Renewable Energy Interview Questions

Renewable energy is energy obtained from sources that are essentially inexhaustible. Examples of renewable resources include wind power, solar power, geothermal energy, tidal power and hydroelectric. The most important feature of renewable energy is that it can be harnessed without the release of harmful pollutants.

Non-renewable energy is the conventional fossil fuels such as coal, oil and gas, which are likely to deplete with time.

The energy consumption of a nation can be broadly divided into the following areas or sectors depending on energy-related activities. These can be further subdivided into subsectors:

1. Domestic sector (houses and offices including commercial buildings)
   1. Transportation sector
   1. Agriculture sector
   1. Industry sector

Consumption of a large amount of energy in a country indicates increased activities in these sectors. This may imply better comforts at home due to use of various appliances, better transport facilities and more agricultural and industrial production. All of this amount to a better quality of life. Therefore, the per capita energy consumption of a country is an index of the standard of living or prosperity (i.e., income) of the people of the country.

2020 is the year of Covid, So the decline in Global Energy Consumption and carbon emissions is -4.5% and -6.3% respectively, the largest fall since 1945 (as per “bp Statistical Review of World Energy 2021”)

As per the production scenario, there is no impact of Covid-19 on Renewable Energy. Despite the huge disruptions associated with the global pandemic, wind and solar capacity increased by a colossal 238 GW in 2021 – 50% larger than at any time in history.

It is the ratio of the reserves remaining at the end of the year are divided by the production in that year, the result is the length of time that the remaining reserves would last if production were to continue at that level.

There is high potential for generation of renewable energy from various sources- wind, solar, biomass, small hydro and cogeneration bagasse. The total potential for renewable power generation in the country as on 31.03.2019 is estimated at 1097465 MW. This includes solar power potential of 748990 MW (68.25%), wind power potential of 302251 MW (27.54%) at 100m hub height, SHP (small-hydro power) potential of 21134 MW (1.93%), Biomass power of 17,536 MW (1.60%), 5000 MW (0.46%) from bagasse-based cogeneration in sugar mills and 2554 MW (0.23%) from waste to energy. (As per India Energy Statistics 2020).

The geographic distribution of the estimated potential of renewable power as on 31.03.2019 reveals that Rajasthan has the highest share of about 15% (162223 MW), followed by Gujarat with 11% share 122086 MW) and Maharashtra& Jammu and Kashmir with 10% share (113925MW and 112800 MW respectively), mainly on account of solar power potential except Gujarat where the share of Wind Power is the highest. (As per India Energy Statistics 2020).

Karnataka had the highest installed capacity of grid connected renewable power (13844.99 MW) followed by Tamil Nadu (12671.13 MW) and Maharashtra (9331.93 MW), mainly on account of wind and solar power.

Energy intensity is energy consumption per unit of GDP. Energy intensity indicates the development stage of the country. India’s energy intensity is 3.7 times of Japan, 1.55 times of USA, 1.47 times of Asia and 1.5 times of World average.

The usage of energy resources in industry leads to environmental damages by polluting the atmosphere. Few of examples of air pollution are Sulphur dioxide (SO2), Nitrous oxide (NOX) and Carbon monoxide (CO) emissions from boilers and furnaces, Chloro-fluoro carbons (CFC) emissions from refrigerants use, etc.  In chemical and fertilizers industries, toxic gases are released. Cement plants and power plants spew out particulate matter etc.

The principle pollutants produced by industrial, domestic and traffic sources are Sulphur dioxide, nitrogen oxides, particulate matter, carbon monoxide, ozone, hydrocarbons, benzene, 1,3butadiene, toxic organic micro pollutants, lead and heavy metals.

Sulphur dioxide is a corrosive acid gas, which combines with water vapour in the atmosphere to produce acid rain. Both wet and dry deposition have been implicated in the damage and destruction of vegetation and in the degradation of soils, building materials and watercourses. SO2 in ambient air is also associated with asthma and chronic bronchitis. The principal source of this gas is power stations and industries burning fossil fuels, which contain Sulphur.

Nitrogen oxides are formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel. The principal source of nitrogen oxides – nitric oxide (NO) and nitrogen dioxide (NO₂). NO and NO₂ concentrations are greatest in urban areas where traffic is heaviest. Other important sources are power stations and industrial processes.

Nitrogen dioxide has a variety of environmental and health impacts. It irritates the respiratory system and may worsen asthma and increase susceptibility to infections. In the presence of sunlight, it reacts with hydrocarbons to produce photochemical pollutants such as ozone.

