Net-Zero Energy Families Show How It's Done

Shifting from coal to natural gas would have limited impacts on climate, new research indicates. If methane leaks from natural gas operations could be kept to 2.5% or less, the increase in global temperatures would be reduced by about 0.1 degree Celsius by 2100. The reduction in global temperatures would be more minor with higher methane leakage rates. (Courtesy Springer, modified by UCAR.)

Saturday found me helping a friend install new batteries for another friend's off-the-grid solar power system. We had fun getting the system back up and running and watching the solar-powered watts come in on a beautiful September day.

At one point my friend asked me to use his multimeter to read the voltage of the batteries. No problem: I put the two testing probes in place on the batteries and got the desired reading. He then asked me to reverse the probes to see if the reading also reversed, as expected.

However, I switched the probes back and forth several times--or at least, I thought I did--while the reading unexpectedly remained the same. After a minute he said, "Wait, you're just moving your hands back and forth between the probes--you're not actually moving the probes." He was right, and we had a good laugh about that. Some changes make a real difference, and some changes amount to nothing more than hand-waving.

Switching to natural gas won't slow climate change

Next month, new peer-reviewed research is being published that will conclude that although the burning of natural gas emits far less carbon dioxide than coal, a greater reliance on natural gas would fail to significantly slow down climate change.

The study by Tom Wigley, who is a senior research associate at the National Center for Atmospheric Research, examines how coal use causes warming through emission of heat-trapping carbon dioxide, but also releases comparatively large amounts of sulfates and other particles. Those particles, while causing acid rain and other environmental problems, help to cool the planet by blocking incoming sunlight. The situation is further complicated by uncertainty over the amount of methane that leaks from natural gas operations. Methane is an especially potent greenhouse gas.

Simulations: climate change to accelerate

Wigley's computer simulations indicate that a worldwide, partial shift from coal to natural gas would slightly accelerate climate change through at least 2050, even if no methane leaked from natural gas operations, and through as late as 2140 if there were substantial leaks. After that, the greater reliance on natural gas would begin to slow down the increase in global average temperature, but only by a few tenths of a degree.

"Relying more on natural gas would reduce emissions of carbon dioxide, but it would do little to help solve the climate problem," says Wigley, who is also an adjunct professor at the University of Adelaide in Australia. "It would be many decades before it would slow down global warming at all, and even then it would just be making a difference around the edges."

Eight net-zero-ready homes, eight families

In the category of changes that actually make a difference, eight families on Martha's Vineyard in Massachusetts recently were able to demonstrate how important energy conservation is in reducing our need for carbon.

As reported in the Environmental Building News article Want a Net-Zero Home? Be a Net-Zero Family, the families moved into nearly identical, superinsulated homes last June. South Mountain Company designed and built the LEED Platinum homes for the Island Housing Trust with the goal of allowing the residents to operate them at net-zero energy, using the 5 kW photovoltaic arrays on the roofs for power. In case the energy cost savings didn't provide enough incentive, South Mountain offered a reward to any household that came in at net-zero energy for the first year. Two families achieved this goal, and won their choice of a $400 dollar gift certificate at a local fish market or a one-year membership at the local CSA.

Submetering of major energy systems

Each of the eight houses in the Eliakim's Way project on Martha's Vineyard sports a 5 kW PV array, which provides most or all of the home's energy. Credit: Derrill Bazzy

South Mountain installed equipment to allow submetering of all the major energy systems in the homes, providing an unprecedented window into exactly how the families use energy. A report by South Mountain engineer Marc Rosenbaum highlights key insights from this experiment--among them the importance of collecting data monthly.

Though variations from the estimated energy use will be greater on a monthly basis than on an annual basis, it allows users to catch meaningful anomalies more quickly. In the case of one family, the data helped reveal that a child had turned off an exterior AC disconnect from the PV system during the first month, allowing that family to generate only 279 kWh instead of the 630 kWh that the other seven homes averaged.

Two families operate at net-zero or below

In a testament to the efficient construction, water-heating energy exceeded space-heating energy in all but one of the homes. Rosenbaum suggests that a good further investment would be for solar hot water or heat-pump water heaters. The submetering also showed that the biggest loads were the two uses of electric resistance heat: the radiant ceiling panels and the water heaters.

In the end, two families were able to operate below net-zero energy, while two others were close. On the other end of the spectrum, one family used a measured 11,635 kWh in one year, nearly twice the 6,873 kWh provided by the solar panels. In all cases, lights and plug loads accounted for about half of total energy use. With that in mind, the report quotes energy consultant Andy Shapiro: "There are no zero-energy houses, only zero-energy families."