All about Solar
What is Solar Energy All About?

We often stumble upon questions such as “What is Solar Energy?”, “What are Solar Energy’s Application?”, “What are Solar Energy’s uses?” But we always get vague answers. So “What is Solar Energy” really?Solar energy is energy from the sun. That much needs no explanation of course.What we can do with solar is however more interesting and diverse than most think.When the term solar energy comes up, most of us visualize either solar panels on rooftops or solar water heaters.Of course, the above two are some of the most prominent end uses of solar energy, but there is more

To enable easy understanding, just as sunlight can be considered in two forms – heat and light – solar energy can also be divided into two main components – Solar Light Energy and Solar Heat Energy.

• Solar Light Energy – In this, the main objective is to convert to electricity the energy contained in sunlight in the form of photons. This sector is known as Solar Photovoltaic or Solar PV in
• Solar Heat Energy – In this, the objective is to use the sunlight’s heat energy as thermal energy or to generate electricity. This sector is known as Solar Thermal.

If you ask an amateur, “What is Solar Energy?”, this is the kind of explanation and classification, they would tell. These above classification sounds really simple, doesn’t it? It indeed is, but do note that each of the above two classifications (PV and Thermal) has a number of categories and components within it.

Such diversity is what makes the question “What is Solar Energy?” an interesting question to answer and also makes solar energy perhaps the most effective renewable energy source of the future.

This diversity is what helps solar energy to be applied for a number of applications – for heating water for your residence, for running a turbine similar to what coal based energy does, for running solar water pumps, for powering your mobile phones in remote areas, or in the form of giant solar farms that can run into 100s of MW and power tens of thousands of houses.

Today, owing to the fast growth in a number of related technologies, solar energy can be used on rooftops, on agricultural farms, in deserts, to power small lanterns, on laptops and mobiles, in electric vehicles and even yachts, on clothes and handbags, on furniture, in thermal power plants, along with wind turbines…the possibilities seem endless.

Let Us Look at Solar Energy Applications in More Detail
The following chart provides the complete list of solar energy applications
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SOLAR THERMAL

Solar Thermal Energy (ST) is the most direct way to use the energy from sunlight – this method used the heat of the sunlight for heating and drying applications. Simple examples of solar thermal applications are solar water heaters and solar cookers. In some select cases, this thermal energy can also be used to generate power too

SOLAR PV

The PV in solar PV stands for photovoltaic, which simply means light to power. Solar PV systems convert the light energy in sunlight (in the form of photons) to electricity, through the use of semiconducting materials. The photons excite the electrons in the semiconducting material, resulting in a flow of electricity.

For an interesting illustration of how solar energy works Click Following link- https://www.saveonenergy.com/how-solar-panels-work/

SOLAR THERMAL (HEAT APPLICATION)

Solar thermal applications are many, and the process of heating can be direct or indirect. Depending upon the temperature of heating application, it is classified into – Low Temperature, Medium Temperature and High Temperature Heat Applications. Common examples include solar water heaters, solar cookers, solar dryers etc.

SOLAR THERMAL (POWER APPLICATION)

Solar thermal energy can be used to generate power too. This is done through concentrating sunlight through mirrors or lenses. The high temperatures achieved are used to run a steam turbine to generate power.

 
OFF – GRID SOLAR SYSTEM

Systems that are not connected to the gird and function independently are referred to as Off grid solar system. They can be in the form of rooftops solar system and other solar related products such as solar street light, solar lanterns, solar water heater etc.

DISTRIBUTED GRID CONNECTED

Solar power plants, owing to their modularity, are ideal for generation from distributed locations – on rooftops of residences or industries, on car parks and more. Such distributed solar power units can also be connected to the grid so that the system gets the twin benefits of a sustainable energy source and the reliability of grid power.

UTILITY SCALE GRID CONNECTED

Utility scale grid connected power plants are the large solar farms with tens of thousands of panels. These could range from 1 MW to upwards of 100 MW in capacity. The electricity produced by such a power plant is generally exported to the grid for sale to the local utility company or to a private company.

