I have a Toshiba “Solar” calculator with an LCD display. It has 10 solar panels just under the display and works with a minimum of light. I have had it since the early 70’s and it still works perfectly. I just never need to use it at night. 
At the cutting edge of the technology, maybe, but what proportion of solar cell production is using such efficient technologies?
(More or less) all of it - I saw this payback time quoted over 5 years ago. The technology has only improved since then.
I don’t think so.
The photo-voltaic effect was discovered in 1839 by French scientist Antoine-César Becquerel.
The first semiconductor (selenium) solar cell was built around 1883, by Charles Fritts.
The first silicon semiconductor solar cell was built by Russell Ohl in 1941.
The first efficient silicon solar cells were built, and connected into solar panels in 1954-1955 by Bell Labs researchers Chapin, Fuller & Pearson. (Up to 6% efficiency!)
Then the first commercial use of solar panels was by Bell Telephone in October, 1955, to power a rural phone system in Americus, Georgia. (It was reliable & effective, but their conclusion was that for reasons of manufacturing efficiency and training of their field technicians, it was better to stay with commercial power systems.)
All of this happened well before NASA was created, in 1958.
That was my point; spending an extra $4 or $5 for a solar-power calculator that is less likely to conk out is a good investment. I was pointing out more that the weirdness of having a non-solar calculator that is only marginally less expensive makes sense primarily for folks who really don’t need a calculator for long.
I see that I misread your first post:
as that the battery-powered calculators would be more expensive. That the solar-powered ones are more expensive makes no sense to me, but probably because I almost exclusivly see only solar-powered calculators over here in Germany. The cheap thingies which can do only +, -, x and / and are given away as freebies by the marketing people have solar strips, because putting a cell in there would make them more expensive, and run the risk that the thingie stops working after one week because the cell is old/ got too much heat during storage/whatever. This would make the receipient angry at the company, instead of delighted at getting a freebie.
I also don’t quite understand what people need a calculator only for a short time for class. True, I don’t have math anymore since I finished school, but I still need a calculator for a lot of times when I don’t want to do math in my head, or want to check that the sum is correct. I would hate having to buy (like the OP thought) a new battery every couple of years just to do a bit of math!
Question: how many people still buy calculators, anyway, since a program for it is included in practicaly every PC, most PDAs and presumably many of the mobile phones that replaced the pure PDAs?
Anyone who needs a calculator for exams will be unable to use any alternative device; a laptop, PDA, or mobile phone would be confiscated at the door, or as soon as it was brought out. Not to mention that the form factor for a calculator is ideal for what one does with it; phones and other devices, not so much.
Aren’t you forgetting slide rules?
Don’t forget slide rules! 
I’ve got a 15 year old TI BA-20 profit manager calculator on my desk.
Current version costs $11, so it was probably in the $6 range when it was bought, maybe lower?
It gets used all day, every day, running off of the overhead lighting. The use of a solar panel means that I can have a calculator that is about 7mm thick, without having to pay for, and replace, watch/hearing aid batteries, which run in the $3-4 range. Why wouldn’t I got solar for this simple calculator?
Whether or not it’s a good investment depends on how much you’ll use it. I have a TI calculator that’s over 15 years old and it still runs - without solar panels and without ever having the batteries replaced.
If I had paid 30-40% more for the solar panel version I would have made up that money in interest by now before having to buy more batteries for it.
But why would people take such complicated math as to need calculators at their exams, if they don’t intend to go on studying something with higher math?
I was in Advanced High School (German Gymnasium) of the math-natural sciences branch, and we were forbidden to use calculators in class* before the 9th grade, we had to calculate things in our head or on paper.
Starting in 9th grade, we had to get scientific calculators to do curve discussion, exponentials and later, logarithms. (I got a TI, everybody else had the same Casio model, which sucked).
We also used that calculator for physics and a bit in chemistry. So anybody going into any natural science field would continue using it.
- The teachers couldn’t stop us from using it at home, but that wouldn’t have been useful in the long run.
These scientific calculators had memories, and around that time, the first programmable calculators were around. I remember a book with tips on how to cheat during normal tests suggested sitting next to the math wiz kid. The wiz kid would program the right answers into the memory, then swap calculators with you, and you could just press the recall button.
Only thing, with our grading system, this wouldn’t work at all. A question would be “Discuss the following function…” so we would do the derivation, the zero points, etc., all five steps, and draw the graph at the end. Each part got points. Getting the whole calculation right on paper, and making a simple mistake in the last line that messed up the end result, would still give you 8 or 9 points out of ten for the whole question for doing it right. Writing down the correct end result without any indication how you got there would get you 1 or 2 points. The teacher wanted to know if we understood how to do things.
In when I did my GCSEs (the last exams you take in secondary school, equivalent to high and middle school in the USA AFAIK, and the last compulsory exams) there was both a calculator and non-calculator paper for mathematics. We were expected to be able to do it in our head and be able to use a scientific calculator for functions like logarithms (the days of consulting a massive table are long gone) or if we need to use an accurate value of Pi.
I was also allowed a calculator when I did A level chemistry, A levels maths and A level computing.
Now that I’m in university, most of my subjects don’t need much maths for my exams (most of that is dealt with in the coursework) but there was a mathematics module, the exam for which allowed the use of a calculator.