SOLAR OVERVIEW

Solar energy is a renewable, free source of energy that is sustainable and totally inexhaustible, unlike fossil fuels which are finite. It is also a non-polluting source of energy and it does not emit any greenhouse gases when producing electricity. The solar electricity that is produced can supply your entire or partial energy consumption.

However every innovation has pros and cons

Pros:

• Pollution free, clean and safe compared to the conventional methods like thermal, fossil fuels, nuclear.
• Weight for weight, silicon solar cells generate the same amount of electricity over their lifetime as nuclear fuel rods & are much safer.
• The amount of energy that goes into creating solar panels is paid back through clean electricity production within anywhere from 1-2 years.
• A solar panel can work for decades as lifetime of a solar module is 25-30 yrs. Some installed in the 1970’s are still generating electricity. Most parts of the solar PV system can be recycled after its lifetime.

Cons:

•  Works only for limited time in a complete day (24 hrs).
• Solar cells have efficiency about 15%-20%, new advancements yields up to 21.5% this can be expected to improve further as cell level research is progressing.
• During the manufacturing process of solar cells there will be certain amount of pollution, which can be minimized using the latest advancements in the manufacturing processes.
• High initial cost but can be retained in the near future.

Solar energy applications:

Solar energy is generally used in two domains

1.Solar Heat energy       2. Solar Photon energy (Light)

Solar heat energy: The heat energy which reaches the earth’s surface is used for heating applications. These include cooking, water heating and thermal power generation.

Solar cooker: Solar cookers use sunlight for cooking, drying.

They are of 3 categories: Box cookers, Panel cookers & reflector cookers.

• A basic box cooker consists of an insulated container with a transparent lid. It can be used effectively with partially overcast skies and will typically reach temperatures of 90–150 °C

 

 Box cooker

• Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures comparable to box cookers.Reflector cookers use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking container. These cookers reach temperatures of 315 °C and above but require direct light to function properly and must be repositioned to track the Sun.

Parabolic reflector type solar cooker

Dish type reflector based solar cooker

Fresnel mirror based solar cooker

Solar water heating:  These systems use heat produced by the sun. The most common types of solar water heaters are evacuated tube collectors ( occupies 44% of existing solar water heaters) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.

Solar water heater

Evacuated tube type solar water heater

Solar thermal power generation:

Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy or electrical energy for use in industry, residential and commercial sectors. In solar thermal energy plants, solar radiation is concentrated by mirrors or lenses to obtain higher temperatures – a technique called Concentrated Solar Power (CSP).

These high-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for fulfilling heat requirements up to 300 deg C / 20 bar pressure in industries, and for electric power production.

Two categories include Concentrated Solar Thermal (CST) for fulfilling heat requirements in industries & Concentrated Solar Power (CSP) when the heat collected is used for power generation.

Concentrating Solar Power (CSP): Concentrating solar power (CSP) plants are utility-scale generators that produce electricity using mirrors or lenses to efficiently concentrate the sun’s energy. The four principal CSP technologies are parabolic troughs, dish - Stirling engine systems, central receivers, and concentrating photovoltaic systems (CPV).

Concentrated solar power plant

Ouarzazate Solar Power Station (OSPS) (Morocco)

Gema solar thermal power plant (Spain)

2. Solar Photon energy: 

This domain explains about harnessing of solar energy particularly for the production of electricity. The basic working principle lies in conversion of photon energy (light) into electrical energy which is carried by solar Photo voltaic cell. The energy obtained is DC similar to most of the renewable energy methods. Again based on the utilization two categories are formed in this domain.

a.      ON - grid PV system

b.      OFF - grid PV system

Photo voltaic: Photovoltaic or PV technology employs solar cells or solar photovoltaic arrays to convert energy from the sun into electricity. Solar cells produce direct current electricity from the sun’s rays, which can be used to power equipment or to recharge batteries.

PV module: Grouping of solar PV cells together is called PV modules that are in turn arranged in solar arrays.

OFF - grid solar system:  This type of system is used to power the specified loads for which it is designed & requires energy storage elements (like batteries) & are free from the utility grid. Mostly used for house hold requirements in the form of rooftop, also other products includes like solar street lights, solar lamps etc.

ON - grid solar system: This is a major and mostly practiced solar application so far. Several KW to hundreds of MW of generated power is being connected to the utility grid, these kinds doesn’t require any energy storage elements.

OFF – grid solar system:

• Roof top solar PV system (OFF – Grid):   Rooftop PV system is a photovoltaic system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a system include photovoltaic modules, mounting systems, cables, solar inverters, batteries other electrical accessories.

• The generated power during the day is stored in the batteries and during night, outages, power cuts the stored energy is used to run the loads.
• Rooftop mounted systems are small compared to ground-mounted photovoltaic power stations with capacities in the megawatt range. Rooftop PV systems on residential buildings typically feature a capacity of about 5 to 20 kilowatts (kW), while those mounted on commercial buildings often reach 100 kilowatts or more.

• Solar lighting (lanterns, street lights): Runs on the same concept of off-grid rooftop system, but here the load is only lighting & generally during day time Generated power from PV panels is stored in the respective battery, during the night the street light/lanterns will extract the energy from the battery to run for its cause.

• Solar Vehicles (Cars): A solar car is an electric vehicle powered by energy obtained from solar panels on the surface of the car which convert the sun’s energy directly into electrical energy. Solar cars are not currently a practical form of transportation. Although they can operate for limited distances without sun, the solar cells are generally very fragile. Development teams have focused their efforts on optimizing the efficiency of the vehicle, but many have only enough room for one or two people.

•  Solar water pumps:  A solar-powered pump is a pump running on electricity generated by photo voltaic panels or the radiated thermal energy available from collected sunlight as opposed to grid electricity or diesel run water pumps. The operation of solar powered pumps is more economical mainly due to the lower operation and maintenance costs and has less environmental impact than pumps powered by an internal combustion engine. Solar pumps are useful where grid electricity is unavailable and alternative sources (in particular wind) do not provide sufficient energy.

Solar water pump

ON-Grid solar PV system:

• Roof top ON- Grid: Roof top On – grid is same as off grid working principle wise but here the generated power is directly connected to the utility grid (distribution level), continuously the power is fed back to the system and a separate energy meter is used to count the reading, rooftop generators do use the utility power and will be charged against it, however they have a reduction in the bill for the feedback power (the costs per unit (KWh) of utilized, feedback power will vary  from region to region and it depends on the policy rules).

• Solar PV power plants: This system is used to generate power in huge amounts and the generation is fed to the utility grid thereby supplying the demand, the range of power varies from MW’s to GW’s. It got popularized than any other renewable option because of its advantages. The working includes the generation of DC power which remains the input to the inverter (converts DC to AC) and output is synchronized & connected to the respective grid.