Solar power plant is a facility, which utilizes or converts sun’s rays to produce electricity.
There are two categories of solar power plants, and both the types are differentiated based on how they are converting the energy from the sun into electricity.
The two types are Photo-voltaic power plants and second one is solar thermal power plants. Both of these power plants use discretely different kinds of techniques to extract the power of sun.
In this article we will elaborate more on the different types of solar power plants and also go through their working mechanism as to how they harness solar energy and produce electricity.
1. Photovoltaic Power Plants
Photovoltaic power plants utilize photovoltaic cells also known as solar cells to convert solar energy directly into electricity. Photovoltaic cells are made of silicon alloys.
Solar energy consists of particles called photons, which strike the surface of photovoltaic cells present in between the two semiconductors.
These semiconductors project a property where they absorb the photons and release electrons and this phenomenon is known as photoelectric effect. The electrons are captured in the form of electricity.
The panels used in the photovoltaic plant are of two types or two forms. One is Crystalline solar panel and the other one is Thin film solar panel, which are elaborated below:
Crystalline solar panel:
These solar panels are made from crystalline silicon, they can be either mono-crystalline or poly- or multi-crystalline. If we talk about in terms of efficiency then mono-crystalline versions are more efficient than others are.
They are 15-20% more efficient whereas the other two forms tend to be 13-16% efficient and if we talk about prices then mono-crystalline version is quite expensive.
Each forms are going under a lot of advancements over time and due to these advancements, the gap between them is becoming very close over time.
Thin-film solar panel:
These solar panels consists of a series of films that extract light in different parts of EM spectrum.
These solar panels are made from materials namely copper indium (gallium) diselenide, morphous silicon (aSi), cadmium sulfide (CdS), and cadmium telluride (CdTe).
These panels are ideal for applications as flexible films or for integration purposes within structural development like roofing tiles.
Photovoltaic power plants generate electricity and then that electricity is fed directly into the national grid. These power plants have following components:
- Solar panels that convert solar power into electricity usually generate DC current with voltages up to 1500v.
- The power plant management will employ step up transformers, if the power plant generates power in excess of 500KW
- These power plants need investors in order to transform DC into AC.
- Efficient monitoring systems are placed in the whole are to control and manage the power plant.
1.1 How Does A Photovoltaic Power Plant Work?
The materials used in most of the photovoltaic cells are made of semiconductors; these materials are usually some form of silicon.
When photons present in the sun’s rays strike the semiconductor material, free electrons are released which can then flow through the material and produce a direct electric current.
This is the principle photoelectric effect which we mentioned earlier as well. The Direct current(DC) then needs to be converted to Alternating current(AC) using an inverter, before it can be used or fed into the electrical grid.
Photovoltaic power plants are quite different from other solar power plants as they utilize the photoelectric effect directly without there being a need to use other devices or processes.
Photovoltaic cells simply convert the photons present in the sunlight and convert them into electricity, which is, transmitted somewhere else, they don’t concentrate any energy.
They work on a very simple principle which is to absorb the light and then convert it to power.
2. Solar Thermal Power Plants
Solar Thermal power plants generate heat and electricity by concentrating solar energy that in turn builds steam, which helps to feed a turbine and a generator to help produce electricity.
Solar thermal power plants can be categorized or subdivided into three types, which are parabolic troughs, solar power towers and solar pond. All the types have been elaborate below.
2.1 Parabolic Troughs
These are the most common type of solar thermal power plants which use parabola shaped reflectors that can focus ranging from 30 to 100 times more sunlight levels on the collector than its normal intensity.
To heat a special type of liquid, this method is used. And then that liquid is collected at a central collection to generate super heated, high-pressure steam.
To keep track of the sun all day, these parabolic systems tilt and thanks to their parabolic shape they can focus more intensively on the collector with a good range.
The first plant, SEGS 1, was built in 1984 and it operated until 2015. SEGS IX is the last plant built with a power generation capacity of 92 megawatts (MW), and it started operating in 1990.
2.1.1 How Does A Parabolic Trough Work?
These sorts of solar thermal power plants work by concentrating sunlight from huge parabolic mirrors onto recipient tubes that run the length of the mirror at their point of convergence.
