1924: Solar Panels

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Solar Panels
This works for a surprising range of sunlit things, including rooftops (sure), highway surfaces (probably not), sailboats (maybe), and jets, cars, and wild deer (haha good luck).
Title text: This works for a surprising range of sunlit things, including rooftops (sure), highway surfaces (probably not), sailboats (maybe), and jets, cars, and wild deer (haha good luck).


This handy decision tree aims to help in finding out whether a given object should have solar panels installed on it.

The root question is whether the object of choice moves. If it doesn't and has no nearby empty space that would be more practical for the solar panel installation, then yes, the object should be equipped with the solar panels. If the object is static, but you could more easily install the panels somewhere else nearby, probably that's the best place. An example of this is a slanted rooftop of a house or a field on a hillside: it's certainly possible to put solar panels there, but if a flat surface, like a flat-roofed house or a level field, is available, it would generally be easier to put them on that. This way, you can select the optimal direction for the panels to face, which might not be possible on a given incline, or even have them move to track the sun. However, if the house has a side that is turned towards the sun (south in the Northern hemisphere) then a house roof could be even better than on the ground, which is why the title text says "sure" for rooftops. For another example of things where "putting next to it" instead of "on it" is generally the easier (and arguably better) option, see the "highway surfaces" of the title text.

If the object moves, the next question is whether its batteries can be recharged or swapped with ease, in which case batteries may be a better option than solar panels, if the purpose of the panels is to power the object. The idea is that solar panels on a vehicle sound like an interesting idea, but batteries can be much more easily (and economically) recharged from a fixed electrical station than using solar panels on the vehicle as a power source. It may be possible to have solar panels on the electrical station, but that is a separate device to consult the table on.

Finally, if the object moves and batteries are not an option, the last question is whether the object heats up during operation. If so, solar panels may not work well. Randall doubts it mockingly, see also the title text regarding his Haha Good luck final option. Solar panels can only produce electrical power equal to about 20% of the solar radiation they receive. Thus, a device that heats up during use likely consumes much more power than the amount which could be produced by solar panels covering its surface - so "good luck". Obviously, many animals are also "moving objects" fitting this condition, and installing solar panels on them is bound to be a challenge. Moreover, solar panels do not work effectively when excessively hot [1] (solar panels are typically designed to operate in temperature ranges of 15-25 Celsius, 59-77 Fahrenheit, 288.15-298.15 Kelvin, 518.67-536.67 Rankine, 12-20 Réaumur, 15.38-20.63 Rømer, 127.5-112.5 Delisle, 4.95-8.25 Newton, 5.968 546×10⁻²¹ - 6.174 608×10⁻²¹ joules of translational kinetic energy or 37-51 Felsius).

But if changing batteries is not an option, and heat production and power requirements are low, then solar panels can be an excellent solution on a moving object. An excellent case for this is on space probes and satellites, which are typically powered entirely by solar panels (and reliably receive sunlight, because there are no clouds to interfere). Randall is well aware of this, as shown with the comics 695: Spirit and 1504: Opportunity about the two solar-powered Mars rovers, although in this comic he seems to have only been concerned with Earthbound objects.

The flow chart, however, does not mention if the thing in question actually needs solar panels, but according to the title text it works very well, and thus Randall implies that if the answer is sure then it is relevant to put solar panels there. The more solar panels in place, the fewer fossil fuels are needed, and this is in line with Randall's general interest in reducing climate change.

The title text suggests that this flow chart is very broadly applicable to anything the Sun hits.

Rooftops are classed as "sure", and those are, indeed, an active subject of solar installation (though, if there's suitable land nearby, it might not be the most efficient).

Highway surfaces are classed as "probably not". There have been proposals and experiments a concerning photovoltaic pavement covering roadways with solar panels, but these have proven to be impractically expensive and prone to damage. The flow chart suggests that, since many highways are near land that could be used for solar panels, that will usually be the more viable option.

Sailboats are classed as "maybe". Unlike boats with motors, sailboats don't consume enough power to heat up, only requiring enough power to provide electricity for whatever equipment and appliances are on board. Since some sailboats are at sea long enough that swapping or recharging batteries may be difficult, solar panels could be a viable option.

Multiple other moving objects, including jets, cars, and wild deer ends up on the haha good luck result. While these examples seem unrelated, they all have the same limitation: they consume far more power while moving than could realistically be harnessed from solar panels (as demonstrated by the fact that they noticeably heat up). There are some experimental solar-powered cars, but these tend to be exceptionally low power (and resultingly low-performance) vehicles. Wild deer are clearly a humorous option, as they'd have little use for the electricity from solar panels, and would likely resist any efforts to install them. Nonetheless, Randall includes them to make the point that the chart is effective, even with ridiculous examples.


