ALL ABOUT SOLAR ENERGY
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Solar energy is heat and sunlight. In general, solar energy means the generation of practical energy from heat and sunlight.
What is the sun
The sun is our closest star at about 150 million kilometers, is 109 times larger than Earth and is 4.5 billion years old. The sun is composed mainly of hydrogen (79%) and helium (19%).
Through nuclear fusion in the center of the sun, hydrogen melts with helium, creating energy. This energy is emitted in the form of electromagnetic energy (sunlight). This sunlight takes about 8 minutes to reach the earth.
The calculated useful life of our sun is 10 billion years. Our sun is currently a yellow dwarf star (class G2) and is much heavier and hotter than an average star.
According to the life cycle of a star, the sun will be in about 5 billion years. It is located at a distance of 27,000 light years from the center of the galaxy. In approximately 250 million years, the sun makes a circle around the center of the galaxy.
Origin of the sun
The sun is a star. Like all stars, the sun originated from a cloud of gas. Areas with a little more gas are created within a gas cloud. These areas attract more gas due to mass and gravity.
Ultimately, a large amount of gas attracts the core of the gas cloud. This creates pressure. The gas condenses and the temperature rises. At a given moment, nuclear fusion occurs. This causes the gas to radiate. When the gas pressure is in equilibrium, a star forms.
Life cycle of the sun
The sun is also a star and originated from a haze of particles of gas and dust that moved towards each other. These particles are concentrated in one or more central points. The sun rose in the middle of these central points. Called a protostar in this phase.
As mass mass increases within the protostar (nuclear fusion), energy is released and nuclear fusion generates a radiation pressure that causes the protostar to start emitting light. In this phase (phase of the main series) the sun is called a star of the main series.
Our sun is halfway through this phase, it is approximately 4.5 billion years old and will go through this phase for about 5.5 years before moving on to the giant red phase. This phase begins after almost all of the hydrogen in the sun’s core has been used.
Nuclear fusion continues in the outer layers, causing the outer layer of the sun to expand considerably. In this way the earth will warm up to a lava bulb. The outer layers of the sun will also cool, changing the light emitted to the red spectrum.
This phase is called the red giant. The outer layers are released during this phase, after which a CO core remains. The sun is then in the phase of the white dwarf and for a large part emits ultraviolet light. Our sun will slowly cool down to eventually come out and form a black dwarf.
The sun as an energy source.
The sun provides direct energy in two forms: light and heat. In short, energy is created by the enormous pressure exerted on the sun’s core. These two forms of energy, together with the secondary forms of energy, such as wind, tides, hydroelectric energy and biomass, constitute 99.9% of the energy on earth.
The atmosphere and magnetosphere protect the earth against most of the harmful rays of the sun. However, the energy that reaches us is still 9000 times greater than the needs of all earthlings together.
What is sunlight?
A process of nuclear fusion takes place inside the sun, as a result of which the sun is heated on its surface to a temperature of about 5500 ° C. The radiation that the sun emits as a result of this temperature is called “light of the sun”.
Sunlight consists of different colors that are more or less energetic. About 45% of the light emitted consists of visible light, light that we can see with our eyes.
In addition to this visible light, sunlight also contains light that we can not see: the so-called ultraviolet light (UV: very high energy and harmful to humans) and infrared light (IR: very low energy and therefore with a good penetration power).
The sun also emits X-rays and microwaves in relatively low amounts. However, not all light reaches us on earth. This is due to the protective effect of the Earth’s atmosphere. There are all kinds of gases in the atmosphere, each one absorbs a specific part of the sunlight. For example, ultraviolet light is absorbed by the ozone layer, infrared light largely by water vapor.
What is solar radiation?
Solar radiation is the amount of sunlight that falls on the earth, also called intensity of solar radiation. It is not a fixed fact. It depends on the climate (the condition of the atmosphere at a given time), the climate (the average environmental conditions in a given area over a longer period), the time of year, the location and the changes with the time of day.
With one hour of full sun, it is assumed that 1000 W per m² (= 1 kWh / m²) are irradiated on the surface of the earth. In the Netherlands, the total annual supply of sunshine is around 1000 hours of sunshine (= 1000 kWh / m²). In the winter, around 0.5 kWh / m² per hour of sun and in summer 5 kWh / m², a factor of 10 difference.
What is solar energy?
Solar energy is the technology with which the energy of sunlight is converted into usable energy: electricity or heat.
We distinguish two ways:
- Indirect solar energy : usable energy is produced through a detour. Examples of indirect solar energy are wind, hydroelectric and biomass energy;
- Direct solar energy: the energy of light is often converted immediately into manageable energy with technical help. These technical aids are: solar collectors, solar panels, CSP systems and solar towers.
