Solar Charging Station | Detailed Analysis



 

SOLAR BASED CHARGING STATION
BRIEF REPORT

Fahad Mushtaq Makhdoomi || 26-06-2021

 

 

 

 

 

 

 THE CONTENT OF THIS WEBPAGE IS FREE TO SHARE FOR EDUCATION AND RESEARCH PURPOSES. PARTIES INTERESTED IN EXTENDING THE PROJECT AND BUYING A FULL GUIDE FOR PROJECT DEVELOPMENT WITH ALL COST ANALYSIS AND REPORTS MAY CONTACT THE CREATOR @makfahad113@gmail.com

 

 

 

 

 

 


Intro__

Solar Energy comes from the electromagnetic radiations emitted by sun which carry photons as a source of energy. When photon is made to strike a metal under appropriate conditions, electrons are ejected from the metal surface thus creating a potential difference on the metal surface. This science led to the development of photovoltaic cells which can convert light energy into electrical energy.

Over years earth has seen a large scale environmental devastation due to industrialization. Emissions from fossil fuels not only increases the risks of environmental loss but also to the depletion of resources to future generations.

Vehicular emission is a cause for a wide scale environmental pollution and also vehicles are large consumers of fossil fuels. There use cannot be stopped but we can develop these vehicles to suit our needs and also make them environment friendly. This is when the role of Electric Vehicles comes into being. As the name suggest these vehicles use electric power for kinetics, thus, make no or very less pollution. But, even with such vehicles problems arise:

      These vehicles need electricity to operate, which not always comes from Renewable Sources.

      These may or may not have a large range and need necessary charging.

      These cannot find a market unless adequate infrastructure is build.

Role of charging stations__

Charging stations can be assumed as petrol stations for an EV. A charging station can clear many hurdles for EV market place in any region. EVs require less maintenance but reasonable charging, hence, any development in charging stations eventually means development toward EVs.

Charging stations require electricity which they can store and offer their service. Much of this electricity could be purchased from an existing electric company but, many places in the world do not have 24x7 availability of energy and many places still observe power cuts. Also not every time electricity is produced by non-conventional source and some places use fossils fuel based engines for electricity generation. This way EVs would only add to pollution and environmental loss.

A great solution would be using the sciences of Photovoltaics (discussed above) to use Sun as a source to produce electricity. Sunlight is a renewable source of energy and being able to utilize it would mean having free energy on much less cost.

This project deals with ideas to harness the solar energy using photovoltaics. I’ve tried my best to keep report simple and insisted on use of graphics for better understanding. This report will talk from basics to decide and build a solar power station in the best possible way keeping in view environmental, economic and durability factors.

 


Solution Design:
  •  System design
  •  Solar Panels
  •  Controller System
  •  Battery
  •  Solar Inverter 
  •  Vehicle Charger

 

PRE-ENGINEERING:

A solution to stated problems may seem simple, but we must keep some important things in our mind. Firstly, location for the project should be such that our machinery should be able to bear the environment of that place. As we are talking of solar energy, thus, a region with adequate supply of sunlight is needed for the project. The environmental conditions should be suitable and the location is to be checked for vulnerability to natural disasters. Political and economic factors of region may affect the project, and one must be sure to have the government and administrative support for a successful project.

 

System Design:

It is really important to come up with a plan before proceeding for action. Hence, we shall discuss briefly some ideas for structuring our project. This way we can choose the best idea for implementation as per our needs.

·      Remote System: This system will have parts working on different locations. A solar farm at a certain place and with transmission system which will help in taking electricity to farther places through power lines. This electricity thus could be stored in batteries at receiving stations and from there it could be sent to charging station for utilization.

 


             Advantages:

§  It can be used to generate large amount of electricity.

§  Much land is available for such farms.

§  The electricity produced can be utilized to power whole city.

§  The energy produced is renewable and would help in recovering the investment in no time.

             Disadvantages:

§  High cost.

§  It’s difficult to find investors for such project.

§  Maintenance and sophisticated technology is required.

§  Dependence on weather conditions.

