“Wind energy’ is in the news all the time.
Some state or other announces a plan, every day, to add more wind turbines in the coming months, the stated target usually running into hundreds of MWs. Wind turbine projects can come up in quick time- few months- and Govts can claim addition of more MWs. And as the addition can come up within their elected term and will strengthen their list of achievements, ruling parties patronize wind energy wherever there is scope.
Wind is truly ‘green”. There is no carbon emission during generation. Its fuel cost is nil and unvarying over the lifetime of the plant.
The lobby for ‘wind energy’ is one of the strongest you can find. The ‘greenness’ of wind imparts a self-righteous virtue to their aggression. Wind manufacturers will tell you that there is an untapped wind potential of 100000 MW in India, enough to wipe out the entire power deficit in the country. What they won’t tell you is that much of this power is useless. At least in the Indian context.
Before we dare to take on the sacred cow, two immutable laws of wind energy need to be remembered.
1) Wind does not blow where you want it to blow. So, the turbines need to be installed at wind-mapped sites which, quite often, are not close to load consuming centres. True, this weakness is not unique to wind. Even hydro and coal plants are sited where there is water or coal pitheads, far from load centres.
2) Wind does not blow when you want it to blow. Vayu, the Wind God, is capricious and dispenses his bounty only when he chooses to and with an intensity that swings with his mood. Therefore, the output from a wind turbine can vary from hour to hour, from season to season, and can be negligible in certain months. The “annual plant load factor” of a wind turbine is less than 25% ( far less in many places), as compared to 80% of a coal plant. In practical terms, a 1 MW coal plant can generate around 8 million units (kwh) in a year. A wind turbine of 1 MW produces less than 2.2 million units. That’s why wind lobbyists will window-dress the MW numbers and gloss over the units it can generate.
When wind energy governed by above laws is integrated with the electric grid, it encounters the following two immutable laws of electricity.
1) Demand for electricity varies on an hourly, daily and seasonal basis. There are hours in a day (evening hours, for example) when there is a peak demand, and hours (late in the night) when there is a dip. Demand can be high on week-days and lower on Sundays. Demand can soar in summer (most parts of India) or in winter (as in the case of Kashmir or HP). The grid must cope with these variations in real-time.
2) Electricity is a commodity that perishes instantly. It cannot be stored (ignore the small amount stored in batteries). It needs to be generated and consumed at the same time.
The electric grid consists of several generating plants spread over a wide area and feeding in power as a networked system. There are many distribution companies that draw power from this central grid and supply to several thousands of consumers, whose individual and collective consumption pattern can vary widely. To prevent the system from slipping into chaos and to ensure discipline, a grid code is followed among all stake-holders. A schedule is drawn the previous day by the generating stations to indicate how much of power they can inject into the grid every hour of the day. Similarly, the distribution companies indicate the expected drawal every hour. Penalties are imposed on over-drawal (linked to grid frequency during that hour) beyond the scheduled quantity, and incentives offered for excess generation (again when frequency is low). There is also a merit order of despatch, specified by the regulator; those plants offering the lowest cost of energy get priority in evacuation.
Our sacred cow, wind energy has been exempt from these rules (“We are green. We set our own rules”). Wind plants get the status of ‘must-run’ plants and are outside the purview of the merit-order system. Whenever wind turbine plants generate power, the grid is expected to evacuate it forthwith. Or else, the green brigade will cry foul. (Only recently, wind energy has been included in the ‘grid code’ but with a generous variation allowance of 30% on the scheduled output.)
What it means is that there is a mismatch between the generation pattern of wind turbines and the demand pattern of the consumers, and the grid has to struggle to balance this out in real-time. The grid also has to manage the flickers, harmonics and sudden reactive surges in the system from isolated and spread-out wind farms.
Take the case of Tamilnadu, which has the highest installed base (6000 MW) of wind turbines in the country. Winds may howl late in the night when power demand is low and taper off in the mornings and evenings, precisely when the consumption of electricity peaks. Also, wind energy tends to peak in the months of July and August, when the agricultural demand drops (as it is monsoon time in several parts), and drops drastically in the months of January to May, when the demand of electricity is at its highest. My belief is that the useful PLF (generation that matches demand) is less than 10%.
Thanks to another convenient system called ‘banking” available only to wind power, captive-power producers can pump in any amount of power into the grid (usually when the grid doesn’t need it) and draw the banked units back any time during the financial year ( even when the grid doesn’t have enough to spare.)
Because of this variability, addition of wind turbines does not result in reduction of even a single MW of investment in a fossil-fuel plant. Worse, as wind energy must be evacuated whenever it chooses to be present, base-load plants must be operated at lower load and lower efficiency during those times. For, large coal plants cannot be stopped and started at will.
When TN has experienced huge shortages in the last few years, it has been able to accommodate wind energy in the system. Whatever came in was considered a bonus. And when wind failed to blow (as it did most parts of the year), it provided the Electricity Minister with an excuse to account for the shortfall as an “Act of God”. This cannot work when more coal plants are added.
I hasten to add that there are ways to harness wind energy in a more disciplined manner. Wind energy needs to be paired off with complementary solutions that neutralize its disadvantages of variability and seasonality.
One option is to use wind energy along with hydro-electric power. The latter has the ability to start and stop instantly. It can come on when wind power is absent and switch off when wind power is active. The two sources can be at different locations, but can communicate with each other, to maintain a fairly steady output. Another way is to use the hydro-power plant during the day (when the demand is high) and use wind energy at night to reverse-pump the water back to the storage. Grid systems in Europe and USA follow such practices. Sadly, in most parts of India, we don’t have the luxury of too many perennial rivers or year-round water storage.
Another option is to use gas-turbines or gas-engines as partnering solutions. The latter, especially, is an excellent wind-chasing tool. With a bank of engines, the operator can bring on one or more of them to match the drop or surge in wind capacity, with great precision. This is catching on in the USA, where ‘banking’ of wind energy is not allowed and where load-shedding is not an option. In India, this has not been tried out because a) gas resource is limited b) gas is sold on take-or-pay basis for 24-hrs operation and so not economical for stand-by or intermittent applications c) gas-based generation is considered expensive d)) excess demand can be managed by the simple expedient of resorting to load-shedding, and there is no ’24 x7’ service obligation.
Mindless promotion of wind energy, without one of the above complementary solutions, is nothing short of a scam. But, amazingly, its tribe of supporters keeps growing.