Building a Solar Panels

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DIY Solar Panels – How To Build A Homemade Solar Panel I created this website to show you how I built my first DIY solar panel. I go through every step of the process. I'm really proud of my homemade solar panel, there's a photo of it just below. If you have average DIY skills it's easy to build a solar panel and there are great guides available that go into all the necessary detail. Thousands of DIY solar enthusiasts are building similar panels and successfully constructing large arrays to power their homes. DIY solar panels are relatively cheap to build and very flexible in design. Part 1 - Planning, Selecting the Solar Cells and Constructing the Frame

Most of the design features of my homemade solar panel are not original, after all how many variations can there be in a basic DIY solar panel design. However, I picked what I thought were the best design elements, added a couple of my own twists, and came up with a pretty robust solar panel for a fraction of what a new panel would cost. I chose to build an 18V panel, one that could handily charge a 12V battery under the most overcast skies. At 0.5V nominal per solar cell that meant I needed 36 cells in series. The cell count is key to starting the design process and determines the final shape and size of the solar panel. Step 1 - Purchasing the Solar Cells and sketching the layout on paper

Before I could draw my design and order materials I had to decide what cells I was going to use. They come in all shapes, sizes, type and price range and are the single biggest determinant of the overall design of the solar panel. I decided to take the popular route and buy some Evergreen multicrystalline 3"x6" cells that you see for sale on eBay. I bought a kit consisting of 50

solar cells, tabbing wire, bus wire, solder and flux. These were untabbed cells (more on that later). They are a bit cheaper but involve more labor and risk of cell damage when soldering tabs. The cells arrived well packaged and in great shape. What a relief. I had visions of opening the box to find a bunch of chipped and cracked cells. At 200 microns thick these are very delicate. I measured several cells for overall width and length and came up with a more precise size of 3 3/16 inches by 6 inches. That extra 3/16 inch on width is very significant when you line up a dozen cells, amounting to an extra 2 inches in panel length.

I decided to use ¼ inch spacing between cells and ¾ inch around the periphery of the frame to run bus wires. I also divided the panel into 2 sections of 18 cells each. I made a full size drawing of the layout on 24 inch wide paper so I could be sure of the final dimensions. ___________________________________________________ Step 2 - Cutting the frame materials

I made the frame from a sheet of 24 x 48 x ½ inch birch plywood. I cut it to 21 1/2 inches by 46 inches on my trusty tablesaw with a 60 tooth cross cut blade. The rim pieces were made from a 4 x 48 x ½ inch piece of finished pine which I ripped into ¾ inch wide strips. I wanted the panel cavity to be ½ inch deep with a ¾ inch rim width. I cut 2 strips to 46 inches and 3 to 20 inches. One of the short strips is a center divider. I drilled 3/16 inch pass through holes in 2 of the 3 short pieces to allow the panel to maintain equal pressure and humidity with the outside and to pass wires through the top and bottom sections (see holes in photo below). Note Except for the hole for the wire pass through (see step 12), I've since concluded that the holes are not necessary. Leaving an open pathway from the cells to the outside environment is not a good idea and leads to accelerated cell corrosion. ___________________________________________________ Step 3 - Assembling the frame

I then glued and screwed the rim pieces to the plywood sheet using #8 x ¾ inch wood screws and Elmers wood glue. I drove the screws from the back of the plywood sheet and into the rim strips so the tops of the rim strips remained one continuous unbroken surface. This made for a better surface upon which to lay the acrylic front face. Prior to assembly I pre drilled clearance holes and countersunk the plywood so the screws would pull the rim pieces tight. I countersunk the holes a little deeper (an extra 1/8 inch) so I could get close to 3/8 inch engagement of the screws in the rim pieces. The photo shows the finished assembly prior to painting. Notice the pass through holes in the center and bottom rim strips.

___________________________________________________ Step 4 - Painting the frame

To give the frame a good seal from the elements I applied 4 coats of exterior grade semi gloss white paint on all surfaces. Good coverage is essential if the panel is to stand up to weather extremes for several years. Part 2 – Cutting the Acrylic Front and Adding Tabbing Wire to the Solar Cells

Step 5 - Cutting the acrylic front
I purchased a 24 x 48 x 3/16 sheet of acrylic to cover the front of the frame. It was shipped with protective paper on both sides which I kept intact during the cutting and drilling process. Cutting is relatively easy if you use the right blade and don't rush the process. I used an 80T blade in my tablesaw and set the blade to a height of about ¾ inch. I cut the sheet to 21 ½ x 46 inches with relative ease.