·      Integrated System: This system derives basis from panel mounting.  A solar panel can be mounted on structures to tap the energy. This includes rooftop mounting, side mounting and building integration. In cities with adequate sunlight but lesser land availability, houses and apartments can be used for solar energy tapping. Solar panels can be installed on rooftops or on walls of structures and roadside charging stations could be installed which will not require AC/DC conversions for transmission of power, thus making it a more efficient system. Obviously we need consent from property holders for action plan and a mutual agreement should be made. In metropolitan cities with high rise buildings it would be easy to use certain floors and sides of building to install solar panel, often these buildings have a parking lot and charging stations could be installed more easily in such areas. In my opinion, this system would be both cheap and profitable among all other systems.

           


     Rooftop mounting 

       

            

                                                           wall mounting       

 


                                                        Integrated Building

 A roadside charging station

            Advantages:

§  It is cheap and profitable.

§  Needs less space.

§  It can be used provide backup power services for the house, apartment or building.

§  Less maintenance.

             Disadvantages:

§  It is difficult to find suitable area for this system.

§  It requires agreements with multiple parties else one needs to own such properties.

§  It is sometimes difficult to access for maintenance.

§  Possibility of being misused or damaged.

§  Subject to the interest of people.

§  Dependence on local vehicles.

 

·      Stationary System: This is a simple solar based commercial charging station. Like a fuel filling station a charging station is built at several places in city and solar power is used to provide energy. This simplest structure requires making solar panel mounted rooftops, but many more designs could be built according to space and finance available. This system does not require A/C-D/C conversions but as we intend to make large scale electricity we need sophisticated technology. It should have highly efficient solar panels and better battery storage systems. It would also need better computers for tracking usage, traffic, charger availability, inlet and outlet power and more. It would also require human resources for better functioning.

             A Tesla solar charging station.

 

          Advantages:

o  Has a good scope and profit for larger cities.

o  Employment generation.

o  Provides better services.

         Disadvantages:

§  It needs a more resources and labor.

§  Needs more space.

§  Needs better engineering and communication services.

§  It requires frequent checks and maintenance.

 

Solar Panel: A variety of solar panels are available in market and research is still in progress to bring up new and better generations of solar panels. A solar panel is the base for generation of power and on the basis of the choice of solar panel stands the success of our project. To decide the best solar panel which suits our need we need to keep in view our design system and also geographical, vehicle population and economic conditions. We shall discuss briefly some important solar cells of our concern.

Crystalline Silicon cells: This is the first generation and most widely used solar panel, crystalline silicon solar cells comprise of different forms but differentiated by their respective purity degrees. That is, when the silicon molecules are well aligned, it gives that particular silicon a better preference over others because solar cells made of that specie will effectively convert the solar energy into electricity.

Monocrystalline Silicon solar cells consist of cylindrical ingots and four sites cut to make silicon wafers. This not only reduces cost but optimize the performance of the ingots as well. Also, the crystals have a higher power efficiency rate of up to 20%, smallness in sizes so space efficient and a longer lifespan of above 25years. Though they have significant edge over other silicon solar panels, they are relatively costly, more fragile and extreme variation in weather temperatures quickly affects its efficiency.

Polycrystalline silicon cells consists of squared ingot wafers, they are less fragile, lower production cycle and slightly lower heat tolerance factor compared to monocrystalline solar panels. But, they do have an efficiency of power generation below 20%, a lower space efficiency and less attractive in terms of market values.

String Ribbon solar cells is another form of multi crystalline silicon cell production introduced by Evergreen Solar Company. Here high temperature resistant wires are pulled through molten silicon to produce polycrystalline ribbon of silicon crystals. It is less costly than monocrystalline because its production requires half the amount of silicon as compared to monocrystalline manufacturing, but it’s inefficient and ineffective because of lower power efficiency value compared to polycrystalline, and also due to its lower space efficiency.

Thin Film Solar Cells: A second generation of solar cells was developed by using semiconductor material on substrate such as glass, plastic or metal or even using organic membranes. These cells have almost same efficiency as first generation cells, but with time more research is adding to the efficiency of these cells for example cadmium telluride thin-films have a peak recorded efficiency of more than 22.1 percent copper indium gallium selenide cells have reached a laboratory record of 21.7% and for commercial use an average efficiency of 18%. Gallium arsenide cells have record of 30% and so on. The main issue with these cells is there high cost but most of them have a payback time of 2 years and thus cannot be neglected.

