Minnesota Home Says Goodbye To Carbon Footprint 

Tucked in Northfield, Minnesota, a town known for "Colleges, Cows, and Contentment," Gary and Mary Carlson are trying to add sustainability to that tagline. Their 1998 Frank Lloyd Wright-inspired home said goodbye to its carbon footprint with a blend of geothermal energy and solar panels. Geothermal or solar may not be the first things that come to mind for a state covered in snow half the year. However, this family seems to have cracked the code and have found a way to make it all work. The Carlsons took their first step by installing a geothermal heat pump when they initially built their house and then coupled that with the installation of solar panels later in 2013. Today, this duo is responsible for a net positive carbon footprint and has experienced a net positive financial investment.

Efficiently Using the Land

Although geothermal may be a lesser-known option than solar or wind, it is an effective way to help cut carbon emissions. Geothermal systems do not generate electricity, but instead, use the earth's natural temperature to heat and cool a house more efficiently than traditional methods. The temperature of the ground is about 55 degrees year-round, at a depth of about six feet below the frost line. This constant temperature is a key factor for both summer and winter energy efficiency, especially in a state like Minnesota, where the weather can reach both extremely high and low temperatures.

A geothermal heat pump usually consists of a series of six 100-foot long underground loop pipes that circulate a mixture of water and antifreeze (usually glycol). The pipes do not freeze because of the fluid mix and that the pipes are below the frost line. In the summer, the lower temperature of the earth naturally cools the fluid. The fluid releases cooler air that is then compressed to an even colder temperature, which is then delivered as air conditioning into the home. In the winter, the opposite occurs. The pipes absorb the heat from the earth, carrying warmer fluid to the system. The warmer air is again compressed and released as hot air into the home. A great way to understand more about a geothermal system is through this informational video.

While some geothermal systems are implanted vertically into the ground, the Carlsons laid their unit horizontally. Horizontal construction can be less expensive to install, but it does require a much larger area of land.

Solar energy, in simple terms, is converting sunlight into electricity. (Solar energy can also be in the form of heat—often termed "solar thermal"—but we are referring here to photovoltaics.) For a more complex definition, Live Science describes how solar panels work: they allow "photons, or particles of light, to knock electrons free from atoms, generating a flow of electricity."

While a commonplace for residential panels are on roofs, Mary and Gary constructed their project on the ground, approximately 200 feet from the house. The Carlson's 80-by-14 foot, 56-panel solar array rests on a sturdy metal frame with a concrete foundation. The productivity of each separate panel can be tracked over its lifetime using a software system. Gary is confident in his system and now only checks his array every other month or after a big storm.

The Carlson's prairie-style house has several features that boost this pair's success. For example, with this architectural design, there is an optimal ratio of walls to windows, which allows for natural light yet keeps the home well insulated. The roof overhang allows the winter sun to come in and shades the house in the summer. This house also has an above-average amount of insulation, with 6 inches in the walls and 10 inches in the roof. Their energy-efficient windows are not only double pane but also Low-E or low emissivity, meaning the surface reflects thermal energy. These features are known as "Passive House Principles" and help lighten the load for the geothermal and solar systems to cover the rest of the electricity that is needed. In fact, due to these design elements and additions, the Carlsons were able to install a much smaller solar panel system, saving them money and yard space.

Give Me The Numbers

Upfront costs can be scary, but carbon-reducing systems manage to pay for themselves in a matter of years. The Carlson's geothermal system took ten years to pay itself off and has been making them money ever since. Geothermal is less expensive to use for air conditioning than it is for heating, but it is still an efficient option for colder states.

Geothermal systems can do more than just heating a cooling a home: they can help heat water—which is one of the most energy-intensive and costly parts of running a household. With geothermal, you can add a desuperheater. A desuperheater is an auxiliary heat exchanger that works to pre-heat hot water whenever the geothermal heat pump operates. With this addition, the cost of heating water is dramatically lowered and allows the house to be free from natural gas.

