Harnessing the Sun's Warmth

How We Use a Climate Battery in Our High Tunnel

🌡 What Is a Climate Battery?

A climate battery — also called a subterranean heating and cooling system (SHCS) — is a way to store and reuse the heat from the sun using the earth beneath your greenhouse or high tunnel. Instead of letting all that heat escape at night, a climate battery captures it during the day and stores it underground in the soil. Then, when temperatures drop at night, that stored warmth is pulled back up to help keep your plants cozy. Think of it like this: it’s a geothermal thermos that reuses energy you already have, all thanks to some buried pipes, fans, and the thermal mass of the earth.

🌱 Why We Installed One in Our High Tunnel

Our high tunnel in North Nashville is home to year-round food production for Roots Ministries. That means we need a way to extend the growing season — without burning fossil fuels or blowing the budget.

Enter: the climate battery.

We wanted a solution that:

• Keeps our tunnel above 40°F at night and around 70°F during the day
• Works even during the coldest weeks in USDA Zone 7
• Supports tender plants like tomatoes, basil, and tropical container trees through winter
• Aligns with our values of low-cost, regenerative systems

We hope after installing it, we see more stable temperatures, healthier soil biology, and less stress on cold-sensitive crops in order to help us grow more food, more consistently — even during unpredictable weather swings.

🔁 How It Works

Here’s the simple version:

1. Fans pull warm, moist air from the roof peak of the tunnel during sunny days in the cold months.
2. That air gets pushed through a network of corrugated 4" pipes buried underground.
3. As it moves, the heat is absorbed by the surrounding soil — charging the system.
4. At night or when it’s cold, that stored warmth radiates back up, passively heating the tunnel.
5. If the temperature continues to drop, low wattage fans kick on to pull heat more quickly from the floor.

This system isn’t powered by propane or gas — just air movement through earth.

🛠 DIY Tips: Building One on a Budget

You don’t need a huge grant or fancy equipment to build a basic climate battery. Here’s what we used:

Materials:

• 4" Corrugated drain pipe
• Drain pipe T fittings
• Small inline duct fans (solar or plug-in)
• A controller or timer (optional, for automatic cycles)
• Shovel or trenching tools

Steps:

1. Dig trenches 18–24 inches below your high tunnel floor spaced 18-24 inches wide.
2. Lay out perforated pipe in your trenches— this is your underground battery.
3. Connect it to your fan system using drain pipe and drain pipe fittings.
4. Backfill with soil and tamp it down gently.
5. Turn on the fan during warm parts of the day to start cycling air!

Pro tip: Angle your trenches slightly for drainage and airflow. And if possible, start small — you can expand later but doing it before plants are in the ground is best.

♻️ Roots That Go Deeper

Our climate battery isn’t just about temperature — it’s about simple solutions, appropriate technology, and giving people access to abundant, homegrown food year-round. It’s a small act of restoration with big ripple effects.

If you’ve got questions or want to try this yourself, drop us a line or visit us at Roots Urban Farm. We’d love to hear how you’re harnessing the earth’s warmth in your own spaces.

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Peace to you,

Nate Hale

Roots Ministries