The third generation of photovoltaic cells is the combination of first and second-generation of solar cells advantages. It must increase in efficiency that maintains the cost advantage of second-generation materials. The approaches include desensitized nano-crystalline or Gratzel solar cells, organic polymer-based photovoltaics, tandem (or multi-junction) solar cells, hot carrier solar cells, multi-band and thermophotovoltaic solar cells. Compared to all other photovoltaic technologies, multi-junction solar cells have a highest theoretical limit of efficiency conversion. The maximum recorded efficiency of 40.7% achieved by Boeing Spectrolab Inc. by using multi-junction solar cell in December 2006.

 

Now the time to decide the best cell for our project is here. As per above shown graph it is clear that the most efficient of all solar cells is the multi junction solar cell which are made up of two or more layers of solar cells which can absorb light of different wavelengths but most of these are costly and short in market. Thin film though having less efficiency should be used in integrated system design as these provide flexibility and for integrated buildings we don’t have a choice other than thin film which could allow some light through them, for remote system we would need cheaper but efficient solar panel as large so that to make large amount of electricity, as we are planning to generate MWs and GWs of electricity multi junction would become, as powers of 10 increase, costlier. Hence we may think of using single junction monocrystalline cells but it will not make much difference as the efficiency of the system will decrease too, thus should be preferred only if land available is more and finance is poor. Stationary system will require both efficiency and high energy to space ratio, thus, for a solar based charging station we should use multi junction solar panels or gallium arsenide cells, if economic conditions do not allow we could use single junction crystalline silicon cells also but if we are setting up at a place with changeable weather then we may not see much success.

 

Charge Controllers: This can be either a standalone device of an integrated circuit system which regulates the flow of current from various components of the system. In brief it is to prevent the current from damaging the units of the systems mainly batteries as it ensures not excess charge gets into a battery or not all the charge in the battery is drained. Some commonly available controllers are:

_Shunt Regulators

_Series Regulators

_PWM Controllers

_MPPT Controllers

Shunt Regulators

Shunt regulators function by short circuiting the solar array when the battery reaches a set voltage. When the battery voltage drops, the array is un-shorted and current is allowed to flow to the battery again.

This is also sometimes referred to as a pulse regulator, since the current can be “pulsed” to the battery as the array current is regulated. As the charge regulation is either on or off, it’s simply a single stage charge controller. As the regulator sees the full current from the solar array during regulation, the shunt regulators get hot and are generally only used for small solar arrays.

Shunt regulators are generally solid-state and contain a blocking diode and a transistor. The solar array is shorted by a transistor (or relay) and the blocking diode prevents the battery from being shorted at the same time. Shunt regulators are generally for negatively grounded systems only as the block diode is usually in the positive line.

Shunt regulators are on/off type controllers. This means the solar array is either on or off; the battery sees the full charge current available or none. The regulator allows current from the array to flow to the battery until the disconnect voltage is reached, at which time the solar array is shorted, preventing any further current to flow to the battery. Without any charge current, the battery voltage will drop until the reconnect voltage is reached at which time the regulator will allow current to flow to the battery again. The battery voltage will rise and the cycle will repeat.

When the shunt regulator shorts the array during regulation, measuring the array voltage during this time will yield an array voltage that should be less than 1V. During normal charging, the array voltage should be slightly higher than the battery voltage (battery voltage + the voltage drop from diodes or transistors). If array open circuit voltage was ever measured during normal operation, this would indicate a problem.

Series Regulator

Series regulators function by open circuiting the solar array when the battery reaches a set voltage. When the battery voltage drops, the array is reconnected and current is allowed to flow to the battery again.

Series regulators generally use a relay or transistor to connect and disconnect the solar array. As the relay (or transistor) can be placed in either the positive or negative line, Series regulators can be used in positive and negative ground systems.

Series regulators (similarly to shunt regulators) are on/off type controllers. The solar array is either on/off, so the battery sees the full charge current or none. The regulator allows the current from the array to flow to the battery until the disconnect voltage is reached, at which time the solar array is disconnected (open circuited) and prevents any further current to flow to the battery.

