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For some time I was interested in testing methods of building a cheap solar panel using cheap solar cells and other things that you might find on the junkyard, so I’ve set up an experiment for this.
My goal was to build a system that would be able to provide the necessary electricity to light up some 8W (500lm) light bulbs, power my 45W laptop and watch my 30W LCD TV. A 65W solar panel will do the job if it’s not used with all the appliances at once. Some people will also look to build solar panels that will last a long period (like 10-15 years) and that’s OK if you actually have decided to build an expensive system which in turn should earn its money (and that takes time). In my case, where I am rather experimenting than make an investment in such a system, I want just to investigate (by trial and error) how much of the cost can be cut. Moreover, I’m sure that the technology will gradually improve such that in the next 5 years I will want to change the panel’s cells with something better, meaning something more efficient (note that the today’s best solar cell tested in laboratory cannot convert more than 44% of the solar light into electrical energy whereas the cheapest polycrystalline cells efficiency varies between 13-16% ).
Note that a similar system (solar panel+charge controller+DC/AC inverter) could be bought from a myriad of providers for just about $300. Can we build it cheaper? – that is the question that my experiment tried to answer.
The project required the following parts:
- solar cells including tabbing and bus wire, flux pen, junction box and cable
- polycrystalline are the cheapest (a kit can be bought for $40 with free shipping from eBay) although it’s less efficient while mono-crystalline are better but also pricey
- an off-the-peg 80W panel would cost $100 + shipping (which could mean more than $50 depending on your location)
- the panel frame which can be:
- aluminium L-shaped frame ($38 on eBay)
- wooden frame (costs just a fraction than the aluminium version)
- solar cells encapsulation:
- nothing – the cheapest method but with some side effects (the cells’ welding might corrode)
- EVA film ($62 for 2.8m2 on eBay); note that you will only need ~0.5m2 for such a panel
- Epoxy resin ($30 for 400g on eBay); 400g should be enough for such a panel
- Sylgard® 184 ($50 for 500gr on eBay + shipping)
- the front and optionally the backside glass sheet (8mm respectively 4mm thick)
- solar panel charge controller (from $10 on eBay)
- DC to AC power inverter (from $32 on eBay)
- a 12V deep-cycle AGM battery (perhaps from $100 and up depending on its storage capacity or other characteristics)
- electric wires, plugs, adhesive tape,silicone sealant, screws and bolts, etc
- some tools (drill,saw,pliers,soldering iron,silicone caulk gun, multimeter, etc)
I will go neither through the design or the build steps, instead I would recommend few online resources that you might use to get an insight of the building process:
- Get almost everything about solar energy: www.freesunpower.com
- How to build solar panel: www.youtube.com/watch?v=mjWHHqNO7qI
- $105 solar panel project: mdpub.com/SolarPanel/index.html
- Another solar panel project: www.r3uk.com/index.php/home/39-cool-projects/61-the-solar-panel-project-chapter-1home
- How to tabbing solar cells: www.youtube.com/watch?v=TDlcaILWP54
- How to build a DC/AC power inverter: www.youtube.com/watch?v=t3yvdXIjGSo
- How to use UPS as current inverter: www.youtube.com/watch?v=HSNF1LWiPWo
- Calculate your home power usage: michaelbluejay.com/electricity
- An $130 solar panel project: mysearchforsolarpower.com/how-to-build-solar-panels-cost-effectively
- Selecting solar energy conversion : www.eetimes.com/document.asp?doc_id=1279741
To build this system I’ve chosen to buy a solar cells kit (cells, tab and bus wire, flux pen, junction box and 1m solar panel cable) where I’ve soldered the cells manually and then I stuck them between two glass layered sandwich which was sealed on a wooden frame with some white silicone sealant.
I choose not to encapsulate the cells with EVA/Epoxy but instead to seal the glass sandwich, as I’ve said, on the wooden frame with a silicone sealant and later to extract the air from the sandwich such that the amount of air that is in contact with the solar cells is kept minimal (almost vacuum). Almost vacuum means almost no moisture and no moisture means to prolong the life of the cells and to make sure they run at their full capacity. By doing this I cut also the cost considerably ($30-$60 at least). Note those red plastic tile spacers used to align the cells and also to create a 4mm space between these glass sheets. They are important!
The panel configuration looks like this:
- 1st layer: a 8mm thick sheet of clear glass exposed directly to the sun light
- 2nd layer: the photo-voltaic cells aligned by a φ=4mm plastic tile spacers
- 3rd layer: a 4mm thick sheet of glass/plastic forms the panel’s backside
This 3-layered sandwich will be mounted (layer by layer) on a rectangular wooden frame. In order to prevent the moisture entering from the outside into inside we are going to seal the glass sheets and the wooden frame. The only air that still exists around the solar cells (within sandwich) are the air that was trapped when we sealed the frame and the glass’ sheets. Now it’s time to suck that air. We already made a vacuum orifice in the wooden frame so that we can use a vacuum pump (or some kind of handcrafted pump) to extract the air and then immediately stop a cork (or something) which later can even be sealed using silicone sealant. Note that this part is very tricky because we have to move fast (otherwise the air will enter in a mater of milliseconds).
