# Latitude/longitude quantity of energy collected differences

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Solar Expert Posts: 31
So I know that the solar "window" is shorter to gather sun through your array this time of year the further north you go. But what I'm wondering is if the energy collected in a given time is any different in quantity?

All things being equal (equipment, array adjusted for optimum angles, etc) does a 100w panel at
N41W87 (Lowell, IN) collect less energy in 1 prime time hour than the same panel at N33W112 (Phoenix) or N32W96 (Dallas)? And if so, how much (is there an equation or rule of thumb)?

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Re: Latitude/longitude quantity of energy collected differences

If you expose a panel of 'X' Watts to direct sun, Winter, Spring, Summer, or Fall, the power it puts out is the same. This is why we call it "hours of equivalent good sun" or averaged output over the time the sun is actually hitting the panel in sufficient quantity to produce power.

Then the variables come in.
For example if the panels are at a fixed angle the sun's angle to them will change throughout the year. Further from the Equator the greater the difference. This will cause a big change in panel output.
Cold temperatures will increase panel Voltage and that will mean more power when using an MPPT controller. Likewise hot temperatures have a reverse effect, and may lower panel Voltage below charging ability in some cases.
Different times of year mean different weather patterns which can also affect panel output.

But otherwise it's 1000 Watts per meter squared when you're right under ol' Sol and nothing else is messing with the insolation.
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Re: Latitude/longitude quantity of energy collected differences

In case anyone has forgotten ...
When it's Winter in the Northern Hemisphere it's Summer in the Southern one.
The Earth is actually closer to the sun in the Northern Winter, but is tilted away from it (hence the sun low on the horizon). (The orbit of the South Pole is less elliptical than the North Pole, as though the planet is 'traveling' on the South Pole like a top.)
These two factors are part of the explanation as to why the Southern hemisphere has an over-all warmer year-round climate.

If any of this has changed since I learned about the Earth's 'weather engine' 40+ years ago ... well I wouldn't be surprised, frankly.
• Solar Expert Posts: 31
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Re: Latitude/longitude quantity of energy collected differences
Then the variables come in.
For example if the panels are at a fixed angle the sun's angle to them will change throughout the year. Further from the Equator the greater the difference. This will cause a big change in panel output.
Cold temperatures will increase panel Voltage and that will mean more power when using an MPPT controller. Likewise hot temperatures have a reverse effect, and may lower panel Voltage below charging ability in some cases.
Different times of year mean different weather patterns which can also affect panel output.

So if adjust my angle in the Winter, by being so far north of Az and Tx - and in a much cooler climate my panel should be more efficient?
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Re: Latitude/longitude quantity of energy collected differences
Brewgonia wrote: »
So if adjust my angle in the Winter, by being so far north of Az and Tx - and in a much cooler climate my panel should be more efficient?

More efficient than what? Than not adjusting the angle for Winter? Yes.
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Re: Latitude/longitude quantity of energy collected differences
Brewgonia wrote: »
All things being equal (equipment, array adjusted for optimum angles, etc) does a 100w panel at N41W87 (Lowell, IN) collect less energy in 1 prime time hour than the same panel at N33W112 (Phoenix) or N32W96 (Dallas)? And if so, how much (is there an equation or rule of thumb)?

The northern panel gets slightly less energy during "ideal" insolation due to the longer path solar radiation has to take through the atmosphere. However other effects will dominate in terms of both instantaneous power production and overall energy production. Systems closer to the equatorial band (tropic to tropic) get more reliable sun year round due to less variation in day length. Weather plays a big role; smog plays a smaller role. Cooler temperatures will improve panel efficiency slightly over warmer temperatures. Rain cleans the panels, but reduces generation, so that's generally an overall negative. Trackers (systems that 'point' the panel at the sun) will increase power received by reducing off-angle sun.

For planning systems there are a variety of tools you can use. The NREL maps are a pretty accurate depiction of "equivalent peak hours" of sun you will see, and you can get maps for a flat plate collector, a one-axis tracker, a two-axis tracker etc. A pyranometer can measure instantaneous power (and thus measure the effects of smog etc.) You can use a solar panel you "trust" for this information, but is less accurate. A deceptively simple tool called the "solar pathfinder" can help you determine if you will see issues from shading.
• Solar Expert Posts: 138
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Re: Latitude/longitude quantity of energy collected differences

Use PV Watts to check insolation at your location and with various pointing angles.

On clear days with the PV panels pointing in the optimal direction and no shading, the biggest factors are temperature, sky clarity (as in smog, haze, water vapor), elevation, reflections from terrestrial objects and the sun's elevation. When the sun is near the horizon, the light must pass through a lot of air which absorbs some of the light reducing its brightness. The difference between 32 degrees north and 41 degrees north is minor in this respect. A higher elevation reduces the amount of air and water vapor absorbing sunlight. Sunlight is about 10% brighter (1,100 W/m2) at 7,000 feet elevation compared to sea level.