Solar panels look as innocuous as can be, quietly going about their business under the sun.
But on the steep slopes of Pennsylvania, it was a different story. The arrays began actively pushing back against nature.
New patterns in the soil and runoff caught scientists’ attention, pointing to an environmental shift.
The expansive structures were impacting natural climate cycles. How do photovoltaic panels manage to force such large-scale shifts?
How the green energy boom delivers ecological surprises
The United States is seeing an expansion in utility-scale solar projects as the country aims to meet climate goals.
No one wants to sacrifice prime agricultural land for solar installations. This means developers have to look further afield at tracts of marginal terrain.
In Pennsylvania, the steep, rugged hills were highly unlikely to be needed for anything else, so solar took over.
Researchers tracked two of these installations to see how the arrays handle heavy weather.
Critics were worried that solar panels of steel and glass would cause soil erosion and runoff. Millions of gallons of stormwater pouring off the infrastructure would have this effect.
These are valid concerns, seeing as PV panels, being impervious to water, function like concrete. Communities downhill could have been at risk of dangerous levels of runoff.
But the one-year-long Penn State field study actually discovered a far more complex situation.
It turns out that healthy levels of vegetation and gravel infiltration trenches did the trick and controlled the water.
And there was something else going on between the rows that went beyond the soil issue. Sunlight and air behavior were shifting, and natural cycles were being altered at ground level.
How were these structures changing the atmosphere?
Photovoltaics are controlling the weather
The water that hits a solar farm doesn’t disappear; it gets redistributed.
The research team from Penn State College of Engineering gathered soil moisture data for a year to check the effects through the seasons.
There was a clear contrast in conditions across the hillsides.
The ground sitting directly under the lower edge of the panels caught a beating from the rain. The water cascading from the glass created distinct driplines.
The moisture in these tracks was measured at 19% higher than the surrounding land. Localized runoff was triggered when these zones reached total saturation during heavy downpours.
It was the opposite right alongside the wet strips. The earth stayed 25% drier than the ground nearby.
An artificial pattern of hyper-local wet and dry zones was the result.
Engineers factored in gravel basins and open interspaces that were effective in preventing mudslides. But the arrays were doing more with their presence beyond rerouting rain.
What did this division of moisture mean for the air?
A drop in evapotranspiration and a shift in microclimate
The answer lies in the air, rather than in the soil, according to the study “Quantifying soil moisture and evapotranspiration heterogeneity within a solar farm: Implications for stormwater management,” published in the Journal of Hydrology.
The research team used micrometeorological monitoring and tracked small-scale weather patterns around the arrays.
Findings revealed that the solar panels were most definitely altering their microclimate.
By blocking sunlight and shifting airflow, the massive structures had an effect on evapotranspiration. This is the natural process where water is transferred from the land back into the atmosphere.
Isolated atmospheric conditions and “drizzle lines”
Potential under-panel evapotranspiration dropped by 37% to 67% in the heat of the summer months.
The difference was minimal in the winter, but the summer drop was enough to change things.
By trapping moisture in the soil, the farms stalled the natural water-air cycle. The result was pockets of isolated atmospheric conditions around the installations.
The standard rainfall in the Northeast was changed on the ground, causing “drizzle lines” of wet soil. But the air under the panels was locked down.
We know now that these vast arrays do more than just harvest sunlight. So what other hidden environmental shifts are waiting to be discovered as we chase our clean energy dreams?