To get the mounting holes in the right position I drew lines 3/8 inch from, and parallel to, each edge and one line across the center where the panel divider sits. I then marked hole positions every 5 to 6 inches. Drilling the holes is trickier than cutting with a saw. I used a special 3/16 inch drill bit for plastics. It's the one on the right in the photos. It's important that the acrylic is well clamped close to where the holes are to be drilled and that the drilling is performed at a very low drill speed. Also, it is necessary to slow the drill further just as the bit is about to break through the bottom of the material. This is where the drill can snatch and crack the material. To countersink the holes I used a 45 degree reamer that fitted in my drill. I lifted the protective paper so I could monitor the reaming process better. Reaming was easier than drilling with little risk of damage to the acrylic. As I reamed I would periodically drop in a screw and check for depth. Once the top of the screw was flush with the top surface I was done and moved on to the next hole. With all the holes drilled and reamed I then placed the cover on the frame and marked the positions of the holes on the frame. Using a 1/8 inch bit I drilled pilot holes in the frame so the #8 screws would be easier to screw in without danger of splitting the wood or, worse still, slipping with the screwdriver and damaging the acrylic. ___________________________________________________ Step 6 - Preparing the solar cells for assembly into the panel This is perhaps the trickiest part of the whole project. The solar cells are fragile and there are plenty of opportunities to screw up and damage cells. If you are working on a single cell it is no big deal but

when you are working on strings and the cell in the center of the string is damaged then there is more work involved in fixing the problem, especially if the string is already glued into the panel. Care is essential and the axiom less haste more speed definitely applies to this part of the project.

The top side of each cell is blue and is the basic crystalline structure of the cell. There are two bus strips across each cell to which are attached several much narrower lengthwise conducting strips forming a giant mesh that electrically connects all parts of the silicon cell structure while exposing as much of the silicon structure to sunlight as possible. This is the negative side of the cell. The back side is completely coated with conducting material and forms the positive side of the cell. No need here to create an elaborate mesh of conducting wires since this is the non working side of the cell. The Evergreen cells have 6 attachment points on the back to make the electrical connection.

Adding tabbing wires to each cell - Since the cells are connected in series the negative bus strips on the top of each cell are connected to the positive attachment points on the bottom of the neighboring cell. Narrow tabbing wires with a length equal to two cell widths are used to make the connection. There are two tab wires per cell. So for 36 cells I cut 72 tab wires each approximately 6 3/8 inch long (2 x 3 3/16 inches). Don't worry about the fact that there is a ¼ inch space between neighboring cells. The positive side attachment points do not extend to the edge of the cell. Soldering iron wattage and tip size - I experimented a lot to find the right iron wattage and tip size for this project. I'd seen recommended wattages of 25 to 40 on the web. I tried my Radioshack dual 15 -

30 Watt iron but found I could not generate enough heat to make good joints. I then bought and tried a Weller 40 watt iron with a 1/8 inch screwdriver tip. It had plenty of power but tended to leave some burn marks on the front of the cells adjacent to the bus strips. In the end I got my hands on a Weller soldering station with adjustable temperature and finally settled on a temperature of 750F and a 1/8 inch screwdriver tip. Soldering the tabbing wires to the negative bus strips - This takes a little practice to get right so if you have some broken cells hanging around practice on those first. The basic steps are: 1. Apply flux to the bus strips on the cell. 2. Lay a tab wire directly over a bus strip with one end flush with the edge of the cell. Use small weights if necessary to hold the ends of the strip down. 3. Apply a small amount of solder to the soldering iron tip. 4. Starting from the edge of the cell with the overhanging bus wire, apply the iron directly on top of the bus wire and, as soon as solder starts to flow, move the iron along the bus wire toward the far edge of the cell. Make sure solder continues to flow as the iron is moved. If the flow stops immediately lift the iron, apply more solder to the iron, and commence soldering where you left off. With practice you should be able to go from end to end with one smooth motion without lifting the iron. I will put together a video sometime soon to show exactly how this is done. ___________________________________________________ Step 7 - Adding tab wires to the end cells

My design required 6 rows of 6 cells. One end of each row would have the negative wires already attached (see previous step) but the other end needed the positive wires. So I took 6 cells with tab wires installed, flipped them over and added the positive tab wires making sure that the wire ends were pointing in the opposite direction to the negative wires. ___________________________________________________

Step 8 - Making the solar cell strings

To help create strings of cells with good alignment I drew an outline of the cells on paper complete with the ¼ inch gaps. I then laid 1 double tabbed cell (positive and negative wires attached) and 5 single tabbed cells (negative wires only) upside down on the outline with the negative tabs oriented above the positive attachment points. While keeping the cells in position I then soldered the tabs working from one end of the string to the other. When finished I slid the string on to another work surface and repeated the process with another set of cells. I continued in this fashion until all 6 strings were assembled.