To make sure that this structure will remain in fixed position we fix the panel’s backside on the wooden frame by using some metal corner brace which are in their turn fixed with wood screw.
Learn from my mistakes:
- make sure you drill the vacuum orifice in the wooden frame before placing/sealing the sandwich; this way is easier and implies no risk in braking neither your glass sheets or the solar cells
- make sure you drill two small holes in the wooden frame in the place where the positive and negative bus wire cable are soldered
- the soldering should be done like this:
- solder the tabbing wire on the negative (the front side) side of each individual cell
- place the 1st layer of glass sheet (8mm) on the wooden frame
- place carefully the solar cells over this sheet of glass such that you can access the backside of the solar cell; make sure you align these cells using those plastic tile spacers and also that the negative tabbing wire is arranged over the cell’s positive terminals (on the cell’s backside)
- solder the cells with each other so that you obtain a straw of series linked cells
- solder each straw of cells with a bus wire on the next straw of cells
- solder two pieces of cable at each side of your positive and negative bus wire and make sure that the other ends are inserted through those two holes made earlier
- test your panel, make sure that your cells add-up to the maximum desired voltage (if you encounter an issue now it would be the time to fix it!)
- pour a drop of silicone sealant on the back of each solar cell
- place the 2nd layer of glass sheet (4mm) on the wooden frame just above the solar cells;don’t be afraid, the 2nd layer of glass will not touch the solar cells thanks to the plastic tile spacers
- make sure you seal the 2nd layer of glass with silicone sealant. Let it a dry properly then fasten the 2nd layer of glass with the metal corner braces; use only wood screw and if necessary drill a hole in place using a small drill bit before using the screw (so that the wood would not crack)
- turn your panel upside-down and seal now the front sheet of glass using the silicone sealant. Let it dry properly.
At this point your panel should be functional. Below you can find a modest picture gallery of this panel:
Test again your panel, if you’ve checked carefully the panel before you have applied the sealant then everything should works just fine.
To mount your panel on your roof you will need some roof hooks/mounting brackets. The size and shape of those mounting brackets varies with the size and the shape of your tiles (take a look at the picture below):
You have to pay around $50 for 4 pieces of roof hooks. If you want to stay on budget then maybe you can manufacture them by yourself. You could use an iron ring of an old wooden barrel that you don’t need it:
I’ve installed the panel on my parent’s house roof where they have Spanish ceramic tile. In my case the Z-shaped hook fitted the best. I’ve taken the measurements, sliced the ring with the help of a disc grinder, straightened each piece with the hammer, welded the base to the hook, drill the necessary holes, polish before painting, apply a thin layer of bronze paint:
At this point you can install the panel on the roof. All you have to do is to connect the panel’s positive/negative wires to the charge controller then you can use the resulted DC current to power on some DC appliances (such as DC bulbs), to store that DC current into a battery and then from battery you can connect a 12 VDC to 220 VAC power inverter that will supply a 110/220 VAC for your light bulbs, laptop and TV (or whatever).
Whether you have an UPS unit that you don’t use it anymore or you just don’t want to spend your money on a 300W power inverter you might “convert” (actually just use directly) your UPS as a power inverter:
- take out the UPS battery and connect instead the battery’s positive respectively the negative terminals of your charge controller
- turn on the UPS, it will provide to you 220VAC that can be used by any of your appliances (with respect to voltage and power usage).
If you want to monitor the voltage provided by the solar panel and the instant amperage then you might buy some voltmeter/ammeter then connect them in parallel respectively in series with your circuit (I’m not going through all the technical details here). In order to protect your circuit for over-voltage and/or overconsumption then you should link in series some blow glass fuses.
I’ve used my old 300W UPS unit as power inverter and also I’ve installed some meters, fuses, switches so that I need a custom-made case for this unit (I know, wood is probably the worst solution but it was handy):
How much does the system costed me:
|Part name||Origin||Price (USD)|
|Solar cells kit||eBay||41.75|
|2xGlass sheet||Local supplier||15|
|Silicone sealant||Local supplier||4|
|Battery clips (black+red)||eBay||2|
Note that the wooden frame, mounting hooks, screws, current inverter or battery are not included in the total price since I’ve used some “junks” that I’ve found in the junkyard. If I want to increase the energy production then all I have to pay would be something like $60/panel. Not bad!
This summer I intend to build two more solar panels, both with aluminium frames: one with EVA and the other one with Epoxy encapsulation. Additionally I am going to build a small wind turbine (including the electric generator) so that the whole system will provide electricity for the most appliances my parents have in their house. More details to come…