When conversations or debates turn to getting off the grid, the usual candidates for doing so, wind and solar power, will always make their obligatory appearance. Perhaps geothermal will get some airtime but what seems to be left out of the back and forth, and what probably wouldn’t even be considered unless you find yourself in the middle of a green-living, kumbaya jamboree is the other solar power.
Passive Solar Energy
As opposed to active solar energy collected through the use of solar panels, passive solar energy uses the angle of the sun and the orientation of the building (your home) to maximize exposure of the sun and heat the space. This method has been in use since ancient Greece and while modern technology has improved on the concept with the creation of more efficient materials, the basics have remained the same. And that is, determine which direction and angle receive the most sunlight, place most of the structure’s windows in that area and design the interior to optimize airflow. To explain the premise of passive solar, this quote by J.K. Paul provides a succinct description;
[A passive solar system is designed to] “collect, store and distribute thermal energy by natural radiation, conduction and convection through sophisticated design and wise selection of building materials”
Now, if we take a given passive solar design for a house in the northern hemisphere, the structure would be oriented with the most windows towards the south so they may act as the collectors of that thermal energy mentioned in J.K. Paul’s quote. The energy is absorbed and stored in the interior materials that the sun has heated throughout the day. The denser these materials are, the higher their ability to conduct heat, in which case they do not have to be directly exposed to the sun. Stone, concrete, brick and ceramic tile are some of the best materials for this. Their properties then allow the heat absorbed during the day to slowly radiate out into the house throughout the night. Then during summer months, these same materials will help cool the home if kept shaded with a roof overhang or strategically placed trees that have full foliage during the summer and loose leaves during winter to let in more sunlight. At night, if the home is left open, ceramic tile (for example) will absorb the cooler temperatures and help keep the home cooler during the day. Coupling this with sound insulation will maintain stable internal temperatures throughout most of the home.
This heat energy is released by these materials creating convection air currents (along with the sun itself heating the air) within the space. As heat radiates from the floor, for instance, it displaces cooler air moving down from a window creating a cyclical air flow about the interior of the home. These currents can be controlled with strategically placed ventilation that will move warm air about to distribute it into other rooms of the house.
Reading through this article so far, it applies more to someone planning to build a new home. What can owners of existing homes do to make their homes passive solar friendly? To answer that question, there are retrofits and advice for anyone doing renovations. Here are steps you can take to improve energy efficiency and take advantage of particular passive solar elements;
- Identify locations of heat leakage and seal the problem areas.
- Windows tend to be the worst culprits for heat and cooling loss. Replace existing windows with high-efficiency windows. This will make a world of difference for many homes.
- If possible, increase the size and/or number of windows along the southern exposure side of the home (for those in the northern hemisphere) and reduce the number or size of windows along the north.
- Build up insulation in existing areas and add insulation to uninsulated walls and ceilings.
- Replace floors with higher density materials like concrete, brick or ceramic tile.
- Some of you reading this may be living in homes already built from high thermal mass materials, such as brick homes found through the eastern and Midwest sections of the U.S. These homes can improve their passive heating properties by;
- Insulating external wall cavities
- Make internal alterations to improve convection airflow distribution to other parts of the home.
Passive solar energy for the purposes of heating and cooling your home is based on concepts that have been around for thousands of years for good reasons…they work. Beyond the initial costs of materials and design, the actual heating and cooling accrue no additional expense. A home designed and built holding true to these elements is self-sustaining on its own. What better design for an off the grid home? Now, all you have to worry about is electricity. But that’s for another article.