175 GW of renewables is a tall target but India seems to be well on its way to achieve that.
There is definitely a revival of investor interest and improvement in deployment capabilities in wind and solar sector. Although there are still road blocks in the form of policy vacuum, regulatory oversight (and overreach!!) and coordination challenges but nothing that cannot be remedied.
On the technology side though, there are still unanswered questions about the integration of this capacity in the grid. We are relying on discrete strategies and expecting that four levels of system initiatives will support the integration over time.
The first level is RE forecasting. RE forecasting can provide dispatch visibility to the grid operators helping them to balance supply and demand more effectively. However, the fact remains that forecasting is still far from a perfect science and our experience with wind forecasting has not been very encouraging. Also forecasting does not really solve the variability problem if the diurnal generation variations are very high, as is the case with wind in many locations.
The second layer of security is the enhanced connectivity proposed under the green corridor project. Preliminary simulation studies suggest that the proposed corridor would help in better evacuation and balancing. However, the fact remains that even in a very complex interconnected system there will be an upper limit of RE penetration that can be supported. In effect, enhanced connectivity does help but it does not provide an assurance of grid stability and load matching at all times under all circumstances. Also, the system risk increases because we are dealing with asynchronous generation technologies that are not natural system allies in the time of grid distress.
The third layer of security is to work conventional and base load plants in flexible mode. While this would help in balancing generation variation dynamically, this approach is limited by two factors: surplus capacity availability in low RE generation period and ramping capability (technical ramp rate and the effects of ramping on economic costs).
The fourth layer would be dynamic demand response. This could be the most effective integration strategy. Allowing participation of retail sector to offer demand variations based on price signals could be a very potent way to ‘up-patch’ demand. New grid interactive mechanisms like V2G and behind-the meter storage systems can play a key role in this transition. However, this is an untested area and will require immense grid augmentation and a lot of investment in the last-mile infrastructure.
In contrast to all these measures, which would require multiple agencies/actors and huge investments, adoption of energy storage is a measure that can make the whole integration problem much more manageable and simpler to solve.
Unfortunately, the awareness about energy storage technologies is still very limited among policymakers and regulators. Most of them are only aware of three main technologies: pumped hydro, compressed air storage and batteries (lead acid and Lithium ion). In the last decade, the research and development efforts in energy storage have really started yielding fruit and we now have many other technologies, including new battery configurations that are innovative and can make a difference. A few technologies that seem promising: Liquid air storage, by Highview Power; Customized Pumped Hydro, by Gravity Power; Copper Zinc batter, Cumulus Energy; Flow Batteries, REDT; Power to Gas, ITM Power, Behind the meter, Powerwall.
But even more important, the biggest advantage of energy storage technologies is their versatility of operation. Their ability to work as a generator, consumer and system manager makes them suitable for nearly all power system operation functions. They can provide nearly the complete range of power regulation services across different network locations for time scales ranging from milliseconds to days/months. Figure 1 below shows the range of services that Energy Storage can offer.
Figure 1 Range of services that energy storage can support
(Reference: DOE and EPRI 2013, Electricity Storage Handbook in Collaboration with NRECA, Sandia National Laboratories)
Interestingly, this versatility of energy storage technologies has made it very difficult to work out the economic costs of its benefits. Nearly all past workings on the economic costs of storage have used simplistic models and have mostly monetized only one service at a time whereas the fact is that a single storage capacity can provide multiple services. The advent of ancillary services market has helped in unlocking part ‘value’ of storage technologies but a comprehensive assessment of economic benefits of storage is still not done.
It is imperative that power planners and policy makers understand the range of system benefits from storage and also acknowledge the lack of accurate ‘valuation’ of energy storage services. At the same time, it is also necessary to come out of this mind-set that energy storage is only required for renewables integration. Energy storage can, of course, help renewables greatly but it can as well provide a multitude of grid services even in a conventional power system. Interestingly, in Figure 1 above, except for the range of services in the red boxes, all the other services are NOT related to renewable energy integration and signify the range of system benefits that energy storage technologies can offer to the grid in general.
It is in this context that the policy makers really need to look at energy storage as a game-changing technology and start working on an intent document (reviving National Energy Storage Mission) and creating enabling policies to support energy storage with a view to future grid requirements.
Mr. Suuhas Tenddulkar
Consultant - Renewable Energy, Sustainability and Climate Change