A Renewable Home Energy Retrofit: How We Did It

We reduced our carbon footprint by incorporating a variety of renewable energy systems into our Maine home, including a geothermal system and solar hot water system. With this home energy retrofit, we now produce nearly all of our power without fossil fuels.

Solar Power Array

The New England-based company ReVision Energy installed the Davis’s ground-mounted, 39-panel solar array, which provides enough electricity to power their home and their all-electric vehicle.

Photo by Ron Davis

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When my wife, Lee, and I retired in 2003, we resolved that one of our primary projects would be to significantly slash our consumption of fossil fuels by converting to renewable sources of energy, as well as by making our home more energy-efficient. This objective arose out of our awareness of the terrible environmental impacts of fossil fuel extraction, processing and transportation, and also of the pollution and climate change caused by the combustion of these fuels.

Lee and I live on the outskirts of Orono, Maine, a town of about 10,000 in the south-central part of the state. Our 2,200-square-foot, single-story home sits along a dead-end country road, near the top of a gentle slope at the head of a hayfield. It’s sheltered by forest on one side and a row of evergreen trees on the other, with our 60-by-20-foot vegetable garden tucked just behind the house. We’ve lived here for 42 years, and we enjoy our solitude, with our nearest neighbor about half a mile away. We have rather mild summers and pretty frigid winters, but, happily, the sunny days typically outnumber the overcast days.

Before retirement, I’d worked at the University of Maine for 33 years as a professor of biological sciences. I got involved in the environmental movement as a graduate student in the 1950s, and, through my activism, I picked up a bit of knowledge about alternative energy options. On a practical level, though, getting a grasp on home-scale renewable energy took patience and a great deal of learning. I consulted a lot of people — both folks at energy-related companies and other homeowners in the vicinity who’d installed systems — asked a lot of questions, and dedicated time to researching. Lee and I decided to put a substantial part of our savings and retirement income toward these home energy projects, but we didn’t dream back when we first got started that we’d eventually be able to power our home and our local transportation almost entirely with renewable energy.

Embarking with Sustainable Wood Heat

We set out on our journey in a small way well before retirement by supplementing with wood heat to decrease our fuel oil use. We added a small woodstove in our living room, as many Mainers do. To distribute the woodstove’s warmth to other parts of the house, I installed an oscillating fan high on the living room wall, which pushed the rising hot air out into both corridors leading to the rest of our abode.

By burning approximately 1 cord of oak per year, we had a pleasantly toasty living room, and our fuel oil use dropped by about 20 percent, for an annual savings of about $350 after fuel wood and electrical costs (for the fan). In recent years, we’ve had to cease running the woodstove, because hauling firewood is no easy feat at our age (I’ll be 84 in August 2015), but heating with wood offered a good introduction to tapping renewable energy, as well as to the concept that energy doesn’t arise from nothing — it takes work.

Segue into Solar Power

Up until 2007, the same oil furnace that heated the house also handled heating our hot water. That year, we took our first major leap in our home’s renewable energy retrofit by installing two solar collectors on our roof’s south-facing side for heating our water. The collectors are Apricus brand, and each consists of 22 evacuated tubes. The collectors absorb the sun’s energy to heat a fluid circulating in a pipe that connects through our roof to an 80-gallon Stiebel Eltron hot water storage tank. The fluid circulates down to the heating coils in the tank, which resides in our basement.

Despite the hefty capacity of the tank, periodic spells of prolonged cloudiness or multiple guests taking showers at the same time have depleted the hot water supply on rare occasions. A small percentage of our water heating has thus continued to require fuel oil. Nevertheless, we’ve saved an average of about $875 a year on water heating, and the net cost for the whole setup, after a rebate from Efficiency Maine — the state agency in charge of energy-efficiency and renewable energy programs — was $8,395, for a payoff period of about 10 years. We’re now only about two years away from recouping that investment.

Limiting Leaks: Our Home Energy Audit

About the same time we were getting our feet wet with solar water heating, we arranged to have an energy audit of our then-35-year-old house. We wanted to identify where it was losing the most heat in winter, as understanding how we could conserve energy seemed wise before we dived into generating our own. A licensed energy auditor performed the service for about $300. We discovered our home was letting out a lot of heat, primarily through the main-floor ceiling and around the top of the foundation.

With the audit results in, the sealing and insulating commenced. Lee and I don’t use our attic, so, in 2008, we added about 2 feet of additional blown fiberglass insulation over the attic floor. (Before, we had just the standard 6 inches of fiberglass batt insulation atop the floor.) This increased the main-floor ceiling’s R-value from about 20 to 60, and we immediately felt the difference. In 2010, we added 3 inches of foam insulation along the underside of the basement ceiling and down the insides of the concrete foundation to 2 to 3 feet below the exterior soil surface. Both the basement and the main floor became noticeably warmer in winter. The cost of all of this work (not including the energy audit) after Efficiency Maine rebates was $2,407. Calculating the payback period for these projects is a bit tricky, because, in the midst of them, we switched to geothermal home heat, and we later began generating our own electricity, but our average monthly heating bill dropped about $70 that first winter after both projects had been completed.

