Solar for parking machines

Researchers from New Zealand’s Southern Institute of Technology, the Auckland University of Technology, and the University of Auckland have proposed a methodology to evaluate the potential of solar-powered parking machines in urban environments.
The scientists said that on-site solar power generation is key to the viability of a new generation of sophisticated parking machines that need much more power than conventional devices, with demand estimated between 500 W and 1 kW. “Large amounts of yearly revenue are consumed in powering the machines, raising questions about their feasibility in places where the parking occupancy rate is low,” they said.
Small solar panels on top of machines are a good way to save energy costs, but the group warned developers to consider partial shading at different times of the day and year in order to implement economically feasible projects. If PV power must play a role, the location of the machines must be planned in advance, in line with available solar radiation resources and all possible surrounding shading factors.
The academics analyzed the solar resource of 15 parking machines installed in the central business district of Auckland. “A high-definition 360-degree camera was used to capture fisheye images (256 by 256 pixels) from the top of the solar panel of each parking machine,” they said. They used a magnetic compass to ensure that the camera’s reference point was always in line with true north.
The sky-view factor (SVF) was measured for each of the 15 devices. They found that the less obstructed machines had an SVF of 72% and 62%.
“The sky view from all the other parking machines was found to be obstructed by 50% or more,” they said. “In other words, these machines would not be able to receive more than 50% of the diffuse solar radiation, at any time during the year.”
The results for direct beam solar irradiance were even more disappointing. Only two machines received a yearly obstruction time fraction of more than 50%.
After evaluating diffuse and direct radiation, the researchers calculated the total irradiation received by each machine over the year. “Once again, only two machines crossed thethreshold of 2880 MJ/m2, which represents the criterion for installing solar panels considering both the technical and economic limitations,” they said.
The researchers presented their findings in “Solar resource assessment of modern parking machines in an urban environment,” which was recently published in Renewable Energy.