Ottobrunn, 15 September 2020. What to do if the roof is already covered with a photovoltaic system, but now an electric car is to be purchased that requires more PV power? Klaus Mayer from Erfurt faced this challenge. His installation company Solardach24 then designed a system extension for heating, electricity and electric mobility which included an additional PV system. Managing Director Robert Fichtner suggested the garage roof as the installation site. Just under 3 kilowatts (kW) of additional solar power output found room on the scarce space thanks to the high-performance HIT® modules from Panasonic. To the owner's delight the solar modules also protect the garage from heat.
Mayer has an air-source heat pump with a ventilation system installed in the 190 square meters detached house. A solar power system was the go-to solution for him. For this reason, PV modules with an output of 5.4 kW were installed on the flat roof when they moved in in 2012. He was satisfied with this for several years.
Until he decided to buy an electric car, and he wanted to drive it as climate-friendly as possible. Initially the idea was to have a photovoltaic system built over the large terrace, but the offer from a specialist supplier seemed disproportionately expensive to Mayer. He preferred Robert Fichtner's suggestion to use the garage roof. "We wanted as much power as possible in the smallest possible area," he summarizes the goal. "The solution was Panasonic Module HIT®. Heterojunction enables acceptable yields even with unfavorable alignment". Thanks to heterojunction technology, which combines crystalline and thin-film technology, the HIT® modules achieve a higher solar power yield on the same surface area than conventional crystalline modules.
Only solar power from March to October
The two solar power plants together have a combined output of just under 8.4 kW. Mayer is delighted with this. "From March to October I don't need any electricity from the energy supplier," he knows from three years of experience. This is made possible by the PV storage system, which Fichtner helped plan.
Since the photovoltaic system on the roof of the house has more power it is connected to the storage system. Because it is a DC storage system the electricity can be used directly on the direct current (DC) side. The conversion losses are lower, thus increasing efficiency.
Solardach24 installed a new inverter for the Panasonic system. If more solar power is needed in the house or for the electric car, this system supplies electricity. This means that the two solar power systems can better balance demand peaks, and on days with little sunshine, the system expansion with Panasonic modules provides approx. 40 percent more power. Excess solar energy is then fed into the grid.
With his electric car (BMW i3), Mayer drives an average of 7,000 kilometers a year. He drives around 2,000 kilometers with solar power from his own roof. He charges the rest at public charging stations.
In 2019, the two systems together generated 8,160 kWh. Of this, Mayer sold around 3,324 kWh of solar power, the rest he used himself. He had to buy about 3,867 kWh of electricity. In 2019, Mayer's own electricity share was 55 percent, and his self-sufficiency quota was 51 percent of the total energy requirements for heating, electricity, and mobility.
PV system protects garage from heat
In addition, the homeowner is pleased about a "very welcome additional effect" of the new Panasonic system. Mayer has a prefabricated concrete garage, which, like the neighboring garage, was covered with pebbles on the roof. The pebbles were removed, and the PV system was placed on the roof instead. Since they should not be visible from the street, the modules have a slope of nearly two degrees. On all sides, Fichtner left about 15cm of space to the edge of the roof so that the modules could be well ventilated. "The photovoltaic system has reduced the heat in the garage," Mayer is pleased to report. "This is a very welcome additional effect." Because unlike the pebbles that store heat, the PV system shields the roof skin from too much sun. "A nice second benefit", summarizes Mayer. He is completely satisfied with his energy concept. "I have a top situation."
Photo credit: Solardach24 / Robert Fichtner