Erb

Project Profile

2017

Solar Electric

It was about this time last year that a major milestone in energy occurred: “For the first time since 1979, America’s cars, trucks, and airplanes emit more carbon dioxide than its power plants do” states an article titled Power plants are no longer America’s biggest climate problem. Transportation is. While there are many reasons for this, including the displacement of coal by natural gas in many power plants, it is clear that we need to address the transportation sector. This is exactly what Dave Erb has been working on in his 36 year career in automotive engineering, specializing in energy and emissions, with a focus on electric and hybrid electric vehicles.

Over three decades of data analysis have made it obvious to Dave (in his words)  that the only way to sustain the access and mobility we enjoy as North Americans is to:  1) reduce our demand for motorized travel, 2) do a better job of matching our vehicles to their loads, 3) electrify vehicle powertrains to the maximum reasonable extent and 4) capture the necessary energy renewably.  After 20 years work and planning, Dave, along with his wife Beth, are living a lifestyle that models these four steps. When they brought their house in North Asheville in 2008 they intentionally chose a walkable neighborhood close to UNC Asheville where Dave teaches Mechatronics Engineering, they purchased a used 2015 Nissan LEAF  (used for about  three fourths of their  driving) and they installed a solar electric system in 2015 that not only provides power for their home but charges up their LEAF as well.

As part of their staging to achieve net-zero energy for their home and, ultimately, most of their driving, the Erbs improved the efficiency of their home and installed a ground source heat pump and heat pump domestic water heater, making all the energy demands electric so that they could be met through photovoltaics. The home was chosen for its solar exposure, but they replaced the roof with a light colored, standing seam metal roof in anticipation of a solar install and for efficiency. Based on their electrical usage (before purchasing the LEAF) Sundance designed a 6 kilowatt system based on their goal of making the home net-zero. The array consists of 21 flush- mounted Solarworld Sunmodule Plus 285 Mono modules, with S-clips attaching to the standing seams. Three rows straddle a dormer on the  south-facing roof (which is the back of the house, and not as visible as Dave would like!) and a single row  is mounted on the east-facing slope of the dormer roof. Solar Edge’s  DC Optimization was chosen for additional efficiency, output, and monitoring.

Indeed, Dave reports that their system has been generating far more than they anticipated. The PVWatts calculator projected that the 6 kW system would generate about 7400 kWh per year.  In 2016, Dave reported that they actually generated over 9400 kWh and is eager to see how this varies as the weather fluctuates from year to year. He said their  original plan was to install the PV system, then buy an EV and live with it for a few years, then add enough PV to ensure net zero in all but the most extreme years.”It’s been a pleasant surprise to find that our calculations were overly conservative, and that we won’t need to add to the system.” Essentially, they are able to drive on sunshine with the system they have.

“Annually, we’ve gone from paying Duke Energy roughly $900 to buy about 7500 kWh, to paying them about $160 and giving them well over 1000 kWh (which they sell to our neighbors for 10 cents per kWh).  Our electric bills are now $13.19 a month, and include only the fee for using the wires, tax, and (ironically) the Renewable Energy Portfolio Standard (REPS) charge,” Dave said. (They have a net-metering interconnection agreement with Duke.)  While these savings are satisfying for the Erbs, it is their ability to live a more sustainable lifestyle that is gratifying, as they tell. Beth, a retired social worker, has many dear friends in eastern Kentucky whose families have been hit hard by black lung and other coalfield maladies. Dave has seen mountains where he learned to hunt and hike blown up for coal, and bulldozed into streams where he learned to fish. “Sustainability, especially energy sustainability, is the only rational way for those of us who care about a healthy, peaceful future to organize our lives,” Dave said.

As far as driving a solar-powered electric vehicle after all these years, this is what he has to say: “The LEAF’s performance has also been a pleasant surprise.  Even though we have the small battery (24 kWh), short range (84 miles EPA rating) version of the car, it easily handles about 75 percent of our driving, roughly 6000 miles per year.  The EPA rates the LEAF’s energy intensity at 290 watt-hours per mile, which would display on the car’s dashboard as 3.5 miles per kWh.  In fact, though, we’ve never seen worse than 250 Wh/mi (4.0 mi/kWh), and summer driving was closer to 200 Wh/mi (5.0 mi/kWh).  With our PV system generating about 1500 kWh/year for each installed kW, 6000 miles of annual driving is being “fueled” by less than four of our 21 panels.  Even with very conservative assumptions, using our PV system to power our Leaf is equivalent to locking in a 30 year supply of gas for a Prius (50 mpg) at well under $1.00 per gallon.  Compared to a 25 mpg Camry, it’s well under 50 cents per gallon.”  Dave would be happy to help anyone make their own calculations; his contact info can be found at engineering.unca.edu.

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