Completing the solar panel

I finished my solar panel project this week. I’ve been working on it on and off for the past two years and it’s finally done. The only thing I need to complete is to put the clear acrylic panel on top to protect the cells.

Here are my previous posts on building the solar panel. Part 1 gives information on the parts I bought to build the 18 volt, 60 watt PV solar panel. Part 2 describes my frustration of learning to solder the cells and the time needed to do this well. Part 3 describes my attempt to solder the tab wire to the negative part of the cell and how I’m going to wire the cells to produce the correct voltage.  This last post will summarize the task of completing the solar panel before school starts and what my future plans are with solar power panels.

Video of the completed solar panel

It took me a couple of days to complete all the soldering. I got better at it as I went along and only broke a few cells. Luckily I bought enough and I still have about ten left. The hardest part was dealing with corrosion that built up on the tip of the soldering pen and getting an even flow of solder to flow onto the three positive connections on the back of the cell. I had to scrap a few cells because of poor solder connections.

As you can see from this image, the back of each cell has six places that need to be soldered. This side is the positive side and was the hardest part to solder because each of the six squares needed to have a small piece of solder deposited before I could solder using the tabbing wire. Some people recommend that you hold down the tabbing wire with a small piece of wood when you are soldering them together, but I found that a small book worked better and was not too heavy.

 Assembling the cells

After all the cells were completed, I had three strings of twelve for a total of 36 cells. Each cell has 0.5 volts so this should give a total output of 36/2= 18 volts.

I was now ready to attach the cells to the inside panel. I put a small drop of silicone on the back of each cell and gently pressed them into place in the panel box. After I had them  lined up in three rows, I soldered the rows together in series using the larger tabbing wire. I then used some spare wire I had to make the final connection between the positive end and the negative end to complete the solar panel.

The big test

I actually completed the solar panel and wiring  in the middle of August, but I couldn’t test it as it was raining for days on end. I did take a quick reading inside by the window then and read 4 volts. I thought maybe one of the cells was not soldered correctly, but thankfully, it was due to the clouds and rain condition. This past Friday I went to school to test the solar panel as it was a bright sunny day. On the first measurement, I recorded 19.0 volts. It made my day knowing the solar panel was working correctly. It went up to 19.1 volts in all sun and down to 18.3 when a cloud passed by. The total cost for this project was about  $160.00. I didn’t need to buy some small pieces of wire, screws and paint as I already had some laying around. The biggest cost was the solar cells.

What’s next

My next task is to research and find a deep cycle battery and an inverter to connect to the panel. The battery is a very important part of the system as it stores the energy to power any appliances. This panel may only light a 60 watt bulb for a short time, but I will investigate other types of lights like LED lights and other small appliances to see how long they can be powered using one or two panels. I also may try and build another solar panel using all acrylic and no wood. This solar panel that I just completed would never hold up on a roof for very long and that was not the intention here. I will put in in the sun during the day and bring it in at night.

My goal was and is to learn as much as possible about manufacturing low cost photovoltaic systems (PV systems) that can be made and used in the Philippines. The Philippines already has some of the largest solar manufacturing plants producing the worlds solar cells. The problem is that the cells manufactured in the Philippines are exported to other countries because of the high cost and regular Filipinos not being able to afford these systems.

I believe that bringing this do-it-yourself solar panels, make-your-own-technology to the Philippines will help with innovation in making and using low cost panels. Professional made PV systems are expensive because of the very high manufacturing cost associated with the solar panels designed to last 20 – 30 years, or more. I believe the cost can be greatly reduced if more people are given a chance to experiment with ( play with) and design smaller systems to last in the 3-5 year range. These smaller systems could be brought in during the night to save on wear and tear due to moisture, rain, and general outdoor conditions.

This was a great project for me to build. It’s a good example of bridging the gap between theory and practice. Much is written on building PV systems and the electrical theory involved, but few people actually build the solar panels and experiment with them. Everything doesn’t have to last 30 years. I’m sure there are better and more cost efficient way to assemble these panels that haven’t been discovered yet. Filipinos are very resourceful and need to have solar electricity development in their economy. Given the Philippines’ abundant sunshine and its large work force, solar power and the Philippines is a perfect fit.

This week I gave a demonstration of the egg in the bottle to my classes. This is a favorite demo and I always enjoy doing it. This is a good demo when learning about pressure. To start, burn a piece of paper and put it into the bottle and quickly put the hard boiled egg on top. As the fire goes out, the pressure inside goes down and the higher pressure on the outside pushes the egg in.

Here is a link to my last science lab- the hexaflexagon, which we did last week and you can see the video to learn how to construct and add content to the hexaflexagon.

I have seen this egg demo using a small water balloon and it works the same. To get the egg out, you can try to blow into the bottle which has never worked for me. I usually use an Alka Seltzer and water to pop the egg out. I have also used putting the bottle under hot water to warm the air inside the bottle to expand and push egg back out.

Extensions and discussion

It’s difficult for students to visualize a change in pressure until they see this demonstration. Some of the students have experience going under the water and experiencing increased pressure in their ears, and that helps to understand the concept.  For the egg here, it’s the pressure difference that pushes the egg in.

Also, be careful to explain that the lack of oxygen alone doesn’t “suck” the egg in. After I question the students, I explain how the egg goes in and then have them explain to their lab partner. At the end of the class, I have them write their explanation on paper about the egg demo and hand it in so I can check for any misunderstanding.

