Using Solar Electric to Reduce Use of Fossil Fuel: A Case Study

The following article written by Sam and Margaret Fogel is a sequel to a post in Green Newton’s newsletter and on our web page written by Ken Mallory. Sam and Margaret Fogel of Halcyon Road in Newton are applying scientific standards to reduce their family’s carbon footprint. The Fogels’ professional careers included consulting on biological degradation of toxic chemicals in soil and groundwater. Now in retirement, they have turned their talents to front and backyard farming, solar arrays, heat exchangers, and improved insulation to reduce use of fossil fuels.

In the fall of 2014, we completed the installation of solar panels on our roof, and started on our home sustainability project. Our goal was to use the electricity generated by our solar panels to reduce our use of fossil fuel. We planned to use solar electric instead of utility electric (which is produced by burning coal and/or natural gas), substitute solar electric for natural gas use in our space heating and domestic hot water systems, and use solar electric instead of gasoline in a plug-in hybrid car.

By the end of two years of gradually introducing these changes, we had reduced our consumption of natural gas by 68%, preventing 8,300 lb. of CO2 from entering the atmosphere, and after 4 months of driving the electric car, we saved 40 gal of gasoline, preventing release of another 770 lb. of CO2.

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Details and costs are discussed below:

Sizing the Solar System

We knew that it is much easier to build a new house that is well insulated, tightly sealed, with triple-glazed windows, and that can be completely self-sufficient using only a few solar panels. But, like many homes in Newton, our house was 88 years old, drafty, with insufficient insulation, and old-fashioned windows. What could we accomplish with the upgrades recommended by our Home Energy Assessment? We estimated that to operate electric heat pumps instead of our furnace, electric hot water, and a plug-in car, would require about 10,000 kWh of solar electricity per year.

Solar Panel System Design

We purchased 26 SunPower (3.5 ft x 5 ft), solar panels, which had the highest efficiency available in 2014, 20.1% (other manufacturers offered 16% to 18 % efficiency). Twenty-six panels would produce 7.5 kW AC (alternating current) under optimal conditions. For our system, factors for shade and panel angle reduced this value to 6.9 kW. The predicted annual production, 365 days at 3.9 hr sun/day for New England, is 9,530 kWh AC/yr. Because our house has a trapezoid-shaped hip roof, which could hold only 11 panels, we planned 9 panels on an awning build to shade the first-floor south-facing windows, and put 6 panels on the East roof. We are taking advantage of Net Metering, which allows us to produce more electricity than we need during the day (excess flows into the utility grid and the meter runs backward), and draw the electricity back during the evening (the meter runs forward). This system avoids the need for a battery system to store electricity.

Cost of Solar Panel System

The initial cost ($41,560) for panels, inverters, and installation seemed very high, but we soon discovered that Federal and MA incentives would reduce the cost to $26,500 within the first year (MA Incentive $2,250, MA Tax Credit $1,000, and Federal Tax Credit $11,790). Then during the next 10 years, we would earn Federal Solar Renewable Energy Certificates (S-RECs), for every 1,000 kWh of electricity actually produced. We are earning 9.5 SRECs per year, each worth about $240, which gives us $2,280 cash/year. In addition, we will be saving the amount that we previously had been paying for utility electricity, about $700/year. At this rate, we calculate that in less than 9 years we will achieve total payback, after which we will still have another year of SRECs. The financial savings on our electric bill will continue indefinitely!

Energy Efficiency Upgrades to Our Home Through Mass Save

Our Energy Audit showed that the major readily-correctable losses of heat in our house were warm air leaks in the 2nd floor ceiling, including a large leak around an improperly-installed bathroom vent, old insufficient attic insulation (5” between the joists in the attic floor) and cold air entering the first floor via an un-insulated plumbing chase in an outer wall. (old blown-in cellulose in our walls was to remain) In order to qualify for the Mass Save rebates on new attic insulation and attic sealing, the old attic floor and old insulation had to be removed. Together with a new smaller attic floor and other sealing and repairs, our cost was $8,000. Mass Save paid $1,000 for the sealing of the attic air leaks, addition of 12” of new attic insulation, and an insulated attic stair cover. As a result of these changes, when winter arrived, we definitely noted a cozier feeling on the second floor.

Up-Grades to Heating and Cooling Systems, Domestic Hot Water, and Other Appliances

We purchased an air-source Heat Pump System from Fujitsu, consisting of two outdoor compressors (18,000 and 24,000 btu/hr) located outdoors, which are 37” x 27” x 15” deep. In winter, these use electricity to move heat from outdoor air to a recirculating refrigerant, which is pumped through a 1” diameter pipe to five wall-mounted indoor units (32” x 10” x 8”deep), where the heat is released into room air. In summer, the process is reversed, removing heat from indoor air, and transferring it via the refrigerant to outdoor air. In cooling mode, our compressors have an Energy Efficiency Ratio of 18 btu/watt, whereas in heating mode, the ratio is only 9.4 btu/watt, meaning that it takes more energy to use the system for heating than for cooling. The cost was $15,340 including a $150 rebate from NStar.

Our existing natural gas heating system was retained for backup in cold weather. Our Energy Audit showed that our 28-year-old gas boiler was operating at 78% efficiency, so we could we could reduce our use of natural gas by getting a new 95% efficient “condensing” gas boiler for $11,600 including installation, and have applied for a $1,600 Mass Save rebate (If your old boiler is 30 years old, the rebate is around $3,000.) Our gas water heater was nearly out of warranty, so to further reduce gas use, and use our solar electricity; we recently purchased a new electric water heater. Finally, we got a front-loading clothing washer with fast spin, put up a clothesline, and stopped using our gas dryer.

Reduction in Fossil Fuel Use to Date

Many of our energy efficiency improvements were made during the heating season 2014-2015. To see what we accomplished, we compare results for the heating season (Sept 1 to May 31) of 2015-2016 with the year before changes were made. In 2013-2014 we used 1,050 Therms of natural gas, whereas during the heating season of 2015-2016 we used only 290 Therms of natural gas.

The recent winter was much milder than the 2013-14 winter. Using data from NOAA for “heating degree days” we estimated that if this winter had been as cold as that of two years ago, we would have used about 340 Therms of natural gas, a reduction of 710 Therms, amounting to a reduction of 68% in our use of fossil fuel. Since burning one therm of natural gas results in the release of 11.7 pounds of CO2, we reduced our production of heat-trapping gas by 8,300 pounds of CO2 ! As for the plug-in car (Ford C Max Energi), in four months we have driven 1,430 miles on solar electricity, saving 40 gallons of gasoline. Since burning one gallon of gasoline releases 19.3 lb of CO2, we reduced our CO2 production by another 770 lb of CO2. For the future, we are still working on air sealing and other insulation, so we are hoping to further reduce our use of fossil fuel.

By Sam & Margaret Fogel