Solar Powered Parking


Powering your car on sunshine has been a persistent dream among electric car advocates. University of California San Diego physics professor Tom Murphy does a great job explaining why designing solar panels into a car is not a great idea is his online tutorial “Do the Math – A Solar Powered Car?”  There is not enough surface area on your car, and the panels would add too much weight for the small amount of power produced. Professor Murphy also points out that putting solar panels on your residence and charging your car with the output can work out quite well. On a roof, carport or garage, you have plenty of surface area available. The panels don't have to move so the weight and the aerodynamics of the panels are not an issue. 

Solar panels over parking spaces provide several additional benefits. They provide shade and shelter for your car, which means it will be a lot more pleasant to get into after a sunny day, and require less energy to cool when you do. They also can simplify installation vs tile roofs, roofs that don't have the ideal pitch or orientation to the sun, or other engineering constraints. 

Solar parking canopies can be installed in either residential or commercial settings. We review two installations, one residential and one large scale commercial, and review the economics for each. 

PHAT Energy is a solar designer and installer based in Montrose and serving California. Philippe Hartley, founder and general manager, described the company's residential canopies while standing underneath a demonstration unit at the US Department of Energy Solar Decathalon in Irvine last October. 

The PHATport 350 is canopy made from steel beams. Philippe explained that one of the main design challenges was to make a structure that was not only sturdy and economical, but also aesthetically attractive – from both the top and bottom. The second challenge was to make a structure that would last very long time without any maintenance.  After experimenting with wood beams, the company chose steel, which does not deform over time like wood, and which can hide the wires and electronics that connect and control the panels. 

An electric car charger can be attached directly to the structure as can other accessories, such as lighting, while keeping the wires safely inside the beams. The PHATport uses translucent panels from SunPower and Sunpreme that allow light to be captured from both sides if the panel, increasing efficiency by about 15%. The carport structure can be fully erected in about 5 hours. 

Since the solar power generated reduces utility upper rate tier usage first, even a small carport can make a disproportionate reduction an a monthly utility bill. For example a system that produces about half of a residence's power can lower the monthly utility bill by 75%.

Solar panels have come down in price dramatically over the past few years, from about $12 per watt in 2000 to under $6 per watt today. The payback is now typically less than 10 years. After that point the electricity is essentially free and represents monthly income, or a return on the initial investment. 

Large commercial installations can provide even better efficiencies of scale. 

Martifer Solar USA completed a 1.142 MW solar photovoltaic installation at Occidental College in March 2013. The system output reaches the upper 900kWs during the midday peak. The solar power plant will generate over 1.7 million kWh/yr, providing about 11% of the campus’s electrical needs. The school expects to save about $250,000 per year on their utility bill. 
"The Martifer-built Occidental College solar array is one of several initiatives on campus to respond to the threat of global climate change," said Dr. Daniel Snowden-Ifft, physics professor and the driving force behind the project.

 The project combined a parking lot carport and a hillside ground-mount array. The carport portion of the system consists of 1,380 panels. The underbellies of the carport systems were retrofitted with special fire-retardant corrugated metal because of high fire danger in the foothills. It will provide shaded parking for 94 faculty and students. Level 2 (240V) electric vehicle charging stations were included as part of Occidental College's sustainability plan.
"While our chief goal has always been to reduce the College's dependence on fossil fuels, the time we spent in developing the array reflects our desire to address solar power in a new, creative way," said Occidental President Jonathan Veitch. "It represents a new paradigm for arrays as architectural objects that, like buildings, are expected to contribute aesthetically to their environment."

The entire system contains 4,996 SunPower 230W panels. Martifer used Satcon inverters with combiner boxes, DC disconnect units and switchgear. The system is monitored by an AlsoEnergy PowerTrack package. The system is interconnected to the 480V medium-voltage transformer of L.A. Department of Water and Power's grid. 
"We are very proud of this beautiful, landmark installation completed in collaboration with Occidental College," said Roland Kiser, CEO of Martifer Solar USA . "Despite the initial challenges faced on this project, we were able to provide the school with a quality, state-of-the-art system that has already proven to exceed performance expectations." 

The project cost $6.8 million, half of the which was provided by a Department of Water and Power rebate.  The lifetime environmental benefits of the system are equivalent to the offset of 60 million pounds of carbon dioxide.
One of the most eminent voices among those advocating solar powered electric transportation is former Secretary of State George Shultz. Shultz, who also served as the Secretary of Labor and Treasury Secretary (under Nixon), is a rock ribbed conservative and long time advocate of energy security and environmental responsibility. He drives a Nissan Leaf powered by solar panels on his house in the San Francisco Bay Area. Taking a stance that's unabashedly tree-hugging he's fond of saying “I'm driving on sunshine.”  With wry humor, he often follows up with a quip ringing with the call for economic and energy independence and security: “Take that Ahmadinejad”.

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