In Mary and Gary's case, they avoided some of the solar installation costs by building the foundation and structure themselves. The average cost is about 40% more for the full installation done by a professional. While most home projects are paid off between 8 to 12 years, they were able to pay off their solar panels in just four years. Now, they use $2,000 worth of energy per year but produce $2,200 worth of electricity. The Carlsons are not only making an additional $200 a year off of their panels, but they are also avoiding an energy bill of $2,000. The savings and the income totaling $2,200 pay off their investment of the array and then provide additional savings for them every year after. In other words, over the next 25 years, Gary and Mary will save a total of $55,000 in energy costs due to their solar panels. (You can learn more about the economics of solar panels here.)

Despite having built 85 percent of the solar structure themselves, the most significant way Gary and Mary saved money was through tax credits and rebates. Without these incentives, most projects would take over 20 years to pay off and, therefore, not be very compelling financially.

Maintenance

Over the 22-year life of the geothermal system and the five-year-old solar panels, neither system has required any major maintenance. Despite the occasional brushing off of snow after a heavy fall, the solar panels have remained in perfect condition despite the weather. In the fall of 2018, a tornado roared through Northfield, but the solar panels stayed strong. Another piece of good news: even if the storm did cause damage, home insurance would have covered the solar panels with no rate increase.

The geothermal system requires rather simple check-ups annually. The maintenance routine consists of monitoring the fluid reserves, checking for leaks, and keeping the system clear of debris and obstructions. Besides these simple check-ups, the Carlsons do not predict any additional maintenance to either system for years to come.

Very Few Downsides

As with any home project, there are always some downsides to consider. Gary's first response to the question about the disadvantages was that solar panels "are an eyesore." It is a common concern. To hide the array, the Carlsons planted a row of trees between the solar panels and their house to make the system barely visible.

Another downside to installing solar panels is that on the rare occasion that traditional power lines are out, the house is without power. They are grid-tied and do not have backup battery storage. While the Carlsons have experienced a few power outages due to severe storms, most of these incidents were short-lived and did not have a significant impact on their lifestyle.

While building the base for the arrays saved a lot of money, it is not practical for most people. Gary advised that one must be a "handyman" to complete this project by saying, "On a scale 0 to 10, 10 being expert, this project requires a 7."

In terms of the geothermal system, the only inconvenience the Carlson family mentioned was that it takes longer to heat the house. This extended time is because the geothermal system is not able to blast out as hot of air compared to a traditional natural gas heater. However, both Gary and Mary said that this delay wasn't a huge problem. It is barely noticeable if you keep your house generally warm relative to the outside temperature.

Lessons Learned 

There is no one-size-fits-all approach to reducing your household carbon footprint. Depending on your location, energy needs, and financial goals, there are dozens of options for alternative energy and decreasing energy needs—and there will be even more to come in the future. It is essential to consider a holistic, well-rounded approach of both efficiency and renewable electricity generation. Some may start small by adding more insulation. Others may want to jump in with more significant investments like solar panels or wind turbines. Like the Carlson's home in Minnesota, it takes a combination of solutions to get to zero carbon emissions.

More Than Just Financially Rewarding

A big take away from the Carlson's project is the importance of tax breaks. Rebates can cut many project costs by almost half. Rise's website is an excellent resource for finding more information about rebates that may apply to you. The economics of both the geothermal and the solar panel systems justifies the Carlson's project alone. However, even without the financial incentives, both Gary and Mary said, "It has been one of the most rewarding things we have ever done." They strive to live a low carbon, sustainable life, and this combination allows them to do so with minimal sacrifice. The Carlson's hope that others can be inspired and that their home in Minnesota can become a model for creating a zero carbon footprint.

Madeline Carlson is a healthy home advocate and consultant living in Minneapolis, Minnesota.

Article by:

Madeline Carlson

Madeline Carlson is a sustainable home consultant. She graduated from Eckerd College with a double major in Economics and Environmental Studies.