Threshold Solar Intensity for Panels

Basic question about minimum sunlight intensity at which various type/brand panels produce power from sunlight.
I assume that even for the monocrystalline panelsl for each brand that number is different.

Is there a way to look up that number? - I do not see it listed in specs commonly.
Is there a general rule of thumb to approximate? Like 100 W/m2?

I ask because as I go around our wooded lot with a solar intensity meter to figure out optimal ground rack panel placement, I am getting rather disappointing readings past noon.

Thanks!

Basically without full sunlight directly onto the full face the panel it will not perform anywhere near it's rated power.
You have got to find a place where they can get full sun for the longest amount of time to generate the power you expect you will need.

PR-Solar said:

Basic question about minimum sunlight intensity at which various type/brand panels produce power from sunlight.
I assume that even for the monocrystalline panelsl for each brand that number is different.

Is there a way to look up that number? - I do not see it listed in specs commonly.
Is there a general rule of thumb to approximate? Like 100 W/m2?

I ask because as I go around our wooded lot with a solar intensity meter to figure out optimal ground rack panel placement, I am getting rather disappointing readings past noon.

Thanks!

Click to expand...

Expect very poor production I am afraid

There is no magic here. Direct sunlight has to hit the panels to produce energy. Shade and shadows kill production.

For example, today I have light but consistent cloud cover, the sort of thing where you don't get shadows but it's bright. My panels were producing about 1/3 of what they are capable of.
Notably the Panasonic panels were doing rather better than the LG or Jinko panels. They do seem to be notably more efficient in lower light conditions.

Quattrohead said:

For example, today I have light but consistent cloud cover, the sort of thing where you don't get shadows but it's bright. My panels were producing about 1/3 of what they are capable of.
Notably the Panasonic panels were doing rather better than the LG or Jinko panels. They do seem to be notably more efficient in lower light conditions.

Click to expand...

Thanks Quattro
Have you ever taken a solar intensity meter to quantify the production?
For example, Sunshine_Eggo puts up this graph here for his panels:


Meanwhile, the panels I am seriously considering from Signature Solar, these Canadian Solar 390W beauties show nearly 90% of max production at meager 100W/m2;


So, as they say, your mileage may vary - and vary quite a bit.

My situation in Minnesota is probably typical for the state:
- On bright sunny days we do get 1000W/m2, especially in the summer (when we need the power for the air conditioning the most)
- On dreary overcast days, the meter says 150W/m2 through the leaves - when they fall next month I will get a better reading.

I would like to put 10 panels on a rack to begin with for 3900W theoretical and 1800W expected in practice
I could place them on a roof, but I REALLY do not want climb and deal with that install, not till the rack system provides some meaningful battery back up for nearly once a month our grid goes down these days...
So if these 10 panels act as a "good enough" trickle charger to keep a couple of EG4's batteries store 10KW-h for those black outs and maybe cut down our electric bill by a third or so...
If/when that happens, I can be inspired to climb the roof come next summer and add/move panels for a 20panel+ system to give 9 theoretical KWs to really dent the grid consumption...

Thanks again.
Any thoughts appreciated.

I wouldn't get your hopes up. The sun is getting lower as we head for winter solstice Dec 22nd. You will soon also have snow to contend with.
You may want to consider tilting your panels steeper, if possible.

45North said:

I wouldn't get your hopes up. The sun is getting lower as we head for winter solstice Dec 22nd. You will soon also have snow to contend with.
You may want to consider tilting your panels steeper, if possible.

Click to expand...

Again,
my hopes are to have a charged up battery pack for the monthly blackout event & may be offset a bit of the bill.

Which one of those hopes is not attainable?

I have a friend in the southern burbs of the Twin Cities (abt 40 miles from us) with an 8KW rooftop system who averages just over half of that on a year-round basis, 2 years into this. My hope is to get under a half, but again, if it's less, it's no biggie.
The snow won't be an issue - I shovel the driveway, I can hit the panels with a broom and subtract the snow days from the total.

PR-Solar said:

Thanks Quattro
Have you ever taken a solar intensity meter to quantify the production?

Click to expand...

No I have not, sorry.

Interesting because I got around to tilting my panels to 47 degrees yesterday.

4240W per string and the charge controller showed at times over 5000W due to edge effect but I did video where it held minimum 4600W and above for over 2 minutes. Pretty amazing.

Half cut cells, absolutely no shade. 530W panels in 8S.

Over 150A going into my battery with just the 2 strings.

PR-Solar said:

I could place them on a roof, but I REALLY do not want climb and deal with that install, not till the rack system provides some meaningful battery back up for nearly once a month our grid goes down these days...
So if these 10 panels act as a "good enough" trickle charger to keep a couple of EG4's batteries store 10KW-h for those black outs and maybe cut down our electric bill by a third or so...

Click to expand...

A bit North of your area, in Ontario.
I used my metal building shop roof to support the PV- partly to get the panels up high enough to avoid the worst of the low winter sun angles.
I tilt the array up to 65-degrees for the winter, this assists alot with snow removal, and gains about 8% on collection during the time it matters most (to me) = November/December.

PR-Solar said:

Again,
my hopes are to have a charged up battery pack for the monthly blackout event & may be offset a bit of the bill.

Which one of those hopes is not attainable?

Click to expand...

I suggest you consider the summer and winter as two completely different scenarios:
Summer - no problem to cut the electric bills, we get a lot of sun hours at our latitude.
Winter - charge from solar 'as much as you can' during the day, if the batteries do not reach full-charge, use the grid to charge them the rest of the way to full, then if there is an outage your ESS is close to 100% and you can rest assured you have some power when you need it. If your outages are like mine, these are far more common during winter storms than during summer.
I recommend a dual fuel back up generator if you are concerned about winter outages that may last days. The unfortunate reality: grid outages are more common during winter storms, winter storms coincide with days of crappy solar potential.
just saying.