School project

[milkymj]

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?

[russ]

Hi and welcome to Solar Panel Talk!

One of the guys should be able to guide you so let us wait and see.

Russ

[sdold]

One thing you could do is measure the voltage and current delivered by the each array periodically during the day, and multiply them to get power, and make a graph of the power vs time and interpolate between the measurements. You'd need four multimeters (two for each array, one measuring current and one measuring voltage) and someone would have to log the readings every 15 min, 1 hour, or whatever you can do. The units of energy produced by a panel in a day are Watt hours (power(Watts) x time(hours).

If you do this, could you let us know what you find? It sounds like fun.

[Living Large]

Here's an idea for starters that can probably be improved. Put a resistor across the output, and use a DC watt hour meter something like the "watt's up". The meter costs $60 but it does what you want. That's a dirty way to do it that may work. Those with more experience may come up with better/cheaper ideas.

EDIT Cheaper would be to use sdold's idea of data points every 15 minutes, and measure the voltage across the resistors. You would just need one meter, and take two measurements each time. You will need power resistors to dissipate the heat. Let's say your panel puts out 4 Watts @ 6V. Volts * Amps = Watts, so the maximum current would be 4/6 = .67 Amps. Then Resistance = Volts/Amps = 6/.67 = 9 ohms. You could use a 10 ohm 10 watt wirewound, which you could get at Radio Shack before they shut them down.

Do you know the rating of your panels?

[milkymj]

Do you know the rating of your panels?

Not yet. I'm putting together a materials list now. Suggestions on where to buy are welcome.

[sdold]

Cheaper would be to use sdold's idea of data points every 15 minutes, and measure the voltage across the resistors.

I like that Idea!

[sensij]

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?

The total output for the day will have units of "energy"... periodically measuring voltage and current as other have suggested will give you a measurement of "power." The sum of all your power measurements throughout the day would give you the total energy, but depending on how often you make the measurements, you will need to make some approximations to turn those measurements into an estimate of energy produced.

Another idea, instead of using a resistor and measuring it, would be to actually use the energy of the panels to perform work. The units of Work are joules, and units of Energy are joules, so you are looking at your value of interest directly, except for maybe some efficiency losses.

What kind of work could be done? Depending on the voltage output of the panels, you might be able to find an inexpensive DC motor that will run directly from the panels. That motor could do something like turn a clock, so you can visually see the energy difference by comparing how much the hands have moved. With a DC source, you could power something like a pair of model trains or an electric race cars (do they still make them?), and compare how much distance they each have traveled.

With some brainstorming, there are probably some low cost ways to make energy generation (and consumption via work) visual, although it would help to know what voltage and power your panels are rated to put out. Even that resistor suggested before could be used in a way to heat water, maybe, and you could measure the temperature of the water to show how much more energy the tracking panel generates. However, the physics of heat transfer are more complicated, and the temperature measurement could easily be affected by things other than the energy produced by the panels.

[FunGas]

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

[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

[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]

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

[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.

[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.

[russ]

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

Good suggestion

[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