Renewable energy: Green push needs a balancing act

While steady ramping up of green power goes a long way in ensuring some leverage for India at climate talks, the integration of large amount of fluctuating renewable energy in the grid remains a serious technical challenge and requires closer monitoring.

Written by Anil Sasi | Published: October 14, 2015 1:18 am
renewable energy, solar energy, wind energy, indian express All over India the balancing potential is sufficient to handle the share of RE generation. (Illustration: C R Sasikumar)

At over 36,000 Mw, renewable energy contributes nearly 15 per cent of the country’s total installed electricity generation capacity. If the capacity addition of renewable projects such as solar and wind were to happen as per plans, this number is expected to go up to 1,75,000 MW by 2022.

The steady ramping up of green power — solar, for instance, was just 2MW in 2010 but is now over 4,000 MW — does go a long way in ensuring some degree of leverage for India at climate talks, but simultaneously poses a serious challenge for grid managers. The availability of solar and wind energy is largely determined by the weather conditions, and therefore characterised by strong variability. As a result, power generation from these sources cannot easily be matched to the electricity demand, like power generated from conventional plants such as coal-fired units and gas stations. Integration of large amount of fluctuating RE in the grid is a serious technical challenge for grid managers to ensure smooth operations of the Indian grid — the fifth largest in the world. To compound matters, RE generation forecasting in the country is in its early days.

Globally, the Germans are the closest to mastering the tenuous task of integrating and balancing high shares of renewable energy with very modest changes to their power system. Renewables provide close to 30 per cent of Germany’s power on an average basis and on some days in 2014, solar and wind supplied close to 80 per cent of peak power demand at specific times of the day. Because of the German feed-in tariff law (EEG), renewables have dispatch priority, which implies that they are always used first, sometimes leaving very little power demand left to be supplied by coal, nuclear, and natural gas plants.

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That Germany has managed to integrate nearly 30 per cent renewable power capacity into their electricity grid has been made possible because of two important factors — the engineering robustness of the German power grids and the flexible operation of its coal and nuclear plants. A slew of ancillary factors too have played a part, including better system control software, day-ahead weather forecasting and the ability to export power to neighboring countries.

In the Indian context, there are a number of takeaways from the German experience. In India, at the moment, balancing of renewables is left completely to the capability of states producing the energy from RE. This is ineffective as the complete available balancing capacity of a region can never be activated, if necessary. For example, in case of high feed-in from RE a single state has less power capacity available to back-down. In Tamil Nadu it regularly happens that the system operator is not able to back-down sufficient conventional generation eventually leading to curtailment of RE.

A report on Forecasting, Concept of Renewable Energy Management Centres and Grid Balancing prepared by GIZ, Germany in partnership with University of Oldenburg and Ernst & Young LLP, India, which was funded by German grant for promoting RE development in India, provides at least half a dozen stumbling blocks in India that need to be ironed out if grid integration of renewable energy is to happen smoothly.

* The biggest constraint is the limited ability of operators to back down coal generation due to a variety of technical and economic reasons.
* Hydro power capacity available for balancing is not significant enough. Hydel capacity is suited to be run in tandem with renewable power as these projects can be delinked from the grid or plugged back in at a short notice.
* Severe fuel shortage is a big constraint for gas-based power plants, which otherwise have the capability to respond to sudden variations in the output of wind and solar plants.
n The entire onus of demand-supply balancing is on the states and the absence of fine balancing mechanism at the regional level to support the states is a big question mark.
n Poor load forecasting ability of states.

Added to all this is that fact that hydro balancing potential was found to be further restricted by the control and use of plants by the irrigation department of states. Also, most hydro power plants in the country are not reservoir-based hence cannot be used for balancing. The major observations in the report centres on the need for developing hydro power plants with storage reservoirs for intraday balancing. Alongside, there is a need to develop large scale pumped storage type hydro-electric plants, which has traditionally been neglected in India.

Most important, though, is the need for a new regulatory framework that effectively makes Regional Load Dispatch Centres (RLDC) more responsive towards the electricity demand and supply situation at the regional level, rather than putting the entire onus on individual states — at present, the entire responsibility of balancing the power supply and demand is of the State Load Dispatch Centre, and the RLDC only monitor the power flows like a traffic policeman.

The report suggests that power storage options need to be explored and a significant push towards the R&D of these technologies is required. This is again a neglected subject in India, and virtually no R&D projects are taken up by the Central Electricity Authority, grid manager POSOCO, transmission utility Power Grid Corporation or power research body CPRI. There are practically no initiative by the private sector or institutions such as the IITs in this area. Contrast this with the focus in the whole developed world, as well as countries such as China, on inventing economical mass energy storage device so that solar energy is stored in the day for use in the evening and night.

The operational weather forecasting structure of the IMD has a good potential for contributing to RE forecasting system in India. Financial resources need to be provided – primarily for training – to enable IMD to fulfil the role of a key partner in future solar and wind power forecasting in India. The fact remains that site-specific forecasting does not contribute to improvements of overall forecast quality on the more important regional level. This is because site-specific forecasting uses post-processing techniques that are adapted or tuned to the specific single site case. Therefore, much effort is spent on the optimization of site-specific forecasts without any benefit for the regional level, leading to a misallocation of personnel and financial resources.

Balancing capability enhancement

The biggest factor, though, is clearly the manner in which balancing of RE is done, which currently is entrusted to individual states. The balancing potential — or an increase or decrease of thermal power plant generation — available in other states is often not taken into account for re-scheduling or improved dispatch in the first place. Analysts are of the view that regional balancing can be incentivised given efficient market mechanisms to export power. The lack of regional balancing is a problem, which is seen as very critical according to all stakeholders at SLDC and NLDC level.

There are commercial issues that need to be sorted out. For instance, in some states central power plants are not used for balancing. This is due to the fact that capacity charges apply even if the capacity is not used. Also, power from central or older thermal stations are usually cheaper than the feed-in tariff paid for RE by the respective state utility. Plus, if water cannot be stored due to full reservoirs, hydro power becomes must-run since spilling of reservoirs would imply a large economical loss. The price of electricity from hydro power too is cheaper in comparison to the feed-in tariff from wind energy. Even if gas power plants would have a sufficient amount of fuel available, the dispatch of conventional power plants has to follow the economic merit-order. Gas-fired power-stations are usually the most expensive to run.

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