What are they tuning, a fog harp?

If you’re as old as I am and like the same music, you may recognize that title. It was a line uttered by Kurt Cobain just before launching into a song in 1993 (minus the word “fog”, which I added for this post). A band called the Meat Puppets had just joined Nirvana on stage for some songs and they were taking a while getting their guitars ready. Thus, that “What are they tuning, a harp?” comment appeared at the beginning of a song on Nirvana’s MTV Unplugged album.

Source: MTV.com

Why am I writing about harps? Because that is what scientists at Virginia Tech call their latest invention, the Fog Harp. It is a device that pulls water from air. When fog is blowing through an area, this device can harvest that water from the air. It’s like sticking a big fishing net up in the air and catching the tiny water droplets. Given that many areas of the world have limited access to fresh water, I think the Fog Harp is a great title for a great invention (more on that below).

Nature Did It First

But as with many other inventions, nature did it first. To prove this point, I give you the Coast Redwood. Redwoods and other related coniferous trees (pines, firs, spruce, etc.) are some of nature’s most efficient water harvesters. They can pull water from thin air, or at least from the foggy air that often fills the skies for months at a time along the coasts of Northern and Central California.

Below is a time lapse video of fog rolling through this region. You can see what amazing potential there is for trees to collect some of the water from this air:

Underneath the tree’s canopy on a foggy day with the wind blowing, you’d be excused for believing you are in the middle of a Pacific storm. When the low fog clouds sweep in, you often cannot feel the water at all because it’s not condensing into droplets; fog is like a cloud of cool steam. But under a big conifer tree such as a redwood, on a very foggy night, it is quite literally raining as much as in any storm. That’s how much water is being captured and dripped down towards the tree’s roots.

I know because I used to live near the foggy coast of Northern California in a house that had a huge redwood tree looming overhead. It was quite frightening during a real storm with high winds. For all the noise that tree made, we were lucky that nothing more than small branches ever fell down because the tree was much larger than the house.

But that tree made plenty of summer days seem like stormy days by raining down water from the coastal fog that came in each morning and evening. If it had never rained a day there, that tree would have had plenty of water because the thin foggy air gave it everything it needed. And I didn’t need to water the garden for more than a few days per year either, since that tree did it for me.

Some of these trees are so big you can drive through them.

Source: Visitredwoods.com

While the closely-related sequoia trees occur inland in the Sierra Nevada mountains, the range of coast redwoods is very limited today. Source: National Geographic.

How do these trees capture so much water from the air? They use their branches and needles as a harvester. Redwoods first appeared just after the time of the dinosaurs and some of these individual trees have been alive for millennia. The oldest ones are 2,200 years old. It is amazing to stand beneath these old growth giants and realize that a few of them may have been standing there since before the time of Julius Caesar, Jesus Christ, or the prophet Muhammad.

Here is another picture of the needles a coniferous relative of the redwood tree (I think this one is a pine). Look at how the needles trap even the smallest water droplets and let them combine until their weight drops them right down to the trees’ roots. It’s a brilliant system and also very simple.

Water Harvesters Made by Humans

Using a similar system, humans have been collecting water from fog for many years. In areas that are arid but get some fog, the simplest method is to sink two posts into the ground and string a mesh net between them. The wind blows the fog through. This method is used in Morocco and in the Andes of South America where fog often forms.

Small water droplets are caught in the mesh. Gravity forces them to combine with others to form larger drops that fall to the ground, where they can collect in a trough or container. It’s like putting the same net in a river until enough fish swim into it that you have a meal. The best fishing grounds are coast-facing hills or mountain ranges with a propensity for foggy weather where that marine layer is blown towards shore by prevailing winds.

Here is a fog harvesting project in Lima, Peru:

There are more complex designs as well, such as multi-story towards of nets, cube designs, swirly designs, and so forth, some of which may catch slightly more than the simple method of hanging a net curtain on two poles.

The Fog Harp

One of the problems with traditional collectors is that they cannot catch too much at any one time. Either they are not very efficient at delivering small drops downward or water gets stuck because of the horizontal mesh lines, which impedes the ability to collect more droplets from fog. So, scientists at Virginia Tech University worked to find the most efficient design.

This turned out to be a set of wires which are held taught by a frame. Each vertical wire can catch water from even tiny droplets in the foggy air, delivering them down to the reservoir where the water is collected. The overall efficiency is better than a simple catch net.

Fog Harp images courtesy of Virginia Tech University.

In fact, the Fog Harp can collect three times as much water as other systems. As with any new invention, it probably needs more testing, but this is not an elaborately complex device. And once the Fog Harp is produced as a workable product, hopefully the cost will be affordable for people in developing countries. These fog harps could help deliver clean drinking water to areas that may not have it, as long as they have fog.

What sound does this harp make when it’s tuned? Drip, drip, drip.

Sources:

https://en.wikipedia.org/wiki/San_Francisco_fog
www.climatetechwiki.org/content/fog-harvesting
https://www.cnn.com/style/article/fog-harp-virginia-tech/index.html
https://vtnews.vt.edu/articles/2018/03/fog-harp-increases-water-collection-capacity.html

Top image shows fog harp and is courtesy of Virginia Tech University. Other images are public domain unless indicated.