I recently bought a small dual solar/dynamo powered flashlight. 30 minutes of solar power can power the light for 10 minutes, but 1 minute of turning the crank can power the light for 30 minutes.
If the sun is out for say, 12 hours a day, that means it can power my light for 240 minutes. But turning my crank for 10 minutes would power the light for 300 minutes.
Is solar really efficient at all, because wouldn't getting a hand-turned generator get more electricity than waiting for the sun?
Solar power is a function of area. If you are comparing a small cell, say one that fits on a flashlight, to a small generator that fits in the same flashlight, then there will not be much solar power available.
If you are expand your solar cell to a square meter then you will make more power than an "in shape" cyclist can sustain for an hour (200 watts).
Rules of thumb:
• 1 square meter in full noontime sun gets about 1000 watts of sunlight.
• Solar panels are about 20% efficient, so 200 watts per square meter at noon.
• Total sun delivered during the day is equivalent to 4 noon hours in the summer, 2 noon hours in the winter.
1. If your solar panel were 30 times bigger than it is, 1 minute of solar power would power the light for 10 minutes too.
2. Even a small solar panel can power your water pump/weather station/radio repeater when you're ten miles away and don't have the time to spend all day walking ther to spend a minute turning its crank.
3. Solar panels break down less than hand-turned generators. They don't have bearings or windings or gears. If you keep replacing the batteries, your flashlight will ber a usable solar-powered flashlight much longer than it is a usable dynamo-powered flashlight. (The "shake light" design, with a magnet sliding back and forth in a tube through a coil, might be an exception there.)
4. Solar panels keep working even without being fed more rice. Human labor does not produce energy, regardless of what you may have heard in The Matrix; it merely converts it quite inefficiently from chemical energy into mechanical energy.
5. An athlete working his hardest might consume 10 000 calories per day in food, but can only convert some 2000 of those calories into work. If your Lance-Armstrong-level athlete is turning a crank 12 hours a day and eating 10 000 calories, he's producing 200 watts during that time, 100 watts averaged over the 24 hours. Three square meters of solar panel can do the same. Six square meters can do twice as much. And the solar panels won't drop dead of exhaustion after a month.
(Supposedly Lance averaged 5200 kcal/day during the Tour de France with a peak power output of 1000W: http://www.wired.com/wired/archive/12.07/armstrong.html --- but presumably ate more on uphill days than on level days.)
> 3. Solar panels break down less than hand-turned generators.
I live in an African country and solar panels have one huge disadvantage. Solar panels are often used now to power boreholes (usually fully submersible pumps which have become fairly cheap and easy to install, compared to so called "mono-pumps" of the old days) and pumps near rivers that are far from grid electricity. It is also used to power electric "energizers" for electric fences.
The problem is that solar panels keep getting stolen. It is something that is fairly valuable that should be outside. I can just imagine the amount of theft that will go on when people have solar panels on the roofs of their homes/shacks.
Also, the article failed to mention the real problem with using candles and fire for lighting - frequent fires.
That's very interesting! What country are you in? What kind of pumps do people use now?
I imagine that for applications in town, the theft problem will be less. If you have ten or twenty houses clustered together, you can probably leave one rifle home with one of the women in case someone tries to steal the solar panels. I mean, that's the same problem as someone trying to steal a motor scooter or whatever, right?
> That's very interesting! What country are you in?
I lived in rural South Africa (not anymore though).
> I mean, that's the same problem as someone trying to steal a motor scooter or whatever, right?
What is funny for me is that motorcycles aren't as popular in the African countries that I have been (e.g. China or India). But yeah, things that is not inside the home is easily stolen. Things like car batteries or solar panels are extremely popular items to steal.
> What kind of pumps do people use now?
In the old days they used mono-pumps (where the motor was above ground and connected with rods).
Nowadays the pump is in one sealed unit that is connected with plastic piping and electricity. Two people can install a pump in less than half a day and everything is light. The price of pumps also dropped.
Cranks have moving parts, and thus are more likely to break and need service. Additionally, those little combo flashlights (I have one too, I love them) have a very small solar panel. Notice the solar panel in the photo is at least as large as an 8.5x11 sheet of paper- I'm sure it produces much more current.
If the sun is out for say, 12 hours a day, that means it can power my light for 240 minutes. But turning my crank for 10 minutes would power the light for 300 minutes.
Is solar really efficient at all, because wouldn't getting a hand-turned generator get more electricity than waiting for the sun?