Although sustainable energy calls to mind things like electricity generation from solar power and wind power, there is something more powerful and more essential and counter-intuitive. It goes by the label passive solar. This curious animal is about both the energy you do not use and energy directly from the sun used for heating and lighting without the intermediate step of converting it to actual electricity.
One of the primary principles of passive solar design is using natural light to provide interior illumination. Some of this can be as simple as throwing open the curtains when you first get up, or it can be as nifty as installing a light tube under circumstances where a skylight won't work. A light tube can help bring light into interior spaces without immediate access to a window.
Passive solar technologies can heat your home, heat the water used at home, or even heat your swimming pool water. Some do-it-yourselfers use the copper piping from the back of old refrigerators to make cheap water heaters. Adding mass such as thicker walls, painting a wall black to absorb heat, and planting deciduous trees strategically can all play a part in using heat from the sun to keep your home warm in winter while not overheating it in summer. Deciduous trees are trees that lose their leaves. They can provide shade in summer, then let the sunshine through in winter. Evergreens can be used as a windbreak in areas where the winter wind comes consistently from a particular direction.
If you live in an older home that predates air conditioning as a widespread standard feature, the odds are good that the windows are situated such that you can open two of them and get a cross breeze going. That can help keep things cool in warm weather without running up your electric bill or adding greenhouse gases.
These are used in many hot, dry parts of the world, like Mexico and the Middle East, to help draw heat out during the summer without electricity. It counts on the principle that hot air rises and that nature abhors a vacuum. So, as the hot air rises out of the house, it creates vacuum pressure that draws cooler air to the lower floors. Many Americans do not realize it, but the staircases and turrets of many Victorian homes are designed very similarly to a heat chimney. Suppose you familiarize yourself with how this works. In that case, it may not be hard to add a window or vent strategically to your house to create this effect with only relatively modest modifications.
You may have heard the saying, "That a penny saved is a penny earned." That is not true. A penny saved is usually worth more than a penny earned. The same principle applies to energy, the environment, and sustainability: Energy saved by passive solar design is more valuable regarding sustainability and environmental protection than energy produced by sustainable means. That is true because it doesn't merely reduce the environmental cost of energy. It essentially eliminates it.
Thus, insulation plays an essential role in passive solar design principles. Adding insulation is something quickly done by most do-it-yourselfers. You can add insulation without buying insulation per se. That can be done by adding a trellis and growing a plant up it or hanging interior curtains from floor to ceiling. It can even be done by strategically placing bookcases on our walls to add mass naturally to your interior space and outside elements.
The Best Answer
If you are looking to make your home more sustainable, the single best thing you can do is educate yourself on passive solar design principles. Some need to be designed into the building from the start before construction; many others can be added to existing construction. Sometimes, it is as simple as planting a tree (or three) in the right place.
Much to many people's surprise, passive solar also produces a more comfortable home than things like forced air heat. So there is no sacrifice involved. It is very much a win-win-win solution: Good for your pocketbook, good for the environment, and good for the quality of life.