The Parabolic troughs consists of distinct systems that are characterized by the use of fields of either linear U- shaped or solar dishes which are elaborated below:
Linear Concentrating Systems
These systems are also called as Fresnel reflectors; they consist of large fields, which are filled with sun tracking mirrors. In order to maximize the sunlight capture, these mirrors are setup in a north south orientation.
This alignment allows the sun tracking mirrors to track the light throughout the day. In similarity to parabolic mirrors, linear concentrating systems collect solar power using rectangular, U-shaped long mirrors.
These systems use Fresnel lens effect, which allows the use of large focusing mirror with short focal length and large aperture, and this type of setup allows to focus sunlight around 30 times more than the normal intensity.
Solar Dishes System
Just like Parabolic systems, solar dishes also use mirrors to focus the solar energy on to the collector. These systems consist of large satellite dishes having small mirrors that focus energy on the receiver at the focal point.
The dish shaped surface directs and focuses sunlight on the thermal receiver and then the heat generated is transferred to an engine generator.
Solar dish systems always point straight to the sun and concentrate the power at the focal point of the dish.
As compared to linear concentrating systems, the concentration ratio of solar dish systems is much higher. Its working fluid temperature is greater than 749 degree Celsius.
2.2 Solar Power Towers
This is an interesting method, which uses hundreds and thousands of flat sun-tracking mirrors called heliostats, which concentrate and reflect solar power onto a central tower.
As compared to directly sunlight alone, using this method increases the concentrating intensity 1500 times than normal. This kind of power plant can be found in Juelich, North-Rhine Westphalia, Germany.
This power plant setup over there amasses a total of 18000 km squared in area and houses more than 2000 heliostats, which concentrate sunlight on the central tower, which is 60 meter high.
Currently in U.S, there are three solar power towers, which are operating.
2.2.1 How Does A Solar Power Tower Work?
In the tower, the solar energy is used to heat the air at 700 degree Celsius.
The heat is captured in the boiler region and then with the help of steam turbine, the heat is used to produce electricity. Likewise, a few towers utilize water as the heat transfer fluid.
These days, more efficient and advanced systems are being researched for the usage of nitrate salts because of their higher heat transfer rate and storage properties, which are better as compared to water and air.
Since these towers have thermal energy storage capabilities so that allows the system to generate electricity during nigh time or during cloudy weather, when there is no sun.
This makes these towers really appealing and these are very well suited for operating in adverse weather conditions. There have been reports which have proved that they have withstood sandstorms and hailstorms. Hence, this shows the durability and the quality which in turns give great results in terms of producing or generating electricity.
2.3 Solar Pond Power Plant
Solar pond power plants utilize a pool of saltwater that collects and stores solar thermal energy and it uses a technique known as salinity-gradient technology.
This technique acts as a thermal trap inside the lake which can either be utilized at that point of time or can be stored for later use.
2.3.1 How Does A Solar Pond Power Plant Work?
Solar ponds utilize an enormous assortment of saltwater to gather and store thermal energy.
Saltwater normally frames a vertical saltiness inclination, known as a halocline, with low-saltiness water on the top and high-saltiness water at the base.
Salt fixations levels increment with depth, and accordingly, density also increments from the surface to base of the lake until the arrangement winds up uniform at a given depth.
The rule is genuinely straightforward, Solar rays penetrate the pond and eventually reach the bottom of the pool.
As the high-salinity water doesn’t blend effectively with low-salinity water above it, convection currents are contained inside each discrete layer and negligible blending or mixing between them occurs.
This process focuses thermal energy and reduces the loss of heat from the water. On an average scale, high-salinity water can reach upto 90 degrees Celsius with low-salinity layers maintaining around 30 degrees Celsius temperature.
Then with the help of a turbine, this hot salty water can be used for the production of electricity or as a source of thermal energy.
We hope this elaboration of the solar power plants, their numerous types and versions and also their working mechanism makes you more interested to know what solar energy has to offer.
Solar power plants are powering cities in the most efficient manner, the power generation is very high and due to their storage capabilities, the utilization of the stored energy is done in a pretty smart way.
It’s a really good thing, when it comes to powering the lives and homes of people in a safe, clean and renewable way. What better way to do that than going solar.
More advancements are being made from the solar application’s perspective and we will be witnessing all the system advancements in the near future and reap its benefits.