We will confess that the authors of the Applied Physics Letters article “Experimental Demonstration of Energy Harvesting from the Sky using the Negative Illumination Effect of a Semiconductor Photodiode” never used the acronym DAD or the phrase “dark absorbing diode.” But we thought it was too good to pass up. The research work uses a type of diode to generate small amounts of power from darkness. Admittedly, the amount of power is small, but it is still an important result and could result in — another coined phrase — negative solar cells providing energy by taking advantage of the temperature differential between the cell and the night sky.
In theory — and with no atmosphere — the technique could only result in about 4 watts per square meter. Not only is this low compared to a solar panel’s 100 to 200 watts per square meter, but it is also far from the prototype’s 64 nanowatts per square meter. Clearly, this technology has a ways to go to become practical.
To make matters worse, the experimental setup used apparatus that surely drew more than the power generated, so we couldn’t help but wonder if this was real power generation as much as just capturing power that was otherwise wasted as heat. However, it wasn’t clear to us at a cursory glance how much of the power used was for performing measurements versus actually providing energy to the diode.
We will let you decide if this is a breakthrough or a fancy free energy device with some math obscuring where the energy is really coming from. If it is workable, we’ll admit it isn’t impressive today, but neither were 1907-vintage silicon carbide light emitting diodes and those turned out well after some technological advances.