Taking a 20-Year-Old Florida House to Net Zero
Starting with an energy-efficient home and using available incentives made it easier
Steve Larson, a builder and home energy rater in Florida, sent me an e-mail with his energy bills for February through July of 2012. When you subtract out the monthly service charges, he paid only $5.35 for electricity during those six months. That's right — less than a dollar a month for electricty... and then $9.88 a month for the service charge.
"Saving energy has been my passion for a long time," Larson wrote. Since he added the solar electric system to the house in 2008, producing it has become a passion, too.
Begin with energy efficiency
The basic idea of net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. energy is having enough onsite power production to offset the energy consumption in the building. I discussed the topic a bit in my article about Amy and Matt’s net-zero-energy home in North Carolina. Lloyd Alter of Treehugger described one way to get to net zero energy: "In Net Zero, you want to generate enough power on site to heat, cool and light your house; it could be a draughty barn, but if you put enough green gizmos on the roof to generate enough green energy to feed it, who cares?" Just a touch of sarcasm there, eh?
Larson chose the smarter path to net zero. He didn’t have onsite power production in the beginning, but he did start with a healthy dose of energy efficiency when he built the house in 1991-92. Here are some of the features that make it so efficient:
Remember: this house was built 20 years ago! A HERS Index of 65 means it's 35% more efficient than the same home built to the 2004 International Energy Conservation Code (IECC International Energy Conservation Code.), so it was 35% better than a code that came 15 years after the house was built!
Adding enough photovoltaics to get to net zero
In 2008, Larson added a 5-kilowatt (kW) photovoltaic (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) system to the house. That didn't take them all the way to net zero, though, because he also has a huge garage and air-conditioned shop. So he added a second 5-kW system in 2010, and that got them to where they are today, paying an electricity bill that's just $9.88 per month in service charges, with rarely any charge for actual net electricity consumption.
In case you're wondering, the first 5-kW PV system cost $40,000, and they got $23,000 in federal, state, and utility tax credits and rebates. About $20,000 of the incentives came from the state of Florida. The second 5-kW system cost only $28,000, a 30% drop in just two years. Their total cost after incentives came to $37,000, giving them a payback period of about 14 years.
The HERS Index of the home including the energy production from the solar modules is an impressive -14. A HERS Index of zero means that the home produces just as much energy as it uses, no more and no less. According to the HERS Index, their home exceeds the net zero energy threshold. "It has been a very comfortable home to live in for the last 20+ years, but the $9.88 electric bills have us in a very nice position. My wife is a very happy camper," said Larson.
According to the electricity bills he sent me, Larson's electricity usage is generally in the range of 500 to nearly 1,000 kilowatt-hours, mostly toward the lower end. Some months they produce more electricity than they use, as you see in the meter readings below, and other months they use more than they produce. The snippet below is from their May 2012 electricity bill, showing that they used 490 kWh that month while producing 965 kWh. They generally run a surplus, as you can see in the bottom number, which is the running total of their electricity production versus consumption.
Steve and his wife are helping to make Florida's nickname — the Sunshine State — true in more ways than one. "We are pretty happy how far out in front of the running of the bulls we are," Steve said. Of course, someone who's been a HERS rater since 1994 is used to being out in front.
- Steve Larson
Jun 12, 2013 3:50 PM ET
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