LOW TEMPERATURE SOLAR COLLECTOR

Low Temperature Solar Collector is a classification of Solar Thermal with Heat Application which has an operating limit of up to 80­ deg C. The heat collection can take place either using Flat Plates Collector or Evacuated Tube Collector. Examples of Low Temperature Solar Collector are Solar Cooker, Solar Water Heater

MEDIUM TEMPERATURE SOLAR COLLECTOR

In Medium Temperature Solar Collectors temperatures of up to 150^◦C can be achieved. They are generally used in industries for specific heating or drying applications. Typically, Enhanced Evacuated Tubes and sometimes Parabolic Concentrators are used to raise the temperature up to 150^◦C.

HIGH TEMPERATURE SOLAR COLLECTOR

High Temperature Solar Collectors are used to attain temperatures of up to 250^◦C. In order to reach such high temperatures, large mirrors and lenses are used to capture the solar heat energy and concentrate the heat on to a small area. As these solar collectors achieve the high temperature through concentrating the sunlight, they are often referred to as Concentrated Solar Thermal (CST).

CONCENTRATED SOLAR POWER

Concentrated Solar Power (CSP) uses the heat from the sun to produce power. By means of large mirrors or lenses sunlight is concentrated onto a small area. This solar energy heats the water and produces steam. The steam is used to run a Steam Turbine and further on a generator to produce electricity.

HYBRID GRID CONNECTED SYSTEM

These refer typically to distributed solar power systems that, in addition to being grid-connected, also are connected to another source of power such as a battery or diesel power generator among a few. The advantages of such a system are that they provide uninterrupted power supply and can be programmable according to the available source of energy and the needs of the consumer.

GRID-TIED SYSTEM

A grid tied system refers typically to distributed solar power systems that are connected to the grid and no other source of power such as batteries. In case of a power outage, this system would disconnect from the utility grid, owing to technical and security reasons. In the absence of the grid, the system stops generating electricity.

ROOFTOP SOLAR SYSTEM

A rooftop solar system generates electricity and supply it to the household based on a solar panels mounted on top of the roof.

CONCENTRATED SOLAR THERMAL

Concentrated Solar Thermal, that can provide heat up to 250 deg C, produces thermal energy by using the heat from the sun. Such a high temperature is achieved through large mirrors or lenses that concentrate the heat energy onto a small area. The resulting heat is used directly or indirectly for heating and drying purposes.

SOLAR WATER HEATER

A solar water heater captures the heat of sunlight through a thermal collector and uses it for water heating. The heat energy harnessed can also be stored in a storage tank and use it for later purpose.

SOLAR COOKER

Solar cooker uses the heat of sunlight to heat and cook food and beverages. Solar cookers use reflecting surfaces to concentrate sunlight onto a small area to prepare food items.

SOLAR FARMS

Solar farms refer to grid connected power plants that produce electricity on MW scales. These are usually ground mounted and export all the power to the grid, for sale to the local utility or to a private consumer.

SOLAR LANTERNS

Lanterns that are powered by solar power are referred to as Solar Lanterns. These lanterns charge their batteries from solar panels during the day and can be used at nights. They generally use LEDs or CFLs. These lanterns are commonly used in rural areas to replace the kerosene lamps.

SOLAR STREETLIGHTS

Solar Streetlights are outdoor light fixtures that work on solar energy. During the day these streetlights get charged and the energy is stored on to a battery. At nights, these solar streetlights switch on to light up the streets.

SOLAR WATER PUMP

Pumps that work on the electricity generated by the photo-voltaic panels are called Solar Water Pumps. These pumps are highly efficient and useful in places where power from the grid is either unavailable or is unreliable. The agricultural sector is the main end user of solar water pumps.

Detailed Inputs on Select Products

You will be eager to know how solar energy can benefit you – your house, your factory, your business or your career. The goal of Solar Mango is to help you understand solar energy in an easy and practical manner so that you will be able to benefit from this fascinating renewable energy source.

SOLAR WATER HEATER

Solar water heaters typically consist of two components – a solar collector and storage tank.

• Solar Collector

Solar Collectors are devices that collects heat by absorbing sunlight. The heat absorbed is then transferred to the working fluid (water or anti-freezing liquid). These collectors consists of an absorber which are generally made up of several narrow metallic strip. It also consists of a metallic tube through which the working fluid flows.

