School project

[Living Large]

If you know anyone who is into amateur astronomy, talk to them about borrowing a telescope mount. Even a cheap equatorial mount would track the sun for you, as would a computerized alt/az mount. Your science teacher, school, or a local astronomy club might be willing to help you out.

You could also just mount the cell on a camera tripod, print out a table of the azimuth and elevation of the sun throughout the day and make manual adjustments every half hour or so.

Ya know, those are two good ideas. I had an equitorial I just sold. The only small challenge is attaching the array to the mount, but since it is so small and lightweight, it shouldn't be a problem.

I have an old school surveying transit that would work for your second idea, with scales for both elevation and azimuth. I just used it to check the shading at a potential off grid sight. If he is going to use a measurement technique that involves visiting every 15 minutes or whatever, then he could adjust the angles as you suggest.

[ericf1]

I've found some fountain/aquarium pumps that will work. I will need a slightly larger panel though. I did find a small tracker. Not sure if it's ok to post links, if not please remove:

http://www.amazon.com/gp/product/B00997KGMC/

If you know anyone who is into amateur astronomy, talk to them about borrowing a telescope mount. Even a cheap equatorial mount would track the sun for you, as would a computerized alt/az mount. Your science teacher, school, or a local astronomy club might be willing to help you out.

You could also just mount the cell on a camera tripod, print out a table of the azimuth and elevation of the sun throughout the day and make manual adjustments every half hour or so.

[Wy_White_Wolf]

May be a little out of your project price range but they do make DC watthour meters.

http://www.rc-electronics-usa.com/ammeters/rv-battery-monitor.html

Hook one up to each panel and have them charge a battery for the day. Make sure the battery has a load on it or is discharged enough that it won't get fully charged by the end of the day.

WWW

[milkymj]

The first thing I came across in a quick search was that trackers add 22-30% in efficiency.
So if your pumps (or other measurement apparatus) are within 2% or even 5% of each other, it should be good enough.
But can you find a pump to run off a small solar panel?

As for sourcing - I'd suggest finding who makes solar trackers, and contact them to see if they'd be willing to lend you the tracking hardware. Quite possibly they have something that's the right size for this, and they use it for sales/marketing.

I've found some fountain/aquarium pumps that will work. I will need a slightly larger panel though. I did find a small tracker. Not sure if it's ok to post links, if not please remove:

http://www.amazon.com/gp/product/B00997KGMC/

[foo1bar]

What do you think? Accurate enough for this project?

The first thing I came across in a quick search was that trackers add 22-30% in efficiency.
So if your pumps (or other measurement apparatus) are within 2% or even 5% of each other, it should be good enough.
But can you find a pump to run off a small solar panel?

As for sourcing - I'd suggest finding who makes solar trackers, and contact them to see if they'd be willing to lend you the tracking hardware. Quite possibly they have something that's the right size for this, and they use it for sales/marketing.

[sdold]

Sounds good, if the pump is small (or the orifice is restricted) and you use big buckets or bottles, maybe you could leave it running all day.

[milkymj]

Okay, great ideas. What I think I'm going to do is a combination of them. Get 2 small dc pumps and run each one on the hour for 5 minutes and see how much water each pumps. Do that over the course of the day and plot it out.

What do you think? Accurate enough for this project?

[Living Large]

Great discussion here. I didn't think my resistor suggestion was necessarily a good one, but I threw it out there as a starting point. I like the ammeter suggestion, and the other ideas are novel.

[bcroe]

I see what you mean, Bruce. How about just using an ammeter
across each panel? Would the current be proportional to the power collected?

An ammeter will accomplish the same thing as a shunt read by a voltmeter. The Vmp
and the ratio of Imp/Isc are constant enough to get a decent approximation of the
instantaneous power. It will take logging to record the energy accumulated.

Using water pumps is probably a good way to access the performance of a direct pump
system. I doubt the pump tracks the max power point at all (without an MPPT controller),
so it may be a rather inaccurate measure of power available. How constant is pump
efficiency over varying input? Bruce Roe

[russ]

Make them pump water, swap the pumps for a control reading - keep it simple...

Good suggestion

[sdold]

The tracking or not will vary the current available, which will change the voltage on the
resistor and the operating point on the cell. Changing the operating point (voltage)
causes an avoidable error. Bruce Roe

I see what you mean, Bruce. How about just using an ammeter across each panel? Would the current be proportional to the power collected?

Small current shunts with panel-mounted analog meters would look good too. I think science displays (if that's what this is) look better with analog meters, for some reason. Maybe it's because you don't have to explain what the numbers mean.

[pleppik]

Make them pump water, swap the pumps for a control reading - keep it simple...

I like this idea...it's much more interesting and understandable to look at how much water is in a tank than to look at numbers on a graph.

[bcroe]

I think resistors would be OK as long as both panels and resistors are the same. The panels will be operating at less than optimum efficiency, but they'll be the same and the only variable will be the tracking.

The tracking or not will vary the current available, which will change the voltage on the
resistor and the operating point on the cell. Changing the operating point (voltage)
causes an avoidable error. Bruce Roe

[sdold]

I think resistors would be OK as long as both panels and resistors are the same. The panels will be operating at less than optimum efficiency, but they'll be the same and the only variable will be the tracking.

[bcroe]

Hello,

Just want to start off saying I'm new to this forum. I'm a middle school student working on a project for science fair at my school. I came up with an idea but cannot figure out how to fully execute it. This forum looked like the best one I've found to ask a few questions. I apologize if this has been asked before or if my terminology is incorrect. I did search but couldn't locate an answer in the vast archives.

My project consists of 2 solar setups with an approximate 6"x6" panel on each one. 1 has a sun tracker and 1 doesn't. My goal is to find out how much more output I can get from the one with the tracker. The problem is I cannot figure out how to measure the total output for the day. I thought maybe there was a meter of some sort that I could attach to each one but I'm unable to locate such a device. Your thoughts?

You can connect a resistor and measure its voltage, but that will introduce more error. The
problem is that you really want a MPPT controller to find the true power. A simple resistor
isn't that, and as it rides up and down the varying output voltage curve, its efficiency will
vary a lot.

My suggestion is put essentially a short on the panel, a (very low resistance) shunt. This
will fix the operation at the Isc point, so comparisons are accurate. The actual power
capability can be estimated as Imp/Isc times Vmp. Once again make frequent measurements
of the shunt voltage (to determine the current). The Vmp will vary little if temperature is
pretty constant. Bruce Roe