Why do they put solar panels on calculators?

Factual Questions
1

Feel free to ignore the following anecdote and skip strait to the question in the next paragraph. About a month or two ago (having finished university early this year, since I was more or less resitting the one previous) I decided to do some drawing (don’t worry, this is going somewhere). While sketching out some guidelines (the mechanically minded graphics programmer I am) I decided I’d better work out how large a circle I should base the head of someone I was drawing in the background (perspective is rather difficult to get right, for me at least) off should be. So I dug through my satchel and found what I was looking for; the (now quite grubby and with a cracked case) “Texet Albert2” scientific calculator I’d bought for a fiver in secondary school. To my annoyance, the battery was dead. But then, as I was grumbling about having to go out and expend about the equivalent of 1 month of WoW subscription’s or a can of airduster’s worth (or about 6 beers worth, as some of my peers put it) on a replacement, (or find somewhere that actually sells those annoying button cells) I saw a ray of hope…literally. I noticed that the often ignored solar panel actually did it’s job, and a faint 0 appeared on the screen when I tilted it correctly. Realising this, I held it under a desklight and carried out my equation (the head in question ended up being based off a 6mm diameter circle, in case you were wondering), then left my faithful old friend on the windowsill. After a few weeks of sunshine it was working as well as it had when little Bisected first tore off the packaging (the fact a strip of duct tape was fulfilling the role originally given to 6 metal screws not withstanding). Clearly the solar panels they put onto every pocket calculator I’ve come across do have some use.

Anyway, this brings me onto my question. What’s so special about calculators that solar panels are so common in them? Plenty of other devices have them built in (torches, houses, etc) and solar powered chargers for various gadgets seem to have emerged recently, but only calculators seem to have them all the time, on everything else they’re a gimmick or a selling point. Who first put a solar panel on a pocket calculator and when did failing to do so become such a mortal sin?

2

The fact that they are one of the few common objects on which can actually operate on solar panels.

Sure you can put solar panels on a flashlight as you note, but the expression “useless as a solar powered flashlight” didn’t come from nowhere. Flashlights are only useful in the dark, you know, when there’s no light. So although you can charge them with solar panels you can’t actually operate them that way. Similarly solar powered watches are great except that you need a watch to operate in the dark and keep time when you’re asleep. The same goes for pretty much every other device in the world: they need to operate in the dark.

A calculator in contrast is only useful when you have enough light to read and write anyway, and that is the same amount of light that it takes to operate the thing with a solar panel. So a solar powered calculator is perfectly feasible. In fact many calculators are only solar powered and they are perfectly useful.

Added to that calculators have very low power demands. The current from a tiny solar cell can operate them in dim light. There’s no hope of that for anything that has to operate a motor or even a speaker.

IOW if you put a solar panel on any other device it basically just means that you have to wait 3 hours for it to charge when the battery dies, rather than buying a new battery. That feature might be useful in remote locations, but most of the time for most people it’s useless. If you put a solar panel in a calculator you extend the batter life indefinitely and produce an object that can operate perfectly even with no battery, as you discovered.

That’s why solar powered calculators have taken off when few if any other products have incorporated solar power.

It was routine at least as early as the early 80s, so it goes back a fair way.

I’m not sure it did.

You can still buy a great many calculators sans solar power. From my experience I’d say about 50% of calculators have no solar panel. Oddly enough function and price doesn’t seem to play any role, being just as common on cheap models as expensive and just as common on scientific calculators as very basic models.

3

There’s a slight price difference; the scientific calcs I usually buy (2-line TIs or Casios) run $9-10 without solar panels, and $13-15 with. You’re right that it’s still quite common to not have a solar panel; not only do a good 50%+ of the 4-function and scientific calcs lack them, but IIRC they’re relatively uncommon on the higher-end graphing, financial, or programmable calcs. They also seem pretty rare on HP calcs of any type.

I suppose someone who only plans on taking math/physics/whatever classes for a couple of semesters appreciates having the lower-priced option, but the extra $4 or $5 for a calculator less likely to conk out mid-exam seems like a good investment to me.

