Yes, you too can reduce nearly to zero (well as good as being free) the cost of living in a comfortable home and do it in a way that is good for the environment & makes your home a green home as well. If you are interested please read on; we have tried to provide as much helpful advice as possible so do read this to the end as there are tips and hints all the way through.
NOTE: In the Southern hemisphere this works only for North facing windows and in the Northern hemisphere only South facing windows. More on what to do with windows on the other sides of buildings later.
Also you need to be careful of during Summer about letting too much solar energy into your house - as light heats whatever it passes through or touches. So use window dressings like horizontal blinds and drapes to reduce the glare. We recommend that you do not use vertical blinds, as you cannot set them to a constant light level over the day and you will be forever fiddling with them. You can also get glass with a special IR blocking coating, but this will stop any winter sun heat gains; i.e. only use in places where you are getting too much solar gain regardless.
So why is this useful? Well, if you had an internal 'bare' brick wall in your house, by opening windows at night it would cool down. Then if during the day you closed your windows you would create a closed environment with a cool brick wall in the middle; thereby helping to maintain the cool relative to the external temperature.
Similarly in Winter, if you opened your windows on warmer days and heated your wall (or had it positioned to catch the winter sun), then at night you closed your windows; you would trap the heat from the wall to keep you warm.
The real trick here is how you place your thermal mass. Tiles close to North facing windows (in Australia) would keep you cooler in Summer and warmer in Winter (think about the solar cycle).
Thermal mass walls you really want both inside in the path of the winter sun (i.e. North Side) and some on the South side as well - this way part of your thermal mass is 'passive' and acts to reduce the natural temperature changes in the house.
Note: If you have a concrete slab in your house, your need for an additional thermal mass could be less, it really depends on if the concrete slab is able to easily 'interact' with the environment of your living space. i.e. if its is mostly tiled, good; if it's hidden under wooden flooring or carpet, bad.
Note2: It is possible to employ other materials like brick veneer, concrete blocks, stone, mud bricks, rammed earth and even containers of water in walls (i.e. a fish tank!) to act as thermal mass.
See this page for details on how to work out the correct ratio of glass to thermal mass to have in your property (remembering it was written for the Northern hemisphere, so reverse the North/South references as required). Also see here for the Southern hemisphere equivalent.
For an instance of how effective utilizing thermal mass in house design can be have a look at this article; basically water with a solar greenhouse was used to wipe out heating bills for a house for getting on for 20 years! Also have a look at this article for a building in UK using thermal mass, timbrel vaulting and passive design techniques to also wipe out heating and cooling bills.