• Storage Tank

Storage tank as the name suggests is used to store hot water. These Storage tanks are either connected horizontally on to the solar collector or are ground mounted. In some cases, a heat exchanger is present inside the storage tank.

There are two types of solar collectors that are available in the market:

1. Flat Plate Collector

Flat plate collectors (FPC) is a metallic box with a completely transparent glass or plastic cover. Inside the box is a series of dark colored heat absorbing plates generally made of copper. The sides of the FPCs are covered with insulating materials to keep the heat loss to a minimal.

1. Evacuated Tube Solar Collector

It consists of several glass tube, with each tube being evacuated to reduce the heat loss within. Inside the glass tube are curved or flat metallic tube that is attached with a fin to absorb the heat.

So how does the water get heated?

• When there is requirement of hot water, cold water flows through the metallic tubes in the collector.
• The absorber present in the collector transfers the heat harnessed from sun light to the water.
• The hot water through the outlet pipe is supplied to homes or is stored in the storage tank for later use
• In some cases, where higher temperature are desired, an anti-freezing fluid flows through the collector instead of water.
• The heat from the absorber is transferred to this anti-freezing fluid.
• The anti-freezing fluid then flows into the storage tank, which would consist of a heat exchanger.
• The cold water too flows into the heat exchanger, where heat transfer takes place between the water and anti-freezing fluid.
• This hot water thus obtained is either stored in the tank itself or sent out to homes.

SOLAR COOKER

Cooking using solar cooker is done by means of UV rays from the sun. A solar cooker lets the solar UV rays in and converts them to Infrared rays. These Infrared light rays has the right amount of energy to make water, fat and protein particles in food to vibrate and in turn heat them up. On the contrary to what people think about the direct heat from the sun being used to cook food, it is the rays from the sun that are converted to heat energy which contribute maximum for cooking of food in the solar cooker. This heat energy is retained in food by covering the lid of the vessel.

There are three major types of solar cookers that are used –
Box Solar Cooker

Box solar cooker is the most common and simplest type of solar cooker. It is based on the design of traditional modern ovens, where the food in the vessel is placed inside an insulated box which is covered with a transparent glass, to allow the sun rays to pass through it on to the vessel. The solar UV rays are converted to longer Infrared rays that heat the vessel. Some UV rays that do not get converted into longer Infrared rays, are retained inside the box to build up the temperature and make the box a desirable place to cook food. Reflecting panels are also used to concentrate the sun rays towards the vessel for higher cooking temperature and effectiveness.

Panel Cooker

Panel Cookers consists of a darkened cooking vessel, an oven cooking bag and reflecting panels. These panels are made of aluminum foil or from tin or sheet metal that are polished to high sheen. Even mirrors are used as reflecting panel.

The reflecting panels concentrate the sun light on the cooking bag. The cooking bag in turns allows the UV rays to penetrate on to the cooking vessel, in trapping the energy and prevent it from escaping. The Panel Cooker works similar to Box Solar Cooker, however it much simpler and economical to build and results in the same effectiveness.

Parabolic Cooker

Parabolic Cookers are also known as curved concentrator oven. In comparison to other solar cookers, parabolic cookers create higher temperature which results in food being cooked faster. They reflect the sun’s rays onto the cooking vessel by means of the curved reflecting surfaces. They are much more expensive when compared to Box and Panel solar cookers. It also requires close supervision and regular adjustments for the cooker to work effectively.

Different Types of Solar Cookers

CONCENTRATING SOLAR POWER  

Concentrating Solar Power (CSP) uses large mirrors to concentrate the heat energy from sun to drive a traditional steam turbine. This in turn is used to create electricity. CSP broadly consists of large reflecting mirrors called Heliostats and a receiver. There are four types of CSP –

1. Trough System

Trough systems consists of large U-shaped reflectors with an oil filled receiver present at the center of the reflector or the focal point. These reflectors are tilted towards the sun to harness maximum solar energy. When sun light falls on these reflectors, they reflect it towards the receiver. Because of the concentrating solar power on the receiver, the oil in the receiver reaches temperatures of 750 °F. This hot oil is used to heat the water, which produces steam to run a steam turbine or generator.




