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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