In other articles I've written I mentioned that simply referring to 'solar energy' was too simplistic, and that we need some distinctions in how we think about solar power if we are to fully understand its potential. There are two broad categories of ways to reap the sun's energy: passive solar and active solar.
Passive solar strategies are exclusively oriented toward thermal energy capture and storage without using additional energy from mechanical or electrical sources. As you might expect, active solar strategies capture the energy of the sun by immediately translating it into mechanical or electrical energy, or use some kind of additional assist to harvest that power.
In this article we'll look at some of the work being done in the passive solar arena.
The simplest and most easily implemented passive technologies are also some of the oldest ways people have been gather solar energy benefits: the ancient Romans made a point of orienting bath houses so they would catch the sun's light and warm naturally, and in the 13th century, in North America, Anasazi Indians were building their communities in southern facing cliffs to achieve the same end.
Modern architects use this same principle when designing homes, although the specifics are more involved in today's construction. In addition to simply aiming a home at the sun to reap solar energy benefits, you can find the following enhancements in buildings using passive solar:
o Window placement to maximize thermal intake AND to reduce loss of heat
o Based on a building's latitude (which dictates how high in the sky the sun is), more or less roof overhang is built into the design. The intent is to maximize sunlight entering home during colder months and minimize it during summer months, thereby reducing need for artificial heating or cooling.
o Thermosiphons are contraptions used to heat water without a mechanical pump. The water is held in a reservoir with a plumbing 'circuit' that takes advantage of the convection current created by temperature differentials (when cold water sinks to the bottom of the circuit and warmer water rises to the top of the circuit).
o Phase change materials (PCMs) are a neat invention used to store thermal energy and maximize solar energy benefits when that heat is harvested. A phase change is the process in which a given substance changes from solid to liquid, liquid to vapor, or the reverse of these. The most commonly seen phase changes take place in water: ice melting or water boiling are two examples of a phase change as thermal energy is being put into water. Condensation and freezing are the phase changes which take place when thermal energy is removed from water.
There are two very interesting things about phase change materials that make them valuable for our purposes:
1. As the material absorbs or releases energy to go through its phase change, its temperature remains stable. For instance, if we are cooling water from 5°C to -5°C, the temperature of the water will move steadily from 5° to 4° to 3° and so on - until it hits 0°. At that point, the temperature of the water will remain at 0°C until it has completed the phase change into ice, at which point it will continue moving down the scale until it hits -5°C. The same thing will happen, in reverse direction, as that water is warmed back to above freezing. In effect, the material either releases stored energy or absorbs it to enable the transition to take place.
2. The second item of interest to us when looking to get the most solar energy benefit is that there a wide variety of materials which can be used to store or release thermal energy, and they have a wide range of melting points. So if you want to keep a flow of air around 72°F, there is a PCM which makes its transition at that temperature. If you want something warmer or cooler you just find the right material.
So you can see there are a wide range of options involved with passive solar designs beyond simply having your home face the sun.
Obviously, some of these are only helpful when we are in the planning stages of building our home. Changing the orientation of your home, the number and placement of windows, or the amount of roof overhang are not items which can be easily or inexpensively changed once the house is in place.
There are a growing number of companies which sell thermosiphons or PCM solutions. Many of these are still expensive, but it might be worth it to you to see what is out there. Before you know it, you might be showering with sun-heated water or staying cool in the summer with PCM chilled air!
The other side of maximizing solar energy benefit is 'active' solar. We'll cover that in another article and in the Solar Energy Advantage mini-course (see below)!
Passive solar strategies are exclusively oriented toward thermal energy capture and storage without using additional energy from mechanical or electrical sources. As you might expect, active solar strategies capture the energy of the sun by immediately translating it into mechanical or electrical energy, or use some kind of additional assist to harvest that power.
In this article we'll look at some of the work being done in the passive solar arena.
The simplest and most easily implemented passive technologies are also some of the oldest ways people have been gather solar energy benefits: the ancient Romans made a point of orienting bath houses so they would catch the sun's light and warm naturally, and in the 13th century, in North America, Anasazi Indians were building their communities in southern facing cliffs to achieve the same end.
Modern architects use this same principle when designing homes, although the specifics are more involved in today's construction. In addition to simply aiming a home at the sun to reap solar energy benefits, you can find the following enhancements in buildings using passive solar:
o Window placement to maximize thermal intake AND to reduce loss of heat
o Based on a building's latitude (which dictates how high in the sky the sun is), more or less roof overhang is built into the design. The intent is to maximize sunlight entering home during colder months and minimize it during summer months, thereby reducing need for artificial heating or cooling.
o Thermosiphons are contraptions used to heat water without a mechanical pump. The water is held in a reservoir with a plumbing 'circuit' that takes advantage of the convection current created by temperature differentials (when cold water sinks to the bottom of the circuit and warmer water rises to the top of the circuit).
o Phase change materials (PCMs) are a neat invention used to store thermal energy and maximize solar energy benefits when that heat is harvested. A phase change is the process in which a given substance changes from solid to liquid, liquid to vapor, or the reverse of these. The most commonly seen phase changes take place in water: ice melting or water boiling are two examples of a phase change as thermal energy is being put into water. Condensation and freezing are the phase changes which take place when thermal energy is removed from water.
There are two very interesting things about phase change materials that make them valuable for our purposes:
1. As the material absorbs or releases energy to go through its phase change, its temperature remains stable. For instance, if we are cooling water from 5°C to -5°C, the temperature of the water will move steadily from 5° to 4° to 3° and so on - until it hits 0°. At that point, the temperature of the water will remain at 0°C until it has completed the phase change into ice, at which point it will continue moving down the scale until it hits -5°C. The same thing will happen, in reverse direction, as that water is warmed back to above freezing. In effect, the material either releases stored energy or absorbs it to enable the transition to take place.
2. The second item of interest to us when looking to get the most solar energy benefit is that there a wide variety of materials which can be used to store or release thermal energy, and they have a wide range of melting points. So if you want to keep a flow of air around 72°F, there is a PCM which makes its transition at that temperature. If you want something warmer or cooler you just find the right material.
So you can see there are a wide range of options involved with passive solar designs beyond simply having your home face the sun.
Obviously, some of these are only helpful when we are in the planning stages of building our home. Changing the orientation of your home, the number and placement of windows, or the amount of roof overhang are not items which can be easily or inexpensively changed once the house is in place.
There are a growing number of companies which sell thermosiphons or PCM solutions. Many of these are still expensive, but it might be worth it to you to see what is out there. Before you know it, you might be showering with sun-heated water or staying cool in the summer with PCM chilled air!
The other side of maximizing solar energy benefit is 'active' solar. We'll cover that in another article and in the Solar Energy Advantage mini-course (see below)!
For more information about including solar energy in your own home, visit me at [http://www.SolarEnergyAdvantage.com], and sign up for a free mini-course.
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