Heliotropic tracker

That's a good question, Chris. Who will judge the responses for the best implementation?

Stick a ladder up against the window, and put the charger close enough to the window that it's always in sunlight.

tape it to the window!

1. Obtain a large potted sunflower. Place flower in proximity to window. Affix the solar panel bit of the charger to the flower, active surface outward.
2. Hire a small child to keep the panel aimed directly at the sun through the window.
3. Duct-tape the panel directly to the window.

Mark L. Fergerson

That's a good answer, Bill, and one that I considered. However, I think Chris is the poster that wants a direct answer to his question rather than alternate solutions.

For a given latitude and time of year, the sweet spot will move in a predefined course across the floor.

Anything that can move (or be moved) carrying the targeted charger can monitor the output of the solar cell (over times longer than any "local disturbances") and advance as long as output climbs, stopping once the output starts to fall (waiting for the sweet spot to catch up to it).

At end of day, manually reposition device at start of the next day's trek.

Assuming this is some sort of abstract, mind-experiment type question, isn't this something that could most readily be implemented with a software solution? Say you surround the main charging cell with four smaller satellite cells. You then mount the phone, charger and satellite cells to a small model car controlled by, for example, a Raspberry Pi which compares the output levels from the satellite cells. You could then come up with a fairly simple algorithm instructing the car to move so as to always be in the spot of maximum light. But there's probably a really ingenious, totally analog, old-school alternative of doing it better and more simply that I'm unable to think of right now.

I don't have an answer, but I think this is a well thought out, simple, simple, solar tracker. Pretty coll!

Mikek

Actually there *is* a simpler solution, Chris. Mark the positions on the floor of the extent of the light patch at dawn and dusk then join 'em up. You now know the arc the light patch will traverse during the day. You also know in which direction it will pass with 100% certainty, so there's no need for 'satellite' cells at all. Just one light dependent resistor on the trailing edge of the 'vehicle' you're using. Arrange things so when that LDR falls into shadow, the wheels get a momentary blip of power; just enough to move them say one revolution or two inches across the floor back into the light zone again. Sorted! :-)

Needs a reset circuit every morning, too, but otherwise works.

The track needs to be adjusted every month or three, though.

Exercise: show why this is true. :-)

Bonus exercise: solve this problem with the RC car and an analog circuit. too. :^)

Tim

Too easy. What's the fancy term for it, now...? Procession? Precession? Anyway, depends where you are on the planet as to whether it's significant or not in this case.

All fine in a clear climate I'm sure, but this approach needs cloud- proofing in this part of the world. A passing cloud's going to send this cart to the end of its day's travel in a few minutes!

If you only charge your cell phone at night (because you work days and aren't home until after dark) you can put the charger anywhere you want and it will work just as well as any other method. If you want it to actually charge the phone, place it beneath a strong electric lamp. If you don't want to use electricity use some strong kerosene lamps.

Any of the above is as good a solution as "assuming" the vehicle has it's own power source.

Here's another good idea. Strap the solar cell and the phone to the back of a cat and let it find the sunny spot when it wants to sleep in the warm. Or a turtle might do as well and consume less food and make less waste.

Better to put a cell on the front and have it run until it gets out of the sun. Then when the light gets blocked it just stops. In fact, the solar cell can be used to power the motor since it can be geared way down and won't take much to make it move.

The unit has half a day to return to the starting point. You can either pick it up each night and move it by hand or it can move in reverse at a

The path won't be a straight line, but can be reasonably approximated by a constant curve given a window of some size. So make the power wheel on one side larger than the other to force a turn. Or just set the steering wheels at an angle which can be adjusted by the season.

Lol, if the car is attached to a string that wraps around pulleys to support a weight, it can be pulled back at night by that weight. No batteries needed, just don't trip over the string.

"axial tilt". te common name is "seasonal variation" or something like that.

and how tall the window is.

But then during the day the motor consumes power to hold position and more power than before to move the cart.

Ratchet. The only power for the return is needed to release the ratchet.

Well, energy is needed for both directions. He's just storing it in the weight, rather than a battery, or such.

If it's coming off the solar cell, who cares? In any event, you are doing the same thing as charging batteries, just with the weight. BTW, it doesn't require energy to hold a position. There can be a lock that does that which is released after some hours of dark. With the trailing photocell it needs battery power to move the thing at all times and if the sun goes away it travels across the room and loses all power for the rest of the day. The leading sensor at least can recover if the sun goes away for less than the time it takes for the sun to pass by the window. Trying to stay in the light is hard if you don't know when the sun is out.

Off the solar cell? A cloud comes by at 10AM and the motor lets go and it parks itself in the shade for the rest of the day.

so now you need a lock (pawl?) and a battery to power the lock...

It's a trailing sensor. forwards power is from the main solar panel. reset is from a battery, or supercap.

possibly it's best to use two sensors and run the motor when they are strongly unbalanced, fleeing the shade.

yeah.