4

I have a solar-powered watch (a Citizen Eco-drive) that works flawlessly. It will run for 90 days (in total darkness) on just 30 minutes of full-sun exposure.

5

My Eco-Drive is still ticking away, going on 12 years now without having to change a battery.

Soon, though, it will be tucked safely away to make room for my Seamaster…

6

I won a solar-powered calculator as a door prize at some work-related party. The thing was a piece of crap. You had to hold it about two inches from a lightbulb for it to work, and if you accidentally moved it to three inches away, it would power down and lose your calculations.

And no, I’m not exaggerating those distances.

7

Just a aside - A bike computer, one that tells speed, distance would also seem a application for a solar panel.

8

It is a bit of a strange thing. Since the power draw is so low, it should last for years on a normal battery. So the solar cells are roughly covering the 4-20 year part of the lifespan. You don’t see many products designed that way.

9

Surely a dynamo would make more sense?

10

It’d work, but IMO wouldn’t be worth it. Bigger dynamos (large enough to run a tail light) rather inefficiently convert your hard work into electrical energy. If you want a tiny one to just power the cycleputer, it’d be tricky to make it efficient and durable, and probably wouldn’t be that cheap. Plus you’d have yet another fiddly little bit attached to the bike.

Solar cells would be cheap (probably an additional few dollars, like with calculators) and wouldn’t require much of a redesign.

11

Aside from the many other objects you can operate with solar panels, obviously …

That expression may have been correct in the 60s (once, for 20 minutes), maybe the 70s, but from the 80s onward that expression only shows that you missed the technological developement of the last 30 years.

Because, you see, nobody says that you have to run the the flashlight directly off the solar panel like a calculator. Instead, people invented this thing called (in Germany) Akkus (or rechargeable batteries in AE), which you charge with the solar panels, and then you put the Akkus in the flashlight. And voila, a miracle!: Light from the sun at night.

True, in the 80s, the early Akkus were NiCd, which had a problem with the so-called memory effect (which Cecil wrote about) - they stored less energy if they weren’t fully discharged. But then in the 90s the NiMH Akkus came along, which don’t have that problem. (Together with LiIon Akkus, but those are still expensive and a bit finicky and thus used primarily for laptops and similar).

In the last 20+ years, development organizations have distributed - either as gift or with a micro-loan - thousands of solar-powered flashlights in Africa and Near East countries. In India, the Barefoot movement uses them to light schools at night for evening classes for adults who work during the day. In Afghanistan, the nomadic women can now prepare their wool and do handicrafts far longer by good lamplight instead of flickering firelight. In Tanzania (near the Equator, where the days are short, and the sun sets around 6:30 pm), the cost of kerosene for a normal lamp for an average family is around 25 Euros a year currently, while a solar panel plus flashlight costs 30 Euros once and then nothing. (And it comes with a variety of plugs, so people can charge their mobile phone, too). A lamp which doesn’t stink, doesn’t produce harmful soot, doesn’t require expensive fuel, doesn’t pose the risk of burn injuries if tipped over, but runs free every night so children can do their homework, parents can do their handicraft in addition to the housework… is a godsend to poor people in 3world countries without regular power cables.

Good thing those people never heard of the “as useless as solar flashlight” expression…

Again, you seem to have missed the developments of the last 20 years. Yes, the very first solar-powered wrist-watches were big, because the effiency of the solar panels wasn’t as high as it is today; and the batteries were less advanced than today. So those very early watches had a tendency to stop after 5 hours of darkness. But the models of the last 10 years need 8 hours of sunlight to run 5 days; and the solar panel in the watch face is tiny compared to earlier models.

You have never heard of the solar-powered radio, either? It’s combined with a hand-crank as supplement, and again, distributed throughout the 3world countries, where a radio that doesn’t need new batteries (expensive) every few weeks, but can receive lectures and information about every subject, from school lessons to agriculture and hygiene and children’s rights, is an important tool in education.