Installing a Geothermal System

In 2009, we did away with most of our remaining fuel oil use by installing a geothermal heating and cooling system. We were drawn to geothermal because, for an existing home, there’s a limited number of ways to get heat that don’t involve fossil fuels, and for us, geothermal was the least expensive and most efficient of those options. Our geothermal system — designed and installed by Elco Electric of Bangor, Maine — consists of a 6-ton-capacity ClimateMaster heat pump in our basement, and a horizontally configured heat-exchange pipe beneath the ground. About 6,000 feet of polyethylene pipe, coiled like a stretched slinky into three 200-foot-long, 6-foot-deep trenches, extends under the hayfield in front of our house.

Two small electric pumps in the basement circulate an antifreeze solution throughout the underground pipe system and to the heat pump. In the heat pump, heat gets extracted from the solution to warm the house in winter, and heat from the house is added to the solution to cool our living quarters in summer. By pumping the solution through the buried pipe, this heat is transferred from or to the ground based on the season. From the heat pump, the heat gets transferred to or from a forced-air ventilation system, heating the house in winter and cooling it in summer. The heating phase pulls the heat stored in the ground during the warm span of the year, so, fundamentally, this is a solar system, and it has furnished all of our heating and cooling since installation.

After installing the heat pump for our geothermal system, we connected it to our hot water system to use waste heat from the pump’s operation to supplement water heating. Since our geothermal system went into operation in August 2009, we’ve used only about 50 gallons of fuel oil per year for backup water heating during cloudy periods, and for when we have a bevy of visitors. The net cost for the geothermal system after an Efficiency Maine rebate and a federal tax credit was $25,495. We’ve saved $2,800 annually on fuel for heating the house and our water (not factoring in the extra electricity cost to run the heat pump, which we eliminated in 2012 when we started producing our own electricity), so the payback period will be just a little more than nine years.

A horizontal layout of heat-exchange pipe like ours isn’t for everyone interested in geothermal. We have enough land with deep enough soil by our house to accommodate the system. Homeowners with less land or with soil that’s too shallow can instead drill deep wells to house the heat-exchange pipe.

In the years since we installed our geothermal heat pump, ductless mini-split heat pumps have become available for supplemental heating and cooling. With these air-based pumps, the heat exchanger is typically mounted outdoors on the residence and is ducted to an interior, wall-mounted unit. Such systems are designed to heat smaller spaces than our full house — they’re effective for heating spaces similar to those that would be heated by a wall-mounted propane heater, with the added bonus of being able to cool the air during summer. They are electrically powered, and more energy-efficient and cheaper to run than propane heaters, yet they’re not as efficient as geothermal systems in cold, lingering winters like Maine’s.

Greener Electricity

Although our geothermal system put an end to almost all of our fuel oil purchases, it increased our electricity usage by about $1,000 per year, and most of that electricity from the power company was being produced with fossil fuels. In the summer of 2012, we took another leap by putting in solar photovoltaic (PV) panels to produce our own electricity. We installed a 9.36-kilowatt (kw) array made up of 39 PV panels from Canadian Solar. Based on our history of electricity use and taking into account our area’s sunshine-to-cloudiness ratio, we calculated that this 9.36-kw array would be sufficient to supply all of our household needs, including powering the heat pump and charging an all-electric car for 7,000 miles of local travel per year.

As the south-facing side of our roof was inadequate for an array of this size and was already partially occupied by our solar hot water collectors, we opted to place a free-standing PV array in the hay-field in front of our house. The entire cost of this installation was $28,790 after an Efficiency Maine rebate and a federal tax credit. In the first two years with the array, we saved an average of $2,400 per year in electricity purchases. At that rate, earning back the installation cost will take us 12 years from September 2012. If the power company’s rates go up, the payback period will be shorter.

How Our Solar Electricity Setup Works

Producing solar electricity is complicated by the fact that the sun doesn’t always make an appearance. One way to address this potential pitfall is to install a bank of large storage batteries. They charge when the sun is shining, and you can then draw electricity from them whenever skies are gray. These batteries are expensive, but this is the only option for homes in remote locations off the electrical grid. In contrast, our solar array is “grid-tied,” meaning it’s connected to the power line by our house, and we co-generate electricity with the power company. We meter our solar electricity output to the grid, and separately meter the electricity we draw from the grid at our house. When we contribute more kilowatt-hours (kwh) than we consume, as is the case from about April to October, the power company credits us for the excess kwh. When we use more than we produce, which happens from November through March, we use up our earned credits.