When people talk about solar energy, it is generally understood the generation of electricity from solar energy through solar panels. This is done mainly by direct conversion of sunlight into electricity through the use of a solar energy facility, also known as “a photovoltaic system” (PV: P = Photo = light, V = Voltaic = electricity).
Forms of indirect solar energy.
Examples of indirect solar energy are hydropower, biomass and wind energy. The usable energy is ultimately produced indirectly.
- Wind energy: solar radiation> temperature / pressure differences> wind> wind motor> electricity.
- Hydroelectric energy: solar radiation> water evaporation> precipitation> storage in a reservoir> turbine blades / generator> electricity.
- Biomass: solar radiation> plant growth> harvest / processing> incineration / gasification> impulse generator> electricity.
Forms of direct solar energy.
We distinguish three forms of direct solar energy:
- Passive solar energy: make optimal use of incoming solar light in buildings for heating and lighting.
- Solar thermal energy: here, the heat of the sun is used, for example, to heat the water. The most common application is a solar water heater.
- Photovoltaic solar energy: photovoltaic systems (PV: P = photo = light, V = Voltaic = electricity)
Why solar energy?
The main reasons to apply solar energy are:
- Solar energy is inexhaustible, sustainable energy source.
- Solar energy can be used in almost all places on earth.
- Solar energy reduces our dependence on energy suppliers, mostly foreigners in unstable countries.
- Solar energy is a clean form of energy, it does not emit harmful gases or particles.
- Solar energy replaces fossil fuels and, therefore, is an important pillar in climate policy.
- Solar energy can be used in many ways.
- Solar energy has no risk of accidents during transport.
- Solar energy is extremely adequate to provide personalized energy.
- Solar energy can make an important contribution to the development potential of people
How does a solar cell work?
The process that takes place in a solar cell is called photovoltaic conversion. The sunlight turns into electricity. The process is more or less as follows: solar cells consist of so-called semiconductor materials, for example, silicon, in which negatively charged electrons are released under the influence of light, which then move and leave “holes” positively charged .
The electrons and the holes are separated from each other because they have a different charge, so that one side is created with a negative voltage and one side with a positive voltage.
By connecting both sides together, an electric current can start to run and, therefore, one has electricity. The photovoltaic process continues as the light falls on the cell.
The current obtained is direct current. This current can be converted by means of an inverter into alternating current so that it can be supplied directly to the electrical network or to a battery. Direct current could also be used directly to drive a pump, for example.
Sunlight consists of different colors that are absorbed to a greater or lesser extent by the solar cell. The degree of absorption is determined by the semiconductor material used to build a solar cell.
Such material is not equally sensitive to all colors of light. Solar panels use mainly visible light (around 45% of sunlight), light that we can perceive with our eyes.
Light consists of photons (= light particles of solar radiation = energy packets) that determine the color of light.
The photon must have a minimum amount of energy required to release electrons in the semiconductor material. If the energy is higher than the minimum required, the excess energy is released in the form of heat. In this process, approximately 55% of the energy in the light is lost.
The electrons then have the property of falling back to their previous state. The theoretically feasible conversion efficiency, therefore, is not higher than 20-30%.
What is the maximum conversion of a cell?
At this time, the best small solar cells with an optimum color sensitivity at the laboratory level have an efficiency of at most 32%. Commercially produced solar cells currently have an efficiency of between 6% and 16%.
Amorphous silicon solar panels (thin film) have an efficiency of between 6% and 8%, monocrystalline solar panels give 15% to 16% and polycrystalline solar panels give an efficiency of approximately 14%.
Types of solar cells
The most important types are:
- Monocrystalline silicon solar cells (mono-Si)
Solar cells made of silicon slabs, cut from a large “single crystal”. The slices are generally square and vary from 10 x 10 to 15 x 15 cm. Round cells are also available.
- Multi-or polycrystalline silicon solar cells (multi-Si or poly-Si)
. They are cheaper, easier to manufacture and the efficiency is slightly lower than that of monocrystalline solar cells. The cells are 10 x 10 to 15 x 15 cm in size.
- Thin-film solar cells (thin-film cells
) Thin -film solar cells are manufactured using evaporation techniques in which the semiconductor material is applied in a very thin layer (1 micron) on a glass substrate or flexible material. Because this requires much less material, these solar cells are cheaper. This technique basically makes all shapes and dimensions possible. The term “amorphous” refers to the lack of a crystalline structure. The different types of thin-film solar cells are:
- Amorphous silicon and silicon germanium.
- Indian Copper Dielenide
- Cadmium Telluride
- Thin film of crystalline silicon.