I thought that this was perhaps a good time to see if the strings would work. I didn't fancy gluing them into the panel only to find I had a bad cell or two to deal with. To do the tests I needed to flip the cells over and place them in direct sunlight. Since the strings were relatively short I simply grabbed the tab wires at each end and lifted and flipped the assembly over. The tab wires were plenty strong enough. All of the strings produced a healthy 3V plus so I felt pretty good that I'd done a good job to this point. Part 3 – Installing the Solar Cells in the Panel Frame Step 9 - Marking the frame for solar cell placement

To get the solar cell strings nicely aligned in the frame I drew an outline of where the strings were to be placed in each half of the frame.

Correctly positioned, the cell arrays would have ¾ inch clearance around the frame edge where I could make all of my bus connections and route connecting wires. ___________________________________________________ Step 10 - Gluing the solar cells to frame

I took my first string of cells and flipped them so the backs were facing upwards. I then added a blob of silicone on to the center of each cell. Grabbing the end tabs, I picked up the string, carried it over to the frame and placed it in the lower right corner with the positive tab wire (coming from the back of the end cell) pointing toward the bottom of the frame. With gentle pressure (so as not to fracture the cells) I slid the cells into position and squished the silicone a little to ensure good contact with the frame.

I repeated the process with strings 2 to 6 paying particular attention to which direction the positive wires pointed. Because I had handled the cells a little more aggressively during the gluing process I retested each string to ensure they were still working then let the silicone cure for 24 hours before continuing.

Here is the panel with the solar cells glued in place. It's starting to take shape. Notice the tab wires hanging from the end of the strings. I was now ready to attach the bus wires. ___________________________________________________ Step 11 - Adding the bus wires

The bus wire that came with my cells was .008 inches thick by .197 inches wide. This is the stuff to use to make the connections between each cell strip and the lead in wires. I cut 4 strips to 9 1/2 inches and 4 more strips to 4 inches in length. The long strips are used to connect adjacent cell strings that reverse direction and the short strips are used to connect the two tab wires at the end of each 18 cell string.

I placed small dabs of caulk on the frame where the bus wires were to sit then positioned the wires on the caulk and pressed them into position allowing caulk to extrude a little but not too much so sufficient caulk remained to hold the wire in place. Once in position I removed the extruded caulk from around the wires and left the caulk to cure overnight. ___________________________________________________ Step 12 - Soldering the tab wires to bus wires

I trimmed the free tab wires so that the ends spanned the width of the bus wires but no more. I then applied flux to each bus wire and soldered all the tab wires.

To connect each half of the panel I cut a short length of 12 gage black wire and stripped and tinned the ends. I passed the wire through a hole in the frame divider and soldered the ends to the bus wires to make the final connection of all 36 cells. To check my bus wire connections I tested the entire string and got a healthy 19V plus in full sunlight. Part 4 – Solar Panel Electrical Connections, Junction Box, Schottky Diode and Testing Step 13 - Assembling the junction box For my junction box I purchased a Radioshack project enclosure P/N 270-1801 which is 3" Long x 2" Wide x 1" Deep.

I placed the junction box on the back of the frame, 3/8 inch from the left hand edge (right hand looking from the back), and oriented lengthwise along the centerline directly below the frame divider. I drilled 3 holes through the bottom of the box and secured the box to the frame with 3 screws. I needed to route four wires into the box. Two from the cell array and two to be routed outside to connect to the load. To connect to the cell array I drilled two 3/16 inch holes in the bottom of the box and through the frame, one each side of the divider. To connect to the external load I drilled a further two 3/16 inch holes in the side of the box. I would later route 12 gage connecting wires into and back out of the box. ___________________________________________________ Step 14 - Installing the terminal block

I used a Radioshack terminal block P/N 274-658 to make the connections in the junction box. I wanted to install the terminal block lengthwise in the junction box but I realized that this would not allow me enough room to properly fasten the connecting wires. However, the block was two long to fit sideways so I had to cut it to fit. I trimmed a little off each end with a small hacksaw and placed it in the box.

