[RE-wrenches] 1.56 Rule

[drake.chamberlin at redwoodalliance.org]

1400 W/Sq M would certainly do it!

Thanks for all of your input.

Drake

---

On 2026-05-18 16:26, Zeke Yewdall via RE-wrenches wrote:

> I've definitely seen this.  I regularly measured over 1200 watts/sq 
> meter in clear day skies on my sites, and if you throw in some edge of 
> cloud too... could get even more.  I've heard ski resorts dealing with 
> 1400 watts/sq meter on vertical windows of lodges facing a big snowy 
> bowl.   I'll try to dig up a graph from one of my sites with monitoring 
> on it.  I was often getting near STC voltage at the same time.  These 
> were high elevation (8,000 feet and up) sites in Colorado, no humid 
> haze, thinner atmosphere, and often a bunch of snow reflection too.  I 
> would measure around 3.6kW peak AC output from a 3.3kW STC rated array 
> at my house at 9,300 feet there (had it on a 3.8kW inverter -- I 
> greatly disagree with certain inverter manufacturers recommendations 
> for overpaneling, but that's a different topic).
> 
> If you're closer to sea level or back east where the humidity blurs out 
> the sun more, probably a lot less chance of it, except during good edge 
> of cloud conditions --  which generally don't last longer than 5 or 10 
> minutes max -- not three hours like altitude/snow enhanced irradiance.  
> I will say, the sun breaking through the clouds on a 95% humidity 70 
> degree day in DC felt hotter than any 95F day in the sun out west -- 
> did not put an irradiance meter on it though.
> 
> I have some rear facing irradiance monitors on some sites now, to get a 
> better idea of how much gain we can really expect from bifacial 
> modules.  Be interested in seeing what they say over time.  I've been 
> doing another 1.2 or 1.25 factor when using bifacial modules in snow 
> country, but not sure how realistic that is.
> 
> Zeke
> 
>> Are there  circumstances where the amperage of a PV module can go up 
>> by 25%?
> 
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