved en enkeltfaset, så her kan man nok høste lidt energi via en kapacitiv kobling - specielt hvis man drejer kablet, så høsteren kommer ud for faselederen.

Energien, der høstes, er i intet tilfælde gratis. Pga. loven om energibevarelse kan den kun komme fra ledningen, så forbruget stiger en lille smule. Desuden kan der naturligvis kun høstes energi, når der er spænding på ledningen og evt. går en strøm, så det er næppe noget, der kan bruges til noget fornuftigt i praksis.

Iøvrigt ved jeg ikke, hvad Johan Pedersen mener med en AC-lysleder:

Omkring en strømførende AC-lysleder