Without any charge current, battery voltage will drop until the reconnect voltage is reached, at which time the regulator will allow current to flow to the battery again. The battery voltage will rise, and the cycle will repeat. It is sometimes referred to as a pulse regulator, since the current can be “pulsed” to the battery as the array current is regulated. The duration of the pulses can be from hours to seconds depending on: battery SOC & health, load current, temp., etc.

Unlike shunt regulators, some series regulators can control multiple relays (or transistors), allowing for multiple disconnect/reconnect set points and stepped charge current. If the series regulator has a single relay, it is simply a single stage charge controller. Additional relays with different set points can make the regulator a multi-stage controller.

As the regulator opens the solar array to regulate the battery voltage, series regulators run much cooler than shunt regulators (especially if a relay is used instead of a transistor). For this reason, series regulators are well suited for large solar arrays.

When the series regulator opens the array during regulation, measuring the array voltage during this time will yield an array voltage that should be close to the open circuit value. During normal charging, the array voltage should be slightly higher than the battery voltage (battery voltage + the voltage drop from diodes or transistors). If an array voltage value is less than the battery voltage was ever measured during normal operation, this would indicate a problem.

Pulse Width Modulation (PWM) Regulator

PWM regulators are similar to series regulators, but they use a transistor instead of a relay to open the array. By switching the transistor at high frequency with various modulated widths, a constant voltage can be maintained. The PWM regulator self-adjusts by varying the widths (lengths) and speed of the pulses sent to the battery. Unlike the on/off charge controllers which instantaneously cut off the power transfer to minimize battery overcharging, PWM regulators act like a rapid on/off controller constantly.

When the width is at 100%, the transistor is at full ON, allowing the solar array to bulk charge the battery. When the width is at 0% the transistor is OFF, open circuiting the array preventing any current from flowing to the battery when the battery is fully charged.

Like the series regulator, the transistor can be placed in either the positive or negative line, allowing the regulator to be used in positive and negative ground systems. The difference between the series regulator and the PWM regulator is the PWM of the transistor. When the modulation width is at 100% or 0%, the regulator is essentially a series regulator, it is that modulation width variation that allows the PWM regulator to create a constant voltage to the battery as opposed to the on/off of the series regulator. The below figure shows an example of a PWM regulator regulating with a 70% on 30% off duty cycle. Some PWM regulators have provisions for converting to a series (on/off) regulator. This could be needed for sensitive loads that have an issue with the noise created by the frequency of the PWM. Some PWM regulators have provisions for converting to a series (on/off) regulator. This could be needed for sensitive loads that have an issue with the noise created by the frequency of the PWM. Because PWM charge controllers require transistors, they are always solid-state; this means heat dissipation can become a problem, especially in larger solar arrays.

As with series regulators, because the PWM regulator regulates by opening the array during regulation (at high frequency), if you were to measure the array voltage during this time, the array voltage can be anywhere between battery voltage and open circuit voltage depending on the regulator’s charging stage. If an array voltage value less than the battery voltage was ever measured during normal operation, this would indicate a problem.

MPPT Charge Controller

The Maximum Power Point Tracking (MPPT) charge controller takes the PWM to the next level, by allowing the array voltage to vary from the battery voltage. By varying the array input, the charge controller can find the point at which the solar array produces the maximum power. The MPPT process works like this. Imagine having a battery that is low, at 12 V. A MPPT takes a voltage of 17.6 volts at 7.4 amps and converts it down, so that what the battery gets is now 10.8 amps at 12 volts. MPPT controllers takes the DC input from the solar panels, convert it to high frequency AC, and then change it once again to a different DC voltage and current. The point is the voltage will exactly adhere to the requirements of the battery. As the MPPT charge controller uses the negative line as a reference and then switches the positive line, they can be used in negative ground systems only. It is crucial to understand that voltage is a potential difference; the ‘difference’ refers to the difference between ground potential and some potential. This means that the starting point is below zero, but this is only used as a reference point. Since MPPT charge controllers can vary the charge current to the battery, the regulator can be a multi-stage charger with bulk, absorption, and float settings. They are always solid state; this means heat dissipation can become a problem, especially in larger solar arrays. MPPT controllers are typically step-down converters, so the array voltage always needs to be higher than the battery voltage. Therefore, an array voltage value less than the battery voltage during normal operation would indicate a problem. 

