A Guide to Understanding Solar Panels Power System Installations

Custom Search

A solar cell can convert the energy contained in the solar radiation of the sun into electrical energy. Due to the limited size of the solar cell it only delivers a limited amount of power under fixed current-voltage conditions that are not practical for most applications. 

In order to use solar electricity for practical devices, which requires a particular voltage and/or current for their operation, a number of solar cells have to be connected together to form a solar panel, also called a PV module. For large-scale generation of solar electricity solar panels are connected together into a solar array. A typical solar panel installation for a residential apartment is shown below:

For a residential apartment, a hybrid/grid connected system is the most appropriate. The system will be supplied electricity during the day through the solar panels as well as store energy in the batteries while the batteries will supply electricity during bad weather or night hours or grid outage. The system can also be supplied electricity through the electricity grid or a portable generator. With the portable generator or the grid, electricity is supplied to the loads and energy is also stored in the batteries. It is a stand-alone system that is self-sufficient. Note that the portable generator is only required in the worst-case scenario where the weather is bad/during night hours when the stored energy in the batteries is used up and there is no electricity from the grid.

In the process of generating the electricity from Solar panel installations, several important components are connected to produce electricity. Which components are required depends on whether the system is connected to the electricity grid or whether it is designed as a stand-alone system.

The objective here is to describe the common components used for stand-alone systems commonly used in residential buildings.

Components of a Solar Panels Power System Installations

The following components typically make up a solar electricity power system for a residential system. These components can also be found installed in large commercial power applications:

1. Mounting Structure

2. Solar Panels

3. Energy storage system

4. Charge controllers

5. Inverters

6. Generators (optional but required for places with poor electricity grid supply)

7. Cables.

Mounting Structure

A mounting structure is used to fix the Solar panels and to direct them towards the sun. Proper positioning of the solar panels will ensure that the maximum solar radiation is captured in a given location and ensures the Solar power system performs as required. There are fixed mounting structures as well as those designed to track and follow the maximum radiation from the sun. Most residential Solar power systems are mounted on a fixed structure on the ground or most commonly on building roofs.

Solar Panels

The main building blocks of a Solar energy power system are solar panels. They are the units that trap the sun’s solar radiation and converts it to electricity. This electricity is then used to supply electrical loads as well as stored in batteries for stand-alone systems. Solar panels are typically mounted on structures or on building roofs for most residential solar PV installations.

Energy Storage Systems

Energy storage is a vital part of stand-alone systems because it assures that the system can deliver electricity during the night and in periods of bad weather. Usually, batteries are used as energy storage units. During the day when the sun’s radiation is very high, the solar PV system supplies electricity as well as charge the batteries during bad weather or night hours. Deep cycle batteries are usually applied for this purpose – batteries that can withstand repeated charge and discharge cycles.

Charge Controllers

Charge controllers are DC-DC converters that are used in stand-alone solar power systems to convert the solar panels variable electrical output voltage to a fixed voltage output that can be used to charge a battery or used as input for an inverter in a grid-connected system. Typically, the voltage output from a solar panel varies depending on the time of the day and the weather conditions which also makes the output current variable. Both a variable current and voltage are not good for good battery performance hence the need for the charge controller. The charge controller also helps to disconnect the Solar panels from the batteries when they are fully charged. This helps to prevent overcharging which affects battery performance and life.

All charge controllers use Maximum Power Point Tracking (MPPT). Owing to variations in the current and voltage output from a solar panel or array installation due to changes in solar radiation (technically called irradiance) and temperature, there exist a Maximum Power Point (MPP) on the I – V characteristic of the installation where the highest power is generated for a given irradiance and temperature. The voltage and current corresponding to MPP is Vmpp and Impp.

Given that MPP is dependent on ambient conditions, any changes in irradiance and temperature will shift the position of MPP on the I-V (current/voltage characteristics) of the solar panel/array installation. Therefore, changes in the I-V characteristics have to be tracked continuously with adjustment in the operating point to correspond to MPP after changes in ambient conditions. This process is called Maximum Power Point Tracking or MPPT. The devices that perform this process are called MPP trackers and they are built-in to modern charge controllers used in solar panel/array power installations.

Inverters

Inverters are DC-AC converters that are used to convert DC voltage produced by the Solar panels to AC voltage to supply alternating current loads. Appliances and loads used in residential apartment usually utilize alternating current hence the need for an inverter. Furthermore, for grid connected solar power systems, there is need to convert the DC voltage from the solar panels before transmission into the power grid. For low power application as are common in small residential PV systems, single-phase inverters are used. They are connected to one phase of the grid. For higher powers, three-phase inverters are used that are connected to all phases of the grid.

Electric Cables

The overall performance of Solar electricity supply systems also is strongly dependent on the correct choice of the cables. Selecting the wrong cable size can significantly affect the performance of the Solar PV power supply system.

