measuring input from solar panels (for a science project)

softcon

My son has had an assignment for several weeks now, and he never came up with a project. Now that there is only two weeks of class time left, he finally decided he should work on something. <sigh> So, since I had several solar panels lying around (half of them unopened), I thought perhaps he could do a project where he measures how much power he can get from the solar panels (based on number of panels, direction facing, and so on). My question is:
Do I need an external sensor/meter, or is this something that can be done by the propeller board directly?
I have 3 propeller boards that can be pressed into service for this project, though two of them are currently in existing projects, the third one was too, but it's since become disconnected, and it's a bit of a hassle to reconnect everything, so I'm willing to sacrifice it for the project. I can always rebuild the speech device later, though my wife has found other things to use instead of my self-built project <sigh>. Anyway, Just curious if I'd need an external sensor, and if so, which one, and how much trouble it would be to connect to the propeller. The one I gave him to use has a human interface board on it already, so I don't know if that will help or hurt in this particular case. I have 4 solar panels, 3 from radio shack, and 1 I got elsewhere (don't remember where), which is much thinner, so figured perhaps he could measure the different panels, and how much power each one gave and if he does this over the course of several days, and multiple times during the day (I was actually thinking of having him connect it to the computer, so it could keep a running tally of the power read-outs), then it would be acceptable as a complete science project. Any help/suggestions would be greatly appreciated, as I've never tried measuring power input levels before.

tomcrawford

Does your prop board have an ADC?

JonnyMac

The INA219 board from Adafruit (Parallax used to carry) will tell you voltage and current; this might be useful for such a project. I'm using that chip in a couple Propeller-powered products.

MikeDYur

Looks like Parallax still does:

https://www.parallax.com/product/29130

kwinn

JonnyMac wrote: »

The INA219 board from Adafruit (Parallax used to carry) will tell you voltage and current; this might be useful for such a project. I'm using that chip in a couple Propeller-powered products.

+1. Excellent choice for this kind of project. Can measure voltage, current, and power.

tomcrawford

'course if you know R, you don't have to measure I.

softcon

All three of my propeller boards are the quickstart board, so if it has an ADC I haven't seen anything about it in the docs, but I know it's possible to do such things sometimes without an actual meter, which is why I was asking. However, I kind of like the suggestion here for using the above mentioned board. That looks useful, and something I can use in other projects once my son is finished with it. However, free is better, since this isn't a fun time for us, so if it can be done w/o the board, all the better, but it won't break the bank too much, (just means I'll have to bail on the kickstarter campaign I wanted to sponsor). <grumble> But, that won't be the first time I had to drop a kickstarter support pledge. <sigh> Anyhow, thanks for the recomendation. I'll go get one now.

jmg

softcon wrote: »

.... I have 4 solar panels, 3 from radio shack, and 1 I got elsewhere (don't remember where), which is much thinner, so figured perhaps he could measure the different panels, and how much power each one gave and if he does this over the course of several days, and multiple times during the day (I was actually thinking of having him connect it to the computer, so it could keep a running tally of the power read-outs), then it would be acceptable as a complete science project. Any help/suggestions would be greatly appreciated, as I've never tried measuring power input levels before.

What range of OC Voltage and SC current do these displays have ?

softcon wrote: »

... However, free is better, since this isn't a fun time for us, so if it can be done w/o the board, all the better..

2 R's and a C will add an ADC to a Prop, so you could avoid buying anything, if you have good resistor stocks.

If you look at the curves here
https://en.wikipedia.org/wiki/Maximum_power_point_tracking#I-V_curve
& here
http://www.embedded.com/print/4216272

you can see the actual shape is highly predictable, and ideally you want to sweep the curve to find which one 'fits' your solar cell under test.
The simplest way to get a few test points, without needing a full curve-sweeper like current sense and smart load, is to just switch in a handful of power resistors
A resistor is a simple straight line thru the origin ( I = V/R), on those curves, so you can create a set of 'fan-load-lines' with multiple loads.

Measure the voltage for each resistor, and work backwards to create the best fit curve.

From the fitted curve, you can extract the Maximum Power Point.

Tracy Allen

How old is your son and how motivated now that the deadline is approaching? He can or should read up on solar panels--There plenty to find on the web at different levels. Measuring power output from a solar panel is a subject in itself. Look up MPP, maximum power point. The question is, what resistor(s) or load(s) do you have available that can come close to the MPP of your panels?

softcon

Hmm, good points, and good questions too. I have a whole array of resisters, that I bought at Radio Shack quite some time ago. I've forgotten what colors mean which, but that's easy enough to lookup. As far as how motivated he is, I'd wager the answer is not very, considering he's waited so long to even tackle any project at all, and this is the only one I could come up with based on available parts. He's fifteen, so I'm not planning to do any building for him, though I will help with the code, since he's not really much of a programmer, despite my best efforts, he likes his games, and he did build his own machine (though it took half a year to get the parts, buying them one per month), so he's no slouch when it comes to computers, he just has no interest in programming them. <shrug> Seems odd to me, but perhaps I'm the odd one, who knows. Plus, anything we do eventually put together (unfortunately) has to be done in a hurry <sigh>, and is likely to be entirely me doing the work (well, except for final assembly, I'm making him do that), but not being able to see puts a damper on how much I can instruct during the process. He's gotten pretty good at listening when it comes to these kinds of things, (too bad that doesn't spill over into other areas), but I can't explain electrical diagrams since I can't see what he's looking at. Understanding the theory and concepts isn't the same thing as passing those on to others. Both of my kids have gotten used to me asking which color this wire is, or what label that pin has on it, so they have learned the process, though they do tend to grumble quite a bit when I pick up the development boards. :)Under normal circumstances, I'd do as much as I possibly could, (even up to and including plugging everything together), then just ask them to verify things are in the proper places, but this is supposed to be his project, so he's doing as much work on it as I can get him to do given the limited time constraints.
I did purchase the INA219 board linked above, and it should be here on Wednesday, so hopefully that will make things easier, so I guess now I need to begin looking for code to tie the detector to the propeller, and wiring information, which I assume will be in the various documentation for said detector. Always a fun time when the kids decide to wait to the last minute. Thanks for any and all help so far, and any still to come. I certainly appreciate it.

