Installing solar panels in semi-arid regions of the world rather than planting new forests would be better for mitigating climate change, according to researchers at the Weizmann Institute of Science in Israel.
Earth and planetary scientist Eyal Rotenberg and colleagues looked at afforestation, which is very different from reforestation. Whereas reforestation means planting trees in existing forests, afforestation is the process of planting in an area where there were no trees before, creating a new forest.
Both trees and solar power are powerful allies in the fight against climate change. Solar panels reduce the greenhouse emissions of burning fossil fuels. Trees, meanwhile, absorb vast quantities of carbon dioxide from the atmosphere. Protecting existing forests is probably best for sequestering carbon emissions, and cutting down large swathes of tropical rainforests has already exacerbated the climate problem. In some cases, developers have pitted solar power and forests against each other by clearing forests to install large solar farms.
In their PNAS Nexus paper, the Israeli team focused on drylands, which represent over a third of the Earth’s land surface. Half of the world’s drylands are semi-arid and have attracted attention for potential afforestation projects, the researchers write. “However, they also have the potential to host a significant proportion of utility-scale PV fields.”
Afforestation and solar power are “complementary climate change mitigation strategies,” they write. But both forests and solar panels also make the land surface darker. This reduces the amount of light reflected by the land surface, a property called albedo, resulting in more heat absorbed by the surface.
The authors wanted to find out whether solar panels or trees, by reducing carbon emissions, make up for that increased heat faster. So they did a comparative assessment of this “break-even time” when previously open drylands are changed to PV fields versus planted forest. They measured surface albedo at a solar field in a very dry region in the Arava valley in Israel. For afforestation, they got data from a research station in the Yatir Forest, the largest planted forest in Israel at the edge of the Negev Desert.
Their results showed that photovoltaic fields break even and begin offering climate change mitigation benefits after around 2.5 years. That is more than fifty times faster than afforestation. Solar power is also about 100 times more efficient in terms of atmospheric carbon reduction.
In more humid climates, afforestation caught up to solar fields significantly, but photovoltaics still had a break-even time that is about 20 times faster. Besides, say the researchers, for afforestation to offer climate change benefits, “land area required greatly exceeds availability for tree planting in a sufficient scale.”
Forests do offer many other benefits though, the team writes. So, depending on climate zone, “both approaches must be combined and complementary, since forests provide crucial ecosystem, climate regulation, and even social services.”
Source: Rafael Stern et al. Photovoltaic fields largely outperform afforestation efficiency in global climate change mitigation strategies, PNAS Nexus, 2023.