# New Toys!



## nephilim (Jan 20, 2014)

I picked up 40x 4.1w Solar Cells today. Cost me £50 for the cells. They are 6x6 inch, and I plan to make a panel which is 48x30 inch. They are polycrystaline, and the panel should in theory max out at 164w and 20V. 

Its my project over the weekend to make a fully working panel which we can use for smaller household items. If it is successful, I will be buying more cells each month and make more of my own.

Total cost for the project including glass moisture free housing, new solder, new flux pen, tabbing strips, blocking diodes etc for it is £90. Cost for a brand new 160w panel in the UK is £190 so by making my own, I am making a huge saving (well at least half of the cost is saved). Cost for a used one is a bit more expensive than me making my own, but a saving is a saving!

Hopefully will be a nice project I can sink my teeth into.


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## nephilim (Jan 20, 2014)

First 8 cells are soldered together . Tested in the garden, it generated 31.6w. Not bad considering the max would be 32.8w. 

Going by this flow I can hope to achieve a yeild of 158w(ish) if it all goes to plan.

Took a little time to get it soldered together but hey, I'm happy with the results


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## budgetprepp-n (Apr 7, 2013)

Will you be using this for 12 volt battery charging?


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## nephilim (Jan 20, 2014)

Yeah. First experiment will be with a car battery. The theory is that if it charges that fine, then I will be using it for things like an emergency car battery charger, or for camping to charge my phone, radio etc.


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## nephilim (Jan 20, 2014)

Looking at taking a picture....how I missed every cell having a crack I don't know. Phoned for a replacement...they're bringing it round now so will do it all tonight...new cells to panel.


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## nephilim (Jan 20, 2014)

Got replacements (company is 20 miles down the road). they picked up all of the panels and gave me fewer, but better replacements.

I got 40x 6.3w polycrystaline cells. Should generate around 250w hopefully!


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## nephilim (Jan 20, 2014)

This is an outline of how the panel is made. However, I emphasize that I'm no expert and the panels I make are not professional or perfect, though they work perfectly well.

*Solar Cells:* The panels are all made using 7.5cm x 15cm (3x6 inch) poly-crystalline solar cells purchased via an ebay shop, from the UK. I paid just over £1 per cell for mine but they can now be purchased for substantially less than £1 per watt from many auction sites and direct sellers, including UK sellers. You can use whatever solar cells you want but 3x6 or 6x6 inch cells are best for higher power panels. Each solar cell has an open circuit voltage of about 0.5V but the current depends on the size of the cell. 3x6 inch cells can generate about 3.5A in full sun.

*Tabbing:* The first step is to tab the solar cells. This involves soldering flat, thin tab wire to each cell. Again tab and bus wire can be purchased from various sellers. A typical panel has 36 cells so you need 72 x 15cm wires. The soldering process is easy after a bit of practice but beware the solar cells are very thin and fragile so care must be taken. You need a good flat surface to put the solar cell on and I find it best to use a beveled soldering tip. I run a thin layer of lead-free silver bearing solder along the bus rails of each cell (the 2mm wide white stripes on the blue side of the cell) and then solder the tab wire on top. As I got the practice, I can do 1 cell in about 2 minutes. A tabbed cell is shown below









*Solar cell strings:* Then you turn each cell over and apply solder to the 6 white squares on the back. My panel will have 4 strings of 9 cells. To get good straight strings, I use a board with 2 wooden strips acting as a guide. A cell is placed face (blue side) down between the strips and it's wires from the front (blue) side are then soldered to the 6 squares on the back of another cell. This process is repeated for 9 solar cells, shuffling the growing string up the board between the wooden strips (See images below). I use small wooden spacer strips (about 5mm spacing) to get a uniform spacing between cells. When the 9 cells are done, two extra tab wires are attached to the back of the end (first) cell which has no wires on it.























This is where I am now. I will crack on and try to finish the panel tomorrow, but so far, so good.


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## sparkyprep (Jul 5, 2013)

Excellent post!


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## PaulS (Mar 11, 2013)

If you are going to use this array to charge a battery without a charge controller you should have at least 14 volts but less than 16 volts. Do you know how much voltage / amperage you will have?


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## alterego (Jan 27, 2013)

I Want A Solar Setup Real Bad. But What I Want Is Big Money. I Have No Plan For A Small Setup Right now.


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## PaulS (Mar 11, 2013)

You can always grow a small setup into a bigger setup. It cost no more to do it a bit at a time.


