The Bumpy Road to Net Zero Energy

By Alan Meier

It’s easy to lose the longer perspective when we are involved in day-to-day efforts to save energy. That’s why I want to focus on a single home—Danny Parker’s house in Florida—to illustrate the bumpy road to zero energy use. The figure on the right shows 21 years of electricity use, along with many of the major events in Danny’s household. (Follow the green line.)

When the Parkers moved into the house in 1989, Danny and his wife used roughly 10,000 kWh per year. (By coincidence, that’s also the national average residential electricity use.) Over the next 20 years, Danny installed many conservation measures and improvements. He added insulation, sealed ducts, installed a whole-house fan, replaced the refrigerator and air conditioner, and installed a PV-powered pump for the swimming pool. He also replaced all the incandescent lights with CFLs.

There were other events affecting energy use. The babies arrived— first Sarah, then Wade. In 1998, the Parkers added 500 square feet of floor area. In 2005, the children—no longer babies—convinced their parents to buy a digital video recorder (DVR) and a flat-screen TV. In 2006, Danny bought an energy feedback device, though it wasn’t clear if anybody besides him understood it. Finally, in 2009, the Parkers installed a 5kW PV system. Meanwhile, appliances were being replaced again. In 2010, the Parkers replaced the “new” refrigerator. The “new” air conditioner was replaced in 2010.

Over those 21 years, the Parkers’ energy use fell about 50% through efficiency improvements. They then eliminated the remaining 50% of grid-supplied power by installing a PV array. Now, in 2011, the Parkers’ house is exporting electricity.

The Parkers’ house was in no way special, yet it was able to reach net zero electricity use through a combination of familiar efficiency measures and investments in renewable energy. Arguably, many millions of households around the country could achieve similar results.

This rare perspective of 21 years of energy use reminds us that we shouldn’t treat a house as a static object. We can see that the progress of the Parker household toward net zero electricity consumption is hardly smooth, and many of the bumps don’t seem to correspond to particular technological events. Some of the bumps are good: The birth of two kids seemed to raise electricity use. That’s not really a surprise, but we shouldn’t forget this connection. The physical size of homes grows, too; this house increased roughly 25%. Nevertheless, we don’t see much increase in electricity use. Perhaps that’s because Danny was careful in the design and construction of the addition. Major appliances, such as the refrigerator and air conditioner, were replaced twice over the two decades. This is a reminder that efficiency experts should expect to visit each home several times in the path to net zero energy.

Of course one can argue that the Parkers’ home is not a fair example for comparison to an average home, and that we ignored natural-gas energy use. These are valid objections, but I don’t think they detract from the basic conclusion that a combination of vigorous conservation measures and appropriate use of renewable sources can achieve some—if not all—of our climate mitigation goals.

- Alan Meier

Tags: climate, editorial, energy, zero

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Comment by Home Energy Magazine on July 19, 2011 at 7:37pm: Pat Dundon, thank you for your question - it is a good one. Below is the response from Danny Parker:

Water heating went like this:
Feb. 1989: moved in with existing electric water heater, EF=0.86; wrapped water heater same month we moved in. Set tank water temperature to 115 F. Installed low flow showerheads
Feb 1993: Switched electric water heater to gas (~200 kWh/month reduction seen in plot)
Feb 1993: Added solar water heating at the same time (two tank system with gas)
Jan 1994: Add solar water heating to existing as tank (two tank system)
Jan 2007: Remove gas tank and add elevated gas tankless gas backup above solar tank as auxiliary (noticeable drop in measured gas consumption)
June 2010: Remove 40 gallon solar storage tank and change to 80 gallon storage tank; insulated piping

So, the system was fundamentally changed three times: gas tank in 1993; solar with same gas tank in early 1994; tankless gas with solar in 2007.

We are submetering the gas use of the current solar/tankless gas system, which is showing an annual use of only 18 therms per year (150-200 therms per year is normal).

Comment by Jim Peck on July 18, 2011 at 2:04pm: Hmmmmmmm,

I've a similar data base in excel on a property dating from 02.

If I can figure out how, I'll load it up here. This gal is great!

Comment by Pat Dundon on July 18, 2011 at 1:54pm: I don't see any notations on the water heater. I doubt a water heater would survive 20+yrs without repalcement. Was the water heater gas or LP all the way through this timeline? Was it electric? Did it change fuels?

Comment by Cindy Matthews on July 18, 2011 at 11:08am: Now this is the sort of information that needs to get widespread news coverage so others can see the advantages of taking conservation measures and looking into using renewable energy sources.

Comment by grey staples on July 18, 2011 at 8:08am: Very interesting and good data collection. Interesting that after Sarah's birth, it looks like the overall moving average was basically flat until the PV came online. So, the "natural" increases were balanced by investments in energy efficiency. Lots more information that would be interesting to know ... weather, electricity prices, gas usage, cost of EE investments/paybacks, etc.

Comment by Sean Lintow Sr on July 16, 2011 at 3:32pm: Now that is cool & a great example of how changes impact the house not only when they are done but down the road - it would be interesting to also see if some unexplained spikes were weather related,or...

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