Are you thinking of installing solar?
If so, you might want to learn from our cautionary tale. We’ve had six years of experience living in a net-zero carbon house, and have learned a sobering lesson about reducing our carbon footprint.
In 2015, my wife and I were ready to retire. We took on a 100-year-old fixer-upper for our move to Minneapolis. Our aim was to demonstrate that an average house on an average lot in a chilly northern city could be rendered net-zero – that is, that it could produce at least as much energy as it used. We had no doubt that the global climate was changing, and so we, being teachers, wanted to model what could be done to decarbonize the aging housing stock of American cities.
The renovation took two years, and we have been living in the house now for six. (You can see it by googling “Net Zero Victorian.”) The house has more than met our dreams by consistently producing more energy than it requires. In a further, unexpected blessing, it envelopes our aging bones in comfort. I have tirelessly promoted the house’s many virtues, including being certified LEED (Leadership in Energy and Environmental Design) platinum. Until the pandemic hit, we gave house tours to more than a thousand visitors.
But while I have talked my head off to anyone about our Net Zero Victorian, I have been slow to grasp how energy actually flows in this house. And the reality is not what I had been imagining. Indeed, the lesson I have learned has redirected my solar enthusiasm to the more significant tasks of insulating and sealing an old house.
We rebuilt the house practically from scratch – a total gut rehab, as it is called. I wanted to do anything and everything that would diminish its carbon footprint and model environmental responsibility. I didn’t just want to reduce our use of natural gas, I wanted to eliminate it altogether. I didn’t just want solar, I wanted to jam as many panels as we could onto our house and garage. I didn’t just want geothermal energy, I wanted a surplus to meet any sustained polar chill. I didn’t just want enough insulation, I wanted to pack in as much as we could.
Economically reasonable counter arguments about the diminishing returns of excess investment made little dent on me – I wanted as much as we could get of everything that would brand our project as sustainable by reducing our carbon footprint. To flip the famous 1964 quote by Barry Goldwater, “extremism in the pursuit of sustainability is no vice.”
And so the house – through the brilliant design work of my architect and the solid construction work by my builder – has 54 solar panels, which is at least twice what most houses carry. Our tiny backyard contains four geothermal wells, each 250 feet deep. The house itself is sheathed with ten inches of insulation; the roof has considerably more. The windows all have triple panes of coated glass. And we cut the gas line.
Particularly dear to my greenish little heart were the 54 solar panels. According to our tracking software, they were offsetting some 13 tons of carbon per year. That is, they were keeping our house from using utility electricity that would have resulted in a side product of 13 tons of carbon emissions per year.
In dollar terms, solar was doing quite well. The solar system generates an average of $1,200 worth of electricity per year. We use about $450 worth and sell the rest – $750 per year, on average – back to the utility. We buy an average of $540 worth from the utility during darker weeks and months. Overall, we have been operating in the black, for our pocketbook and for the earth. Thanks to a rebate from the utility which averages $1,100 per year, the solar system should pay for itself in 13 years or less. And the system is not merely net zero, producing as much energy than it uses. It runs net positive – producing more energy than it uses.
So why am I having sobering second thoughts?
Until now I failed to understand the significance of these solar numbers. The truth is that they are … well, scrimpy. We have 54 panels, and the system was rated at 17 kilowatts. Why were we not producing more? Some hard realities began to intrude on my gauzy solar dreams. First, our 17 kilowatts are measured in DC (direct current). The electricity we actually use is AC, or alternating current. By that measure, our system is only 13 kilowatts in capacity for the electricity in the form that we use it.
Second, we have a low “solar power ratio.” A system which produces 1,000 kilowatt hours per 1 kilowatt of capacity has a solar power ratio of 1:1. In this northerly latitude, there isn’t that much sunlight, and the ratio is 1:2 or less. Our system generates 16,000 kilowatt hours per year on average. So for our 17 kilowatt system the ratio is a disappointing .94. (It should be noted that trees and buildings provide unwanted shade, hardly the sun’s fault.)
The third reason why our solar numbers are so small is the most important – and hurts me the most. The raw fact is that our solar array is not the principal reason that our house achieves net zero. Rather, it is only the icing on the cake. The cake itself is all the design and construction work that went into reducing the amount of energy the house requires: the thick insulation, the triple-pane windows, the geothermal heat and the efficient appliances. What I have learned is that achieving net zero is due only in part to piling on sustainable energy sources. Rather, the key lies in reducing the amount of energy needed to run the house.
Decades ago, the energy guru Amory Lovins invented the concept of a “negawatt.” While electric utilities were striving to expand the number of kilowatts available to customers by building new power plants, Lovins argued that building negawatt capacity could be cheaper, watt by watt. Our architect and builder adopted this negawatt strategy by doing everything they could to reduce the house’s need for energy. The house’s siding was stripped off and thick foam blocks were attached to the raw exterior, then covered over with new siding. A new roof was built over the old, making room to spray in ten inches of foam. All gaps and cracks were sealed. A refrigerator-sized heat pump was installed to concentrate the diffuse heat from underground into a flow of warm air circulating through the house. Other heat pumps were installed to heat our water and dry our clothes. Air for ventilating the house was sucked in through a heat exchanger, to recycle the heat from the air being expelled. And we stocked the house with the most efficient appliances we could find. This work wasn’t cheap – $50,000 for a completely new heating system, $40,000 for the solar system, $80,000 for new windows.
We’ll never recover all these costs, but they enable us to keep our overall electricity consumption to 12,000 kilowatt hours per year, on average – supplying all our needs in a 3,000 square foot house. In contrast, before renovation the house had used some 25,000 kilowatt hours just for heating (not even cooling) – and this was while it was unoccupied. Overall, our house probably was using some 40,000 kilowatt hours per year – three times what we use now.
My wife and I have no intention of freezing in the dark. The dramatic reduction from 40,000 kilowatt hours to 12,000 has entailed no loss of comfort. We keep the thermostat at 73 degrees during the winter and 78 during the summer. We use the appliances as much as we want and have ample hot water. Cutting energy use need not result in cutting comfort. Au contraire, we have found that the insulation and sealing work have produced a house without cold spots, drafts or even winter condensation on the windows. We barely hear the garbage trucks rumbling up the alley. We can bask in our sunroom all year along no matter what the temperature is outside. In short, the cutting of energy use has enlarged – not reduced – our freedom to enjoy our house.
Solar is hot stuff these days. I remain a missionary. But I have to admit now that solar alone could never have gotten us close to net zero. We generate 16,000 kilowatt hours per year (averaged over six years) to cover the 12,000 that we use. The message is clear: for the sake of our continuing existence on earth, we denizens of the northern latitudes need to renovate our aging houses to reduce energy use. Putting solar panels on the roof is a fine gesture, but it is icing on the cake. The real savings come from insulating, sealing and pulling heat from the earth, and from air-source heat pumps, in the most recent and promising engineering innovation. Our experience offers a powerful caution to anyone who wants to pursue net zero in a cold northerly climate – just don’t think solar alone is going to save you or the planet.
Stewart W. Heman is a retired college teacher and now visiting fellow at the Christensen Center for Vocation, Augsburg University.
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