Every now and then we come across news of the government setting up some power plant of 500 MW, 1000 MW or even more sometimes, in different parts . Then we wonder if a power plant rated at 1000 MW will produce 1000 MW electrical energy?
Not necessarily. A lot of people get confused between the power output of a power plant and the electricity which it is producing. While these two are interrelated they are not the same.
There is always a maximum limit of the output of each power plant. Also there is a minimum limit of power which has to be produced by the power plant in order to keep running. When you hear in the news that a power plant of 1000 MW is established, it is the maximum power output capacity (1000 MW) you hear about. The minimum output capacity of a power plant ranges from 40% – 50 % of the maximum output capacity.
When a power plant is established (say having a maximum output capacity of 1000 MW), it means that the power plant would be capable of providing an instantaneous power of 1000 MW. How much of this power is used, is something which determines the electricity production of the power plant. Say if there is a power plant which has the maximum capacity of 1000 MW, and the various stations and sub-stations (which transmit electricity to the poles from where electricity reaches our houses) are drawing all of the 1000 MW output of the power plant, then in 1 hour the electricity production of the power plant will be 1000 MWh (which is equivalent to 1000 x 1000 kWh = 1000000 units of electricity). This will be the maximum electricity which the power plant will be able to provide in 1 hour.
In practice the actual power output is less than the rated power output. The ratio of actual power output over a period of time to its rated output is known as capacity factor of the power plant.
Electricity generation using solar power
There has been a lot of buzz going around about using renewable sources of energy. The renewable energy sources which have got significant policy support in India for power generation include wind and solar. Under the JNNSM (Jawalar Lal Nehru National Solar Mission) launched in 2010 the Indian Government has set the ambitious target of deploying 20,000 MW of grid connected solar power by 2022.
Say there are two power plants of 1000 MW, one produces electrical power from coal and the other from solar energy. So does it mean that they both produce the same amount of electricity (usable units)?
The electrical energy produced by a solar power plant and a coal power plant, both of which have the same maximum capacity, is very different. How? Let us see.
Electricity generation from a coal plant and a solar plant
Solar power depends on sunlight. And because the amount of sunlight falling on it throughout a day is not constant, the output of the solar plant also varies. On an average, a solar plant which has a power output of 1 kW provides 5 units of electrical energy in a day (24 hours) which can be utilised by appliances. (Please note that this is an approximate figure, the total usable energy may vary subject to different factors).
But on the other hand, the 1 kW power which is produced from coal (in power plants), provides 24 units (1 kW * 24 hours = 24 kWh) during a day.
So what does it mean then?
After the above simple calculation we see that
Number of usable units provided by a 1 kW coal power plant in a day = 24 units
Number of usable units provided by a 1 kW solar plant in a day = 5 units
If there is a requirement of 50000 units at a place, then
Required capacity of solar plant should be = 50000/5 = 10000 kW = 10 MW
whereas the required capacity of a coal power plant would be = 50000/24 = 2083.3 kW = 2.1 MW (approx.)
It means that the required capacity of a coal power plant to generate a given amount of electrical energy will approximately be one-fifth of the required capacity of a solar plant to produce the same amount of electrical energy.
Ultimately the whole point of using solar energy is to supplement the coal energy in order to ease the enormous pressure on coal and other fossil fuels used for electricity generation. This is because solar power can be harnessed only during daytime and there is no inexpensive storage technology available as of now where the energy generated could be stored for later use. It means that the power generated would have to be consumed instantaneously. Although harnessing of solar power is not very common today, but is gaining popularity rapidly. In fact, in some countries the solar power market has witnessed tremendous growth in the recent years. And why shouldn’t it? In addition to reducing the expenses on electricity, it also is a perfectly clean and sustainable source of energy. Its just a matter of time when solar energy shall be as popular as the regular sources of energy.