Thermal Battery - a way to store heat

If only we had a great big thermal battery that we could charge up with heat and use it later when we need it! Wouldn't that be a great invention?

For the imaginative and observant among us, it's easy to see various types of these batteries at work now. They are all around us. Think of the blacktop used to pave our highways. Animals crawl out on it at night to stay warm. Think of the warmth of a brick wall after the sun has gone down.

Have you ever had a hot stone massage using smooth, black stones? The heat in the black stones lasts a very long time as they discharge thermal energy rather slowly due to their considerable thermal mass.

Massage rocks like these are a type of thermal battery.

It's the same reason that the first snows always melt off the pavement just as soon as they touch it. The sidewalks and roadways store thermal energy and it takes a while before they cool down to the point where snow can accumulate.

These are all examples of a thermal battery at work. An object or substance get's "charged up" with heat for release later.

The ability of an object to absorb heat is largely determined by it's color. The level of heat absorption and the duration of heat release is largely determined by it's thermal mass. The color of the object also helps determine how quickly it releases its stored heat.

Thermal Mass - the key

Thermal mass is a lot of material that can hold heat. Examples include rock, brick, soil - and best of all - water. Yes, water is one of the best mediums for holding heat. Next best is probably moist soil or sand, largely because of the water that it contains.

In Michigan, the big snows in the western part of the lower peninsula are caused by "the lake effect." The moderate temperatures in the summer and winter in Michigan are attributable to "the lake effect." Lake Michigan is a huge thermal battery for the State of Michigan.

What is this "lake effect" that we keep hearing about? Quite simply, it's the thermal mass of the huge lakes that surround the State of Michigan's lower peninsula. They tend to keep the lower peninsula cooler in the summer and warmer in the winter than surrounding states.

The liquid thermal reserves that surround the state help to moderate the climate by releasing heat in the winter and absorbing heat during the summer. Remember, water is an excellent medium when it comes to thermal mass, and the lakes surrounding Michigan aren't called The Great Lakes for nothing. They are a gigantic thermal battery that surrounds the state.

Example Applications

Here are three examples of the application of a thermal battery to influence indoor environments.

  1. In my greenhouses I have buried water lines under the soil from 1 to 2 feet deep. The water lines are connected to underground reservoirs with pumps and solar water heating panels just outside the greenhouses.

    An underground thermal battery requires hot water piping buried well beneath the surface of the soil.

    When it's sunny, the pumps circulate water from the reservoirs through the solar panels where the sun heats it. The water continues to circulate through the underground piping and it gives off it's heat to the soil.

    Heat migrates in solids, so the soil around and above the piping warms up all day long. This warm soil holds the heat for slow release to the greenhouses above.

    After the sun goes down and the pumps shut off, the soil continues to release warmth inside the greenhouses, thus moderating their temperature throughout the night. Think of this as a slow discharge of the battery.

    This is an example of active solar heating.

  2. Homes and office buildings have been built using a large thermal battery in the basement consisting of a bed of rocks, gravel and sand. Using heat from solar gain in the day, the thermal battery is charged up by circulating building air over and through the bed of rock, gravel and sand.

    At night and during overcast days, the heat stored in the bed is released to moderate building temperature with minimal additional heating required.

    This is another example of heating with active solar techniques.

  3. Pillars and drums constructed of concrete or filled with water have been installed in southern facing "great rooms" in homes to collect heat from the sun during the day, simply by being exposed to it, and releasing it during the night to help keep the house warm.

    This is an example of passive solar heating, there are no pumps or fans required to collect or distribute the energy.

If your approach to frugal living finds you using solar heat to warm your house, heat your water or otherwise provide thermal energy to an interest of yours, then it's probably a good idea to incorporate some form of thermal battery to make use of excess heat that you collect during the daylight hours, especially if you expect heat from the sun to support your interests at night and on cloudy days as well.

Done with Thermal Battery, back to Cheap Greenhouse

Done with Thermal Battery, back to Basement Air

Having your own greenhouse is a key to creating viable marketplace alternatives to the rising price of produce in the grocery store.

A greenhouse is a great way to grow produce year round, even without additional heat. It's also an excellent way to be better prepared for marketplace interruptions.

With a greenhouse, you're in better control of your food supply in terms of variety, cost, availability, and knowing exactly what's in it and on it.

I use the small indoor greenhouse shown above to help get my seeds started. It's lightweight yet strong, and it's a good alternative to a cold frame if you keep it indoors or at least out of high winds.

I own the book shown above, and it's a great reference for those of us involved in greenhouse growing. I've yet to find a better book.