Solar Treeis an environmental enterprise, an ecological sculpture, an artificial solar structure that looks like sculptural trees and exists from small scale (size of a bonsai tree) to large scale (about the size of a wind turbine) power plant. It is an independent unit that produces green energy and provides a place of comfort and energy for a wide variety of services. The structure is ground mounted solar system with a pole that supports many individual panels up in the air. The aesthetics of solar trees differ and they have been designed to provide different means of power to different urban and built environments.
It can be placed in residential areas and in urban areas, courtyards, schools and universities, parks and along hiking trails. It can also be placed in cultural institutions as an icon and a symbol of community, environment and green education.
Solar tree has unique properties in terms of height and multi - angle orientation parameters. By employing the height parameter, solar tree requires less space consumption which can reduce the installation cost. Compared to the traditional solar farm which is oriented in a single direction, the multi-angle orientation parameter from the solar tree panels yields the potential capability to absorb higher sunlight intensity leading to higher output energy. At the same time, this parameter eliminates the necessity to install solar tracker which can reduce the operational cost. To increase the collection Generation of 1MW power from PV module system requires the land of 5-6 Acres approximately for housing the panels only. A tall pole-like structure would take only 1% of land area in comparison to general PV housing. In India there is scarcity of land in urban and even in rural areas. .
It can also be locked at any position to withstand the wind pressure due to heavy storm affecting over the main pole/ trunk. The panels will be naturally facing towards the sun at an angle as required so that they can collect maximum solar energy in a daytime. To get the maximum sun in a day time the top panel should not obstruct the bottom panels.
Solar tree can be designed both for standalone and in synchronization with the power grid. It uses the generated energy form the solar panels and store the energy to the battery by a DC Charge controller. The controller may MPPT or PWM type. During the daytime when the sunlight is sufficient to meet the loads, the generated solar energy directly feed to the loads. Any excess solar energy after meeting the loads should be stored in the battery. The stored energy into the battery can be utilized when the generation from the PV is not sufficient. The inverter has proposed here to convert DC power to AC as most of the common appliances are AC and also facilitate to charge the Mobile, laptops under the shade of the solar tree.
The Solar tree used for lighting purpose is a sensor based lighting system. The automatic control and monitoring unit monitor the Solar panel output and at dusk, the solar tree switches on LED automatically. A sensor measure the amount of light at atmosphere and triggers the switch on automatically at sunset and off at dawn.
The Solar Tree consists mainly of the following components:
Solar Tree provides green energy and a place of comfort in diverse settings and according to different requirements.
By conducting surveys and exhibitions of different models of Solar Trees presented by many researchers can make a good platform for the progress of this technology.
The solar tree - the new symbol of Gleisdorf – was built in 1998 with a capacity of 7 kWp and was connected to the public electricity grid. It stands in the ”solar street” which is a 3.5 km long street section, where about 80 objects are powered by photovoltaics, such as a public solar clock, advertising boards and street lights. Solar cells have also been used for art and the solar tree is one of these examples. It is 17.3 meters high and consists of a 12700 kilogram solid steel sculpture in the form of a tree with five branches holding 140 solar panels. The tree generates approximately 6650 kWh of electricity annually which can supply about 70 city streetlights in the centre of Gleisdorf.
Fig 1‑1: solar tree - the new symbol of Gleisdorf
Ross Lovegrove, a Welsh industrial designer known for his organic designs and designs, conceived an organic-looking solar structure with multiple curve stems and circular collections of photovoltaic cells.It was first manufactured byArtemide, a manufacturer of differentiated design products, based in Milan, Italy.
Ross Lovegrove’s original design consists of a sinuous tree constructed of steel pipes, measuring 5 meters, supporting a light bubble in which 38 solar cells, each with 38 watts of power, connected to a hidden 12V battery system which includes 1W LEDs at the tip.The solar cells for the project were commissioned bySharp Solar.
Fig 1‑2: Ross Lovegrove’s Solar Tree
In 2011,Spotlight Solarintroduced a line of architectural products which customers refer to as solar trees. They offer four different model of solar tree: Lift, Curve, Trestle and Industry.
Fig 1‑3: Spotlight Solar Structure
In 2016, CSIR-Central Mechanical Engineering Research Institute, Durgapur, India invented another model of solar power for its application at villages, besides national highway and power grid system to meet the electricity crisis.The developed structure is capable of generating the electricity in a 3-7 Kwh with a bare footprint of 2×2 sqft area.These solar trees are already installed and operating at the developer’s campus, CSIR’s Headquarter and at the residential campus of the Minister of Science and Technology of Indiato demonstrate the success of the technology.Researchers at
Fig 1‑4: CSIR Solar Structure
CSIR-CMERI are also working on the need for public parks, gardens, market places, etc. The tree is installed with a built-in battery backup system so it can continue providing energy for up to two hours after the sun goes down, and is outfitted with a water sprinkler at the top for self-cleaning the panels. The solar tree’s compact package makes it an appealing option for urban areas and rural regions with limited free space. It’s already completed successful trial runs in three locations in West Bengal, India, as a pilot project. It could be a boon to a country where roughly 300 million people don’t have access to electricity!