Decision to select the best type of controller lies with the system we wish to operate; for a remote system heavy duty controller is needed thus, series controller is preferable as it can handle high voltages easily and does not heat much. Rather, in most of the systems it is better to use series controllers but these controllers reduce the power from the solar panels and cannot be used at places where you need high efficiency as in case of stationary system. Thus MPPT controllers should be used in case of stationary systems which are 98-99% efficient.

Storage Batteries:

Up until now we have seen the basic parts which we shall use to harness the energy but this energy is to be used at particular time and need to be stored in other forms. Let us understand it like this, we know that solar energy gets converted to electrical energy through photovoltaics, we could use this electricity either at the same time or we can transform it to some other form from where we could use it whenever we need it. Clearly, we have this concern of using energy at our desired time and now we must find a way to store this energy for future use. This is where a battery comes for our rescue. So let us see best technologies in this field available for us….

Battery type

Voltage

(V)

Energy density(Wh/kg)

Lifespan

(years)

Cost

(Rs/KWh)

Toxicity

NiCd

1.0-1.2

40–60

15-20

15000

Low

Li‑ion

3.7

150

5

15000

Low to moderate

Li-polymer

4.0


200

10-20

30000

Low to moderate

NaS

2

150-300

(850 theoretical)

15

25000-40000

moderate

Zn/air

1.3-1.45

470 (practical),1370 (theoretical) Wh/kg

3

--

Low

Vanadium Redox

1.15–1.55

10–20

>20

100000

high

Zn/Br


1.8

56–230

10-20

30000

high

 *source:wikipidea

We can explore more on the batteries as much as we desire and we would find a variety of them from lead acid to nickel metal hydride and more. Some important types are already mentioned in the above table. Long story short, we should use flow battery types which are the last in list for a remote system and a Li-po or Li-ion batteries for others. The reason being that flow batteries are usually used in large battery storage systems and more developments are on the way to include hybrid systems for better storage. Vanadium redox batteries are preferable for long term use and these can be recharged even after draining out all its power. These also require least maintenance and thus these are used to design large power banks. The only issue remains the cost that is too high and its toxic nature that should be taken care while handling or disposing. Another great technology is this regard is the sodium ion battery which though are somewhat costly but in future are expected to become cheap and thus a good option for large storage systems. For other systems using flow battery type will be appreciate but for economy Lithium batteries are sufficient.

 

Solar Inverter:

 We know that the electricity produced by solar panels is fluctuating dc current and we need to convert this electricity to constant DC of AC according to our utility. Based on electricity generated by solar cells, there are three basic inverters or converters which convert the DC electricity from the solar panel to AC electricity that can be used to charge the cars both at home sockets or charging stations these converters includes, the string inverters or centralized inverters, micro inverters and power optimizers.

String inverters: Involves arranging the solar panels parallel into sets of strings that relay the power they harnessed into a single inverter. Here the panels produce equal total power at higher voltages. This reduces cost of wiring and lesser internal losses of the harnessed energy leading to improved efficiency

Pros

Cons

Low cost

Performance heavily impacted by shade

Durable

Generally limited to simple systems

Easy to maintain

Inability to monitor individual panel performance


Single point of failure

Micro Inverters: Unlike string inverters, micro converters the DC electricity of each solar panel to the AC per panel- that is each panel is attached to a micro inverters and output of the several micro inverters are combined and fed into the electric grid of the home or load. Here any failure of one of the panels as a result of shadings, debris or snow lines does not affect the functionality of the other panels because each micro inverter harnesses maximum power. Though individual micro inverters generally have lower efficiency values as compared to string inverters, their combined efficiency is increased due to the fact that every inverter / panel unit acts independently

Pros

Cons

Increased performance

Cost

System flexibility

Maintenance

Monitor individual panel performance

Electrical components located on roof

Easy to replace


 

Power Optimizers: Similar to micro inverters in that both systems attempt to isolate individual panels in order to improve the performance of the entire system. Power optimizers are used to monitor the total output of the pane arrays so as to continually adjust and modify the load attached in order the keep the system operational at its peak. This process is known as maximum power point tracking (MPPT) by use of a Smart Module.