The cables must be chosen such that resistive power losses are minimal. The power dissipated across a cable is proportional to the square of the current flowing through the cable. Hence, as the current doubles, four times as much heat will be dissipated at the cables. Therefore, modern solar panels have connected all cells in series.

Color Conventions for Cables

Solar Panels PV systems usually contain DC and AC parts. For correctly installing a solar panel system, it is important to know the color conventions for wiring. 

For DC cables:

Red is used for connecting the positive (+) contacts of the different system components with each other.

Black is used for interconnecting the negative (-) contacts

For AC wiring, different colour conventions are used around the world.

European Union,

Blue is used for Neutral,

Green-yellow is used for the protective earth 

Brown (or another color) is used for the phase.

United States and Canada,

Silver is used for neutral,

Green-yellow, Green or a bare conductor is used for the protective earth

Black (or another color) is used for the phase.

In India and Pakistan,

Black is used for Neutral,

Green is used for the protective earth 

Blue, Red, or Yellow is used for the phase.

Therefore it is very important to check the standards of the country in where the Solar  PV system is going to be installed.

Solar  Electricity Systems with Solar Panels
Types of solar PV Power Supply System

Types of Solar PV Power Supply Systems

Custom Search

A Solar power system contains many different components besides the basic PV modules building block. For successfully planning a Solar PV system, it is crucial to understand the function of the basic components and to know their major functions. Further, it is important to know the effect on the location of the (expected) performance of a PV system whether you are planning this for your home or a small industrial concern or you simply want to power a single load. Understanding the different components in the Solar power system and their interrelationship with each other will help in making the right choice in terms of your financial outlay.

Solar PV systems can be very simple, consisting of just a few PV modules and load such as the direct powering of a water pump motor, which only needs to operate when the sun shines. However, when a whole house is required to be powered, the system must be operational day and night. It also may have to feed both AC and DC loads, have reserve power and may even include a back-up generator to charge batteries during hours of darkness or low sun light.

Types of PV Systems.

There are three main types of PV systems: stand-alone, grid-connected, and hybrid. The basic solar power system principles and elements remain the same. Systems are adapted to meet specific requirements by varying the type and quantity of the basic elements. One key advantage of the solar power system is that it is modular by nature. A modular system design allows easy expansion, when power demands change.

Stand-Alone Solar PV Power Systems

Stand-alone systems rely on solar power only. These systems can consist of the PV modules and a load only or they can include batteries for energy storage. When using batteries charge regulators are included, which switch off the PV modules when batteries are fully charged and may switch off the load to prevent the batteries from being discharged below a certain limit.

The batteries must have enough capacity to store the energy produced during the day to be used at night and during periods of poor weather. Below is shown below for the two commonly applied stand-alone systems: A simple DC Solar power system without a battery. 

A large standalone Solar PV power system with both DC and AC loads

Grid Connected Solar PV Power Systems

Grid-connected Solar power systems are becoming increasingly popular for building integrated applications. As shown here, they are connected to the grid via inverters, which convert the DC power into AC electricity. 

In small systems such as in residential homes, the inverter is connected to the distribution board, from where the PV-generated power is transferred into the electricity grid or to AC appliances in the house. These systems do not require batteries, since they are connected to the grid, which acts as a buffer such that an oversupply of PV electricity is transported while the grid also supplies the house with electricity in times of insufficient PV power generation.

Hybrid Solar Power PV Systems

Hybrid systems consist of combination of PV modules and a backup system for electricity generation such as a diesel, gas or wind generator. A schematic of an hybrid system shown below:

 Hybrid systems typically require more sophisticated controls than stand-alone or grid-connected PV systems. As an example, in the case of an PV/diesel system, the diesel engine must be started when the battery reaches a given discharge level and stopped again when battery reaches an adequate state of charge. The back-up generator can be used to recharge batteries only or to supply the load as well.

Solar Electricity Systems with Solar Panels

Solar Electricity Systems with Solar PV Panels

Custom Search

World Energy Challenge

The world population is still rapidly growing, and several studies have predicted a world population of 9billion around 2040 in contrast to the 7 billion people Currently living on the planet today. 

All these people will need energy, which increases the global energy demand. Furthermore, in many countries the living standard is rapidly increasing like China and India, where approximately 2.5 billion people are living, which represents more than a third of the World’s population. 

The increasing living standards lead to an increased energy demand. Unfortunately, fossil fuels are not a sustainable energy source and may not be able to meet the increased demand for energy. Even with more oil and gas being produced through unconventional methods today, such as extracting oil from tar sands in Alberta, Canada and producing oil and gas with fracturing such as in large parts of the United States, the energy demand still remains a challenge. These unconventional methods use more energy for production and introduces several risks and environmental challenges like oil spill.

A further challenge is that by burning fossil fuels we produce the so-called greenhouse gases like Carbon dioxide (CO2) which contributes to worsening our climate change dilemma. Thus, we have a dual energy challenge of increasing demand and increasing CO2 emissions from conventional energy sources like fossil fuels.

