Solar and wind power should complement conventional sources

In a recent study, leading scientists have concluded that, theoretically, India can completely meet its electricity requirements from solar and other renewable sources of energy. Another report suggests that installing rooftop solar PVs on all Indian households will produce sufficient electricity to obviate our nuclear power programme.

Such news always strikes a chord. We all love renewables, don’t we? After all, who doesn’t want a future where all our energy is from clean, and nonpolluting sources? We don’t have to bother about air pollution and CO2 from coal combustion. Nor do we need to spend sleepless nights worrying about a Fukushima-like accident in one of our nuclear plants.

Alas, if only all this were true. The Utopian dream is still far off. Even if we have sufficient land and rooftops to install solar and wind power plants to meet our future electricity requirements, the issue is much bigger. The challenges are: suitability of lands for power generation, managing intermittency and economics.

A detailed analysis of characteristics and geographical distribution of land is needed to confirm if it indeed meets the requirements for electricity generation from solar and wind. The experience of solar developers in first phase of the National Solar Mission suggests that obtaining suitable lands is not that easy. An electricity generation system should be adaptable to meet the loads, which fluctuate every minute during the day. Typically, we have a morning peak, when the offices and commercial establishments open up and there is an evening peak, when people put on the lights, and TVs to watch their favourite soaps.

Therein lies the problem. Solar and wind are intermittent sources and the generation doesn’t necessarily coincide with system’s demand. Wind exhibits seasonal and hourly fluctuations.

Most of wind generation in Karnataka is during the months of July – September and even then, the generation fluctuates from a high of 1,800 mw to zero!
Solar power peaks during the day around noon. Moreover, solar generation is seasonal and also depends on the local cloud cover. Bangalore’s solar radiation profile suggests that solar radiation is high during the period January - May and falls off during the monsoon months. Further, solar power variations can exceed 60 per cent of the generation in a matter of seconds.

In conventional power systems, electricity generation follows the load demand in real time. However, wind and solar generation has to be absorbed as and when available. Their intermittencies can be handled at low penetrations. However, high penetration of such generation sources poses a challenge to system stability. In Tamil Nadu the wind power is nearly 40 per cent of the total installed capacity and the state faces challenges in managing variability. There are instances in high wind seasons (monsoons) where the state has to back down its wind-mills as there is not enough load demand. Similarly, an unexpected slump in wind generation results in load shedding.

Lesser unpredictability

Therefore, grid operators can’t treat capacity from wind and solar the same way as they do the capacity from coal, hydro and nuclear because of the difference in firmness of power between these sources. Coal and nuclear are firm power in that there is lesser unpredictability in their availability.

Of course, there are several engineering solutions to manage these intermittencies. We can pump water to a reservoir and run it through a turbine when the grid needs energy. Or, we could store the energy in battery, heat oil, or even compressed air. However, everything comes at a cost, which brings us to the next point.

The cost of solar has come down in recent times. Today, solar developers are wiling to build solar power plants at around Rs 10 crore per mw and the industry is bullish about further cost reductions. Solar-based electricity costs Rs 8 to Rs 10 per kWh. However, this is still three times that of coal and double that of nuclear power. If solar has to contribute all of India’s electricity, then the present prices is too high.

A 3 kW solar roof top panel is expected to cost around Rs 4 lakh, including a battery pack and the associated power electronics. While the solar panel has a life of 25 years, the battery pack needs to be replaced every 5-6 years. Notwithstanding our passion for solar, it is pre-mature to expect majority of Indians to pay Rs 4-5 lakh for solar power.

The point is the country needs energy and that too desperately. We should certainly pursue solar and wind, and in fact aspire to be global leaders in the deployment of these technologies. However, let’s be realistic in the energy generation potential and costs. Large scale solar and wind power generation requires significant amount of base load generation from coal and nuclear, to provide the steady power when solar and wind are not available. We also need sufficient reserves of quick ramp up sources such as hydro and natural gas to manage the hourly fluctuations.

It is important to see our generation option as a portfolio rather than bet on a few resources since we are seeking several contrasting objectives from our power sector – affordability, reliability and reduced emissions.

Solar and wind power have to go hand in hand with adding other generation sources.  A system depending on solar and wind alone will be vulnerable to nature’s vagaries.

(The writer is the executive director, Centre for Study of Science, Technology and
Policy)