7 Voc under a full moon

[BackwoodsEE]

Last night there was a full moon at around 22 degrees elevation and the illumination was clearly visible on my array. I decided to see what the open-circuit voltage of each of my two 12-panel strings was.

With the PV disconnect opened, as measured on my Klein tools multimeter (which I'm guessing presents at least 1 Mohm to the voltage source), each string was generating around 7 Volts. It would have been interesting to put different value resistors on the PV output and see what the IV curve was. I wonder what the MPPT of full-moon insolation on 12 series PV panels is in milliwatts? Maybe next time.

[bcroe]

Last night there was a full moon at around 22 degrees elevation and the illumination was clearly visible on my array. I decided to see what the open-circuit voltage of each of my two 12-panel strings was.

With the PV disconnect opened, as measured on my Klein tools multimeter (which I'm guessing presents at least 1 Mohm to the voltage source), each string was generating around 7 Volts. It would have been interesting to put different value resistors on the PV output and see what the IV curve was. I wonder what the MPPT of full-moon insolation on 12 series PV panels is in milliwatts? Maybe next time.

Those are the kind of numbers I observed some time back. Forget what the current was, but
it was pretty small. Not inclined to track down MPPT. Bruce Roe

[J.P.M.]

A very rough est. of reflected lunar irradiance form some stuff I've got has the number at ~~ 0.0018W/m^2, and it's all diffuse, and at a frequency that's mostly unusable to silicon based solar devices. At those levels, even if off by a couple orders of magnitude, hat makes reflected lunar irradiance contribution == 0.

An interesting academic problem maybe, but I doubt if common instrument linearity or reliability would apply at those levels. There was a paper in the Journal "Solar energy" back in the early 80's that discussed the idea. I could root around and try to find it, but it seems a waste of time.

[BackwoodsEE]

Well, the moon is about as full tonight as it was last night (maybe more so), and I figured I'd just go all-out and see if I could characterize the IV curve of a string of 12 290W PV panels under nearly ideal moonlight irradiation. The elevation angle is about 22 degrees, not too far off of the 45 degree elevation of my panels. When I did my measurements, it was nearly lunar "noon."

I measured the input impedance of my Klein tools DMM with another DMM; it is 7.2 Mohm. I put various resistors in parallel with the DMM and also a 10 Mohm resistor in series and wrote down the voltages observed. Then I wrote a little Python script that did the parallel and voltage divider calculations, and calculated current from voltage and resistance.

Believe it or not, I found a maximum power point! It is 35 microwatts at 5 V. Design your lunar MPPT charge controllers accordingly!

Moon_IV.png

[peakbagger]

My midnight solar surge arrestor has a blue LED to indicate its functioning. If the moon is out the LED is on.

[bcroe]

Well, the moon is about as full tonight as it was last night (maybe more so), and I figured I'd just go all-out and see if I could characterize the IV curve of a string of 12 290W PV panels under nearly ideal moonlight irradiation. The elevation angle is about 22 degrees, not too far off of the 45 degree elevation of my panels. When I did my measurements, it was nearly lunar "noon."

Believe it or not, I found a maximum power point! It is 35 microwatts at 5 V. Design your lunar MPPT charge controllers accordingly!

Lunar Noon, 35 microwatts? I guess that makes it official, I won't be using any lunar power units. Bruce Roe

[ButchDeal]

Lunar Noon, 35 microwatts? I guess that makes it official, I won't be using any lunar power units. Bruce Roe

what is the market for LRECs?

[BackwoodsEE]

what is the market for LRECs?

I don't know, but Elon Musk could probably get some subsidy money for it.