Here is the terminal block placed in position in the junction box. ___________________________________________________ Step 15 - Installing 12 gage bus wires

I cut 2 12 gage wires to 30 inches in length, one red and one black. On one end of each wire I installed an 8 gage ring terminal. On the other end I stripped off about 1 inch of insulation and tinned the exposed wire. I passed the wires through the junction box and into the frame where the cells were installed making sure to install the red wire to the positive end of the array and the black wire to the negative end. I left about 4 inches of wire in the box to make the connection to the terminal block.

To route and secure the wires within the frame I used 3/16 plastic wire clamps with a small modification. I removed the nails from the clamps and drilled larger holes to accept a small screw. I then secured each wire in four places.

To make the connection to the cell array I soldered the wires to the preinstalled bus wires. I checked continuity again, this time at the junction box. All was good. ___________________________________________________ Step 16 - Installing the lead out wires and Schottky diode

I cut 2 more 12 gage wires, this time 36 in length and again installed an 8 gage ring terminal on each wire. These wires were passed trough the holes in the side of the box once again leaving sufficient slack inside the box to make the connection to the terminal block.

It was now time to make all of the connections in the junction box and install the Schottky diode. I purchased a 40 volt, 5 amp diode P/N SR504 (can't recall the manufacturer). The diode is used to prevent the batteries from "backflowing" current through the panel when it is producing less than battery voltage (nightime and other low light conditions). Notice that the diode is installed in the positive lead with the white band pointing towards the load. Sometimes this end is also marked with an arrow. ___________________________________________________ Step 17 - Final Testing

On to the final test. I temporarily installed the acrylic front and closed the junction box (no final potting until I was sure my panel worked) and gave the panel a test. Here is the open circuit voltage of the panel in bright sunlight. 19.49 volts. Not bad.

Here is the short circuit current, also in bright sunlight. It's a healthy 3.18 Amps. Not bad also. I ran the panel for several days to make sure it would produce good output without any problems. Once I was satisfied all was good I sealed the panel: (1) I removed the acrylic front cover, applied a bead of silicon caulk on the rim strips, then reinstalled the cover. To ensure that the silicon spread evenly and to prevent the cover from cracking I tweaked the cover screws so that at all times I was applying even pressure to the cover. (2) I filled the junction box with caulk making sure that all the connections were completely covered. I allowed the caulk to fully cure then attached the cover plate. Typical Solar Panel System Schematic

Most solar DIY enthusiasts start out by building a solar panel and hooking it directly to a load just to see how it works. Most likely they will try a 12V light bulb. The panel may have 36 cells producing a maximum voltage output of 18V. The bulb will glow extremely brightly in

full sunlight but will fail to illuminate at nighttime. Check the diagram to the right to see how that simple circuit would look. Having power available only when the Sun shines is not always practical. Most often the power is needed at nighttime or on overcast days. To solve this problem a battery is attached to the output of the solar panel and is continually charged during daylight hours when there is sufficient Sun. The load is attached to the battery output and may be operated any time there is energy available in the battery. A Schottky diode is placed between the panel and the battery as a safety precaution to prevent the battery from discharging into the panel in lowlight conditions, especially at night, when the panel voltage drops below battery voltage.

While the previous arrangement may be OK for limited use, where the panel is erected only when needed, it is not an ideal arrangement. Exposing the battery to the full 18V output of the panel for extended periods will shorten battery life and quite possibly result in a major rupture as the battery overheats. To prevent early battery failure a regulator referred to as a Charge Controller is placed between the panel and the battery. The Charge Controller has two primary functions, (1) to control the power input to the battery, in particular limit the maximum charging voltage, and (2) to prevent the battery from backfeeding into the panel in low-light conditions when the panel voltage drops below battery voltage.

The previous arrangement will work great for 12V DC loads. This might be fine at the fishing cabin but won't be very practical at home where all the appliances run on 110V AC. An Inverter is required to convert the stored energy in the batteries (12V DC) to 110V AC. This is installed between the battery and the load. Now the entire system will not only capture the energy from the Sun, but it will store it for later use and convert it into a form that will run regular household appliances.

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