- Tandem cell concentrator
- Solar cells sensitized by dye
- Organic solar cells (polymeric).
Watt peak (Wp)
Watt peak (Wp peak) is the electrical power that a solar cell supplies with an irradiation of 1000 W / m² and a cell temperature of 25 degrees Celsius, the so-called peak power. Under these conditions, a 1 Wp solar cell delivers 1 watt of power.
What is a solar panel?
It is a transparent device on the front. The back may have a transparent and opaque coating layer. A solar panel initially supplies direct current. With the help of an inverter, the direct current can be converted to 230 volts of alternating current.
With a solar panel, sunlight turns directly into electricity. On average, solar panels have an area of approximately one square meter and a thickness of 5 to 8 mm. Usually, there is a junction box on the back to connect the panels together and connect them to the inverter.
The solar cells are coated to limit the reflection of sunlight. The color of the coating determines the degree of reflection reduction, but the color coatings (yellow, green, purple, brown, gray and purple) have 10 to 30% less performance than dark cells (dark blue or black) .
Performance of a solar panel
The performance (= amount of electricity produced) of a solar panel is determined by the amount of radiation that the solar panel can absorb.
The power supplied by a solar panel is directly proportional to the radiation, but decreases with increasing the temperature of the cell. In other words: the more solar radiation, the more electricity can be generated. However, the warmer the temperature of the solar panel cell, the lower the conversion. The performance depends on:
- Solar radiation: the amount of impacting sunlight.
- The ascending slope: the highest yield is obtained in the Netherlands with a slope of 36 °. At inclination angles between 20 ° and 60 °, the annual yield is only 5% lower.
- Side angle: this angle is the most optimal in the Netherlands when the panel is stationary oriented at 5 ° west of the south.
- The angle of the light barrier: this angle must be less than 15 ° on the roof surfaces.
- Orientation (east, west or south).
- Surface of solar cells and modules.
- Watt peak (= peak power): the electrical power supplied by a solar cell with an irradiance of 1000 W / m² and a cell temperature of 25 degrees centigrade.
- Shade: a solar panel that is shaded can conduct less electricity, which leads to more than proportionally reduced performance because the panels are often connected in series. In the case of shade, think not only of the shadow of the hanging branches or the edge of a roof, but also of the shadow as a result of tall buildings in the area.
- Cell temperature: leave enough ventilation space around the panels so they can lose their heat. A higher temperature ensures a lower electricity yield.
- Quality (material) of the solar cell.
What is the useful life of a solar panel?
Solar panels last from 30 to 35 years. In general, solar panel manufacturers guarantee that solar panels will continue to produce at least 80% of the original performance after 25 years.
Most solar panels also have a product warranty of at least 5 years. If they are discarded, they can go to the municipal cleaning service as electronic waste. The solar industry is working on a complete recycling system.
Is it necessary to clean the solar panels?
It is very prudent to clean the solar panels regularly. A thin layer of dirt begins to accumulate in the installation, which over time results in a loss of efficiency because the amount of solar radiation is limited.
The research carried out by Dr. H. Häberlin on the effect of cleaning the photovoltaic panels shows that the cleaning of the solar panels provides an efficiency improvement of 8% to 12%, if the cleaning is done every 4 years, which means that solar panels lose between 2 and 3% per year of efficiency due to pollution.
In more polluting conditions, the loss of performance can even double.
The speed of contamination depends strongly on the location. Flight routes for migratory birds, incinerators, railroads, busy highways, heavy industry and the like result in significantly faster development of a layer of land.
Due to the slope of the solar panels, the panels are cleaned with rain, but this does not prevent a clear contamination.
It is very important to clean the surface of the solar panels with materials that do not cause damage, since the scratches ensure a permanent reduction in performance. It is also not advisable to polish the solar panels with a high pressure cleaner.
It is not necessary to use a universal cleaner to clean the solar panels, since this type of cleaning product can damage the solar panels. It is best to use osmosis water to clean the solar panels.
Electric assembly of solar panels.
- A system of solar panels with a total capacity of 600 W can be connected to a group in the fuse box. If you want to place a larger capacity, an additional group is required.
- The supporting structure of the solar panels can transmit sound from outside the home. This can be avoided by interrupting the load structure on the separating walls of the house.
- With a sloping roof you must have 1 m² per solar panel; With a flat roof you have to have 2.5 m² per panel. In a flat roof, the panels are placed diagonally in vertical position, which means that additional space is needed to prevent the panels from projecting to each other.
Maintenance of solar panels
Solar panels hardly require maintenance. Performing maintenance once a year is enough. The maintenance can consist of two inspections:
a visual inspection of breakage of cables and panels, inspection of corrosion, loose cables and fasteners, changes of photovoltaic installation and inspection of rubbers and joints;
A functional inspection: inverter reading (s), chain voltage verification, monitoring equipment monitoring and performance analysis.