Trough type CSP
2. Power Tower System

Power Tower System also called central receivers use large number of reflecting mirrors that track the sun in two directions. All the sunlight that falls on the reflecting mirrors are reflected on to a receiver which is placed on top of a tower. Inside the receiver is molten salt, which is heated to temperatures of 1050°F. The heated molten salt is used to produce steam by heating the water. Steam so produced is used to run a steam turbine/generator, which in turn helps in producing electricity. Molten salt can retain the heat obtained for 3-4 days. This helps in electricity being produced even during nights when there is a shortage of sunlight.

3. Dish Engine System

Dish Engine Systems consists of large parabolic reflecting mirrors that are used to focus the sunlight on to the receiver which is placed at the focal point of the mirror. To capture maximum heat from the sun, the mirrors track the sun across the sky. The receiver is integrated with an external combustion engine. This engine has a thin tube consisting of Hydrogen or Helium gas that run along the outside of engine’s cylinder. Due to the heating of the receiver, hydrogen or helium gas expand inside the cylinder which enables the piston to be driven. The piston in turn is connected to the generator to produce electricity.




Dish Engine Type CSP
4. Linear Fresnel Reflector

Linear Fresnel Reflectors work on the principal of Trough System, but with the use of long parallel rows of low cost flat mirrors. The sunlight is reflected from the mirrors on to the elevated receiver tank. This receiver tank consists of a system of tubes through which water flows. The concentrated heat, boils the water to produce steam which is us to run the generator.

MEDIUM TEMPERATURE INDUSTRIAL SOLAR THERMAL

Industrial heating application can be classified into three categories – low temperature (<80°C), medium temperature (80°C-250°C) and high temperature (>250°C). While the usage of solar thermal energy in the low and medium temperature category in the industry are limited, they do exist and are on the verge of emerging into competitive commercial usage. At present only 27% of the industrial heating falls in the category of medium temperature heating, of which only a fraction is used using solar thermal.

The medium temperature usage of solar thermal are suited for food, beverage, textiles, paper, and automobile industries. Processes such as sterilizing pasteurizing, drying, hydrolyzing, distillation & evaporation, washing and cleaning, painting, electroplating, bluing enhanced oil recovery etc. are few processes where medium temperature industrial solar thermal are used.

Solar Rooftops

When photovoltaic panels are installed on the roof of commercial or residential building to generate electricity for themselves, it is called Solar Rooftops. Photovoltaics panels are made up of semiconducting materials.

The generation of electricity through PV panels is based on the concept of Photovoltaic effect – wherein, photons (Sunlight) fall on the panels, exciting the electrons in them. Due to the excitation, the electrons start to flow resulting in electricity. The electricity so produced is sent to the inverter, to convert DC to AC. From the inverter the Alternating Current is sent directly to various load that require electricity. In the case of battery, the electricity is provided to both the load as well as the loads. The presence of battery enables the electricity to be stored for later usage.

Broadly the solar rooftop systems are classified into two – off grid and on grid. In the case of off grid, the system works completely independent of the grid. These systems are effective only in places where there is no electricity. In the case of on-grid, houses are connected to both the rooftop as well as the gird. When there is surplus of electricity being produced, it is sent to the grid. Also in the case of a shortage of electricity being produced, electricity from the grid is used to over the shortage. On grid system too may have batteries for backup.

SOLAR POWER PLANTS

Solar Power Plants also work on the concept of Photovoltaic effect, where – when sunlight falls on PV panels, it produces electricity. These plants produce electricity in large capacity (> 1 MW) by using hundreds and thousands of PV panels. The electricity so produced is fed into the electricity grid or to 3^rd party commercial consumers.

Water Pump

Solar water pumps are those pumps that work on the electricity generated from solar panel as opposed to the conventional water pump. The solar panels matches the power rating for the pump, before supplying electricity. These pumps are extremely useful in places which has abundance of sunlight. The solar panels convert the sunlight falling on them into direct current electricity. A controller acts as an interface between the solar panels and the pumps. It matches the output power that the pump receives with the input power available from the solar panels. Once the energy from the solar panels is matched with the pumps, it is used to power the motors. These motors can be either DC or AC. If AC motors are used, an inverter is used to convert the direct electricity produced from the panels. DC motors directly run on the power produced. These motors are used to drive the pumps which can be either centrifugal or submersible pumps which deliver water from the source to the destination which is usually a reservoir/tank.