Construction Interview Questions and Answers

Human activities, particularly the combustion of fossil fuels, have made the blanket of green- house gases (water vapour, carbon dioxide, methane, ozone etc.) around the earth thicker. The resulting increase in global temperature is altering the complex web of systems that allow life to thrive on earth such as rainfall, wind patterns, ocean currents and distribution of plant and animal species.

Even the minimum predicted shifts in climate for the 21st century are likely to be significant and disruptive.  Predictions of future climatic changes are wide-ranging. The global temperature may climb from 1.4 to 5.8 degrees C; the sea level may rise from 9 to 88 cm. Thus, increases in sea level this century is expected to range from significant to catastrophic. This uncertainty reflects the complexity, interrelatedness, and sensitivity of the natural systems that make up the climate.

Solar energy is an important, clean, cheap and abundantly available renewable energy. It is received on Earth in cyclic, intermittent and dilute form with very low power density 0 to 1 kW/m².Solar energy received on the ground level is affected by atmospheric clarity, degree of latitude, etc. For design purpose, the variation of available solar power, the optimum tilt angle of solar flat plate collectors, the location and orientation of the heliostats should be calculated.

In SI units, energy is expressed in Joule. Other units are angley and Calorie where,

1 angley = 1 Cal/cm².day

1 Cal = 4.186 J

For solar energy calculations, the energy is measured as an hourly or monthly or yearly average and is expressed in terms of kJ/m²/day or kJ/m²/hour and Solar power is expressed in terms of W/m² or kW/m².

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, and in the residential and commercial sectors.

Solar collectors are used to collect the solar energy and convert the incident radiations into thermal energy by absorbing them. This heat is extracted by flowing fluid (air or water or mixture with antifreeze) in the tube of the collector for further utilization in different applications. The collectors are classified as; 

• Non concentrating collectors 
• Concentrating (focusing) collectors

Inverters are used to convert DC to AC. There are two types of inverters: standalone and grid-connected. The two types have several similarities, but are different in terms of control functions. 

A stand-alone inverter is used in off-grid applications with battery storage. With backup diesel generators (such as PV–diesel hybrid power systems), the inverters may have additional control functions such as operating in parallel with diesel generators and bidirectional operation (battery charging and inverting).  Grid-interactive inverters must follow the voltage and frequency characteristics of the utility-generated power presented on the distribution line. For both types of inverters, the conversion efficiency is a very important consideration.

The basic element of a PV system is the solar cell. Solar cells can convert the energy of sunlight directly into electricity. Solar cells rely on a quantum-mechanical process known as the ‘‘photovoltaic effect’’ to produce electricity.  A typical solar cell consists of a p n junction formed in a semiconductor material similar to a diode. It consists of a 0.2–0.3mm thick monocrystalline or polycrystalline silicon wafer having two layers with different electrical properties formed by ‘‘doping’’ it with other impurities (e.g., boron and phosphorus). An electric field is established at the junction between the negatively doped (using phosphorus atoms) and the positively doped (using boron atoms) silicon layers. If light is incident on the solar cell, the energy from the light (photons) creates free charge carriers, which are separated by the electrical field. An electrical voltage is generated at the external contacts, so that current can flow when a load is connected.

A number of semiconductor materials are suitable for the manufacture of solar cells. The most common types using silicon semiconductor material (Si) are: 

1. Monocrystalline Si cells 
2. Polycrystalline Si cells 
3. Amorphous Si cells

The major factors influencing the electrical design of the solar array are as follows:

1. The sun intensity,
2. The sun angle,
3. The load matching for maximum power,
4. The operating temperature

More energy is collected by the end of the day if the PV module is installed on a tracker with an actuator that follows the sun. There are two types of sun trackers:

1. One-axis tracker, which follows the sun from east to west during the day.
2. Two-axis tracker, which follows the sun from east to west during the day, and from north to south during the seasons of the year.

Photovoltaic Power Systems can be classified as

1. Stand-alone PV systems – Stand-alone PV systems are used in remote areas with no access to a utility grid.  Conventional power systems used in remote areas often based on manually controlled diesel generators operating continuously or for a few hours.  Extended operation of diesel generators at low load levels significantly increases maintenance costs and reduces their useful life.
2. Hybrid PV Systems – Renewable energy sources such as PV can be added to remote area power systems using diesel and other fossil fuel powered generators to provide 24-hour power economically and efficiently. Such systems are called ‘‘hybrid energy systems.
3. Grid Connected PV Systems – In grid-connected PV systems, PV panels are connected to a grid through inverters without battery storage. These systems can be classified as small systems, such as residential rooftop systems or large grid connected systems.  The grid interactive inverters must be synchronized with the grid in terms of voltage and frequency.