In anticipation of an electric vehicle purchase, this PV charging station was constructed in 2009. Due to a lag in availability, the all-electric Mitsubishi i-MiEV arrived in 2012.
The home was already equipped with a 2.88 kW batteryless grid-tied system on its detached garage, which offset more than 100% of the household’s annual electricity use. However, with increased usage anticipated for charging an electric vehicle, a suitable location was needed for an additional array.
The carport was designed to provide covered parking and the EV charging station. Because the carport is visible from the street, its appearance was a priority. Custom-designed and engineered, the structure was built with hand-notched beetle-kill Colorado pine from a local family’s forestry operation. The cobblestone-style driveway was constructed with remnants from the slab driveway removed to make way for the project, as well as construction debris from a neighboring property.
Sanyo Double-HIT modules were chosen for the batteryless grid-tied array, both for their aesthetic and production benefits. The semi-transparent cells allow some light to pass through, gently illuminating the carport during the day. The underside of the modules collect reflected sunlight, boosting the array’s production by about 5%. This increased productivity would help make up for increased afternoon shading from a large conifer on the west side of the property that reduces annual production by about 9%.
The car-charging system generates about 2,750 kWh per year—providing enough energy for 11,170 miles of driving. In the past 18 months, the vehicle has logged about 16,800 miles—and the electricity it uses for recharging is well-matched with the PV system’s generation capacity.
Utilized for day-to-day business travel along Colorado’s Front Range, the electric vehicle is equipped with a 16 kWh battery. Although a full charge is rarely required, the carport’s level 2 charger (240 VAC) can provide a full charge in about five hours; a level 1 charger (120 VAC) performs this task in about 16 hours. The same port is used for either type of charge. Most EV owners have level 2 chargers at home, and some public charging stations are level 2 as well. However, with the same port, the level 1 charge can be delivered from any standard outlet, as well as some charging stations, which increases options and flexibility for the EV driver.
Vehicle range is variable, depending on seasonal temperatures and terrain traveled. A mountainous 60-mile summertime one-way trip from Golden (elevation 5,675 feet) over the Continental Divide at Berthoud Pass (elevation 11,306 feet) and into Winter Park (elevation 10,578 feet) is not unusual, but during colder months the battery’s decreased capacity makes such a trip impossible.
Experience indicates an average battery bank range of about 85 miles during warmer months to about 50 miles in the coldest months, depending upon terrain. Regenerative braking noticeably increases battery capacity—and vehicle range—in downhill driving or stop-and-go traffic, compared to highway travel. Familiarity with the vehicle’s performance in various conditions grows with time—similar in many ways to the experience of a household adjusting to an off-grid PV system. You learn to adjust energy consumption habits as energy production allows.
The household couples the EV with a biodiesel-powered Volkswagen Jetta TDI wagon for longer travel. “Most households have two cars, and it makes sense that one of the vehicles is mostly for trips closer to home,” says homeowner Bart Sheldrake. “It’s really convenient to charge our car at home, and we’re glad to know that we’re fueling our transportation with solar energy.” Since adding the electric vehicle in 2012, the household continues to accrue credit on its bidirectional meter despite recharging the car daily.