1. So, are solar water heaters different from solar panels that produce electricity?

Yes, solar water heaters and solar panels that produce electricity are different. Though both use sun as their source of energy, solar water heater uses the heat of sun for heating of water, while solar panels uses sun light (photons) to produce electricity.

2. The solar panels on rooftops, are these technically called solar PV?

Yes, the solar panels on rooftops are called solar PV. Solar panels work on the concept of Photo-voltaic effect, where the photons (sunlight) excite the electrons in the solar panel that results in flow of electricity.

3. If solar is such a great source of power, why isn’t every house using solar?

Even though solar is a great source of power, there are many factors that needs to be considered before setting up solar panel. These panels are expensive, require large area for installing. Moreover, solar power is only effective where there is sufficient sunlight. Because of the above factors, it is not feasible to have solar power in every household.

4. There are other sources of renewable energy such as wind energy, hydro energy, biomass energy wave energy etc. Why is everyone talking only about solar energy?

Though there are other sources of renewable energy, solar energy is considered to be the best as it has no moving part, requires almost no maintenance, has a life of 25 years. Moreover, solar energy has the capacity to supply 35000 times more energy to earth than what is being consumed.

5. Is solar energy growing fast in all regions of the world?

According to International Energy Agency (IEA), as of 2014, 178 GW of global solar PV capacity has been added cumulatively. And by end of 2015, this capacity is set to increase to 233 GW. Canada, UK, France, Germany and India have set high targets for solar power generation by 2020. In short, yes solar energy is growing fast in all regions of the world.

6. I keep hearing that costs of solar power are coming down. Is solar power really very cheap today?

Cost to install 1 kW of solar PV panels in 1977 was $ 76.67/-, while the same cost had come down to less than $1 by 2015. Over the last four decades years, the cost of installing solar panels had thus decreased by almost 99%!

7. Briefly, what are the main applications for which solar energy is put to use in industries currently?

Solar energy is applied in a wide range of industries already. In the form of solar thermal, it is used in industries for a range of heating, cooking and drying applications. In the form of electricity, pretty much any industry (and commercial establishments and residences) can today use solar power at least to a certain extent.

8. You have mentioned about solar products under “Distributed Off-grid”. Do these also generate electricity? If yes, how?

Yes and No! Certain solar products such as solar cooker and solar water heater do not generate electricity. They directly use the heat of the sun to satisfy their needs. However, other solar products like solar lanterns, solar streetlights etc, produce electricity. However this electricity generated is so low that it can only satisfies its own needs.

9. You have mentioned solar CSP (concentrating solar power) generates power from solar thermal energy. How is the growth of CSP when compared to the mainstream method of solar power, which is solar PV?

CSP has a better capacity utilization factor compared to solar PV and also it is easy to store heat when compared to electricity. However, unlike PV, CSP are not scalable (i.e small capacity CSP are difficult to function). It is due to this reason people prefer solar PV over CSP resulting in CSP lagging being solar PV, which is the mainstream method of solar power.

10. How much does solar power contribute to the world’s electricity today? Is it large enough?

Even though solar power contributes about 178 GW of electricity to the world today, in terms of the total electricity consumption, a mere 1% of total electricity is generated through solar power.

11. I keep reading about “utilities” in the context of solar power. What are utilities?

Utilities are commercial body that own and operate facilities for the generation, transmission and distribution of solar energy to residential and commercial consumers.

12. What is the meaning of the term “Distributed Energy”?

Distributed Energy are power generated from a variety of small power sources that are connected to the gird.

13. I heard that many solar installations such as solar streetlights and water pumps do not work for long. Is solar technology immature?

Solar technology came into existence first in 1876. However, in terms of economy, solar technology has be prevalent in the market for about 8-10 years. However, in these 8-10 years the solar technology has grown drastically. This is evident from the fall in the price of generating 1MW of power over the years. However there is still a long way to go for solar technology, in terms of efficiency and life of product.