Installation of solar energy
Types of solar energy installations.
These systems are named after the English photovoltaic (P = Photo = light, V = Voltaic = electricity). Photovoltaic systems use one or more solar panels to convert sunlight into electricity.
There are two kinds:
- Autonomous systems: these systems are not connected to the grid, electricity is supplied to a battery or directly to a device, for example, to a pump. This involves direct current (DC = Direct Current).
- Systems connected to the network: here electricity is supplied to the public electricity grid. To do that, you must first convert the direct current to 230 volts AC using an inverter (AC = Alternating current).
Concentration of solar energy (CSP)
The CSP system uses mirrors to direct sunlight to a receiver that can withstand very high temperatures. This receiver contains liquid or gas that transports the heat to a steam turbine, an external combustion engine or a generator that converts it into electricity. There are three types:
- Parabolic channels: the parabolic channels concentrate solar energy into large U-shaped reflectors. These reflectors direct all sunlight to the oil-filled pipes. The oil is heated to a temperature of 400 ° C and used to heat boiling and producing steam to generate generators and steam turbines, which then generate electricity.
- 2. Energy towers (solar power plants): the energy towers capture the sun’s rays with flat awnings and direct sunlight towards a receiver located at the top of a long tower in which sunlight heats a liquid 570 ° C. The hot liquid can be used to produce steam to power generators that then produce electricity.
- Solar dish motors (plate-shaped energy generation systems): solar dish motors use plate-shaped mirrors to focus sunlight on a receiver located at the focal point. The plate rotates with the position of the sun.
In solar towers, the air is heated by solar heat under a large, flat circular solar collector that is open at the edge. There is a vertical tower in the center of the circle. Due to the heating, the hot air in the tower rises. As a result, the new cold air is attracted to the side of the circle and the process is repeated, creating a continuous flow of air that is converted into mechanical energy by wind turbines. This energy is then converted into electricity by generators.
What is a photovoltaic system?
A photovoltaic system (= solar panel system) is an installation in which sunlight is converted into electricity with the help of one or more solar panels. These systems are named after the English photovoltaic (P = Photo = light, V = Voltaic = electricity).
A photovoltaic system consists of the following elements:
- Solar panels
- System suspension
- Console: only required if the panels are placed on a flat roof.
- Inverter (= inverter) with a system connected to the network
- Battery and charge controller with autonomous system.
How much energy does a photovoltaic system provide?
The average power of a photovoltaic system is always much lower than the maximum power. In sunny desert regions, the proportion is around 23%, for the Netherlands it is 10%.
In other words: a system of 3000 Wp as an example in the Netherlands offers an average power of 300 W. What on an annual basis corresponds to 2628 kWh (300 W x 8760 hours x 0.001)
Golden rule: 1 Wp generates between 0.75 and 0.85 kWh of electricity per year
How much does a photovoltaic system cost?
For standardized systems, connected to the network on the roofs of houses, the indication price for a prepared system is a price between € 2.35 and € 3.25 per Wp, without VAT.
These costs depend in particular on the type of solar cell used. Both the highest and the lowest prices will be found in the market. Due to the improvement of the scale and the technological improvements, this price will fall in the coming years.
How much does PV electricity cost?
The costs of electricity from a photovoltaic system connected to the grid are determined by a series of factors:
- Energy efficiency (850 kWh per year for a 1 kWp system)
- Investment costs for the photovoltaic system.
- The maintenance and management costs.
- the insurance premium
- The amortization period (20 years).
- The real interest rate (5%).
On the basis of the above assumptions, the following general rule can be applied: the electricity costs per kWh are equal to the investment costs per Wp divided by 10.
Based on a price of € 3.20 / Wp, electricity costs are € 0.32 / kWh. This amount does not take into account a possible subsidy for each kWh produced by the solar panels.
What should I save with a photovoltaic system?
For a photovoltaic system connected to the grid, it is globally applied that 1000 Wp of solar panels produce approximately 850 kWh / year with a favorable orientation and slope.
Based on this, this results in an annual saving of approximately € 195.00. This amount does not take into account a possible subsidy for each kWh produced by the solar panels.
What is a solar inverter?
An inverter with photovoltaic systems connected to the grid is needed to convert direct current into 230 volts of AC so that electricity can be supplied to the public electricity grid.
It is important that the inverter can be ventilated naturally, since many inverters have a lower performance if the inverter temperature is too high. Position the inverter as close as possible to the panels to limit yield losses.
Read more about the most efficient solar panels