Renewable Energy Fundamentals


Solar PV Fundamentals

Light can be converted to electricity using the Photo-Voltaic (PV) Cell. If the source of that light is the Sun then the cell is called a Solar Cell.

The photoelectric effect relies on the principle that whenever light strikes the surface of certain materials electrons are released. A variation of this is used in the solar cells. Semi-conductors like Silicon etc are best for capturing this energy

Silica (SiO2) is the compound used to make the solar cells.  It is first refined and purified, then melted down and re-solidified so that it can be arranged in perfect wafers for electric conduction.  These wafers are very thin.

The wafers then have either Phosphorous or Boron added to make each wafer either a negative type layer or a positive type layer respectively. Used together these two types treated of crystalline silicon form the p-n junction which is the heart of the solar– electrical reaction. In the p-n junction the n-type wafer treated with phosphorus has extra electrons which flow into the holes in the p-type layer that has been treated with boron.

Connected by an external circuit electrons flow from the n-side to create electricity and end up in the p-side.


A solar cell is the basic building block of a PV system.

A typical cell produces .5 to 1V of electricity.

Solar cells are combined together to become modules or if large enough, known as an array.


Wind Energy Fundamentals

Wind is created when the sun unevenly heats the earth's surface. Air above a hot surface rises up. Thus, air from a cooler surface flows in.

Wind turbines capture the wind in their blades (or rotor) and then convert the wind energy to rotational or mechanical energy, which is converted to electricity

The electricity generated by the wind turbine is delivered to the electric transmission grid or to the battery bank (in case of small wind turbines) for consumption/ storage

Wind energy changes as a cubic factor over any change in wind speed. Thus if the wind speed becomes double the energy in the wind goes up by eight times

Wind density is a critical factor for energy generated

Generated energy is strongly impacted by Temperature / Pressure / Height / Humidity / Ground surface / Habitat / Turbine type / Turbine layout etc

Wind Turbines Generators are of three types

  1. Large wind turbines on land as well as offshore with massive capacity up to 6 MW per turbine (offshore) needing 6+ met per sec wind  speeds. In India the large turbines are typically of 250 KW to 1.65 MW capacity
  2. Medium wind turbines capable of feeding either the grid or a small community typically 100 KW to 250 KW
  3. Small wind turbines capable of running at low wind speeds and augmenting power for residential and commercial establishments (Upto 10 KW )


Occupies least land area per kw of energy generated.

Compatible with grazing and crops.

Does not emit any climate change inducing Carbon dioxide , and within six months of operation , the turbine has offset all emissions caused by its construction , to run virtually carbon free for the rest of its 20 year life

Modern turbines are almost silent and rotate slow enough to be no hazard to birds

How it works:

The blades of a wind turbine convert the energy in wind to rotational movement of a shaft which is connected to an alternator. The electricity thus produced passes through wires to a charge controller and a battery bank. The battery bank stores the electricity which can be used when required.

Wind turbine has a yaw movement which helps it attain a position to capture maximum energy from the wind. In large turbines this movement is controlled by advanced computers. In small turbines this is done by a tail-vane.

Wind turbine rating is not regulated hence each turbine manufacturer rates his turbine at a different speed. The power curve (power output at different speeds) of a wind turbine is a better measure of its performance. The ideal method is to calculate the output at a particular speed. Considering that the wind speed changes by the day, by the hour and by the minute not mentioning the monthly or seasonal variations, this is a complicated task.