Before we go into detail about our home, there is some argument about how exactly to define Net-Zero Energy homes. For the sake of clarity, we go by the simplest of definitions. Net-Zero Energy basically means that the home produces as much or more energy than it consumes. This means that the home doesn’t buy any external fuel which it cannot also produce and sell back. We make this clarification because we have seen homes use bio-fuel to appear to reach “Net Zero Energy”, but despite whatever environmental benefits bio-fuel may or may not provide, it is still an imbalance in locally produced versus purchased off-site energy (unless of course you are making bio-fuel in the backyard).
To clarify further, Net-Zero is not the same as off-grid. Net-Zero homes are typically still tied to the grid, purchasing energy at night when they can’t produce it themselves. The key is that they then sell more energy back during the day. The positives of this include avoiding batteries which are large and expensive and the ability to sell energy during daytime peak hours. The latter means that a house who’s production equals their use will likely make money by selling day-time energy at a higher rate. That could mean checks instead of bills from the energy company. Tell me that wouldn’t make your month . . . every single month.
Chad will be going into full geeky detail on the Net Zero Energy idea in the next week or so, but for now I’ll tell you a little about the actual house we have cooking.
In a situation that even caught us a bit by surprise, Net-Zero is what we now appear to be building in the Passive Project. Both homes, due to the benefits of the new solar incentives, will be getting solar PV and according to our modeling, at least one, if not both, should be able to hit Net-Zero Energy. We will focus here on the infill house as that is the one which is pursuing official Passive House certification and the one most likely to achieve Net-Zero Energy.
Basically, by using the German Passive House standard we should be able to reduce the home’s energy use by almost 90%. This is accomplished through high insulation values, air sealing, proper solar shading, high efficiency appliances and a greatly reduced HVAC system among other things. Again, Chad will be going into exactly what we did in each of these categories in upcoming blog posts (like the one he did on the foundation). For now, suffice it to say that money and time were spent in ways that they seldom are in conventional building.
This attention to energy efficiency led us to a situation in which a small 2kw solar array should allow the home to produce more energy than it uses. With current incentives this size array is remarkably affordable and thanks to help from EOS, our solar PV provider, we were able to roll that cost into our client’s mortgage. The result is a potential Net-Zero Energy home in Philadelphia selling for quite a bit less than $300k. To us that is pretty exciting.
Now, an important thing to note is that while the construction of the home is important to achieving Net-Zero Energy, the behavior of the occupants is also a crucial element. If the people living in the home leave their lights on 24 hours a day while also spending a good portion of that time in front of their open fridge blow drying their hair, then it doesn’t matter how well the home was built. This is particularly true of our homes which are built at low margins and leave less room for excess than a behemoth carrying a huge roof full of expensive panels. Conservation is a key component here and much of that is up to those living in the home. (Hear that you guys?).
It takes a year of energy readings to determine if a home is truly Net-Zero, and you can bet we’ll be keeping track. With any luck, by September of next year we will be celebrating our first official Net-Zero home. And, since we are building all of our future homes to the same standards, we will hopefully be celebrating the first of many.
I know some of you are itching for details. I assure you, they are coming. For now, tell us what you think in the comments.
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