1119: Undoing

Explain xkcd: It's 'cause you're dumb.
(Redirected from 1119)
Jump to: navigation, search
I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains.
Title text: I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains.


This is another comic in the My Hobby series. It plays on how energy from natural resources (wind, sun, water) gets turned into electricity. Wind turbines convert the wind power into rotational energy, which can then be used to produce electricity. The one seen in the image is the most commonly known wind turbine, which is use on wind farms. Wind turbines provide a renewable resource for homes and cities and a common method for sustainable energy. Turbines have been referenced before in xkcd, in 556: Alternative Energy Revolution.

In this comic, Cueball has rigged it so that the wind turbine powers a fan. He cut the power cable attaching the turbine to the power grid and spliced it with the power cord of a giant fan. The nailed-together 2x4s that form the "tower" for the fan further indicate the "jury-rigged" nature of Cueball's work. The electricity generated from the wind power is then used to power the fan, which in turn produces wind. This is about the complementary nature of wind turbines and fans, which was also covered in 1378: Turbine.

The undoing part refers to how Cueball is using this fan to restore the wind that was used to turn the wind turbine back to the original wind flow, canceling out not only the turbine's electricity production, but also its slight reduction of the surrounding wind force.

Wind turbines have a theoretical limit of 59% of the portion of wind captured. You can see the wind not captured detailed in the image as dotted, turbulent curly lines; turbulent flow. Cueball has placed the giant fan in the direction of the wind so that the wind it produces combines with the windpower not captured by the wind turbine. This is indicated by the lines smoothing like they were at the start. Thus, not only is the electrical benefit undone, but also the change in natural wind currents.

The title text explains that he performs the same undoing process with solar cells, where light energy is converted into electricity using photovoltaic cells, which is then used to power lightbulbs for producing light on the area below them that the sun would normally illuminate. Solar panels only convert 20-25% of the energy captured from the sun into electricity. However, Cueball points out that he sees this as a 20% gain rather than an 80% loss. Since it is Cueball's hobby to waste time and energy, this makes perfect sense.

Incandescent light bulbs only convert at most 5% of the electricity provided into light, the rest is lost as heat energy. Thus less than 1% of the energy absorbed from the original sunlight will be released as light from the bulb. LED bulbs can do quite a bit better, approaching 90% efficiency, and releasing around 17% of the original sunlight, though in different frequencies.

In the case of the wind turbine and fan, the wind will, unfortunately, be moving at a much slower velocity than at the start as energy was lost in converting wind power to rotation energy, then to electricity, then back to rotational energy, then back to windpower. However, in the solar panel and lamp case, the light will be moving at the same speed as it entered the panel thanks to the constant nature of the speed of light, but be less bright instead.


[Caption above the panel:]
My Hobby:
[A large wind turbine is spinning but the electric cord has been severed and rewired to a large fan, with Cueball standing next to it]
[Caption in large text below the panel:]


A similar understanding of the difference between a wind turbine and a fan is presented by Megan in the later comic: 1378: Turbine.

This comic may be a continuation of Randall's mistrust of modern electric wind turbines (see 556: Alternative Energy Revolution).

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


Perhaps his motivation is to restore natural wind patterns to the environment. I remember reading about the ecological impact of wind power includes lessened wind currents. Some organisms rely on the wind to propagate the species, such as winds that blow seeds or how some spiders "parachute" on wind currents. Or it could be that he just likes to mess with people. --Joehammer79 (talk) 13:46, 10 October 2012 (UTC)

I always though that if you put a forest of windmills on top of hill the damage of ecosystem done by the building is enough. Adding the fact about wind used for propagating ... damn, windmills are almost as unecological as solar plants on fields ...
Seriously, how can anyone who things ecologically be AGAINST nuclear power? -- 08:19, 12 October 2012 (UTC)
Ten thousand of mutations from radioactivity? (Seriously, we should be using Liquid-fluoride thorium reactors, only 300 year half-life on the waste, rather than 10,000)-- 15:35, 8 June 2014 (UTC)

At first I thought this should be more of a Blackhat trick, but since he seems to think he is creating good in the world by restoring, it makes sense that it is Cueball-- 14:35, 10 October 2012 (UTC)

Am I the only one who is also entertaining the possibility that the fan setup in the picture is not acting with, but rather counteracting the wind, which is turning the windmill that supplies it power? I understand that the alt-text makes it seem like Munroe's thinking about 'making up' for our interference with insolation (and presumably wind, water etc.) patterns. But, if we're going to bring in logic here, EVERYTHING falls apart :D I had a little fun trying to model what kind of a dynamic equilibrium the hitherto described windmill-fan arrangement would settle into. 17:13, 10 October 2012 (UTC)

I believe you are... The fan's blowing to the right... The wind came from the left... 21:35, 18 October 2012 (UTC)Robert

Indeed, the first thing that comes to mind is the "fan blowing into the sails" arrangement you sometimes see in cartoons, but I don't think that's what's going on here.CityZen (talk) 17:58, 10 October 2012 (UTC)

It's even more fun to do to condoms. --SuspendedPhan (talk) 18:50, 10 October 2012 (UTC)

What the hell is "rotational" energy?!
Although "rotational" energy exists (it is a verbal shorthand for kinetic energy that exists due to a rotating mass), what we actually have here is rotational power, another verbal shorthand for mechanical power transmitted by a rotating object working against a load. Also, Cueball has not disconnected the turbine from the generator but the generator from its electrical load (battery charger or electrical grid tie-in, perhaps).-- 13:20, 13 October 2012 (UTC)

As I understand it, he has disconnected the windmill that was supplying power to the grid and that windmill is now powering a fan which is creating suction which is pulling more wind through the windmill. 16:04, 17 October 2012 (UTC)

Worth mentioning existence of ram air turbines. Pallas (talk) 08:53, 29 April 2014 (UTC)

Um, wind turbines have an motor which is computer-controlled, and which I think isn't completely powered by the blades rotating (if only that, when the wind is still, the turbine stops spinning, and needs a boost to start again when the wind picks up, similar to a battery and starter motor). If the power was cut (which wouldn't happen, BTW. Wind farmers aren't stupid and they realise the problems with normal cables, so it's all underground), the turbine would slow down and stop, like a solar-powered pinwheel. (talk) (please sign your comments with ~~~~)

I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains.

When? I used Google News BEFORE it was clickbait (talk) 17:35, 20 January 2015 (UTC)

Here is the truth: Enough wind turbines over time will kill us all. The wind turbines slow down Earth's rotation. Whit that the trade winds will die and then there would be no life possible on Earth. Maybe and only maybe we already slowed down Earth enough to induce a climatic change (so many strange natural disasters the last few ...) and we will face a real-life "The Day After Tomorrow". (talk) (please sign your comments with ~~~~)

That's a small turbine based on Cueball's size. SilverMagpie (talk) 20:19, 23 November 2016 (UTC)

Disagreeing with the explanation: the speed of light in a medium other than vacuum is not identical for different frequencies. Thus, the light from the hypothetical LEDs would not necessarily travel at the same speed as (all of the) light from the sun. Nitpicking (talk) 23:47, 4 April 2022 (UTC)