Can solar and wind energy increase rainfall and vegetation?

[Thomas Goreau]

A new paper suggests that large scale wind and solar energy farms in the Sahara could increase rainfall and vegetation, with most of the effect coming from vegetation feedbacks on climate:

Climate model shows large-scale wind and solar farms in the Sahara increase rain and vegetation

Science  07 Sep 2018: Vol. 361, Issue 6406, pp. 1019-1022,  DOI: 10.1126/science.aar5629

Yan Li, Eugenia Kalnay, Safa Motesharrei, Jorge Rivas, Fred Kucharski, Daniel Kirk-Davidoff, Eviatar Bach, Ning Zeng

Wind and solar farms offer a major pathway to clean, renewable energies. However, these farms would significantly change land surface properties, and, if sufficiently large, the farms may lead to unintended climate consequences. In this study, we used a climate model with dynamic vegetation to show that large-scale installations of wind and solar farms covering the Sahara lead to a local temperature increase and more than a twofold precipitation increase, especially in the Sahel, through increased surface friction and reduced albedo. The resulting increase in vegetation further enhances precipitation, creating a positive albedo–precipitation– vegetation feedback that contributes ~80% of the precipitation increase for wind farms. This local enhancement is scale dependent and is particular to the Sahara, with small impacts in other deserts.

and a popular version:

https://www.bbc.com/news/science-environment-45435593

The results are easy to understand, but not clearly explained. Windmills and solar panels both have the same physical effects as vegetation: they increase surface roughness and the absorption of solar energy, leading to more energy transfer between surface and atmosphere, increasing surface temperature, and causing vertical convection that increases rain. That is to say, these renewable energy technologies have climatic benefits precisely because they unwittingly mimic the natural physical interactions of vegetation and climate (except for carbon storage!). Moreover they show that the bulk of the increased rainfall effect is due to increased vegetation feedbacks on climate from plant evapotranspiration effects, which they describe as “a previously overlooked vegetation feedback”. 

This is very telling, because it says previous models seem to have ignored the most important natural feedbacks by failing to model the vegetation mechanisms that help regulate climate change!

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.
Coordinator, Soil Carbon Alliance
Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies
37 Pleasant Street, Cambridge, MA 02139
gor...@globalcoral.org
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase
http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration
http://www.crcpress.com/product/isbn/9781466557734

[Renaud de RICHTER]

The full open access paper is here http://science.sciencemag.org/content/sci/361/6406/1019.full.pdf

Dear Prof. Goreau,

You say that Windmills and solar panels both have the same physical effects as vegetation: they increase surface roughness and the absorption of solar energy, leading to more energy transfer between surface and atmosphere, increasing surface temperature, and causing vertical convection that increases rain. 

But  as PV panels transform nearly 20% of the energy they receive into electricity and produce shadow below them, how can they increase surface temperature?

Best,

Renaud

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[Thomas Goreau]

Dear Renaud,

Their argument seems to be largely based on the albedo thermal effect: solar panels are less reflective and more absorptive than the desert sand and rock they shadow, and hence warm the near surface air more, plus some degree of additional surface roughness. Pity they can’t also store carbon like plants do when they increase transpiration of water and transfer of wind momentum!

Best wishes,

Tom

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.
Coordinator, Soil Carbon Alliance
Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies
37 Pleasant Street, Cambridge, MA 02139
gor...@globalcoral.org
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase
http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration
http://www.crcpress.com/product/isbn/9781466557734

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/CAHodn98FAi4OGE6%3D4JTHRkZAbC%2Bh2hOCgtNiK-2VJZgDSdVFFg%40mail.gmail.com.

[Andrew Lockley]

It's more complex than that though... Panels have very low thermal mass and are usually significantly above the deck. So they get very hot in the day, but cool quicker at night than unshielded rock would. 

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/90AD3020-45E1-4007-A7EA-A5F390CD6ABD%40globalcoral.org.

[Thomas Goreau]

Yes, that’s right, the physical effect is less than the biological effect caused by transpiration of water (plus aerosols) through the plants from soil to atmosphere. 

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
President, Biorock Technology Inc.
Coordinator, Soil Carbon Alliance
Coordinator, United Nations Commission on Sustainable Development Small Island Developing States Partnership in New Sustainable Technologies
37 Pleasant Street, Cambridge, MA 02139
gor...@globalcoral.org
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase
http://www.crcpress.com/product/isbn/9781466595392

Innovative Methods of Marine Ecosystem Restoration
http://www.crcpress.com/product/isbn/9781466557734

On Sep 7, 2018, at 12:18 PM, Jane <janem...@gmail.com> wrote:

Isn't the precipitation effect (increased rainfall) of vegetation not just the thermal drafts but also the biological aerosols? How would that albedo thermal effect alone work to increase rainfall? Or is there just enough existing vegetation to create enough of the aerosols that would go with the thermals? 

Sent from my iPhone

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[Renaud de RICHTER]

Many of the articles on "the biotic pump" are freely available.

The aerosols are very important to provide cloud condensation nuclei.

I don't see how wind turbines which slowdown the air and mix (at least at night) air layers of coled and warm air, can induce rain...