PV Gap

Charlie Said:

solar panel - light sensor question?

We Answered:

Hey JT, you might not be aware of it, but most trackers built today do not use a motor drive to keep positioning them at the sun. They use a partially shaded refrigerant tube aligned along the two sides of the solar array. When the sun is shining on the array, one tube gets more sun then the other, causing the refrigerant in that side to vaporize and travel through a balance line to the other side where it recondenses. This causes the shaded side, which is closer to the sun, to be heavier, and gravity slowly forces the array around until the shading on both tubes is even. There is no motor, or electricity being used for positioning.

If you want to use a motor, there are ways to build up a small set of solar sensors you can probably purchase at Radio Shack, and set them down inside a small tube so only certain ones will have the sun shining directly on them. Then you would need a circuit that runs the motor to optimize solar sensing on the one that is perpendicular to the panels. It all sounds great, but to me there is a much easier way. Use a timer. The sun is in the same place every day at the same time, just have a small stepper motor move one rotation each hour, and gear it so the array rotates exaclty 15 degrees west each hour, then after 9 pm, it should be programmed to reset to the east and start over.

Another option is what we did here, build a manual tracker. I just point it southeast at night, then during the day, when I walk by it, I just turn a crank to keep pointing it toward the sun. What I've found is on days when we are not home, we use less energy anyway, so the tracking is not necessary. Keep in mind that a tracker can increase solar electric production up to 30%, but it also degrades your panels 30% faster. In the big picture, you might end up with panels that last 40 years instead of 50, maybe that is of no concern to you, but if it's extra power your making that your system is not going to use most of the time anyway, why add expense and complication. Trackers do break down, and one day you find it pointing east all day, you just lost an entire days worth of production because the motor siezed up, now you also have to fix the tracker. My manual one still works today, and it never needs electricity to move it. Good luck with your project, and take care, Rudydoo

Cindy Said:

How do you get a solar powered panel to light up a light the size of a christmas tree light?

We Answered:

If you're looking specifically for solar Christmas lights, there is a wide variety available. They come with a solar panel that is designed specially for the strand of lights it is attached to.

Beatrice Said:

how many volts does a solar panel in a garden light produce?

We Answered:

When you take these apart you usually find two AA or AAA sized Rechargeable batteries (typically Ni Cad) Ni cad's are 1.25V ea (x2 = 2.5V) the solar cells have to produce more than the battery voltage in order to charge the batteries. So at least 3.0 Vdc. Output will vary with the amount of sun light and direction the cells are facing relative to the sun. With the batteries connected and charging you may expect to find 3 to 4 volts. The surface area of these cells are pretty small so I would expect to see no more than 75mA to 100ma charging current in full sun and probably 50mA on average. (And this is being optimistic)

The load of the batteries being charged helps to limit the solar cell out put. When you disconnect the batteries or use a very small load you may expect to see several additional volts being produced... (No load voltage will be higher)

There are a lot of iff's and unknowns here as you do not know the configuration of the cells on the light. What looks like one cell is actually be many individual cells connected in a series / parallel combinations to achieve the voltage and current required by the application.

Most of these lights use LED's (2 or 3) which draw 10 to 15mA each at fill brightness. And as the battery voltage drops during the night so does the current draw. The point I am trying to make is that not a hole lot of power is being generated during the day to keep a couple of LED's glowing for a few hours.

Kelly Said:

The effect of colored light on a solar panel?

We Answered:

The short answer is that your solar panel can't 'see' that blue light very well because of the limitations of its spectral response..

The ability of something to capture energy is not just determined by the strength of the energy, but by what the thing is able to catch or 'detect'. This is most often related to the energy's frequency/wavelength. The types of energy (as in color, frequency, wavelength) a device can detect is called its 'spectral response'. This is often given as a numerical range of wavelengths (frequencies, or colors), but it's best to see it as a graph. That way, you see what energy bands it can detect, which are not always next to each other, and how well it can see these energies. To make this clear, let's consider the human eye. It also has a spectral response. It happens to peak around the green, and yellow-green range of wavelengths. So we can see those colors better. If we looked at a bunch of lights of all colors, and those lights were putting out the same amount of energy, the green ones would look brighter to us, just because we can see them better. A blue or purple light would have to put out a whole lot more energy for us to see it as brightly as green or yellow one. This is a human limitation. Other creatures and devices see/detect things differently. Dogs can hear things we can't. Owls can see things we can't. Bats are nearly blind by our standards, but can 'see' sound so well, they can catch mosquitoes in flight. Fish can 'see' electricity with sensors that run along their sides. So, even though ultraviolet light is more energetic than green light, we can't see it. Higher energy 'light' like x-rays and gamma rays, can't be seen by the human eye either. (Although x-rays stimulate my retina, allowing me, and a few others to 'see' them with our eyes closed!) The specifications of your solar panel includes it's spectral response. It may be a graph in the documentation that came with it, or you might be able to find it on the internet. But the wavelength/color that corresponds to the highest peak of the spectral response graph, will be the type of light that particular panel can best convert to electricity.

Have fun!

Oh. just for fun, try this! Look at the front of a TV remote control through the screen or electronic view finder of a camera, and push the remote's buttons! Remotes send out infrared light.

Louis Said:

Can a solar panel detect laser light outdoors during the day?

We Answered:

Probably not. The sun at its strongest puts out 1100 W/m^2. The typical red laser pointer puts out a maximum of 5 mW. Because the collecting areas of the solar cells within the panel are so large, the signal from the laser will be swamped but the sunlight.

Some people are confused about the operation of solar cells. They operate in the same visible band as red laser pointers, therefore, they will detect laser pointers under dark conditions. However, being strapped into a full panel will degrade the response quite a bit, but a small panel or a single cell should still respond to laser light.