 

 

Pros

Cons

Increased performance

Maintenance

Monitor individual panel performance

Electrical components located on the roof

Cheaper than micro inverters


 

A solar inverter will be used when we are at our final staging of tapping the electricity, the best way to decide which inverter to use would be to check for the efficiency, performance and cost.

 

Vehicle Charging System:

In order to implement our charging system, we study several electrical vehicles, their batteries and how they are charged.

 

Model

Battery type

Charger

Adapter

Capacity( kW h)

Renault Fluence Z.E.

lithium-ion

3.5kW AC onboard charger Optional Zoe's Chameleon charger (43 kW)

10A 220V-240V household charger; SAE J1772

22

Tesla Model S P90D

lithium-ion

11 kW AC onboard charger 120 kW DC fast charger

SAE J1772 public chargers. Adapters to IEC 60309 5 PIN Red 16A/3- phase (400 V) or IEC 60309 3 PIN Blue 32A/single-phase (240 V) or some other kinds of domestic adapter or general adapters

90

Toyota Prius Plug-in Hybrid

lithium-ion

3.3kW AC onboard charger

120v household outlet; SAE J1772

9

BMW i3

lithium-ion

7.4kW AC onboard charger DC fast charger

SAE J1772 Optional Combo DC)

22

Mitsubishi i-MiEV

lithium-ion

3.3kW AC onboard charger 44kW DC fast charger

adapters for domestic AC sockets (110-240 V); 15 A 240 V AC (3.6 kW) on the SAE J1772-2009 inlet, optional Chademo (max 44 kW 480 V DC[3]);

16

Nissan Leaf

lithium-ion

6.6kW AC on board charger DC fast charger

SAE J1772 CHAdeMO

27

Ford Focus Electric

lithium-ion

6.6kW AC onboard charger

120V convenienc e charge cord 240V Home Charging Station  SAE-J1772

23

*research papers of Department of Electrical Engineering Blekinge Institute of Technology Karlskrona Sweden 2016

All these electrical vehicles generally support connecting household electric socket charging and SAE J1772 standard charging or DC fast charging. Among these charging modes, the DC fast charging is latest. It is supported by several vehicles, mode. In this mode, the charging rate has been raised to two to three times than AC charging. It realized that charging battery up to 80% in an hour. There are three main types of DC fast charging standard: CHAdeMO, Combined Charging Standard and Tesla’ Supercharger.

 

DC Chargers: This type of a charger is installed in a power station for quick charging of vehicles there are a few notable technologies available and these are also continuously under development. All DC chargers must be able to do these main things:

Transfer charge

Exchange data

Earth shorts and leaks

A charging station must have a good variety of connectors most important of them are listed:

Charger

Voltages

(V)

Power

(KW)

 Current

(Amps)

CSS

200-1000

350

350

CHAdeMO

50-500

200

400

Tesla Super chargers

400-500

120

250

GB/T

750-1000

 

250

 *source: TUDelft

AC chargers: Some vehicles have an onboard charger which converts AC electricity to DC electricity for charging the battery. AC connectors are equally important as DC connectors though these perform charging slower, it costs little less and can be used to charge vehicles parked for longer time for example near offices.

Charger

Voltages

(V)

Power

(KW)

 Current

(Amps)

SAEJ1772

120-240

1.44

80

SAEJ1772 TYPE2 1PHASE

130

2

80

SAEJ1772 TYPE2 3PHASE

400

20

63

Tesla

240

17

20

 *source TUDelft

 

Conclusion__

To establish base for an EV market at a place the infra structure must be build, we have discussed so far some of the ideas we can incorporate to make a way for industries to flourish. Its aim does not focus on drawing profit recklessly but to think about the environment first and then look for the places where there is an opportunity to make a change. This change is brought about by replacing something harmful with something good. If for that good, an investment is to be made that may take some time to pay back, we must not hesitate.

 

 

 

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