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Comment by jacob019 | Hacker News Reader

You won't get 200W from a 200W panel in direct sunlight, but it will still generate some watts at other times, so it should work out.

"A 4.6b year old yellow dwarf as a light source" loved that

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I thought that was factored in when he talked about 3 full-hours of 200W across the full day? The day in Australia is certainly longer than 3 hours, so I figured that accounted for panel inefficiencies, indirect sunlight, and other such things. But could be wrong. Not sure how the 3 hours was calculated, but I am sure some solar calculators will take your location, average annual sunlight, efficiency and spit out an "effective daily solar hours" value that can be multiplied by the indicated solar panel wattage.

3 hours comes from averaging the daily power generation my Victron MPPT reports. I’m using a 200 watt panel and it reports and average of 600Wh since I set it up a month ago.

Even better than a calculator - it's your actual experience ;)

In power systems there is a number called the capacity factor that is used to relate the average actual output to the nameplate capacity over whatever time interval. In this article the author note that they are expecting 600Wh in a day, or about an average of 3h at nameplate capacity. That works out to a capacity factor of about 0.13, which sounds about right for a solar installation that wasn't purpose built in an area of high insolation.

Between experience and math, my rule is: on average, buffered with a battery, you'll get 10 watts out of a 100 watt panel (i.e.: 10% efficiency, all common conditions considered).

Did you mean "except in direct sunlight"?

The nominal rating is a peak rating, in my experience the sustained output will be somewhat less, even in direct sunlight.

Nod, unless you are in a place on the planet with perfect insolation (which would still only happen a few weeks of the year), it will nearly always will be below nameplate rating. The nameplate rating/testing if ever done, is done in a test bed with artificial light and perfect angle.

Edit: I remember I did once get an above nameplate actual power output from a panel once - using MPPT, at high altitude, at the maximum insolation time for the year (mid-California in the mountains, right around the summer solstice). It only lasted for 20 minutes though.

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