Roberts: Net zero families find energy savings off the grid

This op-ed is by Tristan Roberts, editorial director at BuildingGreen, Inc., in Brattleboro, which publishes information on green building solutions. The commentary originally appeared on that organization’s Web site,

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.

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.

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.”

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.

The families moved into nearly identical, superinsulated homes last June. South Mountain Co. 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.

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.

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.”

Thanks to Martin Solomon and Nadav Malin at BuildingGreen for their report on the Martha’s Vineyard story, which I relied upon here. Thanks to you readers for your continued e-mails and encouragement — let me know what you think of today’s column by commenting, and what energy questions you’re currently facing.

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  • It is wonderful some people are able to afford to build zero-energy houses, whereas others live in substandard, mobile structures that leak energy the owner/renters can’t afford to pay for, and when big rains come, they get flooded out to boot.

    Should not the housing and sites of those people be attended to first? The crowing about zero-energy can come later.

  • At my off-grid house in Danby this morning, we had a light frost. First thing before milking the cow, I turned on the hot water heating for my office, and now it’s nice and warm, that chill is gone, all from the solar thermal heating system in the basement and on the roof. Hot shower after milking was great. Sun is shining, plenty of electricity to run the heating system. Insulated the ceiling last year, almost finished swapping out the old single pane (plastic-covered) windows with double pane. I’m not rich, just making smart choices. Solar works in Vermont, and off-grid is becoming more realistic.

    I agree with Willem about Vermont’s mobile home park problem, which was just exacerbated by the flooding. Most of Vermont’s 200+ mobile home parks were built in the 1960s and 1970s in low-lying areas. They have failing infrastructure, breaking water and sewer pipes, poor quality drinking water and have been crying out for attention for more than a decade.

    Here’s your challenge, Green Builders: Can you come up with a Katrina-style “Irene House”, and also identify appropriate locations to build them and relocate mobile home parks to dry ground? One thing you learn when you work with mobile home park residents is that they are often the people who keep Vermont running — truck drivers, school lunchroom workers, etc. And they are communities, people who have lived together for years, so relocating one family at a time breaks up the communities.

  • Tristan Roberts

    Willem, the homes discussed in this story are affordable housing units owned by the Island Housing Trust. They are simple, affordable homes, for regular people. This is exactly the type of effort you are calling for.

  • Alex Barnham

    Don’t’cha just love this news? I have a camping trailer that cost me $700.00 and it is run by a 12 volt battery charged with a $150.00 set of solar panels from Harbor Freight, heated with a wood stove, assisted by a solar heat window box I built with aluminum cans for $0, a solar hot water heater I built with scrap parts for $0, I wash the few clothes I wear with a washboard and collected rainwater, and I hang them up on a $1.00 clothes line or on a rack near the woodstove. When the storms come, I move it to higher ground. This is not a step back in time, I am actually waltzing into the future with a smile and a sense of victory over the Beast.

  • Alex Barnham


  • Tristan Roberts

    Great setup, Alex! Say more about your hot water heater — how does it work? Does it work in winter?