Making and encoding the video

Here is my latest video on the egg in the bottle video. Again, I used iMovie and since the demo is short, I used a movie trailer. This worked out well as the audio has music and the audio from the classroom was very chaotic. I encoded the flv video as the highest level, which gave me a file size of about 39 meg.

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This week we built hexaflexagons in class and added science content on each of the four sides. I thought since the water cycle has four main vocabulary terms, it would be creative to put one vocabulary word on each of the four sides. We also used this for the layers of the atmosphere. Hexaflexagons have four sides and can be constructed with only one piece of paper.

This activity builds enthusiasm for learning science and is a good hands-on activity– much like the great bag of science. See the video gallery for all the science videos here.

History of the hexaflexagon

I first learned about hexaflexagon from Martin Gardner when I was in college.  In his book, Mathematical Puzzles and Diversions, Gardner shows a few different ways to construct a flexagon and hexaflexagon. Even though Gardner wrote about the hexaflexagons, others are given credit for their discovery. A graduate student named Authur Stone, while at Princeton University, created the first flexagon by playing around with some paper in math class.

This is a fun activity to do when you have four of something. I also did this with another science class with the layers of the atmosphere.

Here is the video on how to construct your own hexaflexagon. I made this video with iMovie and did a voiceover to give directions on how to construct the hexaflexagon. I exported with mpeg-4 as a Quicktime movie and encoded to flash using iSkysoft Video Converter.

How to fold the hexaflexagon

Start with a piece of paper with the length twice as long as the width. From there, follow my video instructions to complete your own hexaflexagon. Students can add content before or after it’s done. We have made both small and very large hexaflexagons in class over the last few years. Using colored markers is easier that colored pencils as the markers don’t press in on the paper. Remember, the better you make the creases, the easier the hexaflexagon will turn. Watch the video for directions.

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Managing the volcano project

This week my classes researched and made a volcano to demonstrate to the class. The project involved making a volcano resume and building the volcano. They were to present to the class about the volcano and demonstrate how the volcano works. I only let them use baking soda and vinegar because of safety reasons. They can add some soap and a few drops of food coloring to the volcano which will give a realistic look of the lava.

Careful with other solutions demonstrating the volcano

Don’t let them use Mentos and soda to demonstrate the volcano project as this will create a large mess in the classroom and will attract bugs and insects. The Mentos and soda should be done outside on another project. I don’t think using them for the volcano project is a good idea. See my other science videos on the video gallery page here.

Keep the class volcano projects moving along

To help keep thinks moving along, I employ a few strategies for the classroom.

• I keep an index card of each group with their names and class period for each volcano project.
• I use the index cards to show the order of who is going first and the next six groups.
• When the group project is ready to present, I staple the index card to their grade sheet. This helps keep track of what they did and helps me find the location of this group on the video.
• I always require 10 points in the presentation for cleanup of the volcano, ensuring that they learn to help clean up.

I made a grade sheet for each group using this rubric from Science Scope. Use it and change it for your need and let me know how it worked for you.
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I did this activity with all my students and it was a long day yet lots of fun.

If you have any extensions, comments, or ideas let me know in the comments.

I have this drinking bird on my desk and the kids can’t stop watching it. It keeps drinking the water all day long. As long as I keep adding water to the beaker, the bird will keep drinking. It’s not really drinking the water, just dipping its beak in the water. The water evaporates and cools the beak, thus the liquid moves up.

From Wikipedia

1. The water evaporates from the felt on the head.
2. Evaporation lowers the temperature of the glass head (heat of vaporization).
3. The temperature decrease causes some of the dichloromethane vapor in the head to condense.
4. The lower temperature and condensation together cause the pressure to drop in the head (ideal gas law).
5. The pressure differential between the head and base causes the liquid to be pushed up from the base.
6. As liquid flows into the head, the bird becomes top heavy and tips over during its oscillations.
7. When the bird tips over, the bottom end of the neck tube rises above the surface of the liquid.
8. A bubble of vapor rises up the tube through this gap, displacing liquid as it goes.
9. Liquid flows back to the bottom bulb (the toy is designed so that when it has tipped over the neck’s tilt allows this), and vapor pressure equalizes between the top and bottom bulbs
10. The weight of the liquid in the bottom bulb restores the bird to its vertical position

My classes finished the Mars Habitats last week. Everything turned out super. Here is a small video of the final day. Click here to visit my school web site and see a more detailed video.

It’s a fun project that all students can do. First, we begin by blowing up a balloon to about the size of 10 or 15 cm in diameter. Then, rip thin strips of  newspaper maybe one or 2 cm wide and 10 or 15 cm long. Dip the newspaper strips into the solution and wrap them around the balloon. The paper mache is made of water and glue. I have found in the past using this simple mixture makes great paper mache. It’s also easier to clean than using cornstarch or other powders.

By the second day, the students should have two or three coats of paper mache around their balloon. It’s best to have five or six coats of paper mache as this will give the eyeball strength. After the paper mache dries we paint the whole eyeball white, this represents the sclera. Next, they paint the iris color blue, green, brown, or turquoise in the classroom and the pupil is painted black. When this is done I test the students orally and by pointing out the different parts of the eye. I also asked them what are the part of the retina and what is their function. The two parts of the retina are the rods and cones. The rods detect lightness and darkness and the cones detect the color. Also, I ask why do we have a blind spot? The answer is that this is where the optic nerve is located.

This is a nice project for seventh grade science as it takes about three or four days to complete. The whole time they are making the eye, I am circulating around asking about the different parts and discussing how the eye works. The students enjoyed making it and they can take it home when they are done. Give it a try and let me know how it goes.