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Beginner questions on solar energy for a school project-please help!

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Hi Everyone,

Couldn't find the answer anywhere in the forum so I'll put it here and hope you guys can answer. I'm interested in buying some solar panels as a school project (I'm a tech teacher). I have some students that are interested in using solar panels to set up a small kiosk powering station for laptops/phones/tablets as a service project. I know a few basics about electricity, circuits, etc  and have been experimenting with small solar panels. 

My questions: how many/size solar panels would we need to produce enough voltage to power say 2-3 devices at once? I realize we would need an inverter, battery, etc. Would you recommend 1 or 2 300W solar panels? Would this produce 2-3kwh of power per day? I read something about losing efficiency going from DC to AC current. How does this work?  I want this to be a bit of a DIY project rather than a "kit" as I want students to learn how to wire this together, etc. 

My other questions center around cost and calculating CO2 savings. Assuming that we pay 1.24R/kwh, would I be right that solar energy would only save 2-3R/day? If so, it would seem that it would take years to pay itself off. Students will be calculating CO2 reduction through the use of solar energy. I found online that 1 kwh=0.5 kg of CO2 but this obviously matters on how the majority of SA's energy is produced. I've read that most of it is coal so perhaps the savings would be higher. 

Also, if anyone has any tips on where to purchase these materials in Joburg, that would be appreciated.

Sorry for all the questions but any help would be greatly appreciated!

 

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Being a tech teacher you should be able to hook up a photovoltaic (PV) panel directly to a switch mode power supply (SMPS). So by eliminating inverter and batteries your cost would be for components to make a SMPS and some sort of protective circuit. One 300W panel should be more than enough power to power 2-3 devices at once. This will satisfy you quest for something that is DIY and hands on. I would be careful as most devices have lithium ion batteries and incorrect charging will have parents and scholars up in arms. They are not learners in spite of what dept of education says. Learning has its origin in the Old English word "leornung" which is definitely a verb. Whereas scholar can be traced through Old English to the Latin word "scholaris"  and the formal process of instruction. Even pupil is better than learner. 

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11 minutes ago, Chris Hobson said:

Being a tech teacher you should be able to hook up a photovoltaic (PV) panel directly to a switch mode power supply (SMPS). So by eliminating inverter and batteries your cost would be for components to make a SMPS and some sort of protective circuit. One 300W panel should be more than enough power to power 2-3 devices at once. This will satisfy you quest for something that is DIY and hands on. I would be careful as most devices have lithium ion batteries and incorrect charging will have parents and scholars up in arms. They are not learners in spite of what dept of education says. Learning has its origin in the Old English word "leornung" which is definitely a verb. Whereas scholar can be traced through Old English to the Latin word "scholaris"  and the formal process of instruction. Even pupil is better than learner. 

Mr Hobson... I have a diferent take... 

2x 100W (or 1x200w) panels will give 5amps plus via a cheap 12V solar controller (R250)

One old car battery and a set of 12V car cigarette lighters and 12v usb adaptors.

All in a nice packaged setup will do it... I did this with a toolbox...

large.5780d131a2471_2015-12-2111.25.32.jpg.dc3e7af4cb937b24a37b741f7112433a.jpglarge.5780d23e40f0b_2015-12-2111.24.34.jpg.46d6e817efe12682a024bcf4f9faaea4.jpglarge.5780d1a44472e_2015-12-2111.25.38.jpg.0b2a518ee8974a0f169cbe213db000d4.jpg

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I have some concerns about that 300W PV module :-)

Above 150W PV modules are usually made up of 60 or 72 cells, with each cell making roughly 0.5V-0.6V, for a total voltage of between 30V and 45V. This is usually way too high for a small setup such as this, where you would most likely want to use a 12V inverter and a small battery to provide a bit of buffer. So I would say you should be better off going with smaller modules, but to use more of them, ie use 2 x 150W modules (36 cells) instead.

Those make a lower 18V-22V, are easier to handle too, a 300W module is as large as a standard door, whereas the 150W modules are a usually a more manageable 1.7 meters by 700mm or thereabouts. That also provides the opportunity to teach your young padawans (craftily avoiding the whole learner/scholar thing here) about placing things in parallel/series, and current vs voltage.

Now the second part. For a small setup like this I'd use a cheap PWM controller. Not sure if this money is coming from your own pocket or not, but lets just say that a PWM controller is around R500, a good MPPT is more like 2k. With the cheaper controller, your 150W panel (which wants to run at 18V) will be pulled down to 12V and only make around 100W power, or around 8 ampere. Two of those then make around 16A, which you can pretty comfortably push into a 100Ah battery without any danger.

Then put a small inverter on that. Not sure what to advise here, I'd like to tell you to get the small Victron Phoenix inverter (the 350VA) but it will depend on your budget.

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With the automotive 12v to 5v adaptors you dont even need an inverter. So that expense and add danger is out of the equation.
I wouldnt really want kids playing with 220v anyway.

Sent from my SM-G800F using Tapatalk

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With the automotive 12v to 5v adaptors you dont even need an inverter. So that expense and add danger is out of the equation.
I wouldnt really want kids playing with 220v anyway.

Sent from my SM-G800F using Tapatalk



The inverter would only be a requirement of you also want to charge laptops. Sure you can charge them from DC, but it's generally better to use the proper PSU. Many laptops. Lenovo and Dell for example, have ID chips in the charger and won't work properly with a non-genuine supply.

Sent from my GT-I9195 using Tapatalk

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18 hours ago, Mark said:

Mr Hobson... I have a diferent take... 

2x 100W (or 1x200w) panels will give 5amps plus via a cheap 12V solar controller (R250)

One old car battery and a set of 12V car cigarette lighters and 12v usb adaptors.

All in a nice packaged setup will do it... I did this with a toolbox...

large.5780d131a2471_2015-12-2111.25.32.jpg.dc3e7af4cb937b24a37b741f7112433a.jpglarge.5780d23e40f0b_2015-12-2111.24.34.jpg.46d6e817efe12682a024bcf4f9faaea4.jpglarge.5780d1a44472e_2015-12-2111.25.38.jpg.0b2a518ee8974a0f169cbe213db000d4.jpg

I only have one question , can you pick it up by the handle ? :P

 

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I have communicated with Mark (OP) and given their limited budget, a few cig sockets or usb ports, with a 2nd hand 12v battery, cheap but reliable controller (Phocos 5A) and a 80W panel will be a good start. I also suggested a meter (Phocos) to add to the educational experience.
I think Mark has a great project here and also suggested that they charge a fee for the charging so the kit can be expanded.
Any suggestions for sponsorship or contacts for small pieces of kit lying around which can be donated?

Sent from my SM-N910H using Tapatalk

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Mark, yup, that is more important than solar panels and wiring - only just :) Good luck. Hope more members respond to the call for assistance. A visit to Communica or 4x4 direct for all the bits and bobs can add up!

Sent from my SM-N910H using Tapatalk

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