Your panel isn’t going to solve that problem unless I leave the device for hours in direct sunlight somewhere so, no. How about I just plug it into the wall two feet (one meter) away when I need to charge the battery?
Good luck on your kickstarter.
Shut up and take my money.
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The precise answer to this is millijoule counting. I did not measure the precise power consumption of a reference reader per page and per minute of idle operation, so I don’t have a precise answer yet. It should however significantly prolong the battery life even with indoor-grade light.
At 250 lux light, according to a post here, the best to expect is about half watt per square meter, so 8 milliwatts for a 125x125 mm cell.
If the average power consumed by the reader during use does not exceed this, the battery life will be unlimited. Larger cell can be used; 165x115 mm size of a random Kindle will yield 19 milliwatts.
A Kindle Paperwhite will last 28 hours on 1.6Ah battery. That equals 57 mA of current, or 210 milliwatts.
A Kindle 4 will last 15 hours on a 890 mAh battery. That equals 59 mA of current, or 220 mW.
So in a dim room light a matching solar panel on the cover will prolong the battery life by 10% if we don’t take a break, or provide unlimited life if we read only 10% of the time. However, we don’t spend all the time in a lightbulb grade light; daylight is orders of magnitude brighter so the total amount of harvested energy over the course of a day is likely to be significantly higher.
Overcast day is about 1000 lux, which should give us 76 milliwatts. That covers 1/3 of the power demand. Occassional reading during a day gets us even. Full daylight is 25,000 lux, which gets us a noticeable surplus, and a direct sunlight of the kind I like to bask on can be 100,000 lux, which in linear approximation gives us 7.5 watt, or over 30 times of the device’s power consumption. A hour of reading on bright sun will provide enough power for full charge of the battery and then some for the 1.6Ah one, or a bit over half that time for the 890 mAh one.
Edit: Had the numbers wrong, had to recalculate. It’s late.
Tempted, actually very tempted!
But, prototype first.
ok .So how does that change how the device consumes power? If a partial refresh consumes the same amount of power, you’ve gone from a device that lasts for weeks to a device that lasts for hours.
My kindles get charged about once every week or two and I read for an hour or two every night.
The partial refresh uses less power than completely refreshing the screen. That’s why they switched to doing it as the default.
The main drain on kindles is people don’t turn off the wifi.
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@doctorow while the Alphasmart has been discontinued, I did find the Forte, a similar $200 portable word processor sold as an assistive device for students instead of a “distraction free” writer for adults: http://www.writerlearning.com
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