[A flow chart that features four questions in bubbles. Each question has yes/no options in bubbles overlain to the left and right on the question bubble. Curved arrows points from the yes and no bubbles to either the next question or the result. The result written at the bottom is not inside bubbles. The chart has two main branches, that ends up in five places using only four different results, as the middle result is shared by both branches. Above the chart, there is a caption:]
Should I put solar panels on it?
Does it move around?
Does it have regular chances to recharge or swap batteries?
Probably not
When running, is it hot to the touch?
Haha good luck
Is there an empty space nearby where it would be easier to put them?
Probably not [Uses the same sentence as the one in the first branch.]

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Sorry, but who, except the odd American, has *empty space* next to anything that belongs to him? ;-) -- 20:47, 4 December 2017 (UTC)

I think there are a lot of farms and villages where the residents have empty space next to them outside of America. And even inside America anyone in urban areas doesn't have much empty space next to them. But urban areas are prime for rooftop installation, which also has the added benefit of not covering up areas of vegetation. Also apartment buildings are more likely to have flat rooftops which are better for placing solar panels. Rtanenbaum (talk) 14:26, 6 December 2017 (UTC)
Well I'm not going to give up a fifth of my precious garden to solar cells, when I can mount them safe and flat on the roof of the house, where they are already at a close to ideal angle (provided your gable goes east-west, OK). And for most people in the old world, as for American suburbia, the available area on a south-facing roof is more close to a third or half of the free space around the house. And I neither want solar cells or my terrace on the north side. :-/ -- 10:06, 7 December 2017 (UTC)

And really, if it moves, just keep the diesel engine in it, or switch to hybrid if you can. Batteries that are charged from power plants running on fossile fuel are an ecological nightmare. And car batteries are usually charged overnight, when solar panels are dead. -- 20:54, 4 December 2017 (UTC)

You are right that charging batteries from power plants running on fossile fuel doesn't really bring any ecological advantages ... assuming the engine operates close to optimal parameters. Most cars doesn't operate near optimal parameters inside city, but do on highways, hence hybrid. Also, it is much more ecological to have batteries charged by nuclear power plants. -- Hkmaly (talk) 04:15, 5 December 2017 (UTC)
Ja, Germany here. Our whole politics from left to right has this obsessive-compulsive nuclear-power-blows-up-and-poisons-everyone problem, so we're switching them off. -- 07:49, 6 December 2017 (UTC)
Which has happened now ... so we now buy nuclear power from countries with less safe power plants, while energy prices are skyrocketing yay! -- 11:23, 8 June 2023 (UTC)
I always thought of the main advantage of electrical battery powered cars (instead of petrol or Diesel powered ones) was not so much the immediate ecological improvement, but rather that (once they are the norm) you don't need to convince EVERY SINGLE CAR USER to get rid of their old car and get a new one (Like you have to do now, when you invent engines which use less fuel or something). Instead, when you change the overall energy production of a country (hopefully to something more sustainable and envronmentally friendly), the cars will just passively follow. 14:46, 5 December 2017 (UTC)
I think the main motivation for moving to electric vehicles is that it largely moves the pollution away from where people are. (From the energy production, anyway - particulate pollution from brakes, tyres, etc. is a whole other matter...) 09:10, 6 December 2017 (UTC)
Not another matter, but the exact thing that makes mass-use of electric cars pointless in the moment, especially when motors have catalytic converters, which they have since the mid-90ies. -- 10:10, 7 December 2017 (UTC)

I think that the reference to solar panels on roads in the title text could also be talking about the disaster that is solar roadways. 22:50, 4 December 2017 (UTC)

I don't think it's appropriate to use rooftops as an example of where solar panels should not go when the title text of the comic specifically uses rooftops as an example of a good place for solar panels. How many people have an empty field near their house? I also think it's worth mentioning Solar Freakin' Roadways YM Industries (talk) 04:08, 5 December 2017 (UTC)

I agree, rooftops are kinda the prime example for good places to put solar panels. Especially because even in small cities, there are tons of flat-roofed buildings (which would make the alignment to the sun possible) and it is often (nearly) unused space, whereas an "empty" (as in not-build-upon) space could be used for lots of other things, not least just some wild nature. I went ahead and changed the explanation accordingly, putting hte emphasis mor on inclined vs. flat surfaces (and this free to select optimal direction) 14:46, 5 December 2017 (UTC)

The current transcript is not very useful for people who use screen readers, or for any other purpose (e.g. full text search). Could someone please describe the flowchart in a purely textual, "linear" fashion, as was done for other flowchart comics? Thanks very much in advance! Zetfr 15:01, 5 December 2017 (UTC)

I tried to improve it, hopefully it's helpful. Asdf (talk) 18:02, 5 December 2017 (UTC)
Great, thanks a lot! Zetfr 22:06, 5 December 2017 (UTC)

The flowchart doesn't use standard flowchart symbols - they remind me of cars/trucks, each having a (rounded body) plus two wheels (holding yes and no). Anyone think this is deliberate?

