Solar Powered Charging Stations
The combination of solar energy and electric vehicle (EV) charging is the key in drastically reducing our dependence on fossil fuels. Electricity comes from a variety of sources and it’s crucial that electric vehicles will be powered by renewables. Electric vehicles are becoming immensely popular and coming years we expect nearly anyone who owns a solar energy system will install a solar charging station at its home. For this to happen we’ll need a fundamental change in how we think about refuelling our vehicles and a natural evolution of our energy infrastructure
Technical Specs for charging stations
The government, with the help of BIS, ARAI, EESL and other bodies, has already released technical specifications on charging stations and some of the original specifications like the AC-001 and the DC-001 have already been developed and charging stations have been deployed at select locations. The newer guidelines require the charging stations to be equipped with multi standard chargers, viz. AC Type 2, the CCS and the CHADEMO, in addition to the lower power AC and DC-001.
Power flow and Energy Management in solar powered charging stations
The system has 3 sources of power.
First and foremost, are the solar panels. The sizing estimation is beyond the scope of this article, but it is typically a few kilowatts at the minimum. A panel would typically produce at rated irradiance, about 150W/square meter. The solar panels feed the MPPT module. This is a DC-DC converter with a maximum power point tracking algorithm running inside it. These are typically very high efficiency units, running at excesses of 98% electrical efficiency. These are typically multiphase interleaved buck or buckboost converters, and operating levels are at a few hundred volts at both the input and output side. Isolation may or may not be a requirement, but most implementations are galvanically isolated for regulatory and safety reasons. The output feeds a common DC bus, from which downstream energy may be provided to the load. The implementation may be analog, digital or a mix of analog and digital control.
The second source is the grid. This may be optional, as the intent is to maximize the usage of solar. However, in areas where intermittent grid is available, or where the solar insolation is not sufficient for operation yearlong, or during certain seasons, grid helps in fulfilling the demand. Since the system is essentially a solar energy storage setup, it is also possible to use this station to supplement the grid, during peak hours or as a solar farm, using bidirectional grid tied inverters. With proper policies in place for exporting to the grid from solar farms or from captive plants with nett metering, this serves a dual purpose too.
The third source and the sink/storage, is the battery. The trend these days is to use Li Ion batteries, which have very high cycle life, lends itself well to quick charging, very high depth of discharge and very high volumetric efficiency. It is possible to house these batteries underground, to save real estate. These Li Ion battery packs are arranged in a suitable series parallel combination, and in several strings. The batteries terminate themselves into a junction box and termination unit, which also functions as a supervisor. Each battery has a data port, typically CAN or RS485, and these are daisy chained and fed to this termination unit, which then has a top level view of the health and status of every individual battery, string or the entire battery bank. This is essentially a data concentrator and a switching unit, putting battery packs IN or OUT of circuit. In addition, this communicates with the central controller to decide the charge and discharge of the batteries.
Types of solar charging stations
A grid-tied solar energy system is the most straightforward way to charge your electric vehicles with solar energy. A grid-tied solar energy system will feed the power to the grid, regardless of whether your home needs the power at that moment or not. Therefore, when your solar energy system is feeding to the grid, and you are at your office, the electric power generated at home is sold to the utility company. You will get that power back from the utility company in the form of a credit. When you come back from work and park your vehicles at home, you can use that credit to re-charge your vehicles at home
An Off-Grid electrical car charger can also be named "Electric Vehicle Autonomous Renewable Charger" There’s no connection to local utilities required. The solar panel array will feed the battery energy storage system and the entire power needs are drawn from this storage system. Off-grid electrical car chargers can be placed virtually anywhere, as there is no need for a connection to the electrical grid. Some off-grid solar energy chargers have a heavy steel base plate that functions as ballast. Those are extremely easy and quick to install, as no foundation or digging is required.
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