As you may recall, our first 3 design principles all had to do with passive solar design: solar gain (Let the sun shine in), thermal mass (Massticate on This), and insulation (Design Principle #3). Just this week we have decided on the solar hot water system that we will be installing. It is an active system, as opposed to our previous hot water system that was patently passive.
As you may have discovered in the previous posts, a certain level of vocabulary is required to speak accurately about eco-design. Passive and active solar are certainly two concepts central to eco-thrifty designing and building. The difference is quite simple, but if you find yourself talking to an architect, engineer or contractor one day about building a green home, make sure you know the basics so you can ask for what you want.
‘Passive solar’ refers to anything absorbing sunlight energy by simply sitting in the sun: a cat, a parked car, our house.
In new construction, passive solar strategies will pay for themselves in energy savings immediately. In renovation, the payback may take a little longer.
‘Active solar’ refers to a system with some moving elements. In terms of our active solar hot water system, the water is heated by the unit on the roof and flows into the house under pressure. It is actively being moved from outdoors to indoors.
The best data we can find is that the payback period of this system will be around 7 years. That represents a 10% return on investment. Which bank is offering a rate like that?