Or you simply leave it lying in the sun, because you don’t need it during the day.

It’s also useful for everybody who doesn’t want to spend/doesn’t have the money to buy batteries all the time if the sun shines for free; or for anybody who gives two cent about the enviroment and tries to preserve resources and not pollute the ground water with dangerous metals from discarded batteries.

All of my solar-powered calculators don’t have a battery at all.

You mean, aside from the solar-powered satellites in space (for which NASA invented solar panels in the first place), and all the houses with solar panels on the roof to produce their own electricity, the solar-powered cars (still minority, sadly, but doing great in the races), or the big solar-panel power plants? Yes, aside from that (which is outside the US, maybe that’s why you didn’t notice), and inside the US, solar panels haven’t really caught on.

As for the OP question: In Germany, solar panels on calculators really caught on during the 80s, and most calculators had them, without additional batteries, because a lot of calculators were bought for school, and many children were very concerned about the enviroment and doing our best to preserve it.

12

The calculator that’s less likely to conk out during exam would be the solar-powered one, however. A battery can die unexpectedly; solar panel only stops working if the light goes out - but at that point, you can’t write anymore, either.

13

How long ago was this? The first calculators in the 80s had big panels and required a lot of bright light. The later models had far smaller panels and work with normal daylight instead of a bright desk lamp.

Or you simply got a piece of crap. One anecdote about a piece of crap doesn’t invalidate the reports and tests from hundreds of working models from reputable companies like TI, Casio etc.

14

The satellites I’ll grant you, but solar panels on houses or in power plants are only economical because of some pretty hefty government subsidies, and the races those solar-powered cars are “doing great” in are against other solar-powered cars-- They don’t compete against gasoline vehicles.

15

No. The subsidies are to cover the initial cost of investement, because the installation cost of panels plus specialized labor comes to some 10 000 Euros. Faced with a large sum at once, or small sums over a long time, most people will go for small sums, even if they pay far more. But it’s certainly economical to invest once and then get energy free for the rest of your life, regardless of how high the natural gas/ oil/ coal price is at the moment.

And if we’re talking about the subsidies to the renewable energies, we shouldn’t forget all those subsidies to the nuclear industry or the coal plants, should we?

I didn’T say that they compete with gasoline cars. I countered the claim that solar panels can’t be used for anything bigger than a calculator, esp. things with a motor. If a house isn’T big enough (or a whole power plant), and if a car doesn’t have enough of a motor, then I don’t know what satisfies you.

And again, the advances in the past 20 to 30 years are amazing: in the 80s, directly solar-powered cars (with panels on the car itself, as opposed to a normal electric car you charge with the panels on the roof of your house), were hughe things that rolled at walking speed. Today, the panels have shrunk drastically, and the speed is above 40 mph.

16

My solar powered watch has a sleep mode, which it goes into at night when it is on my dresser.

As for calculators, I wonder what the relative costs of batteries and the solar cells is. That could explain a lot.

17

LCD displays took the power requirements down to where a solar cell could power a calculator. A search for “calculator AND photocell” turns up this patent, filed in 1979, granted in 1981:

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=196&f=G&l=50&d=PTXT&s1=calculator&s2=photocell&co1=AND&p=4&OS=calculator+AND+photocell&RS=calculator+AND+photocell

18

Not energy for the rest of your life; energy for the rest of the solar cell’s life, usually a couple of decades or so. For most technologies for making solar cells, the total amount of energy that will ever be gotten out of the cell is actually less than the amount of energy you need to spend to make the thing in the first place. The only reason that such a cell is preferred over a battery is that it’s much smaller and lighter than the equivalent battery. Certainly, there’s room for improvement, and it’s a worthwhile area of research, but with a very few exceptions, solar is not yet ready for prime time.

19

Ah, I give up. As I feared, ideology against solar is simply too strong.

20

You should know better, Chronos.

The energy payback time for PV is two-four years: http://www.nrel.gov/docs/fy04osti/35489.pdf