Geothermal Polytunnel

Extending the growing season with geothermal storage of height under a polytunnel

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Summary

What’s better than a 60ft polytunnel?: A Geothermal 60ft polytunnel!

This project was one of the bigger permaculture projects I took on on this smallholding (alongside the food forest). It’s not finished yet, but the groundwork has all quite literally been completed.

The idea of geothermal greenhouses is to capture the peak heat of summer into the ground beneath the greenhouse by pumping the hot air down 7ft+ through tubes which form a kind of radiator underground. The heat is stored in the rock beneath and then slowly released over the colder months of the year, therefor extending the growing season.
Geothermal Polytunnel
Status: In Progress
Updated: May 6th 2020

Building a Geothermal Polytunnel

Before I got started digging the geothermals in I prepared the ground to receive the full size of the polytunnel with a 5 ton excavator.

Geothermal Polytunnel Project: Image #1

Next I dug two channels which would cap the ends of the pipe runs and ultimately be the exit for the tubing.

Geothermal Polytunnel Project: Image #2

I then dug a 60ft trench about 7ft deep and 4ft wide.

Geothermal Polytunnel Project: Image #3

The first layer I put in was gravel, which was made more difficult by the tight work site.

Geothermal Polytunnel Project: Image #4

Levelled out it created a unique trench environment 😀

Geothermal Polytunnel Project: Image #5

Next me and Alice lay the piping back and forth like a radiator, over the gravel.

Geothermal Polytunnel Project: Image #6

We used duct tape cross members to keep the tubes equally distributed.

Geothermal Polytunnel Project: Image #7

On top of the first layer we put gravel and then sand.

Geothermal Polytunnel Project: Image #8

Here’s an example of the exhaust coming out of one end point.

Geothermal Polytunnel Project: Image #9

Slideshow of laying the geothermals beneath the polytunnel:


The finished Polytunnel base with the in and out end points.

Geothermal Polytunnel Project: Image #10

Next up the polytunnel arrived and was built over the geothermal central axis.

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I built some simple doors using tung-oil treated timber and spare polytunnel plastic.

Geothermal Polytunnel Project: Image #15

Straight away we got lots of tomatoes in and had a great harvest that first year.

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Later I added a mature lemon tree.

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… and beds made from scaffold planks attached to the polytunnel frame. Again treated with Tung oil.

Geothermal Polytunnel Project: Image #21

Over the years the setup is evolving, I’ve found the scaffold board beds to be very effective.

Geothermal Polytunnel Project: Image #22

To help foster a longer year I built this raised heated bed, (so I could bring on seedlings even earlier).

Geothermal Polytunnel Project: Image #23

… because the weather can be a challenge here.

Geothermal Polytunnel Project: Image #24

Daikon radishes make the best kimchi!

Geothermal Polytunnel Project: Image #25

Lots of produce over the years.

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Luna the cat loved to prowl the polytunnel catching crickets.

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As of 2024 the polytunnel is now shared with my friend Sue, who’s built extra beds. The lemon tree is now living in the ground, (and despite a bout of Scale doing well). I’ve added figs, peaches, grapes and more.

Geothermal Polytunnel Project: Image #32

Let’s make mad sh*t.

I’ve made a lot of things in my life, and I intend to make a lot more. My biggest goal is to make a good and happy life.

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