# Solar Panel school project

Hi,
I’m trying to help my 10 year old son out with his school project about using solar panels to generate energy. We are making a cardboard house and wanted to put a solar panel on the roof and link the solar panel to an LED light. I saw that Core Electronics sold this solar panel, https://core-electronics.com.au/0-5w-solar-panel-55x70-seeed-studio.html. Can you please let me know which LED light can be powered using this solar panel (I was told it all depends on the voltage?) and if there are other material I might need to make it work? We would appreciate it very much. Thank you very much in advance for your help.

There are many LEDs that would suit, so it might depend on how you want to light the house.

For instance, you could choose a simple arrangement of single leds and dropping resistors, such as :

If you look at the spec for the Basic Yellow you will see a ‘drop’ voltage of 2.0 - 2.4. Let’s call that 2.2. The solar panel has a rated output of 5.5v - 8.2v. Let’s call that 8v (when the output is lower the LED will be dimmer). This site:
LED Series Resistor Calculator | DigiKey Electronics
provides a calculator that can be used to find the right resistor. At the current rating suggested in the LED tutorial of 15mA, that works out to 387 ohms. That’s a non standard figure, so choose either 330 or 470 from a pack such as

(330 ohm would probably be OK considering that the 15mA is a little conservative, and the solar panel will make less than 8v in typical indoor lighting).

You could wire several LED / Resistor combinations in parallel to light different rooms in the house.

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Hi Lily, Welcome to the forum

Were either you or your son practiced with soldering or is this likely to be a project put together with alligator clips? Just getting an idea of what you want to put together before I make some recommendations.

I think you should just need some generic LEDs and some current limiting resistors to ensure they don’t burn out under the maximum brightness of the sun.

One of our staff members Michael has put together a video tutorial just last week about how to choose the right resistors to protect your LEDs.
https://core-electronics.com.au/tutorials/ohms-law-practical-examples-for-makers.html

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Hi Jeff,

We were actually looking at putting just one or maybe 2 LED bulb for his cardboard house, as it is not a big house. So would the LED Rainbow Pack (the link you attached) work with that solar panel?

I have a bag of of standard Jumper Test Lead kit from Jaycar (Standard Jumper Test Lead Kit | Jaycar Electronics). Would I still need a Resistor kit if I have that?

Thank you!

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Hi Trent,

We want to avoid doing any soldering and I’m hoping to just use alligator clips for the project? I have a bag of them that I previously purchased from Jaycar (Standard Jumper Test Lead Kit | Jaycar Electronics).

I’ll be honest, I’m not good with electronics so I’m just looking for a simple way that my son can demonstrate how you can use solar panels to light up his cardboard house.

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Yes. How you connect the bits together doesn’t affect what the circuit needs to be. With alligator clips the problem is ensuring that they don’t short out against each other - you can clip them, with the wires, onto a strip of cardboard to keep everything in place. A neater, but slightly more expensive option is a solderless breadboard. They come in many sizes - this is a small one:

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Ok, I see. I’ve no idea how to put the resistor, solar panel and the LED together though.

My son and I watched this Youtube video, How to make working model from cardboard l school project - YouTube, and it looked like they only had to use an LED circuit board and a solar panel to get the LED to work? I haven’t been able to find an LED circuit board like that though. Would you know where I might be able to find it? Thank you again!

Something like this:
https://www.wish.com/product/5d45343c8daeec4117153f11
These ones are designed for motor vehicles, so are specified as 12v and probably not suitable for a solar panel rated at 5-8v. You might be able to use the information about that item as mentioned in the video to find one that suits your solar panel, but you would need to carefully check the specifications for voltage and current. It is very difficult to make a recommendation without good knowledge of the detail of the particular item. The best idea would be to find out what items were used in that video, because they apparently match quite well.

The advantage of rolling your own is that you are not relying on parts that are inadequately documented. The details on wiring for the LED are in the tutorial, and are only slightly more complex than wiring a panel.

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Thank you again for your response, Jeff. I read that I can buy LED lights with built in resistors like this, https://core-electronics.com.au/led-blue-with-resistor-5mm-25-pack.html? Could I use this with that solar panel I mentioned in my initial message? Thank you for your help!

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That is exactly the same as the LEDs in the packet plus a resistor. But it is configured for 5v, whereas the resistor I calculated was for a little higher voltage. Those LEDS would be fine if you can confirm that the solar panel will not go above about 5v in the environment where you will be using it. If it is above about 5v for any length of time the LED could blow. Of course, the quoted 8v for the solar panel might be quite optimistic!