Tracy Allen

It's not just 15-year-old kids who procrastinate. Ahem. Effort can be inversely proportional to a time remaining to deadline, or the alternative, blow it off, wing it, it's just a game, let the chips fall where they may.

When you say solar panels, what are we talking about? That is, in terms of physical size, voltage and rated power output? If you have a 10 watt, 12 volt nominal panel, that will require a commensurate load, quite different from a 1 inch, 0.5 volt 20 milliamp single cell.

softcon

I have no idea what the ratings on the cells are, but they're pretty small panels, so it shouldn't be too terribly much. I'll get someone to look tomorrow, and see if it states their capacity on the ones we haven't opened yet, then I'll know better what kind of current to expect from these things. I'd be very surprised if it's more than a watt or so of current, though I'm no expert in solar panels, so I could be completely off on this one. They're about 5 or six inches long, and probably 3 inches wide, so pretty small panels, so I'm not expecting much. It should be a nice simple project for him once the whole thing is assembled, then it's going to be up to him to gather the readings he needs for his project, I'm not going to push him, but since this is supposed to be 20% of his grade, I'm expecting he'll be rather diligent about recording results.

Tracy Allen

Do you have a volt meter? Your son can assign a tracking number to each panel, then take them out in the sun and measure the output voltages. Write them down. Take it into the shade. Same. Those are open circuit voltages. I'm assuming the panels have wire leads or connection terminals.

Does the meter also have a ammeter setting? He can connect the panel directly to the ammeter and measure the short circuit current for all those panels in sun and in shade.

If there are ratings printed on the panels or on their packaging, he can compare those with his own results.

Already he can learn a lot about the panels and can probably have some fun finding things out about how they work as he shifts them around. Also learn more about how to use the meter. Write down all the observations for the science project journal.

softcon

The panels I have (at least the 3 I have info for) say they're max rating is 6 volts at 50 milliamps. I can't remember the formula for conversion to watts, but I think it's 3 watts? Anyway, it's a straight measurement in this case, and the part from parallax should arrive today, so after that, the fun begins. I think I'm looking forward to this more than he is, but then again, for me it's fun, for him, it's work, so it's understandable.

MikeDYur

softcon wrote: »

I think I'm looking forward to this more than he is, but then again, for me it's fun, for him, it's work, so it's understandable.

Maybe that will be the turning point. When he sees that your having too much fun.
He could be intimidated by the big picture, but you can show him how little steps add up to a well rounded understanding of the subject. Then all of a sudden something clicks, and he feels empowered and there is nothing he can't accomplish.

tomcrawford

How does power vary with angle of the incoming radiation?

softcon

I'm going to need help with this ina219 board. It apparently requires soldering, and I can't do that, due to lack of vision, and my son doesn't know how, so we're going to try to find someone in town (preferrably a teacher at the school) who can do the soldering for us, but if that all fails, does anyone have any ideas on how to connect this thing w/o the soldering part? Between some three-pin headers, and a few male-female jumper wires, I think I have enough wiring to make the connections even w/o soldering, but I'm not entirely sure, and my son is having trouble reading the schematics on how to connect things to the propeller (the one for the arduino which I also have) was worse, though I've not tried the bs2 code yet, so perhaps maybe that one can be done w/o soldering, but based on how the resister is built, I'm guessing not.
Anyone have enough experience with these ina219 boards to offer some alternative suggestions?

tomcrawford

If you do not use solder, you cannot get dependable electrical connections, especially in a setup that has to be moved. If you do not have dependable electrical connections, you will not get repeatable measurements. I cannot think of anything more demoralizing.

kwinn

Here is a diagram with the connections. Soldering a 4/6 pin right angle connector and the screw terminal to the board lets you plug it in to a prototyping board and connect the load with wires.

tomcrawford

You may need to add a pull-up to SDA. Cannot remember if 219 has one or not.

RS_Jim

If you lived anywhere near Phoenix, I would be happy to teach your son the "black art" of soldering.
Jim

JonnyMac

tomcrawford wrote: »

You may need to add a pull-up to SDA. Cannot remember if 219 has one or not.

That board has pull-ups on SCL and SDA.

Tracy Allen

To go along with Kwinn's hookup diagram, attached here is the Quickstart side. This assumes you are starting with the demo code for the Propeller found on the Parallax web site. It uses p0=scl and p1=sda.
https://www.parallax.com/downloads/ina-219-dc-current-sensor-propeller-code

My comment about using a multimeter still stands. Do you have one? I know there have been talking multimeters for the blind and for people who like to look at the probes instead of the screen, however my quick googling turns up only do-it-yourself projects based on adapting a multimeter that has RS232 output. Well, that or the ina219 along with a speech synth like the Parallax EMIX2 could make an useful Propeller and science project.

A multimeter has at least two roles here. First, it lets junior set out to measure things at the get-go, to get a feel for how the panels behave. Secondly, if there are questions about the accuracy of what is being measured by the ina219+propeller+programming, the multimeter can help to troubleshoot and resolve.