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## nephilim (Jan 20, 2014)

I have a charge controller. It will likely hit around 18v. I am making a start of the rest of the array this afternoon.

Instead of glass I am going to the shop to get cheaper perspex which is also waterproof. I'm also picking up some EVA thermoplastic encapsulatant and I have an aluminium frame for it. So far so good.

Will be cheaper than the glass I had planned. Glass was around £25 for the panes I needed, perspex is around £4 for what I need.


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## alterego (Jan 27, 2013)

I Understand That You Could Buy Panels One At A Time Or In Groups Of Four To Wire In Series.To Push 48 Volts. But The Transformer inverter And The Charge Controller Needs To Be Purchased To Your Max Need Size. So I Am Looking For Something That Would Run Up To 6000 Watts. No Cheap Way To Do That Or.piece.Meal. The Batteries Are Another Thing That Can Be Done One At A Time.


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## nephilim (Jan 20, 2014)

Firstly....don't capitalise every word...it's annoying and difficult to read.

Secondly you can buy an inverter that can handle the wattage, voltage and amperage you need for no more than $300. Mine handles 10kWh per day with ease. I don't use anywhere near that.

I also have a smaller one for this panel to see what I can get from it. With the cells I have I may push it to 1kw if I buy more of them. Now I know what I am doing, it would be easy


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## nephilim (Jan 20, 2014)

Starting on the rest of the panel now. Will hopefully be done soon and finish the write up for you.


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## nephilim (Jan 20, 2014)

*The window:* Professional panels use special low-iron, toughened glass for the panel window but I use 4mm or 5mm thick clear pespex sheet (again, cheap, 2nd-hand sheets from private sellers on ebay or good local hardware stores). Holes are drilled around the edge for fixing to the aluminium frame. To achieve a good waterproof seal for the cells, I use EVA thermoplastic encapsulant (purchased at the local store at about £1 /sq foot). You need two pieces the same size as the perspex window. One piece is placed on the perspex sheet and I then I use a paint stripping heat gun and a metal roller to heat it onto the perspex. The EVA goes clear when heated and sticks to the perspex. As this is not professionally laminated, there are often small air bubbles trapped in it - I use the roller to squeeze some out but it's not perfect - small bubbles are not critical. This process took 10 mins per panel.

*Mounting the solar cells and connecting strings:* Next, 4 strings of solar cells are laid on the first EVA layer, with the blue side down on the EVA (Picture below). I use a 5mm gap between the strings. They must be arranged in opposite directions, such that if the top solar cell in a string has the end wires coming from the back, the same cell in the adjacent string should have the wires coming from the front. Remember each cell is essentially a battery with a + and - contact and cells and strings must join + to -. I arrange the left most string, as seen from the back, with the -ve end at the intended top end of the panel window (to match the junction boxes I use), the top edge of this cell being about 5cm from the top edge of the perspex window.
















When arranged neatly in parallel lines, bus wire (wider flat wire) is soldered across the top and bottom tab wires of the strings to make the + to - joins. The top solar cells of the central 2 cell strings are joined by bus wire and the bottom cells of the outer pairs of strings are similarly joined. Then two separate bus wires are run from the top cells of the outermost cell strings towards the middle - these will form the final output contacts for the panel. This arrangement provides a 36 cell series string. The free ends of these latter two wires should be bent up vertically with a space between them to match the contacts in the junction box. If the junction box you plan to use has a pair of bypass diodes, you can solder a small length (2-3cm) of bus wire to the middle of the bus bar that joins the middle two cell strings, and bend it upwards. The above pictures and the schematic below show the bus wire connections.









*Weather sealing: *To make a weather-proof seal, the 2nd layer of EVA is melted onto the solar cell layer. I use a self-made narrow roller to press the heated 2nd EVA sheet onto the EVA layer below, in the gaps between the solar cells and around the edges of the panel. The EVA is very sticky when hot so rolling needs to be done a few seconds after the heat gun has been used. It's easiest to play the heat gun over a smallish section of the panel and then run the roller carefully between the solar cells. Practice is needed here to get the heating and rolling right - the EVA can easily melt into a mess if overheated. Try to ensure the 2nd EVA layer adheres to the backs of the cells with as few air bubbles as possible. It's very hard to achieve this as the EVA naturally tends to bubble up and buckle when heated - this is a major downside of using EVA without a laminator. The 2nd EVA layer has been applied in figure 6. The upturned ends of the two output bus wires are the output terminal wires - they (and the extra bus connector if added, as mentioned earlier) should be pushed through pre-cut slots in the EVA and the EVA melted around them.

