Tuesday, November 19, 2013

Perspective: Wind-Hydro hybrid power plants to overcome the demerits of stand-alone wind farms

Introduction:

Wind and Hydro, both renewable forms of energy, both economical and best alternatives to thermal (coal based) energy and avoid harm to nature. But they too come with their baggage of demerits. Wind does not blow when there is a peak demand for energy (i.e. during afternoons) but is at full action in the night generating electricity when we need the least. There are no viable ways to store energy in the scale of mega-watt’s either. On the other hand, hydro, the cheapest source of electrical energy production, has geographical limitations such as elevations which are not significant enough or the insufficient water flow rate to set-up a hydro power plant.

Opportunity:
There are significant water bodies across India acting as reservoirs used for irrigation purposes, but no power generation is done as the elevations are not enough. Often, if not always, wind turbines are co-located around water reservoirs like the one shown in this picture.

So there lies an opportunity to utilize the energy generated from wind-turbines which cannot be stored to pump up the water from reservoir to a tank in upper hill to provide the required elevation needed to set-up a hydro power plant. While this method of storing energy is many centuries old but the benefits of adopting are huge now as Wind turbines these days generate power in the scale of mega-watts and are capable of pumping up great amount of water. The energy that can be recovered could be as high as 80%. Such a hybrid system can turn out to be a cost effective power plant due to higher utilization factor enabling power supply according to the varying demands across the clock.

Financial viability
For such system to be financially viable, capital costs required to set-up a hydro power plant have to be recovered from energy produced from it and there has to be a subsequent increase in the bottom line (profits) of the hybrid power plants. Let us work out a scenario with approximate costs to see if it makes sense or not.

We may consider a pool of wind turbines with a combined capacity of 100 MW, operating 12 hours a day, so generating 1200 MW hours of energy a day. Since there is always a case of production-demand mismatch and with absence of an energy storage system, we may consider an under utilization of capacity, assumed at 30% or 360 MW hours a day. If we consider 80% of energy recovery from a hydro power plant which is being set up which can produce 288 MW hours of energy on daily basis. If thus produced energy is sold at a rate of Rs. 4 per unit, it can create a revenue stream of Rs. 11.5 lakh a day. If we expect that this plant is operational 300 days in a year, it can contribute Rs. 34 crores of additional revenue every year and around Rs. 690 crores in its expected life span of 20 years. If the capital costs for setting up of this hydro power plant with a peak load capacity of 30 MW are around Rs. 100 crores, it would generate 7x returns in its life time or around 30% simple rate of return a year.

Maintenance costs are not considered here as they are minimal and an electrical distribution grid is considered to be already present with wind-power plant is being operational. All these financial figures are for illustration purposes only and the actual figures vary from project to project.

Policy and Regulations
Since the Governments promote production of renewable energy with many incentives, combination of Wind-Hydro power plant would not find any resistance from regulatory bodies even though additional approvals may be needed. Since the water being drawn from the reservoir is being returned to it, it may not invoke any objections from stakeholders of the reservoirs, the farmers.

Adoption and Scalability
While water bodies may not always be present in the vicinity of wind farms, other alternatives such as compressed air or thermal energy storage can be explored (on case to case basis) even though they may not offer the similar benefits of wind-hydro combination.

But if one takes a look at the geographical chart of India, each state on an average has at least 10 locations where wind farms and water bodies are co-located. There lies an opportunity to harness the infrastructure deployed to provide energy for growing India.

This system can be scaled and extended for projects such as linking of water reservoirs to bring a balance in the water availability across geography instead of wasting the enormous power generated by wind turbines when there is no load.


References:

1.     Wind Generates Electricity When We Need It Least  (Institute for Energy and Research) http://www.instituteforenergyresearch.org/2012/10/24/study-wind-subsidies-disproportionately-produce-electricity-when-we-need-it-least/

2.      Calculating the amount of available hydro power
 where,
P is power in watts; η is the dimensionless efficiency of the turbine; ρ is the density of water in kilograms per cubic metre; Q is the flow in cubic metres per second; g is the acceleration due to gravity; h is the height difference between inlet and outlet (Source: Wikipedia)

3.      Picture shown is taken at Vanivilas Sagar in Karnataka

4.      Scientific American magazine, March 2012, page 50, reports energy recovery from pumped up hydro power plants can be 80%