The Solar PV modules which have been supplied are minimum declared output of 100Wp at STC. The modules are IEC 61215 and IEC 61730 certified. The tilt angle and the azimuth of the module for this location are different and it is distributed throughout 360º angle.
Modules are made of crystalline silicon Solar cells. The SPV Modules has been tested & certified by an independent international testing laboratory.
The module frames should be made of corrosion resistant material, which shall be electrically compatible with the structural material used for mounting the modules.
The modules have been provided with a junction box with provision of external screw terminal connection and with arrangement for provision of by-pass diode. The box should have weather proof lid with captive screws and cable gland entry points.
The module mounting structure designed for this project is very innovative and challenging as the load bearing capacity should be calculated accurately for preventing any future difficulties. The main challenge of designing the structure is the stability maintaining the aesthetic view.
The mounting structure is designed for holding 10 to 15 numbers of modules of 100 Wp. The weight of the module is approximately 8kg/Module. The frames assembly of the array structures should be made of 80 micron Galvanized Iron.
Most photovoltaic modules are designed to last 20 years or longer. It is important that the other components in the system, including mechanical components, have lifetime equivalent to those for the PV modules. It is also important that the mechanical design requirements of the system be consistent with the performance requirements as well as with the operational requirements of the system. The mechanical design of photovoltaic systems cuts across a variety of disciplines, most notably civil and mechanical engineering and, to a lesser extent, material science, aeronautical engineering and architecture. More specifically, our mechanical design involves:
The mechanical system which we are providing can affect the array performance in several ways:
This is the heart of the system. The inverter converts the DC power to AC power to facilitate feeding into the grid. In addition it performs many other functions such as synchronization with grid.
Inverter should be having efficiency levels of 98% and above. Each inverter shall be with minimum capacity of 1-2 kVA depending on the design. The output power factor of the inverter should be of suitable range to supply or sink reactive power. The inverter shall have internal protection arrangement against any sustained fault in feeder line and lightning in feeder circuit. The inverter should be single phase static solid state type power conditioning unit. Both AC & DC lines shall have suitable fuses and contactors to allow safe start up and shut down of the system. Fuses used in the DC circuit should be DC rated. The inverter shall have provision for input & output isolation.
Inverter shall have arrangement for adjusting DC input current and should trip against sustainable fault downstream and shall not start until the fault is rectified.
Inverter front panel shall be provided with display (LCD or equivalent) to monitor the following:
Provision should be available in the inverter for Remote Monitoring of all the parameters mentioned under paragraph above and other important data.
The selection of inverter for a solar PV plant is important and project specific. The yearly power output largely depends on the selection of specific inverter. As our application a standalone inverter has preferred. The inverter for this project has been selected based on the following features:
Computer Aided Data Acquisition Unit shall have features for simultaneous monitoring and recording of various parameters of different sub-systems, power supply of the Power Plant at the DC side and AC side. The unit shall be a separate & individual system comprising of different transducers to read the different variable parameters, A/D converter, Multiplexer, De-multiplexer, Interfacing Hardware & Software. Reliable sensors for Solar Radiation, Temperature and other Electrical Parameters are to be supplied with the data logger unit.
The data acquisition system shall perform the following operations, which include the measurement and continuous recording of:
All data shall be recorded chronologically date wise. The data file should be MS Excel compatible. The data logger shall have internal reliable battery backup to record all sorts of data simultaneously round the clock. All data shall be stored in a common work sheet chronologically. Representation of monitored data in graphics mode or in tabulation form will be displayed on the computer screen or can be printed out. All instantaneous data can be shown in the Computer Screen Provision should be available for Remote Monitoring through GPRS system.
Cables used in DC side shall have the following characteristics:
Figure: Typical photographs of DC cable
The Solar tree should be provided with Lightning protection. The Lightning Conductors are made as per applicable Indian Standards in order to protect the entire Array Yard from Lightning stroke. Necessary concrete foundation for holding the lightning conductor in position will be made after giving due consideration to maximum wind speed and maintenance requirement at site in future. Each Lightning Conductor shall be fitted with individual earth pit as per required Standards including accessories, and providing masonry enclosure with cast iron cover plate having locking arrangement, watering pipe using charcoal or coke and salt as per required provisions of IS.
The earthing for solar array & structure shall be as required as per provisions of IS 3043:1987. Necessary provision shall be made for bolted isolating joints of each earthing pit for periodic checking of earth resistance. The complete earthing system shall be mechanically and electrically connected to provide independent return to earth. All non-current carrying metal parts shall be earthed with two separate and distinct earth continuity conductors to an efficient earth electrode.