Solar Charging Station

What is Solar Power?
Solar power is a renewable energy source that harnesses the energy of incoming sunlight and converts it into usable electricity using a solar panel or photovoltaic array.

Source: https://cleantechnica.com/2014/09/04/solar-panel-cost-trends-10-charts/
Solar energy presents a near inexhaustible clean energy source for replacing an unsustainable reliance on fossil fuels. The solar panel market has in the last 15 years seen an unprecedented 29% growth (Al-Rousan, N & Ashidi Mat Isa, Nor & Mat Desa, Mohd Khairunaz. (2017). Advances in solar photovoltaic tracking systems: A review. 10.1016/j.rser.2017.09.077. ) with growing support from governments. With costs quickly falling due to increased manufacture and new research into lower cost materials and manufacturing, solar panel purchases and leases are quickly becoming a feasible way to lower electricity and heating bills in average homes.

Source: https://inhabitat.com/solar-panel-roof-tiles/
New research into increasing solar cell efficiency and the number of ways that solar cells can be integrated into modern infrastructure has led to the development of amazingly unique and varied solar technologies including bendable cells, solar windows, and solar-assisted heating systems.

Sources: https://inhabitat.com/solar-panel-roof-tiles/ | https://discovere.binghamton.edu/features/coe-5885.html | http://scientifist.com/3-in-1-renewable-energy-material/perovskite-flexible-solar-cell/

How Does it Work?
When sunlight penetrates a solar cell it causes the atoms in the semiconductor layers to release electrons which are then collected using conductive electrodes. This creates a current and usable electricity for powering of electronics and storage in battery banks. The figure below shows a schematic of a solar cell’s layered structure. Solar cells create electron flow when a photon or packet of light is incident on the panels surface.

When a photon hits the surface of a solar cell it is transmitted through the glass covering and transparent conductive top electrode. Upon entry into the P-N junction which is the interface of the P-type semiconductor and the N-type semiconductor, the photon temporarily splits hole and electron pairs and they are conducted to the electrodes. The desire of these pairs to recombine causes the electrons to flow through conductive wiring providing the current and voltage for charging of batteries or powering of electronics

The Cloudy Future of Solar
While solar power has a very promising future, low efficiency, high cost, and inability of commercial batteries to meet the needs of large-scale grid energy storage has limited its implementation into modern infrastructure.

The current record for the highest efficiency solar cell to be released commercially released is 22.5%. The low efficiency of solar cells has been an issue that has plagued the research community for years. However, incremental success in improving the efficiencies over the year with the record for a non-commercialized cell currently at 44.5%. Additionally, lowering the cost of panels could outmode the need for higher efficiencies.

Source: https://electrek.co/2018/02/17/solar-panel-efficiency-bloodsport-records-trina-sunpower-hanergy-thin-film-monoperc/

The cost of solar panels has dropped dramatically in the past decade in terms of $/kWhr. However, the cost of processing amorphous and polycrystalline silicon can be extremely high increasing the overall system cost and limiting the practicality of these arrays. However, researchers are working on methods for lower temperature silicon processing.

Source: https://solartribune.com/solar-panels-cost/

The largest issue currently facing the large-scale implementation of solar power is the inability of modern battery technologies to meet the cycling capabilities, the capacity retention and efficiencies, and cost requirements to make solar profitable and equitable to fossil fuels. Current storage technologies present large costs, insufficient cycling efficiencies, and low capacity at the fast charge-discharge rates required for the storage of intermittent renewable energy technologies like solar. Current research has focused on improving these technologies to create batteries at lower cost with better cycling capabilities such as sodium-ion and magnesium batteries. Improvements are being made to these systems however, some believe that other methods of storage should be utilized over electrochemical, such as mechanical storage, water splitting, flow batteries, and thermal energy storage.

Source: http://www.smart2zero.com/news/submersible-solar-cell-promises-water-splitting-renewable-fuel-generation

The Forefront of Solar
There are a large number of issues facing the growing solar industry, but there is also a large field of dedicated scientists and engineers studying and designing new methods for improving efficiencies and lowering costs. The field of solar is fast paced and extremely expansive with researchers and design engineers all over the world attempting to solve the challenges holding back the development of low cost solar infrastructure.

Solar research is at the intersection of dozens of related fields from bio-organic materials to mechanical engineering design. Below are just a few of the cutting-edge technologies being developed today.

Solar Tracking
Traditionally solar installations are installed in fixed positions directed toward the location where the sun is most intense and most present during the day. This position changes depending on the location of installation. However, sunlight is most efficiently utilized by the panel when it is perpendicularly incident upon the panel surface, meaning that panels reach peak efficiency when they are directly facing the sun. In fact, a panel optimally directed at the solar position throughout the day can produce up to 30% more power than a fixed angle system [1].

To help utilize this phenomenon engineers have designed systems which allow the panel to move to orient toward the sun’s position throughout the day for optimized energy generation. This method is particularly helpful in areas that largely experience cloud cover.

The two commercialized methods for solar tracking are known as active and passive solar tracking.

Passive Tracking
Passive solar tracking does not require any electricity, motors, gears, or controllers for panel movement. Instead most use a low boiling point compressed gas is used to mechanically control the panel movement. The gas is encapsulated and as the sunlight hits the gas cylinder it selectively experiences a volume and pressure increase in the location where the incoming solar radiation is most intense, providing the most heat. In this manner, the panel can track the solar position without requiring operational energy.

Source: Al-Rousan, N & Ashidi Mat Isa, Nor & Mat Desa, Mohd Khairunaz. (2017). Advances in solar photovoltaic tracking systems: A review. 10.1016/j.rser.2017.09.077.

This system is beneficial as it does not require the use of any produced solar power to operate, however it is not nearly as effective as active tracking due to the slow reaction times. Additionally, these system often require solar concentrators as morning sunlight does not provide enough heat on its own to begin tracking, and also require dampers to prevent extreme panel motions in high wind, or extreme temperatures. For these reasons, passive tracking is rather uncommon in the solar industry.

Active Tracking
Active tracking usually includes the use of a single axis or bi-axial slewing drive which allows the panel to orient toward the sun using a set of motors. These motors are powered by the produced solar energy. This type of tracking, unlike passive tracking, requires a guidance system to direct the location of the panel and control the motors.
Source: Al-Rousan, N & Ashidi Mat Isa, Nor & Mat Desa, Mohd Khairunaz. (2017). Advances in solar photovoltaic tracking systems: A review. 10.1016/j.rser.2017.09.077.

This guidance system can be provided in two manners, (1) using photodiodes or light sensors to determine the exact position of the sun, or (2) using the known position of the sun to orient the panel. Using photodiodes is often more accurate, however cloud cover can cause tracking errors and reduce the efficiency of this model. Additionally, photodiode trackers require energy to power and interpret. The known position guidance system requires less power to operate, and is not affected by cloud cover or other extreme weather, but it also requires the storage or import of large sets of data for unknown periods of times depending on the longevity of the solar array.

Active tracking with the correctly determined guidance system and optimized adjustment period can significantly increase panel efficiencies in cloudy regions where solar energy harvesting may have previously been thought to be impossibly inefficient like Binghamton University.

While the concept of solar tracking is not new, solar tracking systems have not been widely implemented across industry as they have not yet proven to be cost effective.