Our goal was to make our free-standing solar array just large enough that, over the course of a year, we wouldn’t have to buy electricity from the power company. We estimate that, with the electric car, we’ll use about 11,000 kwh of electricity per year. In its first two years of operation, the array delivered approximately 12,000 kwh of electricity per year. With the recent addition of an electric car, we’ll need another year of experience to see how close we’ve come to meeting our goal of purchasing zero electricity.

A Look Back — And Forward

Rebates from Efficiency Maine and residential energy tax credits from the federal government substantially reduced costs as we tackled all of these home energy retrofits. In the years since we began installing our energy systems, some of the prices have come down, and low-interest financing is now available for some of them, making a foray into renewables possible for younger homeowners and others who may lack financial resources we had.

I must admit that our transition away from fossil fuels isn’t complete. Much of what we buy — including a great deal of our food and even the energy-saving equipment we’ve installed in our home — is produced and shipped using fossil fuel energy. We can and will take further steps to wean ourselves off fossil fuels, but life altogether independent of them may not be possible in our economy without full withdrawal from it and a return to the kind of lifestyle that existed before the Industrial Revolution. Lee and I are incredibly pleased, though, with what we’ve accomplished. Reducing our carbon footprint has been a major emotional boost for us. We value knowing that our home is powered by solar energy that we, ourselves, collect, and that the good Earth shares its heat in winter and accepts our heat in summer by way of our geothermal system. Many people in our community have visited our home to check out our systems and ask us questions as they get started taking steps to cut their own carbon footprints. It’s immensely gratifying to be that example for others.

A Transportation Transition, Too

Our shift away from fossil fuels wouldn’t have been complete without addressing our vehicle use. Public transportation isn’t a viable option for us here at our rural location, and with our volunteer work and involvement in different community projects, Lee and I want the freedom and convenience of having separate cars.

In 2010, we owned a 1987 and a 2002 Toyota Corolla, both getting about 30 to 35 miles per gallon. That year, we replaced the 1987 car with a new Toyota Prius. With this hybrid car, we’ve achieved about 49 mpg in winter and about 52 mpg in summer. As with any vehicle powered entirely or in part by gasoline, mpg depends on many factors, including driving style. It takes practice, but we’ve found that slow acceleration, coasting to stops and timing traffic lights to avoid full stops (when traffic allows), and consistently staying within speed limits considerably ups gas mileage.

Since buying the Prius, we’ve purchased about 850 fewer gallons of gasoline than we would have needed to get around in the old Corolla, saving about $3,000 (at 2013 gasoline prices) and emitting much less carbon dioxide and other pollutants into the atmosphere. We predict that by the end of 2015, we will have recouped the price difference of a new Prius over a new Corolla by our reduction in gasoline purchases, even with the recent drop in gasoline prices.

In 2013, we were still burning about 300 gallons of gasoline annually between our two cars, and by that November, we were ready to replace our remaining Corolla. We sold it, purchased a new, all-electric Nissan Leaf, and installed a 240-volt charging station for the Leaf in our garage.

This car is a terrific fit for us because most of our local trips for shopping and other activities are within 10 miles (one way) of home. We now plan our excursions to minimize use of the Prius for local travel, and we’ve been able to use the Leaf for more than 90 percent of these short trips. The Leaf’s average year-round range in our climate, between charges, is about 85 miles, and about 20 percent more in summer than in winter. Apart from that slight limitation, it’s a silent joy to use. It’s much simpler and cheaper to run than a gasoline-powered vehicle, as it has no exhaust system, no gas tank or tank fill-ups, and no engine oil to change or cooling water to monitor, and it’s easy to plug in for battery charges. A full charge at our home station takes two to three hours, which we typically do overnight. At a quick-charge station, replenishing the battery takes only about a half-hour. The availability of a second family car that can run on gasoline for the occasional longer outing imparts additional practicality to all-electric car ownership. We still rely on our Prius hybrid for such trips.

Since we purchased the Nissan Leaf in November 2013, we’ve bought only about 125 gallons of fuel for the Prius to cover trips to Massachusetts and the occasional simultaneous use of our two cars. The cost of the new Nissan Leaf plus charging station, after subtracting the sale proceeds of the old Corolla and receipt of a federal tax credit, was $25,804, or about the same cost of a new Prius. The zero-emission Leaf is far superior economically, however, because it’s much less costly to run per mile.

Our Vehicles’ Fuel Cost Per 1,000 Miles:

Nissan Leaf (electric): $1.50
Toyota Prius (hybrid): $58
Toyota Corolla: $94