To solve this energy challenge, we are increasingly turning to renewable energy sources like wind, heat and solar energy to reduce CO2 emissions. With improvement in technology for the manufacture of photovoltaic cells, Solar energy is proving to be the energy of the future. Solar energy installations using solar PV panels have increased exponentially over the last few years with Europe, Asia Pacific and North America leading the way.

Advantages of Solar Electricity

Some key advantages of solar power are:

• Energy Independence

• Environmentally friendly technology

• The fuel (sunlight) is abundant everywhere

• It requires minimal maintenance

• Maximum reliability

• Reduce vulnerability to power loss

• Due to its modularity, system can easily be expanded.

Photovoltaic Cells or Solar Cells

Photovoltaic cells are the main building block for solar PV panels. A Solar cell consist of a thin wafer of Silicon just like a computer chip, but it is much larger and much cheaper. The sun light energy that falls on the cells is converted into electric current however, they do not store the electric energy generated. The fuel for solar cells is sun light which is abundant all over the earth.

How Does Solar Cells Change Sun Light Energy into Electricity?

The working principle of solar cells is based on the photovoltaic effect, i.e. the generation of a potential difference at the junction of two different materials in response to electromagnetic radiation in this case sun light radiation. Most solar cells consist of a P-type and N-type semiconductor material. A simple model of a typical solar cell is shown below:

As shown above, Light penetrates the cell. Particles of light called photons bounce into negatively charged electrons around the silicon atoms of the cell and knock these electrons free from their silicon atoms. The energy of the photon is transferred to the electron in the process. There are billions of billions of photons falling on the cells every second, so there are lots of electrons knocked loose. Each electron is pushed by an internal electric field that has been created in the factory in each cell. The flow of electrons pushed out of the cell by this internal field is what we call the electric current which can be used to drive an electric circuit.

As long as there is light flowing into the cells, there are electrons flowing out of the cells. The cells do not use up its electrons and loose power, like a battery. It is just a converter, changing one kind of energy (sunlight) into another (flowing electrons). For every electron that flows out of the wire connected to the front of a cell, there is another electron flowing into the back from the other return wire.

Difference between Solar PV Systems and Solar Thermal Energy Systems.

Photovoltaic (photo = light; voltaic = produces voltage) or PV systems convert light directly into electricity using semiconductor technology, while solar thermal systems, convert sunlight energy into heat which is then further used to produce electricity.

Solar PV Terminology

PV Cells

The photovoltaic cell or PV cell is the basic building block for PV modules. Some PV cells are round while others are square. A typical solar cell or PV cell produces 0.5V or 0.6V. PV cells can be connected in series or parallel. When the cells are connected in series, the voltage = the number of cells in series x open circuit voltage of one cell, while the current remains the same. If the PV cells are connected in parallel, the current = the number of cells in parallel x current per cell. A PV cell is shown below:

Most Solar cells in a Solar PV panel are connected in series to achieve larger voltage levels.

PV Modules

A group of PV cells connected in series and/or parallel and encapsulated in an environmentally protective laminate make up a PV module. The names PV module and solar module are often used interchangeably. Modern PV modules often contain 60 (10 × 6), 72 (9 × 8) or 96 (12 × 8) solar cells that are usually all connected in Series in order to maximize voltage and minimize resistive losses. A typical PV module is shown below:

A solar Panel

A solar panel consists of several PV modules that are electrically connected and mounted on a supporting structure. However these days, reference to a solar panel refers to a single PV module which is kind of a misnomer but it has stuck.

A solar Panel

PV Arrays 

A PV array consists of several solar panels. An example of such an array is shown below:

This PV array above consists of two strings of two solar panels each, where string means that these panels are connected in series.

Typical Specifications of Solar PV Panels

Most solar PV modules in the market today have the following technical electrical specifications at standard Test Conditions (STC) at irradiance of 1000W/m2 , temperature of 25 degree C, AM1.5:

(1) Rated Power (Pmpp) – This is the maximum rated power of the solar module

(2) Rated Current (Impp) – This is the rated current in Amps of the PV module at peak power.

(3) Rated Voltage (Vmpp) – This is the rated voltage (volts) of the PV module at peak power.

(4) Short Circuit current (Isc) of the PV module.

(5) Open Circuit Voltage (Voc) – This is the voltage of the PV module without load at the terminals

(6) Dimensions – Every Solar PV module has its stated dimensions and it different from                            manufacturer to manufacturer.

(7) Maximum Warranty on Pmpp – This is the warranty on the maximum power provided by the 

      solar module, and it is typically 25 years for most solar panels.

There are other specifications such as mechanical properties, certifications and warranty and temperature coefficients that manufacturers of solar panels usually produce in addition to the electrical specifications.

Types of Solar PV Power Supply Systems