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Thanks Jeff. So it can still blow even though the LED has a built in resistor? How can the solar panel go above 5v? Does that depend on how long it is exposed to sunlight?

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It depends on the amount of light that falls on it - more light means a higher voltage.

• Typical voltage: 5.5V (presumably at the ‘typical’ current of 100ma - about 4 LEDs).
• Open-circuit voltage: 8.2 V - maximum light and no load.
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Thanks Jeff. In summary, to make this project, we would need the following:

1. The solar panel
2. The LED light
3. Resistors - Can I use this pack instead, https://core-electronics.com.au/600-pack-of-1-4-watt-1-resistors-30-values-20-of-each.html? We don’t need much and we didn’t want to spend more than what we need.

Also, I found a Youtube video on how to wire the LED and resistor together, Wiring LED and Resistor Together - YouTube. Is that what you meant? I can then use the alligator clips to connect it to the solar panel? I looked up the breadboard you mentioned (and other similar size ones) but they are not currently in stock, which is why I thought I would use the alligator clips instead? If I do, I think I have to cut the white clip off the solar panel (I’ve circled the white clip in the attached pic) and I would have to join the wire between the alligator clip and the solar panel. Is that correct?

Hi Lily,

That pack of resistors should be fine.

Best practice would be to use a breadboard but if you would prefer alligator clips you can use those as well, just remember you need to prevent them from accidentally touching where they aren’t supposed to or you will create a short circuit and potentially damage your LEDs.

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That resistor pack will work just fine, and is better value for money. Note that you could start with a higher value such as 510 ohm and see how much light you get. It could be that the house looks better with a dimmer glow. If the light isn’t enough then try a lower value, but I wouldn’t go below 200 ohm.

The video leaves out a very important point. The LED is polarity sensitive - see

So before doing anything with your connection make sure you have identified the + and - sides, and that you can follow that identification through any changes you make. I would recommend following the method in the MakeCode tutorial exactly and stick to that standard: ie, the resistor goes to the anode (positive, longer) side. It doesn’t actually matter which side the resistor goes to, except that consistency makes it easier to check things and avoid mistakes. That tutorial also gives you the wiring connection you need, except that you have a solar panel and not a battery. The resistor on the anode side then goes to the red wire on the solar panel, and the other side of the LED goes to the black.

Clipping the alligator clips to the solar panel leads is one point where you will need to be careful that they don’t short out against each other. Normally I would recommend that you insert wires into the socket to give you the connections, but it will be much easier to keep the alligator clips apart if you pull the wires out of the socket (or cut them off) in order to clip to them, as you suggest.

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Thanks Jeff. I am a bit worried about shorting out anything on the project!

I found a breadboard that’s more expensive but it is available, https://core-electronics.com.au/170-point-breadboard-orange.html. Would this one be suitable too? If I have the breadboard, how do I link everything up together? I’m not sure where I would link the solar panel socket to the breadboard and how I would place the LED bulk and resistor on it?

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That breadboard would work very well. The bit you have to know about it is that the columns of holes are all connected, but are separate for each half. So any two wires that you want to connect together go into the same column in the same half. That gives you that 34 columns of 5 connectors each - much more than you need. The advantage of the breadboard is that you can rearrange things to get the results you want, such as experimenting with different resistors and different lighting, as I mentioned above, or adding a second LED after you get the first one working. I will post a diagram.

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Ok great, I would love a diagram, just to get my head around how to connect everything. I’ve only seen videos where they use alligator clips, which is why I thought that might be the easiest way to do it. Thank you for your help!

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Thank you very much for the diagram, Jeff. I noticed you have the red and black wire from the solar panel without the socket. So do I need to cut the socket off the wire so I can do what you are showing in the picture? Then do I just put a tape to hold down the wires underneath the breadboard?

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The wires for the solar panel are probably stranded: these don’t fit very well into the breadboard. The arrangement I would recommend (which might require a bit of fiddling) is to leave the socket in place, but find some short lengths of wire that fit firmly into the breadboard and also into the connector from the panel. You might have to bend them over double or even triple on the connector side. Then insert half into the breadboard and half into the socket. If you can get it right then the connections should be quite firm. Note that Core can supply wires that match the breadboard, but it is quite likely that you will find short pieces of wire around the house that work just as well.

How you fasten everything down is going to depend on how you arrange things in the house. I imagine the solar panel would sit on the roof. You could place the breadboard as required to make the lighting look good, then just tape things together as required. The resistor and LED will be quite firm in the breadboard and don’t need fastening.

If you are concerned about shorting things out then you can place the panel in a paper bag until you are finished - that way there will be no voltage of any sort and no risk of any damage until you are ready to expose the panel to some light.

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