Weather Effects On Solar Panel Output

 

Introduction

It comes to no surprise that more solar power is generated during the summer months. The sun is out longer, few clouds, and there is no snow. We expect that the peak performance during any given day is when the sun is directly above the solar panels. This is called solar noon. Energy from the Sun travels to the Earth via photons. Photons have radiant energy. This energy is quantified and refered to as solar irradiance. Solar irradiance is the dominating parameter when analyzing weather effects on solar panel output.

 

Various Weather Effects

In Figure 1 below, the data from September 24th is displayed. There were clear skies the entire day and 90 degree temperatures. Here we see a nearly perfect curve. As expected the peak is at around 1:00pm (solar noon).

 

 

How do clouds add variability to the output? See Figure 2 Below. When clouds form between the panels and the Sun solar radiation is reflected and does not reach the panels. [1]

 

 

Solar Irradiance

 

August 8 August 10

Max Temp: 84 F

Min Temp: 52 F

Max Humidity: 89

Max Wind: 16 mph

Conditions: Partly sunny

Max Temp: 85 F

Min Temp: 58 F

Max Humidity: 93

Max Wind: 16 mph

Conditions: Partly sunny

 

As we can see from the Wood Hall Weather report August 10th was a hotter day than August 8th. Based upon our analysis from above, we expect August 10th to have produced more power than August 8th. Let us look at their power generated graphs to confirm this.

 

 

 

As one can see from these graphs, August 8th produced more power than August 10th even though August 10th was a hotter day. This means that we can conclude that there must be another factor that is involved when analyzing solar energy and weather. This factor is solar radiance. Solar radiance is defined as the power density of a particular wavelength, in this casae light. In other words, solar radiance is the measurement of how powerful the sun rays are when they hit the Earth, in this case the solar panels. Let us compare the solar radiance on August 8th with August 10th:

 

August 8 August 10

AVG Solar radiance: 1.125

AVG Solar radiance: 1.069

 

August 8th had a higher average solar radiance than August 10th. This means that the power of the sun rays on August 8th were greater than the sun rays on August 10th. Therefore, we can conclude that solar radiance is needed when analyzing weather with power generated from solar panels.

 

Snow Effects

Similar to cloud coverage, snow prevents the solar radiation from reaching the panel surface. Figure 3 displays the data from January 8th on a day when the panels were likely covered with snow. There is some power being generated, however, if we compare this graph with Figure 1 we can see how much the weather is affecting the output. Figure 4 below plots both Figure 1 and 3 on the same axes.

 

 

 

References

[1] Graham, Steve. “Clouds & Radiation Fact Sheet : Feature Articles.” NASA, NASA, 1 Mar. 1999, earthobservatory.nasa.gov/Features/Clouds/.