How Hot Rocks May Lead to a Cooler Planet

Rocks absorb heat, a fact first discovered many thousands of years ago when someone realized that a rock near a fire could be moved to provide warmth where needed. That discovery produced the world’s first thermal battery.

Fast forward to today and the struggle to move past the environmental hazards of fossil fuels. Solar and wind power are helping to provide energy for millions of people. But heavy industry has yet to take advantage of renewable energy. Factories frequently need energy 24/7 and can’t rely on the variability of sun and wind.

That’s where hot rocks come in. Massive towers of stacked bricks are already used in smelting plants, where they absorb the wasted heat of blast furnaces, heat up past the melting point of steel and then provide heat energy for about 20 minutes each hour. Several companies are taking this concept a step further and experimenting with different kinds of rocks in insulated boxes to find the most efficient combination.

Cheap and abundant graphite is very promising. Heated by solar panels, the graphite blocks in a thermal battery the size of a small building reach 3000ºF and glow like the sun. The light is used to create steam and to produce high-temperature heat for heavy industries like cement- and steel-making. Hot rock batteries have a distinct advantage over chemical batteries in that they can store heat as well as power. By doing both, the cost of scaling up for large industrial sectors becomes more manageable. Manufacturers may be able to simply plug their factories into as many thermal batteries as they need and proceed full steam ahead. By switching away from fossil fuel, the atmosphere-warming carbon emissions will be eliminated and hopefully the temperature of our planet will stabilize.