Around the world, cities have developed unique solutions for passive solar energy collection. By adapting to local and sometimes extreme climates, solar energy systems now take on many diverse forms.
With so much available “green” technology for homes, it is often to forget that some of the most effective techniques are not “high-tech.” Instead, many simple innovations seek to work with the environment rather than control it. However, a major challenge to this goal involves Earth’s diverse climates.
Perhaps the most ubiquitous thing on Earth, whether at Point Barrow, Alaska or Mumbai, India is sunlight. By the 21st century, it’s well-known that uses for solar energy are wide and varying. It grows plants, energizes our power grids, and heats our homes. It’s a big battery in the sky. However, across the world the characteristics of sunlight and climate can drastically affect people’s ability to utilize it toward creating sustainable lifestyles. For cities across Earth, this means pursuing local innovations to maximize this incredible, limitless natural resource.
Hot, Arid Climates
One of the challenges of a desert climate is the extreme daily temperature differential: extreme heat in the day, bitter cold at night. Traditional desert architecture adapts to this by using a thick thermal mass as a building material, such as adobe or mud-brick, rather than insulating the building. Heat transfers slowly through the mud brick, so it will absorb the heat of the sun during the day while the inside stays cool. By nighttime, that heat will be radiating inward, warming the interior of the building. In buildings that are not occupied at night, you can open the windows to flush the building with cold night air to set the temperature for the building the next day.
Hot, Humid Climates
Major cities: Houston, USA; Rio de Janeiro, Brazil; Lagos, Nigeria; Singapore
The most important principle in a hot, humid climate is to keep things shady and let the breeze in. Vented shutters in these locations serve as more than just hurricane protection; they block solar energy while allowing the building to breathe. It’s important to understand which direction from which the breeze comes and orient the building with the broadest side facing it. Long, narrow houses are great for this with large openings on the longest sides of the building. This way, the cross-breeze doesn’t have to go very far to travel through the house and has minimal obstructions. In addition to cross-ventilation, houses can also take advantage of stack ventilation. As hot air inside the house rises, it is vented out the top. This creates a natural air flow, sucking in cooler air from first floor windows and pushing hot air out the top.
Major cities: Anchorage, USA; Astana, Kazakhstan; Calgary, Canada; Harbin, China
While insulation is important to keep the cold out and keep the heat in, there’s more to designing a building for a cold climate. We can take advantage of solar energy to heat the house directly. Long, narrow buildings are also good for this with as much surface area devoted to window glass as possible on the broadest side facing the sun, with minimal openings on the opposite side. In the Northern Hemisphere, this means a building should face south. In the Southern Hemisphere, a building should face north. In addition to direct sunlight, there are ways to passively circulate the heat and store it for nighttime use when the sun is no longer out.
Trombé Walls use a layer of glass on the outside, and a solid (not hollow) thermal mass wall behind it, preferably some kind of dark stone or brick to help absorb sunlight through glass. As the air heats up between the glass and the stone, it rises and moves naturally through a vent at the top of the stone wall into the main space of the building. This movement of air sucks cold air from the bottom of the room through a lower vent into the space between the glass and the stone where it gets heated up and continues the cycle. Much like the adobe walls of the desert, this thermal mass wall also absorbs heat directly from the sun during the day and radiates the heat inward at night. This system can also be adapted for warmer summer days when some cooling is preferred over heating. The hot air is vented outside at the top of the glass and the air movement sucks cool air through an open window at the back of the house, instead of cycling in a contained space.
Major cities: Kansas City, USA; Paris, France; Beijing China; Buenos Aires, Argentina
If you live in a temperate climate, you may have the fortune (or misfortune) to experience both extremes of a cold climate during the winter and a hot climate during the summer. Designing passively for these climates is challenging, but not impossible. Solutions need to be adaptive to work at both times of year. One essential strategy for temperate climates is designing for the different angles of the sun during all seasons. Sun shading devices can be sized and placed strategically to block direct sunlight when the sun is at a high summer angle and allow the direct sunlight through to heat the windows at the low winter angle. As long as you know the highest and lowest angle of the sun for your geographic location, these sun shading devices can be permanently fixed and don’t need to be closed or opened depending on the time of year.