Not particularly as he used similar design in 1688: Map Age Guide. --Kynde (talk) 09:01, 6 December 2017 (UTC)

The reason that you don't want to put solar panels on something that is hot is not because hot things use more power. It's because the efficiency of solar panels decreases as a function of temperature: See here for example http://news.energysage.com/solar-panel-temperature-overheating/. This is why solar panels on a road are not a great idea (among other reasons). 01:23, 6 December 2017 (UTC)

Maybe I'm just a bit slow here, but why are jets, cars and deer considered hot to the touch when running? Sure, jets and cars do have hot parts when running - but so have many modern sail boats (at least motorized ones). And what about deer? The only deer being hot is the one in my oven - and there's no sun. Elektrizikekswerk (talk) 14:31, 6 December 2017 (UTC)

well sailboats have only a small part (the motor) that is becoming really hot, since the body is watercooled. While deer are not getting that hot, a quick google search told me that their regular body temperature is 38.5-39.5°C. Also they do not regulate their temperature by sweating through skinpores as humans, but by sweating in their mouth, and regulating their temperatures through their ears. This means, in my understanding, that when they are running, the body cannot cool down as good as a human one, so i guess the can get up to 40-42°C during that period.
The second thing to consider is, that hot is always relative. In this context it should mean "hot compared to the cooling water of a solar panel", as solar panels generate power by heating up water in a circuit (on a deer it should be a small cirquit to not put to much ballast on the deer). Heating it up can only generate power, when it is also cooled down. For this it needs a colder reference. When the deer itself is getting ~40°C, thats too hot to have cooling capacity. Lupo (talk)
While I see that PV get less effective if heated up and as such cooling makes sense, this was the first time I heard of that. So thank you for that (really!). In the wiki https://en.wikipedia.org/wiki/Solar_panel cooling isn't even mentioned at all. However, this still does not convince me. https://en.wikipedia.org/wiki/Solar_car https://en.wikipedia.org/wiki/Solar_Impulse Granted, these are all protoptypes/experiments (and the plane is definitely no jet) and will most likely not come to serial production, but nevertheless... -- Elektrizikekswerk (talk) (please sign your comments with ~~~~)
Just revisiting this comments 1.5 years later I notice that I was not entirely correct. Solar panels usually (with exceptions) do not "generate power by heating up water in a circuit". Nevertheless overheating of solar panels can be problematic. The reason why "getting hot" is an argument might just be, because things that get hot while running use (waste) a lot of energy. --Lupo (talk) 07:43, 13 August 2019 (UTC)

Randy SO missed the "If you like it..." angle. All the single rooftops! (I'll show myself out) 15:20, 8 December 2017 (UTC)

Why does animals being classified as "moving objects" require a citation? (talk) (please sign your comments with ~~~~)

What about a Tesla with a solar unit with panels that that pop out of the hood storage? 01:24, 4 June 2019 (UTC)

While I get that using solar panels as the sole power source will be a problem on Cars. I think using them to add some charge to the battery of an electric car when it's in a spot where it can not be plugged in, but still in a sunny spot would still be a plus. Think about it a person drives their car to work, and then leaves it sit in the parking lot for hours, and unless they are in a parking garage or at a graveyard shift, the car is going to be in full or nearly full sun all day, not moving. I know during the summers here this is why the cards are always ovens to get into, because of how much solar heat got trapped in the drivers compartments. I think after sitting out in the sun for 8 hours it will at least have some charge on the battery. 22:28, 12 August 2019 (UTC)KitRamos

There are some cars which will go in production soon, using this concept, google for e.g. lightyear cars or sono motors. In the end the car has to be specifically enginered to be able to use solar power efficiently. I also remember to have read somewhere, that for some electical cars (or hybrid) there is a optional solar panel, which can extend range on a sunny day by a few miles. --Lupo (talk) 07:21, 13 August 2019 (UTC)

I would just like to point out that this even works for the sun. 17:22, 19 April 2022 (UTC)