*Solar panel backsheet:* To form the back of the panel (to protect the cells) one can either make a shallow perspex tray which can be bolted to the back of the cell sheet when finalizing the panel or one can use Tedlar sheet. If using a perspex tray, cut another perspex sheet the same size as the front window and glue/epoxy 4 narrow (1cm wide) perspex strips around the edge - it must be water-tight. I have now started using tedlar sheet instead as it circumvents the problems of the perspex tray bulging due to trapped hot air when the panel is in use. It also better allows the cells to stay cool and makes a lighter panel. If you used a perspex tray, holes will need to be drilled to match the bolt holes around the edge of the perspex front window and also where the output terminal bus wires come through - the junction box will be fixed to the perspex tray over these bus-wire holes.









*Junction box: *Once the tedlar is on, the junction box can be fitted on to the back of the tedlar (using epoxy and/or good quality silicone sealant). I bought pre-fitted junction boxes from an electrical store which come with MC4 connectors already attached. The +ve and -ve bus wires from the panel then need to be soldered to the relevant terminals in the junction box. If the junction box has a pair of bypass diodes, the extra upright bus connection from the bus wire connecting the central pair of cell strings needs to be soldered to the central connector between the diodes. If you use a simple plastic box, you'll need to connect the bus wires to a terminal block glued inside the box and then attach output cables to the +ve and -ve terminals of the block, which then pass out through holes in the lower side of the box.

*Solar frame:* Finally, I make an aluminium frame for the panel using aluminium angle (4cm x 2cm, 3mm thick) from a scrap dealer. The size is 68cm x 86cm so the window just fits inside. I screw these together via angle sections on the inside at the corners. The whole window can now be bolted into the aluminium frame. Run a bead of silicone sealant around the edge of the frame so the window clamps down onto it. The corners of the window may need to be cut/shaped (before doing the first EVA layer) to fit the internal frame corners.









The panel is finished (above picture). The above mentioned cells yield a panel with a Voc of about 20V, a current of 12.8A and a peak power of around 256Wp. I plan to use 8 such panels in series and connect to a DC isolator switch, then to a Steca 500 grid-tie inverter and then through an AC isolator switch and generation meter, to the household supply. A properly qualified electrician must do the final connections and check the system.

*Remember two key thing where great care is needed.*

a) Working with cells - they are fragile

b) Arranging the cell strings -

The strings must be laid out in opposite directions so that bus connections between the strings maintain the + to - pattern throughout. If you get this wrong, you will end up with reduced power due to opposing voltages and, once the cells are encased in the EVA, there is no simple fix.


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## nephilim (Jan 20, 2014)

it fully charged 3 car batteries this weekend and this morning. May buy a 4th just for good measure and start running stuff from them


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## budgetprepp-n (Apr 7, 2013)

nephilim said:


> it fully charged 3 car batteries this weekend and this morning. May buy a 4th just for good measure and start running stuff from them


Nice post
I have a question over there you use 220 or 240 volts something like that,,, So are small inverters that do that easy to find?


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## nephilim (Jan 20, 2014)

I picked up a solar panel battery charge regulator, which was around £10. This is able to take everything the solar panels can bring in and convert it to a steady current (converted it to 12v and 10 amps), this was used for charging the batteries. I picked up 3 small car batteries for free last weekend which have a max of 200AH. They were my test bed and had some charge in them i think maybe 10% or so. I got them for free as they were from cars which were being crushed and cubed. 

I was able to charge all 3 over 10 hours of direct sunlight. I think fully charging 1 empty 200AH battery will take 2 days or so if it is completely dead, however this wont be so much of an issue when I get another panel done...theory being, more panels = more batteries charging at any one time. 

I picked up a 12v - 230v inverter for the batteries for £30 to put into a usable current for household electricals. The plan is, have 14 full sized car batteries (or 2 solar batteries which can store 1400AH) fully charged ready for use. When 1 is expended, the solar panel can charge it whilst the next battery is used with the inverter to keep the electrics going. So far so good, it worked on boiling the kettle and charging the phone. 

I hope this helps!
Next plan for me is to buy some decent batteries, but I know now that the practice is sound and works, so just need to expand and buy better batteries.


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