Passive Solar Collection Technology

The term, "Passive Solar Collection", dates back to a time when there were many fewer practical options available for solar collection. Thus a division was made in available solar technology such that very simple systems with few moving parts were called passive, while everything else was more complicated and called active. PV systems were in their infancy and too expensive to really fit into this categorization at the time these terms were coined.

Most people think of solar patios, or sky lights, or even carefully placed deciduous trees as examples of passive solar systems. In fact, passive solar has been used for thousands of years. By selecting the direction of the mid-day sun as the side of your house with the most windows, you are counting on solar heating. Place a row of deciduous trees in front of them and you have a system that shades in the summer yet floods the house with heating sun in the winter. Simple, but thoughtful steps like these can have pretty dramatic effects on heating and cooling expenses for most homes in the United States.

Many agricultural uses for passive solar heating exist as well. By constructing a barn or shed with the right sort of heat trapping materials, indoor animal habitats can be made much more comfortable and sickness and mortality can be minimized. A well constructed passively solar heated barn can have very positive effects on the bottom line of a farm operation.

Another use for passive solar that is popular is the use of heated tube, integrated hot water tanks. These are typically purchased as a unit and assembled on roofs or anywhere that has a 20 ft^2. The idea of these systems is to create sealed evacuated tubes that capture heat and pipe that heat in the form of automatically circulating water currents. These tubes are installed on an incline and heat is carried up the tube where it is transferred to a water tank by conduction. This system is simple enough and monolithic. Thus it can be called passive. The water tank is then piped to a conventional water heater. The conventional water heater may need to add heat to maintain the desired water temperature, but the amount of energy required is a small fraction of that without solar pre-heating. Care must be taken to make sure the water tank and associated piping does not freeze, but simple electrical freeze tape can handle that. If you are just considering your first DIY project and want some encouraging results and relatively immediate gratification, this might be an ideal first project for you. You can expect to save $800 or so per year (depending upon your household hot water needs) so you may be able to pay for a self installed system in one year (in other words you pay nothing more than you would for hot water for one year). If you have a teenaged daughter who plays sports and takes lots of long showers, you might pay for a system like this in a month.