Measure Daily Output of a Solar Panel

ronp849 · Feb 28, 2009

With a fixed resistor the power is proportional to the sq of the voltage - sample the voltage on a regular basis and calculate the total ENERGY over a given time. (Ie Integrate the calculated power value.)

Mike_2545 · Feb 28, 2009

Sampling voltage won't give current.

ronp849 · Feb 28, 2009

If the load is a fixed resistor, you do not need to measure the current:

Power = Volts x Volts / Resistance

Mike_2545 · Feb 28, 2009

Give that a try and let me know how that works for you.

ronp849 · Feb 28, 2009

If you have two identical solar panels then I suggest you test both panels at the same time - for the reasons Mike gives, duplicating the conditions for both panels at different times would be very difficult. You could monitor both voltages with a single micro and even calculate/display the energy/power difference in real time.

Ron

Willbe · Feb 28, 2009

Since a solar panel is a current source in parallel with a voltage clamp the voltage across your measuring device should probably never exceed <50% of the open circuit voltage of your solar cell.

Nigel Goodwin · Feb 28, 2009

Willbe said:
Since a solar panel is a current source in parallel with a voltage clamp the voltage across your measuring device should probably never exceed <50% of the open circuit voltage of your solar cell.

Did anyone understand that?.

Mike_2545 · Feb 28, 2009

No, that's why I said "Give that a try and let me know how that works for you."

Willbe · Feb 28, 2009

Well, if you open circuit the panel, each cell maxes out at about one diode drop, 0.7v or so, so you really can't tell what the cell is capable of by using a very high load resistor value.

If you short the cell, the Isc should vary with illumination but this also doesn't tell max power level, only max current level.

And you can't use the max. power xfer idea, where the load resistance = the internal resistance, because the internal resistance varies.

So, I guess keeping the load voltage at less than 50% of max. open circuit voltage will give some reasonable approximation to the max. power available.

Mike_2545 · Feb 28, 2009

Gibberish I tell ya

Willbe · Feb 28, 2009

mike2545 said:
Gibberish I tell ya

Duly noted and recorded!

Mike_2545 · Feb 28, 2009

Willbe

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If you get more than 0.15 hp per sq. yd. of solar panel, you're doing pretty well.

Actually Willbe,

.15 hp is around 111 watts. I know of many 3X5 panels rated for 170 watts and up to around 200 watts. So, a sq yard is 9 sq ft. you,re saying that if you can get 55% out of a solar panel you're doing pretty good?

be80be · Feb 28, 2009

what happen to the 6 sq feet you lost and don't most calculate the power by the solar cell charging a storage battery. I don't see how you could get a power reading that would show you any thing about how much your cell can supply with out seeing how much it can save to storage.

KMoffett · Mar 1, 2009

We calculate the instantaneous (....well almost) maximum power output of our research panels by measuring the open circuit voltage, followed be the short circuit (0.1Ω) current, and multiplying by 0.6 (0.5-0.7 ranges depends on the type of panel). We also ran computer-controlled, swept-resistance loads to verify our calculations. And we switch between two panels, a polycrystalline and an amorphous, for comparison.

A ~24-hour sampling is shown.

Ken

umer27 · Mar 1, 2009

I have a sunny boy SWR1700 inverter , in the application Im using it in ..

Tell me how to keep track of the output ?

Willbe · Mar 1, 2009

mike2545 said:
Actually Willbe,

.15 hp is around 111 watts. I know of many 3X5 panels rated for 170 watts and up to around 200 watts. So, a sq yard is 9 sq ft. you,re saying that if you can get 55% out of a solar panel you're doing pretty good?

"The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1,366 watts per square meter (W/m²)"

I don't know how much of this is converted by solar panels; maybe half?

Mike_2545 · Mar 1, 2009

Ulmer27 Get a sunny web box to hook to the inverter.

Nigel Goodwin · Mar 1, 2009

Willbe said:
"The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1,366 watts per square meter (W/m²)"

Do you mean in space?.

I don't know how much of this is converted by solar panels; maybe half?

No where near that sort of efficiency, at least not on earth.

Mike_2545 · Mar 1, 2009

I don't know how much of this is converted by solar panels; maybe half?

The most expensive, carefully designed, and complicated solar panels in the world operate at about 40% efficiency.

The rest are about 10% efficient.

duffy · Mar 1, 2009

Are they up to 40%? Last time I checked, it was only in the 30's, and that was an exotic concentrator cell with multiple layers and using a dang magnifying glass to "concentrate" the sunlight.

Measure Daily Output of a Solar Panel

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