Cities need to accelerate the uptake of renewables and sustainable transport to meet their rising energy needs, maintain a healthy living and avoid climate change. The combination of PV and e-vehicles (EV) is the most effective tool for this transition
However, cities are densely populated, and available solar energy collecting surface per capita is small. For example, the 2018 November issue of the reference magazine of the PV Industry, Photon International, presents an analysis of a broad set of world cities in all continents, confirming that in all cases, practical rooftop surface for PV installations cannot cover their present electricity demand, which on the other hand is set to increase in the coming years with the foreseen transition to electric mobility and heating.
Solar is a ubiquitous but relatively low-density energy source; therefore, tapping it in per capita surface-scarce locations such as cities requires the highest possible photovoltaic conversion efficiency. High Concentration Photovoltaics (HCPV) is presently the source of solar electricity with the highest conversion efficiency, which already doubles conventional silicon-based photovoltaics and increases its efficiency by 1% annually (check the purple line at NREL's table of best cell efficiencies). However, HCPV developments have usually targeted the market of large-scale solar plants, and only seldom that of urban PV applications
The design was initially shaped by the rising new product trend of the so-called Solar Trees. Essentially a solar tree is a structure incorporating solar energy technology on a single pillar, like a tree trunk. The primary advantage of this format is the low surface footprint: only the trunk's section, with the solar generator being displayed overhead, not interfering with pedestrians or vehicle traffic underneath. Furthermore, when based on conventional silicon photovoltaics, solar trees complement rooftop installations and build awareness and interest in solar technology and provide shade and meeting places.
In the PowerTree, the tree-like form is obviously embodied by the accuracy sun tracker required by HCPV - a two-axis azimuth elevation pedestal type - that combined with the higher energy surface density of the modules, boosts energy production. Additionally, this tree-like sun tracker is designed to integrate additional features of interest in urban environments, especially in public areas, such as a pollution air cleaning system based on greenery panels embedded in the tracker's pedestal or an efficient lighting system integrated into the rear face of the HCPV collecting surface. Optionally some greenery modules can be replaced by a TFT screen that can be programmed to display commercial ads or public information
About the HCPV System
The HCPV subsystem consists of 9 BSQ-D280 HCPV modules. In their current version, these use GaInP/GaInAs/Ge 3 junction cells and BSQ's proprietary design of domed Fresnel lens with an 820X concentration factor. The HCPV module has a 280W/m2 output at Standard Test Conditions (1000W/m2, 25C cell temperature). BSQ's auto-calibrated sun tracking controller manages the sun tracking system to deliver sub-degree tracking accuracies with tracking errors below 0.1° 97% of the time. The system is certified according to all relevant quality standards in HCPV technology. Compared to a conventional silicon PV rooftop installation with the same active surface of 9m2, assuming a standard roof tilt, the PowerTree can render up to 3X more yearly electrical energy compared to an East or West facing roof and up to 2.6X more energy than a South facing roof.
About the Modules for Air Cleaning System
The MUAC (Modules for Urban Air Cleaning) is a high-efficiency air purification system that merges technology and vegetation to capture, absorb and purify air pollution in cities. The biofilters used to clean the air are composed of plants, roots, and microorganisms within the substrate, which serve as carbon sinks (they can absorb pollutants such as PM2.5/10, NOx, SOx, COx, etc.)
This Nature-Based Solution (NBS) reproduces the natural air-purification process that occurs within the ground of the forests, and it is thanks to this feature that MUAC systems can create small micro-climatic "oases" by improving climatic conditions around them by lowering temperatures and increasing the relative humidity.
PowerTree integrates into its "trunk" a 6m2 MUAC system where the plants are selected native species in the installation location.
About the Lighting System
In the PowerTree's collecting surface, the HCPV modules are surrounded by the lighting panels, which in the current design version contain three LED lights each. 8 x 8W LED lights which would be equivalent to 320W halogen bulbs. They are dimmable lights so that their intensity can be programmed to follow the readings in its also integrated ambient light sensor. These modules have a curved contour so that the collecting surface can have an organic-inspired shape breaking with the dull rectangular display of conventional solar arrays. The HCPV tracker stows the collecting surface horizontally at dusk to present the least wind profile and reduce fatigue and clutter in the tracking drive. In this horizontal position, the LED lights will be switched on and cast their light beneath the PowerTree with a maximum 300 lx luminous power at its base.
About the Visual Information System
The PowerTree, as an option, can also be used as an advertisement totem by repacing some vegetation panels in the “trunk” by a TFT screen. The TFT screen size can be made to measure upon customer requirements. It is powered by an embedded computer and web server so that the customer can cycle any videos or display any website through a remote control access. The screen and the lighting systems combined, create an alluring ambient around the PowerTree.
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