HP Forums

Full Version: I Wish HP Higher End Calcs Were Solar-Powered!
You're currently viewing a stripped down version of our content. View the full version with proper formatting.

I don't know why they aren't. While the solar panels might not have enough capacity for real time use, they could be used to charge rechargeable batteries.


Back in the early 1980s, I managed to hook up a small solar panel to successfully run the HP41 (except for the card reader) in ambient light. That panel was around 20 square inches - around the same size, or possibly slightly larger than the HP41 itself. I hope that cells have gotten much better in the past three decades or so to do the job.


The 41 manual says it takes about 20mA when a program is running, which is a lot to get from calculator-sized solar cells at 5 to 6V even in the sun. Common indoor lighting in a house will be well under 1% of the brightness of sunlight. The 50g, inspite of bigger batteries, has very short battery life compared to the 41.

Why they aren't is that photovoltaics not only don't supply enough current to run the calculator, but also don't supply enough to charge a rechargeable pack in any reasonable interval. They barely supply more than the self-discharge of NiCd and NiMH (except the low-self-discharge NiMH). The amount of power you can get from 10-15 cm^2 of photovoltaics even in bright sunlight is negligible.

Photovoltaics only are sensible on calculators with *extremely* limited processing power, which means not beyond low-end scientific or business calcs. You might notice that on solar-powered scientific calculators, the transcendental functions are often very slow. Such calculators use ultra-low-power masked-ROM microcontrollers which have very little memory and run at amazingly slow clock rates. For obvious reasons that is unsuitable for high-end calculators.