How much do your panels produce when it is overcast and raining?

[1201]

Does anyone have a light meter they can recommend to measure irradiance? I see them online but never used one. Would be handy when comparing panel outputs rather than saying "it was sunny out"

You mean your pv panel output is not a good enough proxy?

 

[Checkthisout]

Your solar panels measure irradiance quite well.

No separate meter needed

 

[42OhmsPA]

Nice day yesterday, shitty day today.

 

[wpns]

Unfortunately it’s worse than KWHR/day, you need to have more generation than consumption for every instant of the relevant time period.

 

[wpns]

On days with arbitrary amounts of sunlight with random timing my generators can make 120 KWHR but I still will need batteries or the grid for when my load exceeds 5KW.

 

[wpns]

Your solar panels measure irradiance quite well.

No separate meter needed

Only when you are in MPPT mode and using all the available power. When they are throttled down it’s harder to tell

 

[wattmatters]

Unfortunately it’s worse than KWHR/day, you need to have more generation than consumption for every instant of the relevant time period.

Most systems are not PV only, usually there is either the grid and/or a battery which keeps the supply in balance with demand.

 

[wpns]

Most systems are not PV only, usually there is either the grid and/or a battery which keeps the supply in balance with demand.

Indeed, I was confusing this thread with the ‘offgrid but no batteries’ thread, apologies.

 

[seneysolar]

You mean your pv panel output is not a good enough proxy?

I mean sure, assuming you dont have anything wrong.
When folks are trying to compare output based on kinda clowdy, rainy, or gloomy it seems we are missing the point. We are throwing around precise measurements everywhere except the actual light.

 

[Mattb4]

Aaack! These poor weather day solar panel production testing just caused me to purchase 4-(2-100w Bifacial packs) (800w front rated) that were on 20% off special over at Ebay. (total price with free shipping and tax $407.13) just so I could see how they will produce.

I don't really need more frickin solar panels but my curiosity has got the best of me. I can setup them with a spare AIO I have on hand and see what happens.

 

[1201]

I mean sure, assuming you dont have anything wrong.
When folks are trying to compare output based on kinda clowdy, rainy, or gloomy it seems we are missing the point. We are throwing around precise measurements everywhere except the actual light.

So if you had that data, how would it help?

 

[Checkthisout]

My weather station measures irradiance.

It uses a solar panel to do so.

What trips me out is how good the online chart is at predicting solar output for the given location and azimuth of the panels.

I mean it's literally dead to nuts correct.

Global Solar Atlas

The Global Solar Atlas provides a summary of solar power potential and solar resources globally. It is provided by the World Bank Group as a free service to governments, developers and the general public, and allows users to quickly obtain data and carry out a simple electricity output...

globalsolaratlas.info

 

[seneysolar]

So if you had that data, how would it help?

To compare performance of different panels in low light conditions.
To verify output of panels vs STC ratings vs nmot ratings.
Ive always been curious.

 

[Checkthisout]

Currently raining. 2430 watt array. 9:00 Local Time.

 

[Mattb4]

Currently raining. 2430 watt array. 9:00 Local Time.

That comes in at 5% (120W/2430pW). Likely be more once the day gets further along.

 

[42OhmsPA]

Rains picking up more since the morning.
MPPT 1 (angled ground mount) - 5180W
MPPT 2 (flatter roofs mounts) - 5670W

 

[AntronX]

It does make me wonder though if there are panel types that would produce more wattage even with low light daytime conditions.

I measured light intensity in lux vs. panel output. I found power output to follow light intensity linearly down to 1% of rated power and that's where MPPT controller loss took over. There is no free lunch. Light power = electrical power.

 

[Mattb4]

I measured light intensity in lux vs. panel output. I found power output to follow light intensity linearly down to 1% of rated power and that's where MPPT controller loss took over. There is no free lunch. Light power = electrical power.

The chart posted for Qcell panels (Thanks to Rhino's post #21) does not show a linear decrease. It seems to follow a semi logarithmic scale after you get below 600w/m2. I admit that I expected what you describe.

 

[AntronX]

The chart posted for Qcell panels (Thanks to Rhino's post #21) does not show a linear decrease.

You are correct. I was talking from memory. I just looked up my measurement and turns out I only measured from 50W/m² and down. Efficiency numbers seem to agree with Qcell chart. These are 19% efficient panels. That 13 lux row is inaccurate. I left it there to show where accuracy totally falls apart due to MPPT PV power measurement becoming nonsensical.

LUX	PV (watts)	Solar W/m²	PV eff.
6700​	145​	53​	17%​
3300​	70​	26​	17%​
1200​	27​	9​	18%​
670​	12​	5​	14%​
440​	8​	3​	14%​
280​	5​	2​	14%​
13​	1​	0.1​	61%​

 

[JRH]

That comes in at 5% (120W/2430pW). Likely be more once the day gets further along.

Still over cast and drizzle , 2:00 pm …50 F…. Fog is moderate ..
Panels still not tilted ,just laying flat…....array producing about 5%ish since 10:am ..
4-5 % seems where a happy spot in this condition of sky and temp…for the last two days.