Wednesday, April 25, 2018

Building a net-zero house

A couple of days ago, I saw my brother grinning broadly and occasionally giggling. The occasion for this mirth was a recent encounter with his meter-reader for the local utility company—Duke Energy. The news was that last month his photo-voltaic cells had generated roughly 300 kw of electrical power more than he had consumed. While much of this joy is due to the fact that he was billed the $9.86 minimum for being connected to the grid while most of his neighbors were getting $350 bills for homes of similar sizes, the giggling was probably due to the idea that he is "sticking it to the man."

Tony heard this story yesterday and insisted I explain what was involved in producing such a house. So this morning I asked and while his story was hardly complete, it highlighted the parts he thought important. So in no particular order, here they are.

1) His property in the country was large enough so the house's site orientation was pretty much anything he wanted. So the house's ridge line runs east-west, the roof pitch was selected to maximize solar gain, and the overhangs are large enough so the south wall is completely shaded between the equinoxes.

2) The holding tank for the solar hot water heater was located close to the showers so the water used to get hot water on start-up is minimized.

3) The air handler for the air conditioning system was located smack dab in the middle of the house which does wonders for efficiently distributing the cool air.

4) Room for the insulation was designed in from the beginning. The exterior walls were framed with 2 x 6 studs and the roof trusses were scissor-type which made for higher ceilings while provided plenty of space for 16" of insulation.

5) Because excessive heat was the primary problem in Florida, aluminized Mylar was chosen for the moisture barrier.

6) The steel roof was put on sleepers which allowed the underside of the roof to stay cooler and dry.

7) The original air conditioning compressor was a SEER 13, which in 1992 was the most efficient unit one could buy. It was replaced in 2010 with a SEER 18.

And so on. They key to understanding this house is that VERY important decisions that significantly affected long-term performance were made in the planning stage. None of the features mentioned above cost much to implement but have saved thousands in energy costs over the years. As I have said since the 1980s, pollution is a function of design.

Then in 2008, the decision was made that photo-voltaic cells were now inexpensive enough so adding them to the mix should be cost effective. This was pretty easy to do because the roof was already pointed in the right direction. PV cells were still pretty spendy in 2008 so only 5 kw were purchased. By 2011, the costs had dropped significantly so another 5 kw were added which leads to the monthly grinning when the meter is read.

So while the costs of building a solar home from scratch are not much more than conventional construction, retrofitting an existing house is difficult, time-consuming, AND quite expensive—even though the price for PV cells is now lower than $1 per watt.


  1. Thanks for the write up. We enjoy our home we have been in since 1992. Not only is it very energy efficient, it is quiet, clean and very comfortable. Like I was telling Jonathan, we are on a well & septic tank, so we have pumps to run & a spa to keep warm and an air conditioned 1000 sq ft shop I work in. We still have a very affordable electric bill every month...nice when thinking about a fixed income. All planned in the early 1990s. Nice!!

  2. OK, but I don't think that would work in Idaho (though I would still like to have a solar & a battery system to keep a few things running during utility outages).
    According to the EPA's website, electricity generation accounts for 28% of America's greenhouse gas emissions. Presumably that 28% includes electricity for industry as well as for residences. Let's guess that half of electrify goes to residences, or about 14% of greenhouse gas emissions.
    So if every single American residence had 10kw of rooftop solar and energy efficient construction like your brother's house, best case that would reduce per capita greenhouse gas emissions by 14% ... assuming zero population growth, and ignoring the carbon required to manufacture the solar panels and ship them across the ocean. But ... if the population grows 14%, that will offset the 14% per capita reduction. In any event, a 14% reduction in greenhouse gas emissions will not make a dent in climate change.
    So to get back to your previous post, "Are We Doomed?" Yes, we are probably doomed. Since we don't know for sure that we are doomed, we should still try to straighten out the mess we have made. If nothing else, maybe our efforts will buy our children and grandchildren a few more years of life.

    1. You are absolutely correct that what works in Florida will not work in Idaho (or Minnesota.) The point I was making is that there is now an abundance of good parts that allow amateur engineers to construct net-zero homes of their own design. This is an amazing turn of events—as anyone who has ever tried such a project will attest. What was unavailable in 1992 is available now. And yes, it is worth the effort. It is truly amazing to watch the sun shine on some panels and with no noise or fuss, they just start producing electricity. Yes, I know that is the whole point but it is fun to see it in action.